Advances in Child Development and Behavior Volume 5

ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR

VOLUME 5

Contributors to This Volume John H . Flavell Kathryn S. Goodwin L. R. Goulet

Frances K. Graham Tryphena Humphrey Corinne Hutt Jan C. Jackson

ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR edited by Hayne W. Reese Department of Human Development University of Kansas Lawrence, Kansas

Lewis P. Lipsitt Department of Psychology Brown University Providence, Rhode Island

VOLUME 5

@ 1970 ACADEMIC PRESS

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London

COPYRIGHT @ 1970,

BY

ACADEMICPRESS,INC.

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U n i t d Kingdom Edition published by ACADEMIC PRESS. I N C . ( L O N D O N ) LTD. Berkeley Square Houre. London W I X 6BA

LIBRARY OF

CONGRESS CATALOG C A R D

NUMBER: 63-23237

P R I N T E D IN T H E U N I T E D S T A T E S OF A M E R I C A

Contents LISTOF CONTRIBUTORS ....................................................

PREFACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONTENTSOF PREVIOUS VOLUMES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

vii ix

xi

The Development of Human Fetal Activity and Its Relation to Postnatal Behavior TRYPHENA HUMPHREY

. ...... .......... .................. 2 Historical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Theories on the Development of Behavior ................. 4 ............ Methods of Investigating Behavioral Devel Activity in Response to Tactile Stimulation of Human Fetuses Fetal Activity in Response to Other Types of Stimuli . . . . . . . . . . Spontaneous Activity . . . ............................ VIII. The Relation of lntegratio the Development of Behavior . IX. Other Considerations ............................................... 49 References . . ........................... 51 I. Introduction

11. 111. IV. V. VI. VII.

Arousal Systems and lnfant Heart Rate Responses FRANCES K. GRAHAM A N D JAN C. JACKSON

I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

........................................................ 111. Developmental Studies of Evoked HR Response . . . . . . . . . . . . . . . . . . . . . . . I V . Summary and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II. Procedure

60 67 78 108 1II

Specific and Diversive Exploration CORINNE HUTT I. Introduction . . . . . 11. Complexity as a De 111. Novelty as a Determinant of Exploration IV. Specific and Diversi V . Summary and Conclusions . . . . References . . . . . . . . . . . . . . . .

..........

120

V

vi

Contents

Developmental Studies of Mediated Memory JOHN H . FLAVELL

I . Introduction ....................................................... I 1 . The Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1 . Some Impressions Regarding the Nature and Development of Mediated Memory ................................................. IV . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

182 182 193 208 209

Development and Choice Behavior in Probabilistic and Problem-Solving Tasks L. R . GOULET A N D KATHRYN S . GOODWIN

I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I I . Probability Learning ................................................ 1 1 1 . OtherTasks ...................................................... IV . Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

214 214 241 249 250

INDEX AUTHOR

.........................................................

255

INDEX SUBJECT

..........................................................

263

List of Contributors Numbers in parentheses indicate the pages on which the authors' contributions begin.

JOHN H . FLAVELL, University of Minnesota, Minneapolis, Minnesota (181)

KATHRYN S. GOODWIN, West Virginia University, Morgantown, Virginia ( 2 1 3 )

L. R. GOULET,' West Virginia University, Morgantown, Virginia ( 2 1 3 )

FRANCES K. GRAHAM, University of Wisconsin, Madison, Wisconsin ( 5 9 )

TRYPHENA HUMPHREY, Department of Anatomy, Medical Center, University of Alabama in Birmingham, Birmingham, Alabamu ( 1 )

CORINNE HUTT,* Human Research U n i t , University of Oxford, Oxford, England ( 1 19)

JAN C. JACKSON, University of Wisconsin, Madison, Wisconsin ( 5 9 )

'Present address: University of Illinois, Urbana, Illinois. 2Present address: Department of Psychology, University of Reading, Reading. England. vii

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Preface The amount of research and theoretical discussion in the field of child development and behavior is so vast that researchers, teachers, and students are confronted with a formidable task in keeping abreast of new developments within their areas of specialization through the use of primary sources, not to mention remaining knowledgeable in areas peripheral to their primary focus of interest. Moreover, there is often simply not enough journal space to permit publication of more speculative kinds of analyses which might spark expanded interest in a problem area or stimulate new modes of attack on the problem. The serial publication of Advances in Child Development and Behavior is intended to ease the burden by providing scholarly technical articles serving as reference material and by providing a place for publication of scholarly speculation. In these documented, critical reviews, recent advances in the field are summarized and integrated, complexities are exposed, and fresh viewpoints are offered. They should be useful not only to the expert in the area but also to the general reader. The publication of Volume 5 marks a change from a biennial to an annual rate, made desirable by the unabated increase in the number of primary sources being published and by an increase in the rate at which new advances seem to be made. No attempt is made to organize each volume around a particular theme or topic, nor is the series intended to reflect the development of new fads. Manuscripts are solicited from investigators conducting programmatic work on problems of current and significant interest. The editors often encourage the preparation of critical syntheses dealing intensively with topics of relatively narrow scope but of considerable potential interest to the scientific community. Contributors are encouraged to criticize, integrate, and stimulate, but always within a framework of high scholarship. Although appearance in the volumes is ordinarily by invitation, unsolicited manuscripts will be accepted for review if submitted first in outline form to the senior editor. With the publication of Volume 5 of this ix

X

Preface

series, Lewis P. Lipsitt will have phased out as coeditor and Hayne W. Reese will be the sole editor of Advances in Child Development and Behavior. We wish to acknowledge with gratitude the aid of our home institutions, the University of Kansas and Brown University, which generously provided time and facilities to produce this volume.

HAYNEW. REESE August, 1970

LEWISP. LIPSITT

CONTENTS OF PREVIOUS VOLUMES Volume 1 Responses of Infants and Children to Complex and Novel Stimulation Gordon N . Cantor Word Associations and Children’s Verbal Behavior David S . Palermo Change in the Stature and Body Weight of North American Boys during the Last 80 Years Howard V . Meredith Discrimination Learning Set in Children Hayne W . Reese Learning in the First Year of Life Lewis P . Lipsitt Some Methodological Contributions from a Functional Analysis of Child Development Sidney W . Bijou and Donald M . Baer The Hypothesis of Stimulus Interaction and an Explanation of Stimulus Compounding Charles C . Spiker The Development of “Overconstancy” in Space Perception Joachim F . Wohlwill Miniature Experiments in the Discrimination Learning of Retardates Betty J . House and David Zeaman AUTHOR INDEX -SUBJECT

INDEX

Volume 2 The Paired-Associates Method in the Study of Conflict Alfred Castaneda Transfer of Stimulus Pretraining in Motor Paired-Associate and Discrimination Learning Tasks Joan H . Cantor xi

xii

Contents of Previous Volumes

The Role of the Distance Receptors in the Development of Social Responsiveness Richard H . Walters and Ross D . Parke Social Reinforcement of Children’s Behavior Harold W . Stevenson Delayed Reinforcement Effects Glenn Terrell A Developmental Approach to Learning and Cognition Eugene S . Gollin Evidence for a Hierarchical Arrangement of Learning Processes Sheldon H . White Selected Anatomic Variables Analyzed for Interage Relationships of the Size-Size, Size-Gain, and Gain-Gain Varieties Howard V . Meredith AUTHOR INDEX-SUBJECT

INDEX

Volume 3 Infant Sucking Behavior and Its Modification Herbert Kaye The Study of Brain Electrical Activity in Infants Robert J . Ellingson Selective Auditory Attention in Children Eleanor E. Maccoby Stimulus Definition and Choice Michael D . Zeiler Experimental Analysis of lnferential Behavior in Children Tracy S . Kendler and Howard H . Kendler Perceptual Integration in Children Herbert L. Pick, Jr., Anne D . Pick, and Robert E. Klein Component Process Latencies in Reaction Times of Children and Adults Raymond H . Hohle AUTHOR INDEX-SUBJECT

INDEX

Volume 4 Developmental Studies of Figurative Perception David Elkin d

Contents of Previous Volumes

xiii

The Relations of Short-Term Memory to Development and Intelligence John M . Belmont and Earl C . Butterfield Learning, Developmental Research, and Individual Differences Frances Degen Horowitz Psychophysiological Studies in Newborn Infants S . J . H u t t , H . C . Lenard, and H . F . R . Prechtl Development of the Sensory Analyzers during Infancy Yvonne Brackbill and Hiram E . Fitzgerald The Problem of Imitation Justin Aronfreed AUTHOR INDEX -SUBJECT

INDEX

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THE DEVELOPMENT OF HUMAN FETAL ACTIVITY AND ITS RELATION TO POSTNATAL

Tryphena Humphrey UNIVERSITY OF ALABAMA IN BIRMINGHAM

1. 11.

INTRODUCTION

............................................

HISTORICAL B A C K G R O U N D

................................

111. T H E O R I E S O N T H E D E V E L O P M E N T OF BEHAVIOR

.........

A. T O T A L PATTERN C O N C E P T O F C O G H I L L A N D O T H E R S B. LOCAL REFLEX C O N C E P T OF W I N D L E . . . . . . . . . . . . . . . . . C. O T H E R VIEWS O N BEHAVIORAL DEVELOPMENT . . . . . . . IV.

M E T H O D S OF INVESTIGATING BEHAVIORAL DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

'This investigation was supported by a U.S. Public Health Service research career program award, NB-K6-167 16, from the National Institute of Neurological Diseases and Blindness. *Aided by Grant HD-00230, National lnstitute of Child Health and Human Development, National Institutes of Health. The present paper is publication No. 55 in a series of functional and morphological studies on human prenatal development begun under the direction of Dr. Davenport Hooker in 1932. The cinematographic records and the morphologic material upon which this paper is based were accumulated under the support of previous grants from the Penrose Fund of the American Philosophical Society, the Carnegie Corporation of New York, the University of Pittsburgh, the Sarah Mellon Scaife Foundation of Pittsburgh, and Grant 8-394 from the National Institute of Neurological Diseases and Blindness, National Institutes of Health. I

2

Tryphena Humphrey

A. METHODS O F RECORDING ACTIVITY . . . . . . . . . . . . . . . . . . B. TYPES OF STIMULI USED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. EFFECTS O F ANOXIA, ASPHYXIA, ANESTHETICS, NARCOTICS. AND OTHER DRUGS . . . . . . . . . . . . . . . . . . . . . . V. ACTIVITY I N RESPONSE TO TACTILE STIMULATION OF HUMAN FETUSES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. T H E PERIOD O F WIDESPREAD REACTIONS-COGHILL’S TOTAL PATTERN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. THE DEVELOPMENI- OF LOCALIZED REFLEX ACTIVITY C. FUNCTION O F FETAL REFLEXES . . . . . . . . . . . . . . . . . . . . . . . D. T H E RELATION O F SUPPRESSION (OR INHIBITION) OF ACTIVITY T O T H E DEVELOPMENT O F BEHAVIOR . . . . . E. POSTNATAL REPETITION OF FETAL REFLEX ACTIVITY SEQUENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI. FETAL ACTIVITY IN RESPONSE T O OTHER TYPES O F STIMULI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII. SPONTANEOUS ACTIVITY . . . . . . . . . . . . . . . . . . . .

8 9 10

12 12 16

30 36

40

41

43

VIII. T H E RELATION O F INTEGRATION T O T H E DEVELOPMENT O F BEHAVIOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

46

IX. OTHER CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

49

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

51

I.

Introduction

Prior to the meticulous investigations of Coghill that correlated functional changes with the development of the nervous system in Amblysroma ( 1909- 1930), most of the observations on the development of vertebrate behavior were limited in scope. Coghill’s correlations of structure and function and his theory on the development of behavior mark the onset of the organized attempts to correlate the sequence of behavioral development, as demonstrated by the progressive changes in reflex and spontaneous activity, with the development of the nervous system. Differences in views on the mode of behavioral development arose, as differences do in connection with any significant new concept. Adequate evidence to support the theories that were advanced was not forthcoming and the interest in such behavioral investigations declined. In some recent review papers particularly, the value of Coghill’s investi-

The Development of Human Fetal Activity

3

gations of behavioral development has been minimized or even casually dismissed as of no significance in determining either the mechanisms or the causal factors of behavior (e.g., Jacobson, 1966). Indeed, the brief and none too accurate references lead one to speculate, in some cases, concerning the degree of familiarity of the authors with these concepts. Following the advances in experimental neuroembryology, in neurophysiology, in the relation of genetic factors to the development of the nervous system, in the ultramicroscopic structure of neurons and synapses, in histochemistry of the nervous system, and in endocrine interrelations, attention has turned to the relationship of data from such fields to behavior, with little or no attempt at correlation with the sequential changes in activity, or overt behavior, as development progresses. However significant the data from any specialized field may prove to be, they can contribute only in an ancillary capacity to our knowledge and understanding of the manner in which behavior develops. Discovery of the causes and mechanisms involved in behavior will depend upon acquiring a more complete knowledge of the developmental sequence of the reactions of the fetus to its total environment, upon correlating this knowl-. edge with the morphologic development of the nervous system, with the relevant knowledge from neurophysiology, and with the part played by genetics and prenatal function, when their roles are better understood than at present. Neither the mechanisms nor the causes of behavior can be determined when prenatal activity, which constitutes the “taproot of behavior [Gottlieb, 19641,” is ignored.

11. Historical Background Because we are concerned here with the development of human fetal behavior, a routine review of the behavioral literature related to other vertebrates would contribute little value. Therefore, only the references that are relevant to the points considered will be included. The reviews of Carmichael (1934, 1954), of Coghill ( 1 940), of Hamburger (1 963, 1964), of Hooker (1942, 1944, 1952), and of Windle and his collaborators ( 193 1- 1950) cover these fields. For the observations on human fetal behavior, however, a short resume of the various investigations is appropriate. Some mention of human fetal movements was made in the nineteenth century, even as early as 1837 (Erkbam), but the systematic collection of data began in 1920 with the well-organized investigations of the psychiatrist, Minkowski. The isolated observations made earlier by Strassman ( 1903) and by Yanase ( 1 907) will be considered later (Section

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Tryphena Humphrey

IX). Although the data of Minkowski (1928) were based on “75 or more fetuses [Hooker, 19521,” including both normal fetuses and those having transection of the central nervous system at different levels, no fetuses under 40 mm in crown-heel length were examined. Consequently, the earliest developing reflexes were not seen. All of his conclusions were based on observations dictated when the reflexes were elicited. For fetal reflexes that include action in several areas, the rapid speed of execution makes complete analysis of the movements virtually impossible. Therefore, the accuracy of the reports of Minkowski is truly remarkable. Other investigations of human fetal reflexes during this period were made by Bolaffio and Artom ( 1 924), who reported on about 28 fetuses, but without the maintenance of as satisfactory environmental conditions or methods of stimulation as used by Minkowski. Somewhat later several human fetuses were tested with a variety of stimuli by Windle and his collaborators [Fitzgerald & Windle, 1942, 15 fetuses, 18.0 to 26.0 mm crown-rump measurement (CR); Windle & Becker, 1940, 3 fetuses, 34-40 mm CR length]. Only four of the small fetuses (20.0-26.0 mm) were motile, but “Continuous motion picture records of the experiments performed at the operating table were made [Fitzgerald & Windle, 1942, p. 1601.” Unfortunately, the pictorial records were not published. Reports on human fetal reflexes have appeared during recent years from the USSR (Golubewa, Shulejkina, & Vainstein, 1959; Mavrinskaya, 1960). Most of the data are from observations on older fetuses and premature infants. It has not been possible either to determine satisfactorily the total number of cases studied or to correlate activity with fetal age in many instances. The present account of human fetal activity is based almost entirely on the observations begun in 1932 by Davenport Hooker at the University of Pittsburgh. From 1938 to 1963 the author was associated closely with this program. The investigations on fetal activity include premotile embryos and a total of 136 motile fetuses and premature infants. Motion picture records are available for the majority of these cases and dictated records for the others. It is on the analysis of these motion picture records, however, both by Hooker and by the author, that the interpretations presented in this paper are based.

111. Theories on the Development of Behavior Most theories tend to emphasize one major aspect of a problem without equal consideration of other points. After one theory is set forth, an opposing one is proposed, supporters for both appear, and variations

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5

and modifications of the theories arise. The theories, or parts of them, may be applied in related fields, with beneficial or adverse effects. Without additional evidence, however, interest diminishes, only to reappear later, when new evidence is found. Such is the history of the investigations on the development of human behavior. The revival of interest and the relation of prenatal activity to the development of postnatal behavior make it especially appropriate to review the major theories at the present time. A. TOTALPATTERN CONCEPT OF COGHILL AND OTHERS

From his observations on tailed amphibians, Coghill ( 1929) found that reflex activity in response to touch began in the cervical region and spread caudalward throughout the trunk to include the tail, as development progressed. At first the extremities were moved passively by the change in the position of the trunk. Consequently, the forelimbs were moved earlier than the hindlimbs. Later, when the extremities moved independently, the action appeared in a proximodistal sequence. From these observations Coghill (1929, p. 38) concluded that “Behavior develops from the beginning through the progressive expansion of a perfectly integrated total pattern and the individuation within it of partial patterns which acquire various degrees of discreteness.” Coghill found that gill movements, like limb activity, occurred with head and trunk movements before appearing alone. Similarly, jaw movements began in association with a forward jump involving both trunk and extremities. After making extensive correlations with the observations of Minkowski (1928) on human fetal activity, and with the development of behavior in other higher vertebrates, Coghill ( 1 940) concluded that mammalian behavior followed the same general sequence in development. Whereas Coghill stressed the basic pattern underlying development throughout vertebrate phylogeny and emphasized the involvement of the total organism in the development of overt behavior, others attached more significance to the differences between behavioral development in Amblystoma and that in other vertebrates, particularly mammals. Because the first reflexes to appear were usually limited to the neck region (or the neck and upper extremities) they were interpreted as local reflexes (Windle, 1950; Windle & Becker, 1940) rather than the initial stage in the development of a total body response which is limited in its extent because only the cervical region of the neuromuscular system has attained a functional level of development. In his recent investigation on the development of activity in macaque fetuses, Bodian ( 1 968) also made this interpretation.

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Tryphena Humphrey

Coghill related the primitive sensory and motor systems in Amblystoma with the early total pattern phase of behavior, and the permanent motor neurons and sensory ganglia with the appearance of independent limb reflexes. Although it was later shown that some nerve cells comparable to the primitive neurons of lower vertebrates may appear briefly and degenerate in human embryos (Humphrey, 1944, 1950), the supposed lack of a primitive neuronal system in mammals led certain investigators (Ranson, 1943; Windle, 1934) to deny that mammalian behavior could include a total body reaction comparable to Coghill’s total pattern. From his observations on rat fetuses, however, Angulo y Gonzalez ( 1932) concluded that mammalian behavior developed in the general sequence demonstrated by Coghill. The observations of Coronios ( 1933) on cat fetuses support the concept of Coghill to a considerable degree, although those of Windle and his associates on the cat and rat do not (Windle, 1934; Windle & Griffin, 193 I ; Windle, Minear, Austin, & Orr, 1935; Windle, Orr & Minear, 1934). Carmichael (1934, 1954) did not agree with Coghill’s concept in all respects, but the behavioral sequence that he demonstrated for guinea pig fetuses has a surprisingly close relationship. For the sheep, Barcroft and Barron (1939) found localized (or segmental) reflex activity relatively early in development, but concluded that local reflexes “do appear to become segregated out from the total responses in the sense implied by Coghill.” B. LOCALREFLEXCONCEPTOF WINDLE

In the early papers of Windle and his associates (Windle, 1931; Windle & Griffin, 1931; Windle, O’Donnell, & Glasshagle, 1933), behavioral development in the cat was reported to follow the pattern shown by Coghill. After Swenson (1928, 1929) described the simple local limb reflex of rat fetuses secured by lifting a limb and releasing it, Windle .nd his collaborators made similar observations on other mammals SL :h as the cat, (Windle, 1934; Windle & Griffin, 193 1; Windle et al., 193 4) as well as on the rat (Windle et a f . , 1935). From these investigations and from their observations on the behavior of chick embryos (Orr & Windle, 1934; Windle & Orr, 1934), Windle and his associates concluded that in the higher vertebrates simple, local reflexes constitute the units of behavior which are combined and integrated secondarily to build up coordinated behavioral patterns. Because the observations on human fetuses were not made with the placental circulation intact, but while the fetal oxygen supply was diminishing and carbon dioxide and other metabolites accumulating, Windle considered total pattern reflexes to be abnormal mass movements and not the beginning stage in normal behavioral development.

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C. OTHERVIEWSON BEHAVIORALDEVELOPMENT

Other theories on the development of behavior that deserve special mention are those of Kuo and of Hamburger, who studied the development of behavior in birds, and of the Soviet investigators who worked with human fetuses. In his book on the development of behavior, Kuo (1967, p. 92) emphasized that for any given response and in any given stage of development, the entire organism is involved, either actively or passively. Kuo introduced the concepts of “behavioral gradients” and “behavioral potentials” and stressed that visceral activity and biophysical and biochemical changes are essential parts of the responses of an animal. As the resuIt of their investigations on the development of activity in the chick, Hamburger and his collaborators (Hamburger, 1963; Hamburger, Balaban, Oppenheim, & Wenger, 1965) recognized two components in the development of behavior that “can be dissociated from each other [Hamburger, 1963, p. 35 I]”- spontaneous activity and reflexogenic motility. Furthermore, Hamburger postulated that spontaneous activity is the primary type of behavior and that reflexogenic activity is secondary to it (see Section VII). Spontaneous activity is not integrated and consists of periodic (or cyclic), rhythmic movements resulting from the “self-generated automatic discharge of neurons [Hamburger, I963 p. 3511.” Spontaneous activity was recognized by Weiss in 1955 as uncoordinated. The activity is not random, however, and the marked periodicity is not altered by sensory input (Hamburger, Wenger, & Oppenheim, 1966). The views of the Soviet workers are based mainly on their observations on human fetuses, but data on the earliest stages in the development of reflex activity are lacking. Their theory of behavioral development stresses heterochronic maturation of the different organs of a system and systemogenesis during behavioral development, that is, selective maturation to create the functional systems which must be mature enough at the time of birth for survival (Anokhin, 1964; Golubewa et al., 1959).

IV. Methods of Investigating Behavioral Development Because the following account is concerned particularly with the development of human fetal behavior, the methods discussed are those related to mammalian investigations. Studies of subhuman mammalian fetal activity can be made with the fetus in situ, but, although tried by Fitzgerald and Windle (1942), this procedure has not been used by

8

Tryphena Humphrey

others for human fetuses. Instead, either the fetus and placenta are removed together at Cesarean section or the umbilical cord is cut. Consequently, the fetal oxygen supply is soon diminished and metabolites accumulate. Anesthetics and drugs given the mother also affect the fetus. In other mammalian investigations, the placental circulation can be maintained for some time and the effects of anoxia and of maternal drugs and anesthetics can be avoided. In addition, the activity can be observed for a longer time, both within the amniotic sac and after removal. Therefore, both reflexogenic and spontaneous movements may be documented repeatedly. Upon removal from the amniotic sac, however, an isotonic fluid bath is essential in order to allow free movement and prevent surface drying. Maintaining the fluid bath at normal body temperature helps to simulate the intrauterine environment. Also the state of relative weightlessness and the lack of gravity effects within the uterus (Reynolds, 1962) are partially reproduced when the fetus is immersed in fluid. A. METHODSOF

RECORDING ACTIVITY

Motion picture recording of fetal activity is unquestionably the most satisfactory and accurate method, for each action may be studied repeatedly. Normal speed (16 frames per second) suffices for the most part, but an exceedingly fast reflex or a rapid part of a complex reaction may be completely missed. Slow motion photography eliminates this handicap, but provides other disadvantages, the major one being the increased cost. Slow motion and normal speed together overcome most of the technical problems. Photographic prints can be made for study andlor publication when color photography is used, but the advantages of color may not be great enough to offset the increased cost. Many of the drawbacks of photography at normal speed may be overcome by studying the films with a motion picture projector that can be slowed, stopped on a single frame, and run by hand so that adjacent frames may be compared repeatedly. Even so, some points may escape detection, may be uncertain, or may be wrongly interpreted without photographic prints. Spaced prints are sufficient if the action is slow, but every frame is needed if the action is quick. By this method each frame showing a reflex can be compared with every other frame. The mouth opening of small fetuses (26.0-28.0 mm CR; Figs. lB, 2B, and 22C) and the position of the tongue in older fetuses (Figs. 7A-B, 8B, 9B, and 19B) are examples. When mouth opening reflexes are first demonstrable, usually only the more extensive, rapidly executed head, trunk and extremity movements are seen, either when the reflex is elicited or later

The Development of Human Fetal Activity

9

when the motion pictures are viewed at normal speed. Likewise, any local activity of older fetuses that either requires less than half a second or is not near the area stimulated is easily missed (Humphrey, 1968a, Figs. 6-7 and 11). By far the greater number of investigations of vertebrate behavior have been based on dictated records alone, although the action was watched by more than one observer. Sometimes magnifying lenses have been used (Windle & Griffin, 1931). Angulo y Gonzalez (1932), Coghill (1929), and Coronios (1933) supplemented their direct observations to a varying degree with motion picture recording. Angulo documented his published account with photographs and Coghill (1929) illustrated the reflexes that he described with drawings from his motion pictures. However, the few reports on the development of reptilian behavior (Lacerta, Hughes, Bryant, & Bellairs, 1967; turtle, Smith & Daniel, 1946; Tuge, 1931) are not based on motion picture recording. In the study of Gottlieb and Kuo (1965) on the prehatching behavior of the Peking duck, motion picture color photography was used, but neither the more recent investigations of Hamburger ( 1 963, 1964) and his associates (Hamburger & Balaban, 1963; Hamburger & Oppenheim, 1967; Hamburger et al., 1966) on avian behavior nor the earlier ones of Windle and his collaborators (Orr & Windle, 1934; Windle & Orr, 1934) employed this technique. Bodian ( 1 968) used cinematographic recording in studying the activity of macaque fetuses, but he did not supplement his published descriptions with photographs. Although Fitzgerald and Windle (1942) recorded the activity of four small human fetuses with motion pictures, no photographs were published. B. TYPESOF STIMULI USED

Reactions to tactile stimuli precede vestibular sensitivity in the chick, according to Gottlieb (1968), and proprioception follows later. Sensitivity to touch develops early for human embryos also. When light touch first constitutes an effective stimulus, all sensory nerve fibers approaching the sensitive surfaces consist of naked, growing nerve tips. Those nearest the epithelium are in the region of the lips (Hogg, 1941; Humphrey, 1966b), but the most superficial cones of growth are still 13-20 p below the basement membrane that separates the epithelium from the underlying tissue when they first become sensitive to light touch. Lightly stroking the cutaneous surfaces with graded hair esthesiometers of known pressure values provides adequate stimulation for eliciting reflexes from human (Hooker, 1942, 1944, 1950, 1952) and other mam-

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Tryphena Humphrey

malian fetuses. Stroking the skin several times is the most effective technique because it produces both spatial and temporal summation; repeated punctate stimuli rarely elicit a reflex. The tips of the stimulators must be covered with an inert, smooth coating to prevent penetration of the epithelium and cause muscle contraction by direct stimulation. If comparisons and correlations are to be made with investigations on other mammals or with other observations on the same one, it is essential to record the type of stimulus and the area stimulated, as well as the reaction elicited. Heavy pressure over a muscle with a probe, for example, or stretch stimuli produced by abducting or extending a limb do not excite the polysynaptic reflex arcs stimulated by light touch but activate the monosynaptic arcs of stretch reflexes. Pressure on the amniotic sac produces effects that are practically impossible either to evaluate or to equate with other types of stimuli. Because the stimuius is transmitted through fluid, it is not only intensified, but also probably transferred to almost all surfaces of the fetus to a varying degree. Therefore stimuli applied to the amniotic sac produce stronger excitatory effects than those of the same strength applied to the fetus directly. Because the fetus is in a confined ovoid space, both lateral flexion and extension of the head and trunk will be more limited in extent than extremity movements. Since they are so inconspicuous, the head and trunk movements may be missed entirely unless photographic prints are compared carefully. Sharp needles or even a stiff hair may cause direct stimulation of the underlying muscle, not reflex action. In the perioral region before the underlying muscle has developed, such strong “mechanical” stimuli will elicit a true reflex distally in the neck and trunk muscles before light touch is effective (Fitzgerald & Windle, 1942). Faradic stimulation of the snout of a small fetus is also effective (sheep, Barcroft & Barron, 1939). Such types of stimuli demonstrate that the polysynaptic arcs are capable of functioning before the epithelial surfaces become sensitive to stimulation. C. EFFECTSOF ANOXIA, ASPHYXIA, ANESTHETICS, NARCOTICS, AND OTHER DRUGS

Almost all investigations on the development of behavior in mammalian fetuses discuss these effects to some extent and extensive accounts are given in the papers of Hooker (1942, 1944, 1952), Humphrey (1 953), and Windle (1944). After placental separation or severance of the umbilical cord, anoxia develops progressively as the oxygen supply is depleted. As carbon dioxide and other metabolites accumulate, asphyxia suppresses all reflex activity.

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When the fetus is first removed from the uterus, most investigators have noted a brief period of quiescence during which reflexes are elicitable with difficulty or not at all (Hooker, 1952; Windle, 1944; Windle & Becker, 1940). These observers and others have suggested that the slight increase in carbon dioxide that soon follows placental separation heightens the excitatory state before asphyxia suppresses activity enti re1y . From their observations on mammalian fetuses, Angulo y Gonzalez (19321, Hooker (1952, 1954) and Windle (1940) all noted that anoxia suppresses the most recently functional reflex arcs first of all, whereas the first arcs to mature remain functional longest. The difference depends on the fact that the more mature reflex arcs require less oxygen to function than do those more recently formed. I t is evident, therefore, that for human fetuses the most newly acquired reflexes can be elicited only at or near the beginning of a period of observation. Consequently the total pattern reflexes remain after asphyxia suppresses other reflex activity. Because the total body reactions are present when anoxia is well advanced, Windle ( I 944) considered them abnormal. However, an analysis of the research literature (Humphrey, 1953) indicates that a reflex may be weak or strong, but otherwise true to type. A reflex that is absent when the nervous system is intact, however, may be seen when there is damage (Humphrey, 1968a, 1969d). Sometimes also a reflex, such as the Babinski sign, may be a normal part of development during fetal life and for a period postnatally, but indicate brain damage in adult man. General anesthetics, including the barbiturates (Goodman & Gilman, 19651, cross the placental barrier and anesthetize the fetus as well as the mother. Narcotics like morphine, codeine, and other opium derivatives also suppress fetal movements, as do tranquilizers. If such drugs have been administered preoperatively and a general anesthetic used, the fetus may be completely inactive. If, however, a spinal or a local anesthetic is employed, the fetus will be active. Although Demerol enters the placental circulation as do other opium derivatives (Goodman & Gilman, 1965), apparently it is transferred to the fetus more slowly, for Hooker ( 1 952, 1958) noted no depression of fetal reflexes when it was administered approximately an hour preoperatively. Examination of the known effects of such drugs leads to the conclusion that fetal reflexes are either suppressed or diminished, but, as in anoxia and asphyxia, they do not become abnormal. Because the effects of anoxia cannot be eliminated entirely, however, the reflexes elicited under the best conditions may not represent the most recent functional capabilities of the fetus. The true capacity at any age will be demonstrated only when the conditions are optimal. In interpretating data on human fetal behavior, there-

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fore, it must be remembered that the activity that has been demonstrated at any given age level may not represent the full motor potential for the age in question.

V. Activity in Response to Tactile Stimulation of Human Fetuses The following behavioral sequence for human fetuses is based almost entirely on light tactile stimuli as described by Hooker (1942, 1944, 1952; see Section IV, B). Stroking the cutaneous surfaces with graded hair esthesiometers was the common technique employed. In a few cases, a glass rod was used, so some degree of pressure was probably exerted also. Except for fetuses approaching the age of viability, the observations were made with the fetus in an isotonic bath (usually Tyrode’s solution) kept at normal body temperature. Three or more crownrump measurements (CR) were made after the reflexes ceased while the fetus was still in the isotonic bath. These were checked with the tables of Streeter ( 1 920) in determining the menstrual ages used throughout the following account, unless otherwise stated. A. THEPERIODOF WIDESPREADREACTIONS - COGHILL’S TOTALPATTERN

The youngest fetus from which Hooker elicited a reflex by stimulation of the nose-mouth area (the perioral area) supplied by the maxillary division of the trigeminal nerve was 7.5 weeks of menstrual age (20.7 mm). The reflex consisted of contraction of the neck muscles on the side opposite or contralateral to the stimulus with flexing or bending the head away from the stimulator. This is the avoiding reaction of Angulo y Gonzalez (1932), Coghill (1929), Hooker (1952), Humphrey (1952, 1964), and others. Fitzgerald and Windle ( 1942, p. 167) elicited contralateral head flexion “without movements of the trunk and arms” by “strong mechanical stimulation” of the maxillary region of a 20.0 mm embryo for a period of “about 3 minutes.” The 22.6 mm fetus (No. 131) of Hooker’s motion picture series was stimulated after removal from the amnion. Eleven contralateral flexion reflexes were elicited. The single ipsilateral response consisted only of lateral head movement. The contralateral reactions varied from lateral flexion involving the upper trunk, and extending to the pelvic region in one of the reflexes, to muscle contraction in the neck region alone toward the end of the active period. At this age, the hands of the living fetus at rest obscure the mouth with the palms toward the chest and the finger tips close together but not overlapping. The soles of the feet face

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13

each other. The hands uncovered the mouth a trifle in only one of the contralateral flexion reflexes of the 22.6 mm fetus, a shift in position that is clearly due to active backward movement of the arms at the shoulders (arm extension). In the other reflexes, the arms were moved passively with the trunk when it flexed lateralward. The soles of the feet did not separate, even when the pelvis was included in the reflex. Because the soles of the feet pull apart if there is movement at the hip joints (Figs. IB, ID, and 2B), it was concluded that the lower extremities were moved passively in the single reflex showing lateral flexion of the pelvis. This extensive reflex was elicited near the beginning of the observations, whereas most of those restricted to neck and upper trunk flexion were noted toward the end of the activity. Using a probe to exert pressure on the mouth and nose area, Fitzgerald and Windle ( I 942) elicited contralateral neck and trunk muscle contraction in a 22.5 mm human fetus (considered to be affected by anoxemia before the observations began) and stronger stimulation over a greater area of the face resulted in a response of “greater magnitude” with movement of both the arms and legs “with the body at their attachments [p. 1621.” They reported that ipsilateral responses predominated. Probably these reflexes were elicited with the embryo still in the amnion but this point is not clear in their account. Pressure on the amniotic sac with a 23.0 mm fetus inside and with the placenta still attached was reported to cause quick reactions of the extremities and lower trunk, sometimes the arms or the legs alone, or with a stronger tap on the amnion, sometimes together, but no head movements were seen, either at the time the reflexes were elicited or identified in the motion pictures. N o reflexes were obtained from any of these small fetuses (20.0-26.0 mm CR) by stroking or touching the trunk and extremities. The differences between the activity reported by Fitzgerald and Windle and that just described from Hooker’s motion pictures are due in part to the differences in the stimuli used (see Section IV, B) but also to failure to see the slight trunk and head movements when the extremity action is much greater (see Section IX). Twelve contralateral flexion reflexes were elicited by perioral (nosemouth area) stimulation of a 25.0 mrn fetus (No. 4) in Hooker’s series, but none ipsilaterally (Humphrey, 1968a, Table 1). By 26.0 mm CR (Figs. l A , 1C) or 27.1 mm CR (Fig. 2A), the fingers covering the mouth may overlap. In 4 of the reflexes at 25.0 mm, both the hands and the soles of the feet separated, showing that both shoulder and hip girdle muscles contracted. In 3 others, the hands separated, but not the feet, so only the upper limbs moved actively. The remaining 5 reflexes were limited to trunk and pelvic flexion, with neck flexion appearing only once. Rump rotation was seen twice, and lateral flexion of the pelvis was

Fig. 1 . A and B are prints f r o m a motion picture sequence showing contralateral head, trunk, and rump flexion in response to stimulation of the f a c e with a hair esthesiometer (black line across nose). C shows the return t o the rest position, followed immediately by an ipsilateral flexion reflex (D)including rotation of the pelvis as well a s flexion of the head, trunk, and rump. A s part of the contralateral reflex, the mouth opened (arrow on B), but the hands obscure the mouth during the ipsilateral flexion reflex in D . The photographs of the fetus are slightly larger than its 26.0 m m C R length ( N o . 24, 8.5 weeks, menstrual age). The action illustrated in A and B required '/4 second and that shown in C and D just under $5 second. The entire reflex sequence was reproduced by Hooker (1939).

Fig. 2. A and B are prints from a motion picture sequence following stimulation of the face by drawing a hair esthesiometer from the area lateral to the mouth upward over the bridge of the nose of CI 27.1 nim human fetus ( N o . 116, 8.5 weeks, menstrual age). T h e stimulator overlies the nose in A but does not touch it. In addition to a contralateral bending of the head. trunk, and rump there is some pelvic rotation in B. where the mouth is also open (arrow at corner of mouth). the asymmetrical extremity movements include finger spreading, and there is separation of the soles of the feet. The photographs are about 1.5 times natural size and the action shown covered less than h a l f a second. C is a photograph showing the peak action of a comparable contralateral flexion reflex of a 34.3 m m fetus ( N o . 134, 9.5 weeks, menstrual age). Note the more widely open mouth ( a t arrow) and the greater separation of the soles of the feet. T h e photograph is reproduced at about I .3 natural size. Approximately % second elapsed f r o m the beginning of the reflex to the frame reproduced here.

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15

maintained even after the return to position was complete. Probably active mouth opening also accompanied the vigorous reflex in which the soles of the feet separated (Humphrey, 1968a). Many of the contralateral flexion reflexes elicited by perioral stimulation of the active fetuses from 26.0 to 36.0 mm, CR length, included active mouth opening. The head, trunk, and pelvic flexion was accompanied by rump rotation more often in the older fetuses of the group and the extremity movements increased in amplitude and complexity. This is demonstrated by comparison of Fig. 1 A-B with Fig. 2. At 26.0 mm (Fig. 1 ) the upper extremity movements consist mainly of extension at the shoulder, whereas at 27.1 mm (Fig. 2A-B), the arm extension is accompanied by some forearm flexion and flexion at the wrist, and even some spreading apart of the fingers (Fig. 2B). At 9.5 weeks (Fig. 2C, 34.3 mm CR), these upper extremity movements are more pronounced and distinctly asymmetrical. Movement of the lower extremities at 26.0 mm (Fig. 1 B) was limited to sufficient lateral rotation and abduction at the hip joints to separate the soles of the feet slightly and rotate the knees lateralward. The soles of the feet separated farther in slightly older fetuses (Figs. 2 8 and 2C), and study of the motion pictures indicates that both the toes and the fingers sometimes spread apart. However, the toe action could not be documented satisfactorily by photographic prints due to the minute changes in position of these short digits and the separation of the toes even in the rest position (Fig. I 1A-B). Mouth opening constitutes an integral part of the more vigorous contralateral flexion reflexes elicited by perioral stimulation during this period. Active depression of the lower jaw separates the lips, at first only in the midline region (arrow on Fig. 1 B), but in a fetus only a little larger the lips may part slightly as far as the corners. By 9.5 weeks the lips sometimes separate completely to the corners (Fig. 2C). There is a distinct time sequence for the movements in these total pattern reflexes: first the head bends lateralward, then the hands uncover the mouth as the upper extremities move backward at the shoulders, and additional trunk and pelvic movement follows. The mouth may be open when uncovered by the hands, or may open on the succeeding motion picture frame, or may remain closed until the lower extremity action separates the soles of the feet. The mouth closes more slowly than it opens, just as the trunk and extremities return to the original position more slowly than the lateral flexion developed. Beginning mouth closure is not often seen for the hands usually return to their rest position before the change commences (Humphrey, 1968a, Figs. 4-5). When the motion pictures are observed at normal speed, the small differences between these total pattern lateral flexion reflexes are not seen, and the stereo-

16

Tryphena Humphrey

typed character of these reflexes, as emphasized by Hooker (1952, 1958; Humphrey, 1964), is a prominent feature of the reactions during this period. Ipsilateral flexion reflexes were not elicited either so early or so frequently as contralateral responses from the fetuses studied by Hooker and his co-workers. A single ipsilateral reaction, involving head movement only, was recorded from the 22.6 mm fetus although there were 11 contralateral reflexes extensive enough, as a rule, to include trunk flexion. There was enough active extension of the arms at the shoulder joints to move the hands away from the mouth in only 1 reflex. From 8to 10 weeks (25.0-40.7 mm CR, Humphrey, 1968a, Table 1) only 10 of the 208 total pattern lateral flexion reflexes elicited by perioral stimulation were ipsilateral (4.8 %). Mouth opening accompanied over 43 % of the 198 contralateral flexion reflexes, but was seen with ipsilateral reactions only once during this period (at 10 weeks), probably because the ipsilateral hand usually obscures the mouth. Most of the ipsilateral reflexes are less extensive than the contralateral reactions, but in a few instances may be greater (compare Figs. 1A-B and 1C-D). In general, the ipsilateral reflexes appear to be executed more slowly than those contralateral to the stimulus (Humphrey, 1968a). In other words, the negative avoiding reaction, or withdrawal, is a more rapid one than the positive reflex in which the area touched approaches the stimulus (Section V, B, 2 and 3). From 7.5 weeks to 10 weeks of menstrual age, no local reflexes have been elicited from human fetuses by tactile stimuli of cutaneous surfaces. Mouth opening, reported earlier (Hooker, 1952, 1958; Humphrey, 1964, 1966b) as a local reflex at 9.5 weeks has now been shown to occur as part of the total pattern reflexes, as just described (Figs. 1A-B and 2; see also Humphrey, 1968a, 1968b, 1969b, 1969c, 1969d, 1969e). The limb reflexes reported by Fitzgerald and Windle (1942) for 23.0 mm and 26.0 mm fetuses were elicited either by tapping or by pressing on the amniotic sac (Section V, A) not by stimulating the cutaneous surface. Until 10 weeks also, only the areas of the face supplied by the maxillary and mandibular divisions of the trigeminal nerve are sensitive to stimulation. The oral mucosa has not been tested for reflexes, but it may be sensitive to stimuli early because the nerve fibers are closer to the mucosal epithelium than to the cutaneous surfaces at the age when the earliest reflexes have been elicited (Humphrey, 1966b).

B. THEDEVELOPMENT OF LOCALIZED REFLEX ACTIVITY 1. The Transition Period Beginning at the 10.5 week age level (Hooker, 1960), the palms of the

The Development of Human Fetal Activity

17

hands become sensitive to stimulation, then the soles of the feet (1 1 weeks). The upper and lower extremity reflexes elicited by palmar and plantar stimulation are independent of head and trunk reactions (Section V, B, 4). Also there appears to be a decrease in the number and in the amplitude of the reflexes elicited by perioral stimulation at this time (Humphrey, 1968a). However, the motion picture material at 10 to 10.5 weeks is less adequate than either earlier or later, because more of the fetuses were influenced by the drugs given the mother. Consequently, the decrease in activity may be partly due to the effect of the drugs. Nevertheless, the character of the activity changes between 10 and I 1 weeks. The position at rest also differs. The hands no longer cover the mouth but face each other, and the soles of feet face somewhat downward (Figs. 3 and 6). Lower extremity movements are a less consistent part of the total pattern, contralateral flexion reflexes and mouth opening are less frequent. In these reflexes also, the chin occasionally rotates ipsilateralward when the head flexes contralateralward, and the hands may extend instead of flex. By 11 weeks, head, trunk, and pelvic extension reflexes (Fig. 3) often replace the lateral flexion reflexes, particularly when the perioral stimulation is near the midline. No mouth opening accompanies these extension reflexes. At rest (Fig. 3A), the vermilion borders of the lips show, but at the height of the reflex (Fig. 3B) the lips often appear to tighten somewhat or to be compressed (Humphrey, 1968a, 1969d), for the borders almost disappear. Sometimes the lower extremities extend at the hips, knees, and ankles (Humphrey, 1968a, Fig. 8A), but this action may be limited to slight extension at the hips (Fig. 3). The arms may move forward (flexion at the shoulder joints), there may be forearm extension, and the fingers may extend a little. Although there is some variability in response to perioral stimuli, both the head and trunk extension reflexes and the contralateral flexion reflexes are stereotyped (Hooker, 1952). Like the reflexes during the earlier period, these reflexes are characteristic for the age level. On two occasions, mouth opening reflexes were noted at 1 1 weeks in response to pulling the fetus by the umbilical cord with its back toward the substrate. Both of these oral reflexes were accompanied by some lateral head and trunk flexion and by extremity movements (Humphrey, 1968a, Figs. 6-7; 1969d). These reflexes are of particular interest because of the rapid mouth closure and the equal (but slight) separation of the lips at the midline and at the corners. Just prior to this period, there is an increase in development of the superficial muscles about the mouth (Gasser, 1967) which may account for the changed contour of the lips. The quick, snaplike closure indicates that stretch of the muscles of mastication has become an effective stimulus for their contraction.

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Tryphena Humphrey

Fig. 3. T w o photographs showing an extension reflex following stimulation of the lips of an I I-week fetus ( N o . 6 5 , 48.5 m m C R length) when touched by the clamp on the umbilical cord. In A the action has not yet begun. In B the head, trunk, and rump extension is illustrated just after the peak of the reflex was attained when there was some beginning return to the rest position. At its peak, this reflex included also a slight compression of the lips, extension of the left forearm with some j e x i o n at the shoulder, and extension of the lower extremities at both the knees and hips. The reproduction is at ubout I .2 normal size.

The extension reflexes following perioral stimuli decrease in frequency by 11.5 weeks. An initial head extension may be followed by some contralateral head and trunk flexion combined with rotation of the head, and accompanied by rump rotation and approximation of the palms of the hands (Hooker, 1939, plate on p. 43; Humphrey, 1968a Fig. 9). In these reflexes the mouth is open farther at the midline than laterally. From 11.5 weeks onward stimulation of the perioral region usually produces little or no lower extremity activity. The upper extremity action decreases also, but to a lesser degree. Activity is more often limited to the facial area and is more variable. Head movements frequently constitute part of the reaction when the perioral area is stimulated, but movements of the hand largely disappear (Humphrey, 1968a, 1969b, 1969d).

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19

2. Avoiding and Protective Reflexes The first contractions of the cervical muscles on stimulating the perioral area are avoiding or withdrawal reflexes that are potentially protective, for the area touched is moved away from the stimulus (Humphrey, 1964, 1968a, 1969b, 1969c, 1969d). The extensive total pattern contralateral flexion reflexes that involve all extremities also are avoiding as are the head and trunk extension reflexes that follow them. The quick, snaplike mouth openings and closures accompanied by head, trunk, and extremity action at 1 1 weeks have also been considered potentially protective (Humphrey, 1968a, 1969d). As these total pattern reflexes disappear, local reflexes of a potentially protective nature replace them. Stimulation of the eyelids at 10.5 to 1 I weeks elicits a squintlike contraction of the orbicularis oculi muscle. This reflex is the first truly local reflex elicited by stimulation of the face, for at first there is no other activity with this eyelid movement. Slightly later, contralateral head, trunk, and pelvic flexion may accompany the reflex (Hooker, 1952; Humphrey, 1966b). Contraction of the corrugator supercilii may follow stimulation over the eyebrow area to give a scowl-like movement at 1 1 weeks, as a separate reaction at first, but soon combined with the orbicularis oculi action. At 14 weeks the squintlike orbicularis oculi reflex was accompanied by retraction of the angle of the mouth and elevation of the ala of the nose following stimulation upward over the mandible and across the eyelids (Fig. 4). In this reflex, trunk and lower extremity extension may be present or absent (Humphrey, 1968a, Fig. 14). In a 16-week fetus (Fig. 5 ) orbicularis oculi and corrugator supercilli contraction (squintlike and scowl-like reflexes) have been seen combined with slight closure of the lips, with no trunk or extremity movements and only a minute amount of head extension at the end of the reflex. Potentially, at least, reflexes of this type are protective, just as are the avoiding total pattern reflexes during earlier development. Combined with bilateral corrugator action and bilateral retraction of the corner of the mouth, these reactions in animals bare the teeth and produce a ferocious appearance. In human postnatal development they constitute one of the mechanisms for emotional expression.

3 . Reflexes Related to Feeding The first total pattern reflexes related to feeding are the ipsilateral flexion reflexes that bring the perioral area stimulated toward the stimulus (Humphrey, 1964, 1968a, 1969b, 1969d). Ventral head flexion and rotation of the face ipsilateralward serve the same purpose. These positive reactions, in which the area touched approaches the stimulus, have

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Tryphena Humphrey

Fig. 4 . Four frames from a reflex elicited by drawing the stimulator from the cheek (in B). The head extended and flexed or bent to the side opposite the stimulation ( B and C ) , the angle of the mouth retracted, and the upper lip elevated slightly near the corner ( 0 and C ) . Also, the orbicularis oculi muscle contracted so that the ipsilateral eyeball was flattened and the fusion line between the eyelids almost disappeared (Cj. Finally the fuce rotated away f r o m the side stimulated and the mouth opened more widely f D),but without the upper lip elevation seen in 0 and C . The entire reflex, as reproduced by Hooker (1939), shows trunk extension in the lumbosacral region and extension of the lower extremities (between C and D ) . The part reproduced here covered a time span of I !4 seconds. Other reflexes of this 14-week fetus are reproduced in Figs. 13, IS, 17, and 18. Those in this figure are slightly less than 0.4 the size of the fetus. A) upward across both eyelids (in

neither been seen so early prenatally nor occur so frequently as the avoiding reactions (contralateral head flexion, head extension, and rotation of the face away from a stimulus; Humphrey, 1964, 1968a, 1969b, 1969d). Mouth opening (and closure) as part of the total pattern reflexes at 8.5 weeks precedes swallowing. In these reflexes mouth opening is due to contraction of the muscles that lower the mandible (Humphrey, 1954). Until 11 weeks, closure is probably passive, that is, due to relaxation of the muscles, for the time involved is significantly greater than the time for mouth opening (Humphrey, 1968a, 1969b, 1969d). By 1 1 weeks, at least, and also at 12.5 weeks, when the mouth has been seen to snap shut rapidly (Humphrey, 1968a; Figs. 6, 7 and 1 l), evidently closure is sometimes due to a stretch reflex resulting from the pull on the muscles when the jaw is lowered. Swallowing has been reported as early as 12 to 12.5 weeks (Hooker, 1952; Humphrey, 1964, 1968a), and a characteristic reflex at 13 weeks is shown in Fig. 6 following stimulation in the oral area. Slight head extension as the mouth opened and the larynx elevated (Fig. 6B) is fol-

The Development of Human Fetal Activity

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lowed by ventral head flexion as the larynx is lowered and the sternocleidomastoid muscles again became prominent (Fig. 6C). N o other movements occurred in this reflex or in another illustrated previously at 14 weeks (Hooker, 1939; Humphrey, 1968a, 1969d). No tongue movements have been seen or recorded photographically for human fetuses until 14 weeks when protrusion and retraction of the tongue were photographed following hand stimulation (Fig. 7). Head movement accompanied the oral activity, and finger closure followed the hand stimulation (Humphrey, 1968a, 1969c, 1969d). At 15.5 weeks stimulation of the lips and tongue may cause mouth opening (Fig. 8A), tongue elevation with formation of a groove (or trough) running lengthwise (Fig. 8B), and lip closure on the stimulator when the jaw lifted (Fig. 8C), but no other movements. In the swallowing reflexes (Fig. 6) and in mouth closure following hand stimulation (Fig. 7), the action was due to elevation of the mandible by the muscles of mastication. In lip closure on the stimulator (Fig. 8), both jaw and lip movement occurred. Slight protrusion of both lips accompanied by mouth opening has been seen at

Fig. 5. Drawing the stimulator downward over the left eyebrow, the upper and lower eyelids and along the side of the nose in ( A ) elicited muscle action in three areas, allshown in B . Contraction of the cvrrugator supercilii is shown by the less prominent light area over the superciliary ridge ihat gives a scowl-like effect when the movement is seen (compare B with A and C). The contraction vf the orbicularis oculi muscle pattens the eyeball and obscures the fusion line between the eyelids (see arrow on BJ to give a syuintlike effect when seen in motion. The lips at the time of stimulation were slightly parted ( a s in A). then closed slightly (B), and reopened again as the eyebrow and eyelid returned to position, and the head extended a trifle ( C ) .N o other action took place. The time covered by this figure is just vver one second. T h e photographs of this 16-week fetus ( N o . 27. 114.0 m m C R length) are about 0.4 of its size.

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Tryphena Humphrey

Fig. 6 . Part of a swallowing reflex elicited by stimulating the lower lip in ( A ) of a fetus of I3 weeks of menstruul age ( N o . 45, 75.0 mm C R length). The grid shown in these photographs was tried to bring out small differences in position, but wus found to contribute little if anything. Following stimulation, the head extended and the mouth opened f B). As the larynx was elevated, the curve from chin to sternum rounded (see arrow) and the outline of the sternocleidomastoid muscle disappeared. When the larynx descended ( C ) , the head Jexed forward slightly and the outline of the sternocleidomastoid muscle again became clear (see arrow). but the lips remained slightly parted. There were no movements of the extremities or trunk. The action reproduced here required approximately 1 % seconds, and the photogruphs show the fetus at about 0.9 normal size.

16 weeks (Humphrey, 1968a, Fig. 22). The sequence reported by Hooker ( 1 952; Humphrey, 1964) places upper lip protrusion (1 7 weeks) before lower lip protrusion (20 weeks) with simultaneous protrusion and pursing of both lips by 22 weeks. Protrusion of the lower lip with puckering of the upper lip, on stimulation of the lower lip, has also been seen at 20 weeks (Fig. 9) with the tip of the tongue elevated behind the lips (Fig. 9C). Golubewa el al. ( I 959) reported sucking at 24 weeks and at 29 weeks Hooker ( 1 952) noted sucking strong enough to be audible. At what fetal age it is first possible to elicit a gag reflex has not been determined, but possibly much earlier than the one thus far recorded

The Deveiopment of Human Fetal Activity

23

(Fig. lo). Considerable stimulation with a glass rod was required, probably over both the back of the tongue and the posterior wall of the pharynx. N o doubt the stimulus included pressure as well as touch. The gag reflex itself was rapid and rather violent, although it was not accompanied by extremity or trunk activity (Humphrey, 1968a, 1969b, 1969d). Wide mouth opening, laryngeal elevation, spasmodic contraction of the diaphragm, depression of the floor of the mouth (Fig. 1OA-B), and partial mouth closure (Fig. 1OC) all occurred. The changes in facial expression show that some of the muscles of facial expression participated as well as those that lower and raise the mandible.

4. Extremity ReJlexes Until the hands are pulled away from their rest position covering the mouth, the upper extremities are moved passively with the trunk. As soon as the shoulder girdle muscles contract and pull the upper arm

Fig. 7. The mouth opening and tongue elevation and protrusion in A and the partial mouth closure shown in B and C followed stimulation of the palm of the ref! hand of a 14wseek fetus ( N o . 37, 88.5 mm C R length) when amniotic tissue that was caught in the fingers was pulled awa-y by the stimulator ( A and B). After the tissue was removed, the fingers closed tightly IC). The portion of the reflex shown here, from about its peak to a return to position. involved approximately 3% seconds. The photographs are shown at about 0.9 normal size.

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Tryphena Humphrey

Fig. 8. Three photographs illusrruting lip and tongue reflex activity of a 15.5-week fetus ( N o . 135, 107.5 m m CR),following stimulation by pushing the stimulator inside the mouth and moving it from the midline area across the tongue und lips to the corner of the mouth (A and B). Separation of the lips in A rims fvllowed by elevation of the tongue at the sides (light areas between lips) to f o r m a groove or trough in B (dark spot between lips near the midline). I n C, the lips closed tightly on the tim mu la tor when the lower jaw was lifted. N o other activity M ~ U Snoted. T h e period covered by the portion of the rejlex shown is upproximutely % second. The illustrutions show the fetus at about 0.7 normal size.

Fig. 9. Stimulation of the lips of this 20-week fetus ( N o . 55, 166.0 m m C R ) was followed by lip and tongue movements. A t the time of stimulution (A) the upper lip was a1ready IiJied slightly near the corner and the lips were distinctly separated. T h e lips then closed partiully (B) and, us closure becume more complete. the lower lip HWSprotruded and the tongue appeared between the lips (C). In addition, the upper lip puckered, us indicated by the greater prominence of the vertical lines. The outline of the mentalis muscle, identiJiuble in all three photographs, is more prominent in C where the lower lip is pushed outward, or protruded, and the mandible lifted slightly. N o other action took place. The portion of the rej?ex reproduced here was executed in a little under one second. T h e illustrations lire at about 0.4 the size of the fetus.

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Fig. 10. Three stages in a gag reflex elicited f r o m an 18.5-week fetus ( N o . 111, 144.5 m m C R ) by inserting a glass rod fur back in the mouth ,$,here it undoubtedly touched the back of the tongue and probably the posterior phuryngeal wall. T h e action did not begin until over 2M seconds after the rod was inserted, but was then distinctly rapid. i n A. the mouth has opened widely, but % second later it is tlosing on the rod (B). Here the change in the contour in the neck area (see arrow) indicates elevation of the larynx. T h e glass rod has been removed in C . one second later, and the mouth has reopened slightly. The surface outline in the neck region indicates that the larynx is no longer elevated. Although the uction resulting in the gug reflex was rapid, there were no movements of the lower extremities and only a $light amount of extension at the shoulder near the end of the reflex (compare C with A and B). T h e facial expression in A and B is characteristic f o r a gag reflex postnatally. Diaphragmatic spasm may have accompanied the reflex but this could not be determined satisfactorily. The time spanned by the action in this figure is I YZ seconds. and the photographs are a little less than half the size of the fetus.

backward (or extent it), the hands pull apart, then move downward away from the face. Arm extension and some separation of the hands accompanied a few reflexes of a 22.6 mm embryo and in one reflex the mouth was uncovered completely (Section V, A). By 26.0 mm (Fig. 1A-B), 27.1 mm (Fig. 2A-B), and 27.7 mm (Fig. 1 1A-B), the active upper extremity movements that are part of the total pattern contralateral flexion reflexes sometimes include flexion at the wrists (Figs. IB and 2B) and the fingers spread apart (Figs. 2B and 1 I B). Extension at the shoulder (Fig. 2B) is sometimes accompanied by slight forearm extension (Fig. 2C). By 34.3 mm CR (Fig. 2C) all of these movements of the upper extremity are more marked. During this entire period the contralateral

26

Tryphenu Humphrey

Fig. 1 1 . A and B show purr of a contralaterulflexion reflex of a fetus of 8.5 weeks ( N o . 61,27.7 mm C R length). I n A, the reflex has not yet begun and the stimulator still touches the face. I n B. the head and trunk are bent to the side opposite the stimulus: the hands no longer cover the mouth after the arms extended slightly at the shoulders und the hands flexed at the wrists and the fingers spread apart (compare leji hand in A and B). The soles if the feet separated and. when the film is viewed, the toes also appeur to spread apart. but their small size makes it impossible to document rhis motion from still pictures. I n a partial full face view like the one in B, it is not possible to determine whether the mouth is open. Part of a refex elicited within the amnion is shown in C . The small v-shaped area at the arrow is the open mouth. I n this reflex also, the fingers spread apart and the soles of the feet separated bur again it is not possible t o determine whether the toes separared beyond the position at rest. The time spunned in A and B is about 1/4 second. The fetus is shown u t about twice the normal size. In C, the letters am touch the border of the amnion.

flexion reflexes that include these active upper extremity movements are elicited only by stimulation of the perioral areas supplied by the maxillary and mandibular divisions of the trigeminal nerve. At 10.5 weeks and perhaps earlier (Hooker, 1938, 1952, 1958; Humphrey, 1964, 1969b, 19694 the palms of the hands become sensitive and stimulation over the shoulder has been followed by movement in the underlying joint. These first reactions to palmar stimuli consist of incomplete finger flexion usually without participation of the thumb (Hooker, 1938 and later) and with an almost equally rapid return to position. At 1 1 weeks flexion at the wrist and elbow, medial rotation of the upper arm, and forearm pronation may all accompany the partial finger closure (Fig. 12). By 12 weeks the fingers no longer flex equally, the thumb may

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27

move a little or not at all, and the extent of flexion of the hand has decreased. By 13 to 14 weeks, finger flexion following palmar stimulation may be either complete or incomplete (Fig. 13) with some fingers flexed very little. and others more (Fig. 13B-C). Shortly afterward ( 1 5- 15.5 weeks) finger closure may be maintained for a short time. By 18.5 weeks a weak grasp has developed (Fig. 20A). At first the thumb lies outside the closed fingers (Fig. 20A) but may be within (Fig. 21A) o r outside of the fingers by 23.5 weeks (Fig. 2 1 B). Grasp at this time is stronger and in the youngest viable fetus of this series (27 weeks) grasp was almost strong enough to support the entire body weight. In some instances, stimulation of the palm of the hand at 14 weeks has elicited other reflexes in conjunction with movements of the digits and the hand. One of these reactions to palmar stimulation consisted of mouth opening, tongue protrusim and withdrawal, and ipsilateral face turning, followed also by finger closure (Fig. 7). Another and different reflex followed drawing the hair esthesiometer across the palm of the hand of another fetus of 14 weeks. In this reflex, the fingers closed, the face turned away from the hand stimulated, the upper lip on the ipsilateral side retracted, and the lower lip was lifted (Humphrey, 1 9 6 9 ~ )In . neither reflex were there movements other than those of the head, the

Fig. 12. Incompleiefinger closure elicited by stimulating the palm of the hand of a fetus of I I weeks of mensirual age ( N o . 26, 48.5 mm C R length). In A , the stimulator is still in contact with ihe hund. but no longer iouches it in B. Note ihai a s ihe fingers pariially closed in B and C ihey moved alike and there was no movement of the thumb. although there waspexion of ihe hand itself, the arm moved backward at ihe shoulder, and the forearm changed posiiion. In D. the fingers have reiurned to their original position. Except for the finger and arm movement on ihe side stimulated, there M ~ noS oiher action. This entire repex was shown by Hooker (1939). T h e part reproduced here required slighily over one second. T h e illustrations are about 0.8 normal size.

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Tryphena Humphrey

Fig. 13. Partialjinger closure elicited by stimulating the palm of the hand of a fetus of 14 weeks, menstrual age ( N o . 13, 88.5 m m C R length). Following the stimulation (A), the third to jifth digits moved ( B ) before the index.finger (C). but3nger closure was not complete and in this reflex the third digit moved differently than the fourth andjifth. Toward the completion of the action (D), the forearm Jlexed and supinated slightly and the arm rotated medialward to bring the two hands opposite each other. This reflex was reproduced in greater detail by Hooker in 1939. The part shown here required I 1% seconds. The photographs show the fetus at less than half its true size.

oral area, and the hand stimulated. These reflexes illustrate the close relationship found perinatally and postnatally between oral activity and hand movements. The similarity to the Babkin and palmomental reflexes has been discussed elsewhere (Humphrey, 1969c, Figs. 16- 17). The lower extremities also move passively at first, due to the flexion of the lower trunk and pelvis. The soles of the feet face each other and are partially in contact by 22.0 mm. Although the contralateral flexion reflex of the 22.6 mm fetus that included arm extension was also accompanied by lower trunk flexion and pelvic flexion, there was no separation of the soles of the feet. However, sufficient movement in the hip joints (lateral rotation and abduction) to pull the feet apart did occur in at least 3 of the 13 contralateral flexion reflexes at 25.0 mm in which lateral pelvic flexion was greater than at 22.6 mm. Active movement of the lower extremities, therefore, like that of the upper limbs, begins as part of the total pattern lateral flexion reflexes elicited by perioral stimulation. At 8.5 weeks (Figs. l B , 2A-B, and I I ) , the soles of the feet separate farther, as the extent of movement in the hip joints increases, and a

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lesser amount of action may appear at the knee and probably at the ankle joints (Fig. 2B). In the motion pictures, the toes appear to spread apart slightly when the fingers separate (Fig. 1 1 B), but the shortness of the toes and their separation at rest (Fig. 1 I A ) make it impossible to demonstrate this movement satisfactorily with photographs (Fig. 1 1 B). All of these lower extremity movements take place as part of the total pattern lateral flexion reflexes elicited by perioral stimulation before a n y surfaces of the lower extremity are sensitive to stimulation. The sole of the foot was reported to respond to stimulation as early as 10.5 weeks (Hooker, 1952, 1958; Humphrey, 1964), but these reflexes have not been verified from the motion picture films (Hooker, 1960). However, plantar sensitivity to stimulation is consistently present at 1 I weeks. The first reflexes observed (Hooker, 1952, 1958) consist of plantar flexion of the toes without other action. By 11.5 weeks, the plantar toe flexion may be accompanied by flexion of the foot (Fig. 14) and flexion at the knee and hip. By 11.5 weeks also dorsiflexion of the great toe and fanning of the other toes sometimes follows plantar stimulation. Dorsiflexion of the foot, and flexion at the knee and hip joints may be included in the Babinski reflexes (Fig. 15) or the action be limited to movements of the digits. During the earlier age levels, the plantar flexion reflex is elicited more frequently than the Babinski reflex, but later dorsiflexion of the great toe with fanning of the other digits predominates (Hooker, 1952, 1958; Humphrey, 1964, 1969b, 1969~). As a rule, action following stimulation of the sole of the foot is limited to these ipsilateral lower extremity reactions. On rare occasions, however, responses other than lower extremity movements have been elicited. One of these reflexes was an exceedingly rapid but complete mouth opening and closure at 12.5 weeks, accompanied at the time only by slight lateral head flexion (Humphrey, 1968a, Fig. 11) although followed almost immediately by a kick on the side stimulated. In another instance, stimulation of the sole of one foot of a 14-week fetus (Fig. 16A) was followed by a series of movements that included wide mouth opening two times by depressing the lower jaw (Figs. 16B and 16D), with closure and swallowing between them (Fig. 16C). Rapid action of both upper and lower extremities also occurred (Fig. 16B-D) as well as some ventral head flexion (Fig. 16D), marked head, trunk, and rump extension (Fig. 16C), and flattening of the abdominal wall with flaring of the rib cage in an inspiratory gasp. This reflex is of particular interest for it includes action of almost all regions in which movements have been elicited at this age, as do the total pattern reflexes of the first 2.5-3 weeks of fetal activity (7.5-10 or 10.5 weeks).

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Tryphena Humphrey

Fig. 14. A plantarflexion reflex elic,ited by stroking the sole of the right foot of a I3week fetus ( N o . 45, 75.0 mm C R length) with the stimulutor. T h e position at rest is shown in A. where the stimulutor touches the sole of the f o o t as shown by the arrow. In B , there is plantar flexion, both of the toes and the foot. These movements becume more marked in C . There was evidently some flexion ut the knee, f o r the left leg was curried backward, but no other movements were demonstruted. The photogruphs in this figure cover an interval of I !4 seconds. The fetus is shown at approximutely normul size.

C. FUNCTION OF FETALREFLEXES

Opinions differ concerning the function of reflexes during fetal life. Some experimental embryologists believe that development proceeds normally according to a predetermined genetic pattern regardless of whether function occurs (Hamburger, 1963, 1964; Jacobson, 1966; Weiss, 1937, 1941a, 1941b). The literature is far too extensive to review here. The role of genetic factors in early development is well established, but whether function influences development and, if so, the point where the influence begins is difficult to determine and probably varies

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throughout phylogeny. In lower vertebrates, neural function appears to be of little significance for normal development, as shown by the experiments of Harrison (1904) and others (see Hooker, 1952, p. 107; Humphrey, 1966a, p. 266). For the most part, however, the evidence favoring the concept that function does not affect development is limited to experiments on the spinal cord or brain stem of lower vertebrates in which the postoperative effects were followed for only a relatively short period (Weiss, 194 I b, 194 lc). Long-term experiments have demonstrated that when the postoperative observation time is extended the animals do not remain completely normal (SzCkely & Szenthgothai, 1962; Weiss, 194I b, p. 7 1). SzCkely and Szentigothai suggested that the departure from normal behavior is probably related to the involvement of higher

Fig. IS. Three stages in N Babinski reflex elicited by stroking the sole of the right f o o t of a fetus of 14 weeks of menstruul age ( N o . 13, 88.5 m m C R length). The stimulator (dark line) touches the sole o f t h e f o o t in A. In E. thejrumefolloMing !he peak of the repex, the toes ore still in motion slightly. but the great toe is cleurly dorslflexed. a s is also the f o o t . T h e flexion ut the knee and hip seen in E is increased in C. in which fanning of the toes hus appeared. T h e portion o f the rejlex shown here took plmce in h a l f o second. T h e return to the resting position u'as m u c h slower, f b r the entire wflex U S shown by Hooker ( I 939) required approximtrtely three seconds. I n thisJigirre the ,fetus is uhorrt 0.7 norniul size.

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Tryphcna Humphrey

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centers of the nervous system. Because both development and function proceed from cervical spinal cord levels cephalad, abnormalities of function that depend on higher centers are not likely to appear during short term experiments. The observations of Gottlieb (1965, 1968) demonstrate that either depriving duck embryos of auditory stimuli, or increasing the amount of exposure to them, alters the responses to auditory stimuli after hatching. Following hatching, increased auditory stimulation also enhances the responses (Gottlieb, 1966, 1968). Satisfactory evidence for comparable effects of stimuli on mammalian fetuses is difficult to secure and not available. Postnatally, however, both functional and structural neural effects of sensory deprivation (Held & Bauer, 1967; Scherrer & Fourment, 1964) and sensory enrichment have been demonstrated (Diamond, Lindner, & Raymond, 1967; Rosenzweig, Krech, Bennett, & Diamond, 1962). I t would be surprising indeed if the effects of function were to begin at the arbitrary point of birth (or hatching). It seems more logical to assume that lowering the excitatory threshold of the neurons when function of the fetal neural circuits begins (Gottlieb, 1968, p. 170) leads to their more frequent activation, and that, in consequence, development will be modified to some degree throughout the remainder of fetal life as well as postnatally. According to Windle (1940, p. 164) there is “scanty evidence” that any fetal movements demonstrated outside of the uterus occur normally in utero due to lack of stimulation, especially during the early stages of development. However, there is nu evidence that they do not occur. Inasmuch as fetuses are more readily stimulated when the oxygen supply is good (Fitzgerald & Windle, 1942) and reflexes have been demonstrated outside of the uterus (Hooker, 1944, 1952, 1958; Windle, 1940, 1944) as early as 7.5 weeks and spontaneous activity that needs no stimulus by 8.5-9.5 weeks, it would be surprising if no movements occurred within the uterus during this period. Although there are differ-

Fig. 16. Four illustrations showing the major part of the action in a complex reflex elicited by drawing the stimulator f a t arrow in A) d o n g the sole of the left foot of u fetus of 14 weeks of menstrual aye ( N o . 37, 85.5 mm C R length). In B. the upper extremities are Jlexed ut the shoulders, the elbows. and the rc-rists. and the lower extremities are in motion slightly. I n addition. the head is bent forward a little and the mouth is open. In C , there is marked head and trunk extension with closure of the mouth and elevation of the larynx (note prominence at arrow), accompanied by extension of both upper and lower extremities to a variable degree at all major joints. In C. the mouth has reopened and the head, trunk. und extremities are returning toward their original position. The action illustrated in this figitre reyuiredJust over two seconds. The illitstrations are about 0.8 normal size.

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Tryphena Humphrey

ences in the amount of stimulation (Humphrey, 1953, 1966a), stimuli are not completely absent except for gravity effects (Reynolds, 1962). Since a slight increase in the carbon dioxide level heightens the excitability outside of the uterus, fluctuations in the carbon dioxide level in utero may also provide stimulating effects (Section IV, C). During early development when the uterus is in the bony walled pelvic cavity, pressures from adjacent viscera could be transmitted through the uterine wall and the amniotic fluid to the fetus, especially when there is increased intraabdominal pressure due to coughing, bending, and other movements of the mother (Humphrey, 1966a). On passing through the amniotic fluid, the minor surface pressures will be intensified and have widespread effects. The greater degree of activity noted by Fitzgerald and Windle (1942) in response to tapping on the amnion, as compared with the reflexes elicited by Hooker after removal, support this suggestion. In one instance also, Hooker found that a 10 mg esthesiometer was adequate to elicit two extensive reflexes (including mouth opening, Fig. I IC) by pressure on the amnion, but was not equally effective immediately after removal. Stronger stimuli may have been necessitated by the decrease in the oxygen supply after removal of the amnion, but the brief time interval makes it unlikely that this was the only factor involved. Turning now to the question of a possible function served by specific fetal reflexes during development, the following points might be mentioned. Mouth opening reflexes on perioral stimulation of human fetuses begin slightly before the tongue is withdrawn from between the palatal shelves (Humphrey, I968b, I969e). These mouth opening reflexes aid in tongue withdrawal through pull on the tongue when the jaw is depressed. Suppression of this activity, or even delay, would slow the change in position of the palatal shelves and so increase the likelihood of the epithelial fusion of the tongue and the palatal shelves that was shown experimentally for rats (Steffek, King, & Derr, 1966). There is no evidence, as yet, that reflex retraction of the tongue (His, 1901) as well as depression of the jaw plays a part in palatal closure. However, the growing nerve tips are closer to the base of the mucosal epithelium of the mouth than to the epithelium of the lips (Humphrey, 1966b) when the perioral area becomes sensitive to stimulation. Therefore, pressure of the large tongue against the oral mucosa might easily provide sufficient stimulation to cause reflex withdrawal from between the palatal shelves. Tongue reflexes do begin at a comparable period of development in other mammals, such as the rat (Angulo y Gonzalez, 1932), and were seen as spontaneous movements of macaque fetuses within the amnion by Bodian ( 1 968) before they were elicited by stimulation. Swallowing was reported by Hooker (1944, 1952) to begin at about

The Development of Human Fetul Activity

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12.5 weeks. At I3 weeks (Fig. 6) and at 14 weeks it is more frequent if either the lips or the inside of the mouth are stimulated. Possibly swallowing develops as early as 10.5 weeks, as was reported earlier (Hooker, 1954, 1958; Hooker & Humphrey, 1954), but the reflex seen at that age was not verified photographically. Probably closing the mouth on the amniotic fluid leads to the beginning of swallowing even earlier, for the external nares are already plugged with epithelium when mouth opening begins and for a long time after swallowing is well developed (Humphrey, 1969e). Swallowing reflexes of normal fetuses have been shown radiographically in utero by 12 weeks of “gestation age [Davis & Potter, 19461.” These reflexes serve to maintain the level of amniotic fluid, evidently by absorption through the gastrointestinal mucosa, for fetuses with atresia of the esophagus or anencephalic fetuses that cannot swallow (Pritchard, 1965) develop hydramnios (Hamilton, Boyd, & Mossman, 1962). Arshavskiy ( 1 959) suggested that the substances swallowed in the amniotic fluid serve a nutrient function, as had Preyer many years earlier ( 1885). Because the gut returns from the umbilical cord to the abdominal cavity in fetuses of 42.0 to 48.0 mm in C R length (Hamilton et ul., 1962), or between 10 and 1 1 weeks of menstrual age, it is tempting to speculate that swallowing reflexes may play some part in its rotation and return to the abdominal cavity. The suggestion is supported, in part at least, by the fact that the cranial loop of the gut returns before the caudal one. Possibly also the swallowing reflexes may be a factor in the resolution of the excessive growth of esophageal and upper intestinal epithelium that takes place during the tenth week of menstrual age (toward the end of the second month, fertilization age, Patten, 1968, p. 384), and so be significant also in the recanalization of these regions of the gastrointestinal tract. One might also theorize concerning the value of orbicularis oculi contraction in separating the fused eyelids, concerning the role of reflex spreading apart of the fingers (and probably toes) in preventing minor fusion between the digits, and concerning the part played by extremity movements in the development of the joints. In this connection, however, there is some experimental evidence that immobilization leads to ankylosis and other skeletal deformities (chick, Drachman & Coulombre, 1962; Hamburger & Waugh, 1940) and some orthopedic surgeons (Badgley, 1943; Drachman & Banker, 196 I ) consider that joint deformities of infants are the result of immobilization during fetal life. Whether or not any or all of these postulations concerning the function of fetal reflexes in normal development may prove correct, fetal activity certainly strengthens the muscles during prenatal life.

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Tryphena Humphrey

D. THERELATIONOF SUPPRESSION (OR INHIBITION) OF ACTIVITY TO THE DEVELOPMENT OF BEHAVIOR The total pattern reflexes elicited by perioral stimuli from 7.5 to 10.5 weeks become less frequent thereafter, and mouth opening gradually becomes independent of trunk and extremity activity. The change is effected by the suppression of the latter reflexes through inhibition of the reflex arcs centrally in a caudorostral sequence (Section V, B, 1 ; also Humphrey, 1968a, 1969b, 1969d). Inhibitory synaptic end bulbs are present both on the dendrites and on the somata of neurons (Bodian, 1966; Walberg, 1968), and there are also special inhibitory regions in the central nervous system such as the bulbar reticular inhibitory center (Magoun & Rhines, 1946), and parts of the cerebellum, of the striatal complex, and of the cortex (Ruch, Patton, Woodbury, & Towe, 1961). In the cervical spinal cord of fetal monkeys, Bodian ( 1 968) found that the F-type synaptic end bulbs, which he concluded to be inhibitory in function, increased sharply in number just before the period of “secondary, integrated local reflexes [Bodian, 1968, p. 1241,” which is comparable to the period of suppression of the total pattern reflexes and the appearance of local reflexes and combinations of reflexes in human fetuses. Because brain stem levels are the most important regulatory centers during early phylogeny, probably the differentiation of bulbar and midbrain regions is responsible for the transition from total pattern reflexes to local reflexes during this early period of ontogenetic development. First the total pattern reflexes must be largely suppressed; then localized reflexes and functional reflex combinations are possible. In suppressing the total pattern reflexes, their neural arcs are retained, not lost. Therefore, these reflex arcs are activated by perioral stimuli when anoxia and asphyxia set in at these ages (Section IV, C) or under various other circumstances thraughout development (Section VIII). When suppression of the gross movements begins, local reflexes and functional reflex combinations are few. By 14 weeks, however, a wide range of reflexes has appeared in which the lower extremity and trunk are completely inactive, but the head and some upper extremity movements may remain. Fetuses at 14 weeks are extremely active, and sometimes a stimulus sets off activity in almost all parts of the body. Probably this peak of activity is reached at the height of midbrain regulation, just before higher brain areas in turn suppress and regulate the midbrain centers. Three illustrations of these reflexes follow. One is a reaction to plantar stimulation at 14 weeks (Fig. 16). Even swallowing was included in this total pattern type of action, although ordinarily swallowing is not accom-

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panied by trunk or extremity movements, only head extension and flexion (Fig. 6). In another instance, a comparably widespread, but quite different reflex resulted from stroking the back from the lower spine up to the neck (Fig. 17). The resulting trunk and head extension, shoulder elevation, mouth opening, inspiratory gasp, and upper and lower extremity movements constitute a total type of reaction that clearly resembles a postnatal reaction to tickling. Another reflex elicited from the same 14-week fetus followed chance contact of a glass rod with the genital area in changing the position of the fetus (Fig. 18). At least the genitofemoral groove and the base of the penis were stimulated (Fig. 18B), and light pressure was probably applied as well as touch. Among the movements that followed were marked head extension with mouth opening, then closing, and rapid movements of all extremities. Although these reflexes do not involve all of the neuromuscular system capable of functioning at this age level, they do include the head, trunk, extremity, and lower jaw movements of the total pattern reflexes at the height of their development and, incorporated with them, other motor activities

Fig. 17. Part of a reflex sequence following stimulation of the back by drawing a hair esthesiometer upward from the lumbosacral area to the neck. In A the stimulator (shown by arrow) is touching the midscapular region. T h e reaction involved both extension and twisting of the trunk, head extension with slight rotation, elevation of the shoulder on the side toward the observer, and lifing the opposite leg. A n inspiratory gasp accompanied the mouth opening in B and C . This fetus (No.13, 88.5 m m C R length) is shown here a t approximately half the normal size. The time spanned by the action in this jigfigure is about one second. The entire reflex, which required about 2% seconds, was reproduced by Hooker in 1939.

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Tryphena Humphrey

Fig. 18. Three photographs f r o m a motion picture sequence following touching the genital area with a glass rod when the position of the fetus was changed. T h e reaction of this fetus ( N o . 13. 88.5 mm C R length, 14 weeks, menstrual age) involved extension and slight rotation of the head with mouth opening ( B ) and closing ( C ) two times, flexion of the upper extremities at the shoulders, elbows, and wrists with some Jinger flexion and hand adduction, and complex lower extremity movements that differ on the two sides ( B and C ) . From the time of stimulation in A to an approximate return to the original position involved about 2% seconds. The action covered in the presentfigure (A, B and C ) was executed in just over one second. The illustrations are at approximately 0.6 normal size.

that have been added by 14 weeks. At this age, however, the stimuli not

only activate earlier total pattern reflex pathways, but also additional neural circuits for the various newly acquired local reflexes and reflex combinations. Between 15 and 16 weeks, the fetuses become relatively inactive (Hooker, 1952, 1960) and the few reflexes elicited by facial stimuli usually involve only the oral area and head (Fig. 8). From 18 weeks until the fetuses can be resuscitated temporarily, there are few reactions. This period of sluggishness has been ascribed by Barcroft and Barron (1 937) to the reduced oxygen supply resulting from the rapid growth at 18- 19 weeks and later. After artificial respiration is established at 23.5 weeks and later (Figs. 1 9 , 2 l ) , there is a period of marked activity during which almost any stimulus may set off movements of the head, trunk, and extremities. Indeed, from this period into postnatal life it is often uncertain what activity is directly related to a specific stimulus. After

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resuscitation also, the characteristic scowl, the tight eyelid closure, the wide mouth opening, and the tongue position of the “pain cry [WaszHockert, Lind, Vuorenkoski, Partanen, & ValannC, 19681” are present (Fig. 19). Although the lower oxygen supply after the fetal increase in size may account for the reduction in activity, reflexes are decreasing in frequency before there is much change in size. Therefore, the initial decrease in aciivity is probably due in large part to the inhibitory effects of neural circuits through the dorsal thalamus and striatal complex, which again must first suppress the activity through the midbrain IeveIs, in part at least, before imposing the higher level pattern of function on the final common pathways of the brain stem and spinal cord. At this time the motor activity becomes typical of striatal function, with progression movements of the extremities a conspicuous part of the action. These automatic associated movements via the striatal complex must, in turn, come under the inhibitory, or regulatory, control of the cerebral cortex, so that localized actions appropriate to the sensory input become possible. As Kuo (1967, p. 92) indicated for the adult when he wrote “in any given response of the animal to its environment . . . the whole organism is involved” the greater part of the neural activity is frequently the suppression (or inhibition) of most of the potential overt action in order to allow specific, discrete, localized, purposeful acts to take place. The

Fig. 19. Photographic prints from four successive frames of a motion picture sequence of a nonviable premature infant of 23.5 weeks of menstrual age for which breathing was initiated with a resuscitator. When the mask was removed f r o m its f a c e , the infant cried ( A and B). Note the typically tightly closed eyelids and the position of the tongue in crying f i n B) with the tip turned upward. Crying is ceasing and the mouth closing in C and D , where the line between the eyelids is again clear when the orbicularis oculi muscle relaxed. These smallprints, only aboui 0.1 the size of this 205.0 m m premature infant ( C R length), show the eyebrow clearly only in D so evidently the corrugator supercilii also contracted t o produce a scowl while crying.

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brain-damaged spastic child or the one with choreiform movements is not able to execute the essential movements of everyday living, because he cannot sufficiently suppress and regulate the gross activity. E. POSTNATAL REPETITIONOF FETALREFLEX ACTIVITYSEQUENCES

Although the repetition of fetal activity sequences and their probable anatomic basis were discussed in some detail earlier (Humphrey, 1969c), the structural arrangement of the central nervous system that determines this repetition is worthy of emphasis here. Two main factors are involved. The first is the arrangement of the motor neurons that innervate the skeletal muscles in a longitudinal somatotopic pattern (Section VI I I ) extending from the upper midbrain (oculomotor neurons) to the ventral horn neurons of the last sacral segment of the spinal cord. Thus the head muscles are innervated primarily by the brain stem motor neurons and the neck, trunk, and upper and lower extremity muscles by motor neurons arranged in the proper cervicocaudal order throughout the spinal cord. The second factor is the order of development of the neural tube. Closure begins in the upper cervical region and proceeds caudally and rostrally from this area (Kingsbury, 1924). Therefore, the motor neurons mature and become functional, except for minor variations, in the same general order (Humphrey, 1954, 1969~).An obvious variation in brain stem development rostrally concerns the motor neurons of the trigeminal and facial nerves, for those that participate in mouth opening reflexes mature earlier than do the other motor nerve cells of these nerves (Jacobs, 1970). Both the structural and the functional order of development at spinal cord levels progress from cervical (neck and upper extremity) through thoracic (trunk) and lumbosacral (lower extremity) levels. These longitudinally arranged motor neurons constitute the final common path of Sherrington (1 906) over which all activation of skeletal muscles must be transmitted. Therefore, not only the total pattern reflexes are executed over them, but also both the facilitatory and the inhibitory effects from all levels of the central nervous system. Because both the sequence of maturation and the order of functional activity are established with the development of the primary (Humphrey, 1953, p. 9) or fundamental (Sherrington, 1906, p. 320) reflex arcs by the order of neuronal maturation, and “all the other neural arcs” are superimposed on them, the descending fiber tracts from higher brain centers will establish functional relationships in the same general order that the reflexes developed. Upper spinal cord levels will be reached (and regulated) by descending tracts before they grow into lumbosacral levels, whether

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they arise in bulbar, midbrain, striatal, or cortical areas. Consequently, the general sequence of development of the activity is repeated, although the character of the individual actions changes. One of the most obvious examples of this repetition of motor sequences is found in the development of grasping (Hooker, 1938, 1952, 1958; Humphrey, 1964, 1969~).Partial finger closure in which all fingers move alike (Fig. 12) is followed by more complete finger closure with variable finger movement (Fig. 13). The thumb takes no part at first, but later thumb action is included (Fig. 21), closure becomes complete, and grasp increases in strength. Perinatally and postnatally the infant again demonstrates partial finger closure before variable finger action and thumb movements appear, but the activity at this age is regulated from the extrapyramidal cortical areas by multisynaptic pathways through the striatal complex and the midbrain tegmentum. When voluntary control begins, partial finger closure is again the first type of finger movement, thumb participation appears later, and grasp follows. Apposition of the thumb and the forefinger, a movement not yet seen prenatally, is the last refinement of finger movements to develop. At each central nervous system level of regulation, the developmental sequence is repeated, but at each level also the complexity and variability of action increase to culminate in the fine individual movements that are possible only through the function of the motor area of the cortex.

VI. Fetal Activity in Response to Other Types of Stimuli In addition to the light tactile stimuli used by Hooker to elicit most of the activity already described, pressure directly on the fetus or pressure on the amnion were used by Fitzgerald and Windle (1942). As pointed out by Hogg (1941), even lightly stroking the surface probably produces some slight deformation of the growth cones when the nerve fibers still lie below the epithelium. Heavy pressure would have a similar effect when the nerve tips are still farther from the surface. Pressure on the amnion is not only intensified on transmission to the fetus, but affects many areas, including both sides of the fetus if it is moved by the pressure. This difference in the strength and in the extent of the stimulation is probably as significant a factor in the amount of activity noted by Fitzgerald and Windle (1942) as the better oxygen supply which they emphasized. Only a relatively few attempts were made by Hooker to elicit reflexes by stretch stimuli, as reported by Windle and his collaborators for other mammals (Windle, 1934, 1944). Reflexes of this type were not reported

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by Fitzgerald and Windle (1942) in their observations on small human fetuses (20.0-26.0 mm CR, or 7.5-8.5 weeks of menstrual age by the tables used by Hooker). However, such reflexes were identified for the arm and hand at 9.5 weeks by Hooker (1939, 1952, 1958), two weeks after the first reactions to tactile stimuli. Possibly in the cat, such reflexes do appear earlier than those from tactile stimuli, as reported by Windle and Griffin (193 l ) , but as yet there is no evidence that this is true for human fetuses. In the total pattern reflexes elicited by perioral stimulation from 7.5 to 9.5 weeks, stretch stimuli evidently do not cause the return to position because a distinctly longer time is required than for the muscle contraction itself (Humphrey, 1968a, Figs. 4-5). At 1 1 weeks and again at 12.5 weeks sufficiently rapid mouth closure was seen (Humphrey, 1968a, Figs. 6-7 and 1 1 ) to indicate that stretch must have been the effective stimulus to close the jaw so quickly. Perhaps stretch stimulation is also a factor in producing the characteristic postural changes that take place at about this time in development, for static stretch reflexes maintain posture in the adult. This postural change also begins at about 9.5 weeks and by 1 1 weeks both the upper and lower extremities have a different position at rest than at 8.5 weeks (compare Figs. 1A and 2A with Fig. 3). In the development of sensory modalities in birds, Gottlieb (1968, p. 154) listed touch stimuli as effective before vestibular excitation and proprioceptive stimuli from muscles following vestibular sensitivity. However, for some mammals vestibular reflexes have not been demonstrated until after the body righting reflexes are present (sheep, Barcroft & Barron, 1937, 1939; cat, Windle & Fish, 1923). According to Minkowski (1928) vestibular reflexes begin as early as 10 weeks in human fetuses. Hooker (1942, 1944) interpreted two reflexes following rolling a fetus of 9.5 weeks as vestibular in origin, but later (Hooker, 1952, 1958) concluded that they were probably body righting reflexes. Minkowski ( 1928) found that the lateral vestibular nucleus differentiated early. By 10 weeks the neurons of this nucleus are slightly better differentiated than the best developed nerve cells in the upper cervical spinal cord a week after the first reflexes involving them have been recorded (Humphrey, 1965, p. 55). Also the sensory neurons of the vestibular ganglia at this age are as well developed as the best differentiated cells of the semilunar ganglia a week after function begins. If the sensory receptors and the synaptic connections of the vestibular reflex arcs are functional also, vestibular reflexes should be present by 9.5 weeks. The reflexes first reported by Hooker ( 1 942, 1944) at 9.5 weeks as vestibular consisted of rapid lateral flexion of the trunk accompanied by

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upper and lower extremity movements bilaterally. This type of reaction indicates integration of the vestibular stimuli into the existing functional neuronal network of the total pattern reflexes in human fetuses, as Coghill ( 1930) believed for Amblystoma. Indeed, certain vestibular stimuli cause an essentially total reaction of the infant (Moro reflex, Prechtl, 1965). Even in the adult, a vestibular stimulus may set off a total body reaction. There are two points of view concerning the question of self-stimulation. Gottlieb and Kuo (1965) reported that the duck embryo is constantly stimulated by its own activities, including both touch and auditory stimuli from its own vocalizations. However, Hamburger et al. ( 1966) were in sharp disagreement concerning the role of self-stimulation in the development of chick embryos. Among mammals, except for human fetuses (Humphrey, 1969b), the question of self-stimulation has received little attention. In view of the position of the fetal hands covering the mouth during the time that the total pattern contralateral flexion reflexes are at their peak of development (8.5-9.5 weeks; Figs. I , 2, 1 1 , 22), stimulation of the perioral area (the only skin area sensitive during this period) could scarcely be avoided in the confined space within the amnion. Later in development, also, the hands are often near the face, and the thumb frequently touches the lips (Figs. 20A, 2 0 0 Because the mouth is often open after 14 weeks, the thumb can easily slip inside (Fig. 20B), especially when the fetus is confined within the amnion as shown in the photographs of Nilsson (1965). Sucking does not occur at this time, however, for puckering the lips, a necessary part of sucking, does not begin until 22 weeks (see Section V, B, 3). Therefore, thumb sucking before birth, as reported by Murphy and Langley ( 1963), for example, must take place toward the end of gestation. Because little is known about the function of the other sensory modalities before the age of viability, they will not be considered. An extensive account is given in the review by Carmichael ( 1954).

VII. Spontaneous Activity The term spontaneous activity was used by Minkowski (1928) and by Hooker (1944, 1950, 1952, 1954, 1958, 1960) to denote activity for which the stimulus, if any, was unknown. The term was used in the same way by Angulo y Gonzalez ( 1 932) and by Windle and his associates (Windle & Griffin, 1931; Windle & Orr, 1934; Windle et al., 1933). Considerable attention was focused on whether spontaneous movements in mammals like the cat developed earlier than reflexes, as Tracy (1 926)

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Fig. 20. Three photographs selected to show the hand-mouth positional relationship often seen at this period of development (18.5 weeks, menstrual age) and even earlier, as well as later. This is the same fetus f o r which parts of a gag reflex are shown in Fig. 10. I n A the right hand of thefetus is grasping a glass rod and in B thefingers have loosened on the rod. In A also the Left thumb is pressed against the upper lip, but in B it is inside the upper lip. Both hands are close to the mouth in C with the left thumb behind the upper lip and apparently against it. T h e index Jinger lies against the nose near the hair esthesiometer, the black line that touches the tip of the nose. A t this age neither the upper nor the lower lip has been seen to purse (or pucker) and although the thumb may enter the mouth. sucking has not been demonstrated at this age.

found for the toadfish. The term spontaneous activity, as used by Comer (1964; Corner & Bot, 1967), by Hamburger (1963, 1964; Hamburger el al., 1965, 1966) and by Hughes (1966; Hughes et al., 1967) applies only to periodic, rhythmic motor discharges of endogenous origin that depend either on the “automatic, self-generated discharge of neurons [Hamburger, 1963, p. 3501” of genetically determined motor patterns or on chemical stimuli. In other lower vertebrates, as well as in fishes, spontaneous movements appear before reflexes can be elicited. In the aglossal toad, Xenopus luevis, spontaneous activity develops into swimming (Hughes & Prestige, 1967) before any cutaneous area becomes sensitive to stimulation. In another toad (Eleutheroductylus, Hughes, 1966), the earlier

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developing spontaneous activity builds up independently to diagonal walking, whereas reflexes develop into bilateral swimming. In frogs, also, Youngstrom ( 1938) found that spontaneous movements appeared before reflex activity. In both the lizard (Lacerta vivipara; Hughes et al., 1967) and the turtle (Tuge, 193 I ) , spontaneous movements also appear before reflexes, by a difference of two days in the lizard and at least several hours in the turtle. In the study of avian behavioral development, spontaneous movements appear some time before reflexes and constitute a large part of the activity. They have been described for the pigeon (Tuge, 1934), the chick (Hamburger, 1963, 1964; Hamburger & Balaban, 1963; Hamburger et al., 1965, 1966; Kuo, 1932; Orr & Windle, 1934), and the duck (Gottlieb & Kuo, 1965), although certain differences in the time of development and in the character of the activity were found by the different investigators. Spontaneous activity has received less attention in the behavioral studies on mammals. Windle and Griffin (193 1) reported a sequence of development in cat fetuses that indicated a possible relationship to righting reflexes. Spontaneous activity was found later in development than reflexes in the rat (Angulo y Gonzalez, 1932), but earlier in sheep (Barcroft & Barron, 1939), and in cat fetuses (Coronios, 1933; Windle & Griffin, 1931). Later, however, Windle et al. (1933) reported local reflexes to be the earliest observed activity of cat fetuses. Bodian ( 1968) found no difference between the time that spontaneous activity and reflexes appeared in macaque fetuses. Spontaneous activity was not mentioned by Fitzgerald and Windle ( 1 942) for the 20.0-26.0 mm human fetuses that they observed and Hooker (1960, p. 436) did not see spontaneous movements until 9.5, or possibly 8.5 weeks. For human fetuses spontaneous movements were usually present only at the beginning of the activity (Hooker, 1952, 1960; Minkowski, 1928) until after resuscitation became possible. Although the available information is by no means satisfactory, there appears to be a trend throughout phylogeny (with the exception of birds) for spontaneous activity to be reduced in amount and to be manifested progressively later in development. Thus, in the macaque spontaneous movements coincide with reflexes in time of development (Bodian, 1968), and for human fetuses the evidence at present indicates that spontaneous movements do not develop until a week to 2 weeks after reflex activity. In human fetuses, either the endogenous neural activity does not build up sufficiently early in development to discharge spontaneously prior to reflex activity or there is an initial period of inhibitory regulation of spontaneous discharges by the sensory input, with discharge set off later by the

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sensory stimuli. At certain periods in human development (for example, 8.5-9.5 weeks and 14 weeks) the fetuses are particularly active and spontaneous movements are seen more often. Upon resuscitation, spontaneous progression movements (Fig. 21) are nearly continuous at times and almost any stimulation sets off head, trunk, and extremity action of the same type as the spontaneous movements.

VIII. The Relation of Integration to the Development of Behavior Integration of activity is achieved in two fundamental ways. One is by the synaptic end bulbs on the motor neurons constituting Sherrington’s final common path. The other consists of the central nervous system areas (or centers) in which sensory impulses are brought together and from which discharge is made over efferent circuits to the appropriate motor neurons of this final common path. Integration by the first process is operative through the inhibitory and excitatory synaptic boutons and the chemical mediators from the onset of reflex action throughout the course of development. The second integrative mechanism begins somewhat later when sensory centers of increasing complexity differentiate in the brain stem, the dorsal thalamus, and the cortex. Sensations from within the fetus, as well as from the external environment (Hooker, 1960), are integrated in these areas. Integration at the synaptic level becomes effective as soon as sensory impulses from the environment are transmitted to enough motor neurons to elicit a response. Closing the neural circuit brings the fetus and its environment into relation with each other, as well as the site of the stimulus into relation with the muscles that respond. This unification begins with the first reflex, and all reactions that follow become integrated into the existing neural circuits when they are first executed. Endogenous spontaneous movements that are unrelated to any sensory stimuli, however, are neither integrated nor coordinated. When the sensory input is transmitted to more motor neurons and the reflexes increase in intensity or in extent (or both), the additional neural activity is likewise integrated when function begins. The development of the S-type excitatory synaptic boutons on the dendrites of spinal motor neurons in monkeys (Bodian, 1966, 1968) probably occurs in human fetuses during the development of the total pattern reflexes, and the dramatic increase in the Ftype inhibitory synapses on somata should coincide with the period during which these total pattern reflexes are suppressed and local reflexes appear.

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Fig. 21. Two photographs f r o m a motion picture sequence involving rapid extremity movements of the 23.5-week premature infant illustrated in Fig. 19. Almost any stimulation was followed by quick rhanges in the position of the arms and iegs with the hands opening and closing, either with the thumb inside of the fingers (B) or outside ( A ) .Similar movements occurred without known stimulation. In B , the deep inspiratory movement is shown by the depressed sternum, the elevated rib cage, and the flattened abdominal wall.

Stretch stimuli are not integrated into the behavior pattern in the same way as are those from the external environment (exteroceptive stimuli) and those from the internal environment (visceral afferent stimuli). The two-neuron stretch reflex arcs close later than the polysynaptic reflex arcs of exteroceptive (and probably visceral afferent) reflexes (sheep, Barron, 1944; chick, Hamburger, 1963, 1964; Scharpenberg & Windle, 1938; cat, Windle, 1931; human embryos, Windle & Fitzgerald, 1937). Static stretch reflexes build up into posture and those of kinetic type become the tendon reflexes (see Humphrey, 1953). Integration is closely linked with the complex muscle spindles and their interrelations with the motor neurons, These sensory receptors develop relatively late as compared with the simple receptors for general tactile sensitivity (Hogg,

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1941; Humphrey, 1966b), for Cuajunco (1940) did not find them distinguishable from motor endings in the biceps brachii muscle until 11 weeks, although primitive sensory terminals on large muscle fibers were identified at 10 weeks by Hewer (1935; see also Humphrey, 1964). The groups of neurons or nuclei that receive sensory impulses from all parts of the body and head constitute the centers of integration in which the different types of sensory impulses, and those from different body areas, come together and are correlated or integrated. Whereas the motor neurons that constitute the final common path have a longitudinal somatotopic pattern in the central nervous system (or topographic representation of the body parts innervated by them; Section V, E), the neurons that receive the various types of incoming sensory impulses from cutaneous surfaces, from tendons, from joints, and from the viscera have somatotopic patterns that are essentially transversely arranged. The earliest developing center of integration, and the most primitive one, is situated at the junction of the spinal cord with the medulla where the nuclei of the dorsal funiculus, the gray matter of the dorsal horn of the spinal cord, and the nucleus of the spinal tract of the trigeminal nerve are arranged in a sacral to ophthalmic pattern from the dorsomedial to the dorsolateral border of the medulla-spinal cord junction area, corresponding to the pattern formed by the fibers that terminate there (Humphrey, 1955, 1969a). By the time that the total pattern lateral flexion reflexes include active mouth opening and active extremity movements (8.5 weeks), all of these somatic fiber systems and the general visceral afferent fibers of fasciculus solitarius have grown into this region (Humphrey, 1952, 1955). However, all reflexes at this age, and until after 9.5 to 10 weeks, are elicited only by stimulation of the perioral area supplied by the trigeminal nerve. There are no investigations that indicate at what age the bulbar inhibitory and facilitatory areas and the superior collicular level of the midbrain become dominant integration centers for human fetal activity. Evidently the change is accomplished gradually during the period that the extremities become sensitive to stimuli (or local extremity reflexes appear), local reflexes in the facial areas develop, and functional combinations of reflexes arise (from about 10.5 to 14- 15 weeks). At 15 to 16 weeks, another period of reduced activity begins, probably by inhibitory effects through the association nuclei constituting the thalamic centers of integration and their discharge to motor neurons of the final common path through the striatal complex. The coordinated progression movements of the extremities that make up much of the activity of premature and full-term infants are characteristic of the function of these neural circuits through the dorsal thalamus and striatal complex.

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Integration at cortical levels begins postnatally with the inhibition and regulation of the automatic movements from the striatal complex. The first areas for cortical integration are the somesthetic association cortex that relates touch with other general sensations, and later the association areas related to the special senses, such as the auditory association cortex. From these cortical association areas impulses are discharged for the response appropriate to the major stimuli reaching them, first over multisynaptic extrapyramidal pathways (gross movements), then over direct corticospinal (and corticobulbar) tracts (fine movements). The prefrontal cortex constitutes the highest center of cortical integration where past experience, decisions, and similar activities begin in childhood. So far as overt behavior is concerned, however, integration in this area probably results more often in suppression of activity than in action.

IX. Other Considerations Often the basis for differences in views on the development of behavior can be determined if one seeks for them. The early reports on small human embryos, like the accounts of Strassman (1903) and Yanase (1907), mention only extremity movements. In the ovoid confined space within the amnion only the extremity activity may be seen, for the amount of head and trunk movement is reduced and not easily detected, even with motion pictures. However, when photographic prints of fetuses within the amnion are examined closely, head and trunk action are demonstrable also (26.0 mm, Fig. 22). Slight lateral flexion away from the observer (compare A and B of Fig. 22) may be followed by extension of the head and trunk (compare A with C). The conspicuous part of the activity, however, and the only portion seen on examination of the motion pictures at normal speed, is the arm movement that pulls the hands away from the mouth, and lower limb movement, if both are present (Fig. 11C). Neither the open mouth nor the trunk movement is seen. Tapping on the amnion may move the fetus and so stimulate the side away from the observer by pushing the face against the substrate. Such stimuli probably result in a reflex ipsilateral to the tap on the amnion, but contralateral to what was probably the stimulus that elicited the reflex. In the development of behavior, Coghill emphasized the integrated reaction of the entire organism to its external environment. However, because the earliest response to external stimulation is confined to the neck region due to the limited neuromuscular development, this reflex

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Fig. 22. Three prints from a mntion picture sequence of a reflex elicited by pressure of the stimulator (dark line) on the surface of the amnion of the 26.0 mm fetus illustrated in Fig. 1. A und B ure from cnnsecutive frumes and C is the sixth frame in the series taken at 24 frames per second. In the beginning movement in B. the arms have moved just enough to uncover the nose und there is a beginning lateral flexion 10 the side opposite the stimulutnr. In C. the trunk movement has changed to exiension (see text). The soles of the feet did nor separute in this reflex us they do in equally extensive reflexes outside of the amnion. The open mouih is indicuied by the arrow.

has been, and continues to be, confused with the local reflexes that appear later in development (Section V, B). The gradual spread of the reaction from flexure in the neck region to rump flexure is clear for human fetuses, but is compressed into so short a period that this fact is easily missed without motion picture recording (Section V, A). For an equally short period the upper and lower limbs are moved only passively with the trunk as it flexes, without the contraction of limb muscles. The earliest extremity muscle contraction also moves the limbs as part of the total reaction of the fetus and so constitutes a further elaboration, or expansion, of the total pattern reflex. Even the digits spread apart and the mandible is depressed to open the mouth. All of this activity is in response to stimulation of the perioral area, and only this area. In seeking to understand the development of behavior and the mechanisms involved, various pitfalls await the enthusiast who focuses his attention too sharply on one facet of the problem, whether it be the genetic patterns involved- to the exclusion of function-or the synaptic relations of individual neurons-to the neglect of the overall sequential

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changes in the nervous system as a whole. Differences in the development of behavior are to be expected throughout vertebrates. If rapid, automatic, stereotyped activity is the significant factor in determining survival, as in fishes, spontaneous movements play a major role. For reptiles, and especially for birds, rhythmic spontaneous activity also is important in behavioral development. When mammalian postnatal survival depends on early ability to stand and run, the extremity reflexes develop early, as in the sheep and guinea pig, and there is a more or less complete suppression of the total pattern reflexes. For the infant monkey that must soon cling to its mother’s fur for survival, arm movements and grasp appear early. For the completely helpless human infant, for whom specialization appears to be lacking, the total pattern reaction of the fetus is more fully developed and retained for a significantly longer period than for the other mammals that have been studied.

ACKNOWLEDGMENTS The author is greatly indebted to Miss Blanche Page Cushman and Mrs. Gwen Barnett for their technical assistance in the preparation of the illustrations and the manuscript. She is also deeply indebted to Dr. Elizabeth C. Crosby for her helpful suggestions and criticisms. REFERENCES Angulo y Conzalez, A. W.The prenatal development of behavior in the albino rat. Journal of Comparative Neurology, 1932,55, 395-442. Anokhin, P. K. Systemogenesis as a general regulator of brain development. Progress in Brain Research, 1964, 9. 54-86; discussion, 99- 102. Arshavskiy, 1. A. Mechanisms of the development of nutritional functions during the intrauterine period and following birth. Journal of General Biology ( U S S R ) , 1959, 20, 104-1 14. Badgley, C. E. Correlation of clinical and anatomical facts leading to a conception of the etiology of congenital hip dysplasias. Journal of Bone and Joint Surgery, 1943, 25, 503-523. Barcroft, J., & Barron, D. H. Movements in midfoetal life in the sheep embryo. Journal of Physiology (London), 1937,91, 329-35 I . Barcroft, J . , & Barron, D. H. The development of behavior in foetal sheep. Journal of Comparative Neurology, 1939,70,477-502. Barron, D. H. The early development of the sensory and internuncial cells in the spinal cord of the sheep. Journal of Comparative Neurology, 1944,81, 193-225. Bodian, D. Development of the fine structure of the spinal cord in monkey fetuses. 1. The motoneuron neuropil at the time of onset of reflex activity. Bulletin of the Johns Hopkins Hospital, 1966, 119, 129- 149. Bodian, D. Development of fine structure of spinal cord. 11. Pre-reflex period to period of long intersegmental reflexes. Journal of Comparative Neurology, 1968, 133, 1 13- 166.

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Bolaffio, M., & Artom, G. Richerche sulla fisiologia del sistema nervosa del feto umano. Archivio di Scienze Biologiche (Bologha), 1924,s. 457-487. Boyd, E. Outline of physical growth and development. Minneapolis: Burgess, 194 1. Carmichael, L. An experimental study in the prenatal guinea-pig of the origin and development of reflexes and patterns of behavior in relation to the stimulation of specific receptor areas during the period of active fetal life. Genetic Psychology Monographs, 1934,16,337-491. Carmichael, L. The onset and early development of behavior. In L. Carmichael (Ed.), Manual of childpsychology. (2nd ed.) New York: Wiley, 1954. Pp. 60- 185. Coghill, G. E. The reaction to tactile stimuli and the development of the swimming movement in embryos of Diemyctylus torosus Eschscholtz. Journal of Comparative Neurology, 1909, 19, 83-105. Coghill, G. E. Anatomy and the problem of behavior. Cambridge, Eng.: Cambridge University Press, 1929. (Republished: New York, Hafner, 1964.) Coghill, G. E. The structural basis of the integration of behavior. Proceedings of the NationalAcademy of Sciences US.,1930,16,637-643. Coghill, G . E. Early embryonic somatic movements in birds and in mammals other than man. Monographs of the Society for Research in Child Development, 1940,5, 1-48. Comer, M. Rhythmicity in the early swimming of anuran larvae. Journal of Embryology and Experimental Morphology, 1964, 12,665-67 I . Corner, M. A., & Bot, A. P. C. Developmental patterns in the central nervous system of birds. 111. Somatic motility during the embryonic period and its relation to behavior after hatching. Progress in Brain Research, 1967, 26, 214-236. Coronios, J. D. Development of behavior in the fetal cat. Genetic Psychology Monographs, 1933,14,283-386. Cuajunco, F. Development of the neuromuscular spindle in human fetuses. Contributions to Embryology (Publications of the Carnegie Institution), 1940,28,95- 128. Davis, M. E., & Potter, E. L. Intrauterine respiration of the human fetus. Journal of the American Medical Association, 1946, 131, 1 194- 1201. Diamond, M. C., Lindner, B., & Raymond, A. Extensive cortical depth measurements and neuron size increase in the cortex of environmentally enriched rats. Journal of Comparative Neurology, 1967,131,357-364. Drachman, D. B., & Banker, B. Q. Arthrogryposis multiplex congenita. Archives of Neurology, 1961, 517-93. Drachman, D. B., & Coulombre, A. J. Experimental clubfoot and arthrogryposis multiplex congenita. Lancet, 1962, ii, 523-526. Erkbam. Lebhafte Bewegung eines viermonatlichen Fotus. Neue Zeitschryt f i r Geburtskunde, 1837,5324-326. Fitzgerald, J. E., & Windle, W. F. Some observations on early human fetal movements. Journal of Comparative Neurology, 1942,76, 159- 167. Gasser, R. F. The development of the facial muscles in man. American Journal of Anatomy, 1967,120,357-376. Golubewa, E. L., Shulejkina, K. V., & Vainstein, 1. I. The development of reflex and spontaneous activity of the human fetus during embryogenesis. Obstetrics and Gynecology ( U S S R ) , 1959,3,59-62. Goodman, L. S . , & Gilman, A. The pharmacological basis of therapeutics. (3rd ed.) New York: Macmillan, 1965. Gottlieb, G. Animal behavior: genetics and development. Ecology, 1964, 45, 899-900. Gottlieb, G. Prenatal auditory sensitivity in chickens and ducks. Science, 1965, 147, 1596-1598.

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Gottlieb, G. Species identification by avian neonates: Contributory effect of perinatal auditory stimulation. Animal Behaviour, 1966, 14, I8 1-290. Gottlieb, G. Prenatal behavior of birds. Quarterly Review of Biology, 1968, 43, 148- 174. Gottlieb, G., & Kuo, Z.-Y. Development of behavior in the duck embryo. Journal of Comparative and Physiological Psychology, 1965, 59. 183- 188. Hamburger, V. Some aspects of the embryology of behavior. Quarterly Review of Biology, 1963,38,342-365. Hamburger, V. Ontogeny of behavior and its structural basis. In D. Richter (Ed.), Comparative neurochemistry. New York: Macmillan (Pergamon), 1964. Pp. 2 1-34. Hamburger, V., & Balaban, M.Observations and experiments on spontaneous rhythmical behavior in the chick embryo. Developmental Biology, 1963, 7 , 533-545. Hamburger, V., Balaban, M., Oppenheim, R., & Wenger, E. Periodic motility of normal and spinal chick embryos between 8 and 17 days of incubation. Journal of Experimental Zoology, 1965, 159, 1-14. Hamburger, V., & Oppenheim, R. Prehatching motility and hatching behavior in the chick. Journal of Experimental Zoology, 1967,166, 17 I - 104. Hamburger, V., & Waugh, M. The primary development of the skeleton in nerveless and poorly innervated limb transplants of chick embryos. Physiological Zoology, 1940, 13, 367-380. Hamburger, V., Wenger, E., & Oppenheim, R. Motility in the chick embryo in the absence of sensory input. Journal of Experimental Zoology, 1966,162, 133- 160. Hamilton, W. J., Boyd, J. D., & Mossman, H. W. Human embryology. (3rd ed.) Baltimore: Williams & Wilkins, 1962. Harrison, R. G. An experimental study of the relation of the nervous system to the developing musculature in the embryo of the frog. American Journal of Anatomy, 1904, 3, 197-220. Held, R., & Bauer, J . A., Jr. Visually guided reaching in infant monkeys after restricted rearing. Science, 1967, 155, 71 8-720. Hewer, E. E. The development of nerve endings in the human fetus. Journal of Anatomy, 1935.69, 369-379. His, W. Beobachtungen zur Geschichte der Nasen- und Gaumen-bildung beim menschlichen Embryo. Abhandlungen der Mathematisch-physischen Klasse der Konigliche Sachsischen Akadernie der Wissenschaften, 1901,27,349-389. Hogg, I. D. Sensory nerves and associated structures in the skin of human fetuses of eight to fourteen weeks of menstrual age, correlated with functional capability. Journal of Comparative Neurology, I94 1,75,371-4 10. Hooker, D. The origin of the grasping movement in man. Proceedings of the American Philosophical Society, I938,79,597-606. Hooker, D. A preliminary atlas of early human fetal activity. Pittsburgh: Author, 1939. Hooker, D. Fetal reflexes and instinctual processes. Psychosomatic Medicine, 1942, 4, 199-205. Hooker, D. The origin of overt behavior. Ann Arbor: University of Michigan Press, 1944. Hooker, D. Neural growth and the development of behavior. In P. Weiss (Ed.), Genetic neurology. Chicago: University of Chicago Press, 1950. Pp. 212-213. Hooker, D. The prenatal origin of behavior. f 8 t h Porter Lecture. Lawrence, Kans.: University of Kansas Press, 1952. Hooker, D. Early human fetal behavior, with a preliminary note on double simultaneous fetal stimulation. Research Publications, Association for Research in Nervous and Mental Disease, 1954,33,98- 113. Hooker, D. Evidence of prenatal function of the central nervous system in man. James

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Arthur lecture on the evolution of the human brain. New York: American Museum of Natural History, 1958. Hooker, D. Developmental reaction to environment. Yale Journal of Biology and Medicine, 1960,32,43 1-440. Hooker, D., & Humphrey, T. Some results and deductions from a study of the development of human fetal behavior. Gazeta Midica Portuguesa, 1954.7, 189- 197. Hughes, A. Spontaneous movements in the embryo of Eleutherodacrylus rnartinicensis. Nature, 1966,211, 5 1-53, Hughes. A,, Bryant, S. V., & Bellairs, A. d’A. Embryonic behaviour in the lizard, Lacerta vivipara. Journal of Zoology, 1967,153, 139- 152. Hughes, A., & Prestige, M. D. Development of behaviour in the hindlimb of Xenopus laevis. Journal of Zoology, 1967, 152, 347-359. Humphrey, T. Primitive neurons in the embryonic human central nervous system. Journal of Comparative Neurology, 1944.81, 1-45. Humphrey, T. lntramedullary sensory ganglion cells in the roof plate area of the embryonic human spinal cord. Journal of Comparative Neurology, 1950.92, 333-399. Humphrey, T. The spinal tract of the trigeminal nerve in human embryos between 7% and 8% weeks of menstrual age and its relation to fetal behavior. Journal of Comparative Neurology, 1952,97, 143-209. Humphrey, T. The relation of oxygen deprivation to fetal reflex arcs and the development of fetal behavior. Journal of Psychology, 1953.35, 3-43. Humphrey, T . The trigeminal nerve in relation to early human fetal activity. Research Publications, Association for Research in Nervous and Mental Disease, 1954. 33, 127-154. Humphrey, T. Pattern formed at upper cervical spinal cord levels by sensory fibers of spinal and cranial nerves. Relation of this pattern to associated gray matter. A.M.A. Archives of Neurology and Psychiarty, 1955.73. 36-46. Humphrey, T. Some correlations between the appearance of human fetal reflexes and the development of the nervous system. Progress in Brain Research, 1964, 4, 93- 135. Humphrey, T. The embryologic differentiation of the vestibular nuclei in man correlated with functional development. In International symposium on vestibular and oculomoior problems. Tokyo: Japan Society for Vestibular Research, 1965. Pp. 5 1-56. Humphrey, T. Correlations between the development of the hippocampal formation and the differentiation of the olfactory bulbs. Alabama Journal of Medical Sciences, 1966, 3, 235-269. (a) Humphrey, T. The development of trigeminal nerve fibers to the oral mucosa compared with their development to cutaneous surfaces. Journal of Comparative Neurology, 1966, 126,91-108. (b) Humphrey, T. The development of mouth opening and related reflexes involving the oral area of human fetuses. Alabama Journal of Medical Sciences, 1968,5, 126- 157. (a) Humphrey, T . The dynamic mechanism of palatal shelf elevation in human fetuses. Anatomical Record, 1968. 160, 369. (b) Humphrey, T. The central relations of the trigeminal nerve. In E. A. Kahn, E. C. Crosby, R. C. Schneider, & J. A. Taren, Correlative neurosurgery. (2nd ed.) Springfield, Ill.: Thomas, 1969. Pp. 477-492. (a) Humphrey, T. Function of the nervous system during prenatal life. In U. Stave (Ed.). Physiology of the perinatal period. New York: Appleton-Century-Crofts, 1969. (b) Humphrey, T. Postnatal repetition of human prenatal activity sequences with some suggestions on their neuroanatomical basis. I n R. Robinson (Ed.), Brain and earl) behaviour. New York: Academic Press, 1969. Pp. 43-71. (c)

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55

Humphrey, T. Reflex activity in the oral and facial area of human fetuses. In J. F. Bosma (Ed.), Second symposium on oral sensation and perception. Springfield, Ill.: Thomas, 1969. Pp. 195-233. (d) Humphrey, T. The relation between human fetal mouth opening reflexes and closure of the palate. American Journal of Anatomy, 1969, 125, 3 17-344. (e) Jacobs, M. J. The development of the human motor trigeminal complex and accessory facial nucleus and their topographic relations with the facial and abducens nuclei. Journal of Comparative Neurology, 1970, 138, I6 1- 194. Jacobson, M. Starting points for research in the ontogeny of behavior. In M. Locke (Ed.), Major problems in developmental biology. New York: Academic Press, 1966. Pp. 339-383. Kingsbury, B. F. The significance of the so-called law of cephalocaudal differential growth. Anatomical Record, 1924,27,305-321. Kuo, Z.-Y. Ontogeny of embryonic behavior in Aves: 1. Chronology and general nature of behavior of chick embryo. Journal of Experimental Zoology, 1932.61, 395-430. Kuo, Z.-Y. The dynamics of behavior development. An epigenetic view. New York: Random House, 1967. Magoun. H. W., & Rhines, R. An inhibitory mechanism in the bulbar reticular formation. Journal of Neurophysiology, 1946, 9, 165- 17 1 . Mall, F. P. On the age of human embryos. American Journal of Anatomy, 1918, 33, 397-422. Mavrinskaya, L. F. On correlation of development of skeletal muscle nerve endings with appearance of motor activity in human embryo. Arkhiv Anatomii Gistologii i Embriologii, 1960,38, 61 -68. Minkowski, M. Uber Bewegungen und Reflexe des menschlichen Foetus wahrend der ersten Halfte seiner Entwicklung. Schweizer Archiv f i r Neurologie und Psychiatrie. 1920.7, 148-151. Minkowski, M. Neurobiologische Studien am menschlichen Foetus. In E. Abderhalden (Ed.), Handbuch der biologisches Arbeitsmethoden, 1928, Abt. V. Teil 5B, Heft 5, Ser. 253, 5 1 1-6 18. Murphy, W. F., & Langley, A. L. Common bullous lesions-presumably self-inflictedoccurring in utero in the newborn infant. Pediatrics. I963,32. 1099- 1 10 I . Nilsson, L. Drama of life before birth. Life, 1965.58.54-69. Orr, D. W., & Windle, W. F. The development of behavior in chick embryos: the appearance of somatic movements. Journal of Comparative Neurology, 1934,60,27 1-285. Patten, B. M. Human embryology. (3rd ed.) New York: McGraw-Hill, 1968. Prechtl, H . F. R. Problems of behavioral studies in the newborn infant. In D. S. Lehrman, R. A. Hinde, & E. Shaw (Eds.), Advances in the study of behavior. Vol. I . New York: Academic Press, 1965. Pp. 75-98. Preyer, W. Specielle Physiologie des Embryo. Leipzig: Grieben’s Verlag, 1885. Pritchard, J. A. Deglutition by normal and anencephalic fetuses. American Journal of Obstetrics and Gynecology, 1965, 25, 289-297. Ranson, S. W. The anatomy of the nervous system. (7th Ed.) Philadelphia: Saunders, 1943. Reynolds, S. R. M. Nature of fetal adaptation to the uterine environment: a problem of sensory deprivation. American Journal of Obstetrics and Gynecology, 1962. 83, 800-808. Rosenzweig, M. R., Krech, D., Bennett, E. L., & Diamond, M. C. Effects of environmental complexity and training on brain chemistry and anatomy: a replication and extension. Journal of Comparative and Physiological Psychology, 1962, 55, 429-437.

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Ruch, T. C., Patton, H. D., Woodbury, J. S., & Towe, A. L. Neurophysiology. Philadelphia: Saunders, 196 I . Scharpenberg, L. G.. & Windle, W. F. A study of spinal cord development in silverstained sheep embryos correlated with early somatic movements. Journal of Anatomy, 1938,72,344-35 1 . Scherrer, J., & Fourment, A. Electrocortical effects of sensory deprivation during development. Progress in Brain Research, 1964,9, 103- 1 12. Sherrington, C. S. The integrative action of the nervous system. New Haven, Conn.: Yale University Press, 1906. Smith, K. U . , & Daniel, R. S . Observations of behavioral development in the loggerhead turtle (Caretta caretta). Science, 1946,104, 154- 155. Steffek, A. J., King, T. G., & Derr, J. E. The comparative pathogenesis of experimentally induced cleft palate. Journal of Oral Therapeutics and Pharmacology, 1966, 3,9- 16. Strassman, P. Das Leben vor der Geburt. Sammlung Klinischer Vortrage, Neue Folge, 1903. No. 353 (Gyndkologie, No. 132), 947-968. Streeter, G. L. Weight, sitting height, head size, foot length and menstrual age of the human embryo. Contributions to Embryology (Publications of the Carnegie Institution), 1920, 11, 143- 170. Swenson, E. A. The simple movements of the trunk of the albino rat. Anatomical Record, 1928.38, 31. Swenson, E. A. The active simple movements of the albino rat fetus: the order of their appearance, their qualities, and their significance. Anatomical Record, 1929, 42, 40. Sztkely, G., & Szentigothai, J. Reflex and behaviour patterns elicited from implanted supernumerary limbs in the chick. Journal of Embryology and Experimental Morphology, 1962.10, 140-151. Tracy, H. C. The development of motility and behavior reactions in the toadfish (Opsanus tau). Journal of Comparative Neurology, 1926, 40, 253-369. Tuge, H. Early behavior of the embryos of the turtle, Terrapene Carolina (L.), Proceedings ofrhe Society for Experimental Biology and Medicine, I93 I , 29,52-53. Tuge, H . Early behavior of the embryos of carrier-pigeons. Proceedings of the Society for Experimental Biology and Medicine, 1934,31,462-463. Walberg, F. Morphological correlates of postsynaptic inhibitory processes. Wenner-Gren Center International Symposium Series, 1968, 10, 7- 14. Wasz-Hockert, O., Lind, J., Vuorenkoski, V., Partanen, T., & ValannC, E. The infant cry. A spectrographic and auditory analysis. Clinics in Developmental Medicine No. 29. London: Heinemann and Lavenham, Suffolk, Eng.:Lavenham Press, 1968. Weiss, P. Further experimental investigations on the phenomenon of homologous response in transplanted amphibian limbs. IV. Reverse locomotion after the interchange of right and left limbs. Journal of Comparative Neurology, 1937,67,269-3IS. Weiss, P. Nerve patterns: the mechanics of nerve growth. Growth, 1941,5, 163-203. (a) Weiss, P. Self differentiation of the basic patterns of coordination. Comparative Psychological Monographs, 1941, 17, 1-96. (b) Weiss, P. Does sensory control play a constructive role in the development of motor coordination? Schweiterische Medizinische Wochenschrif, 1941, 71, 591 -595. (c) Weiss, P. Nervous system (neurogenesis). In B. H. Willier, P. A. Weiss, & V. Hamburger (Eds.),Analysis of development. Philadelphia: Saunders, 1955. Pp. 346-401. Windle, W. F. The neurofibrillar structure of the spinal cord of cat embryos correlated with the appearance of early somatic movements. Journal of Comparative Neurology, 1931,53,71-113.

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Windle, W. F. Correlation between the development of local reflexes and reflex arcs in the spinal cord of cat embryos. Journal of Comparative Neurology, 1934.59.487-505. Windle, W. F. Physiology of the fetus. Philadelphia: Saunders, 1940. Windle, W. F. Genesis of somatic motor function in mammalian embryos: a synthesizing article. Physiological Zoology, 1944, 17, 247-260. Windle, W. F. Reflexes of mammalian embryos and fetuses. In P. Weiss (Ed.), Genetic neurology. Chicago: University of Chicago Press, 1950. Pp. 214-222. Windle, W. F., & Becker, R. F. Relation of anoxemia to early activity in the fetal nervous system. A.M.A. Archives of Neurology and Psychiatry, 1940,43,90-101. Windle. W. F.,& Fish, M. W. The development of the vestibular righting reflex in the cat. Journal of Comparative Neurology, 1923.54.85-96. Windle, W. F., & Fitzgerald, J. E. Development of the spinal reflex mechanism in human embryos. Journal of Cornpararive Neurology, 1937,67,493-509. Windle, W. F., & Griffin, A. M. Observations on embryonic and fetal movements of the cat. Journalof Comparative Neurology, 193 1,52, 149-188. Windle, W. F., Minear, W. L., Austin, M. F., & Orr, D. W. The origin and early development of somatic behavior in the albino rat. Physiological Zoology, 1935.8, 156-185. Windle, W. F., O’Donnell, J. E.,& Glasshagle, E. E. The early development of spontaneous and reflex behavior in cat embryos and fetuses. Physiological Zoology, 1933, 6, 52 1-541. Windle, W. F., & Orr, D. W. The development of behavior in chick embryos: spinal cord structure correlated with early somatic motility. Journal of comparative Neurology, 1934,60,287-307. Windle, W. F., Orr, D. W., & Minear, W. L. The origin and development of reflexes in the cat during the third fetal week. Physiological ZoSlogy, 1934, 7, 600-617. Yanase, J . Beitrage zur Physiologie der peristaltischen Bewegungen des embryonalen Darmes. Archiv fur die gesamte Physiologie des Menschen und der Tiere, 1907, 117, 345-383; 119,451-464. Youngstrom, K. A. Studies on the developing behavior of Anura. Journal of Comparative Neurology, 1938,68, 351-379.

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AROUSAL SYSTEMS A N D INFANT HEART RATE RESPONSES'

Frances K . Graham and Jan C . Jackson UNIVERSITY OF WISCONSIN

I. I N T R O D U C T I O N ............................................ A. AROUSAL SYSTEMS .................................... B. OR-DR D I F F E R E N T I A T I O N I N A D U L T SUBJECTS . . . . . . . 11.

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P R O C E D U R E ................................................ A. I N F A N T SUBJECTS ...................................... B. LABORATORY A R R A N G E M E N T S ........................ C. H R RESPONSE MEASUREMENT .........................

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DEVELOPMENTAL S T U D I E S O F E V O K E D H R RESPONSE . . . A. NEWBORN H R RESPONSE ............................... 8. H R RESPONSE IN O L D E R I N F A N T S ..................... C. FACTORS A F F E C T I N G T H E D E V E L O P M E N T A L S H I F T . .

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IV. SUMMARY A N D DISCUSSION REFERENCES

'Preparation of this paper, and much of the research described, was supported by grants HD01490 and K05-MH-21762 from the National Institutes of Health and by a predoctoral Public Health Fellowship to the junior author. Computer services were provided through grant FRO0249 to the Laboratory Computing Facility and an N S F grant through the University of Wisconsin Research Committee. 59

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I.

Introduction

Several writers have recently proposed that there are two arousal systems which affect behavior differently, one energizing response while inhibiting receptive and consolidative processes, and the other facilitating these processes and, thus, memory and learning. Sokolov’s work, in particular, has stimulated considerable interest but attention has been largely focused on the facilitative “orienting” system to the neglect of an opposite-acting “defense” system. The present paper considers briefly the evidence from adult studies that these two systems can be distinguished by the direction of heart rate (HR) change. It next reviews typical procedures and problems encountered in studies of infant H R response, and then reviews the data from these studies to determine whether there is a developmental shift from primarily defensive reactions during the newborn period to increasingly probable and larger orienting reactions with increasing age. A. AROUSAL SYSTEMS

Arousal or activation level is an important concept in psychology because it is believed to affect a wide variety of psychological processes. It has generally been viewed as a unitary dimension which could range from low levels during coma or deep sleep to high levels during alert wakefulness or agitation. However, the unidimensionality aspect is being vigorously challenged by recent work. Lacey (1967) has reviewed a number of the findings which pose critical problems, including low intercorrelations among autonomic measures of arousal, evidence for dissociation among central, behavioral, and autonomic measures, and specificity of autonomic “arousal” responses as a function of stimulus situations. In reply, Malmo and BClanger (19671, major proponents of unidimensional arousal theory, have argued that the theory may still be valuable as a general description; and they note that some confusion has arisen because relatively long-term background changes are not separated from discrete, short-term responses. It is the former which are relevant to activation theory, in Malmo’s usage at least. While the unidimensionality argument may not be resolved for some time, it is probably not an all-or-nothing matter, but, like many earlier arguments concerned with general versus specific factors, a question of the relative proportions of variance that can be accounted for by a single common factor in comparison with the variance accounted for by the sum of specific factors. Another approach, exemplified in a recent review article by Routten-

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berg (19681, asks, essentially, whether a larger proportion of variance can be accounted for by two arousal systems than by a single one. Routtenberg suggests that many neurophysiological findings can be better accommodated by postulating two mutually inhibiting arousal systems which have different functions. The first, evoked by high intensities of stimulation and associated with the Moruzzi and Magoun (1949) reticular activating system, functions to energize response and limit the effects of stimulation. The second, evoked by low to moderate intensities of stimulation and involving the limbic system, is assumed to prolong the effects of stimulation and thus to facilitate memory and learning processes. Routtenberg’s theory, while primarily directed to neurophysiological data, has many features in common with Sokolov’s conceptualization (1963) of two generalized reflex systems, labeled a defense reflex (DR) and an orienting reflex (OR). The DR, like Routtenberg’s first arousal system, is evoked by high intensity stimuli and functions to limit the effects of stimulation. The OR is similar to Routtenberg’s second arousal system. It is evoked by “novel” and by “signal” stimuli that are below the intensity sufficient to evoke defense and it functions to enhance the effects of stimulation and in the strengthening of associations. With repeated presentations of an initially novel, non-signal stimulus or after a signal-event connection is fully established, the OR can no longer be evoked. Sokolov has not attempted to identify in any detail the neural structures that might be associated with the two systems. Subcortical areas are assumed capable of initiating either reaction but separate loci have not been elaborated although Lynn ( 1966), in discussing Sokolov’s theory, cites evidence from other investigators that is compatible with involvement of limbic structures in eliciting an OR and of brain-stem reticular formation in eliciting a DR. While not specifying subcortical mechanisms, Sokolov does argue that the cortex plays an important role in amplifying or habituating the OR. He postulates a 2-stage model in which the cortex acts as a comparator-analyzer of incoming stimuli and subcortical mechanisms amplify or dampen the response depending on signals fed back from the cortex. Other theories have also emphasized a fundamental distinction between the effects of high and low-moderate stimuli. Schneirla ( 1 959) cites historical precedents and himself advances a dual system which has communalities with those discussed above. Most importantly, he also relates the system evoked by low-moderate intensity stimuli to facilitative functions. Berlyne (1967), in his most recent discussion of activation theory, recognizes a similar distinction between what he calls re-

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ward and aversion systems. These are explicitly related to Schneirla’s and Sokolov’s concepts. While there are many differences among these various approaches, the important similarity is that they all propose different and, at least in some respects, opposed functions depending on whether stimulus intensity is low or high. If there are two arousal systems with differential effects on such psychological processes as learning and perception, development of these arousal systems during early infancy becomes a matter of interest. It would be expected that the system facilitating “information processing” and mediated by higher nervous system mechanisms would be relatively less developed at birth than the system concerned with energizing and protective functions and mediated by the relatively mature reticular formation. If this is true, further study of the factors influencing development of a facilitating system might aid in understanding why early learning is relatively slow and in determining the conditions under which it could be maximized. The present paper surveys studies of infant HR and discusses, in more detail, studies from our laboratory which are relevant to the question of whether there are developmental differences in the ease of evoking the two arousal systems. For several reasons, the question has been formulated within the framework of Sokolov’s theory. The theory describes objective criteria for distinguishing an OR from a DR and it is based on a substantial body of experimental work employing psychophysiological techniques with human subjects. Such techniques are well suited to the study of infants. B. OR-DR DIFFERENTIATION I N ADULTSUBJECTS

The OR and DR are generalized response systems which produce widespread, unconditioned changes in motor, autonomic, and central activities. Because of their generality, they have many response components in common, including EEG desynchronization, electrodermal resistance changes (GSR), and peripheral vasoconstriction. Curiously, these components, which do not differentiate the two systems, have been the most commonly employed in psychophysiological research, even when the research was explicitly concerned with orienting behavior. There are a number of other response components which probably do differentiate the systems, although the evidence for differentiation is not conclusive. Sokolov (1 963) claimed that the two systems could be distinguished by changes in cephalic vasomotor activity, with cephalic vasodilation indicating an OR and cephalic vasoconstriction a DR. Unfortunately,

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western investigators have not been able to replicate this finding unequivocally. Studies by R. C. Davis, Buchwald, and Frankmann (1955) and R. C. Davis and Buchwald (1957) offer some support but Royer’s work (e.g., 1966) suggests qualification of the findings; other studies (W. K. Berg, 1968; Raskin, Kotses, & Bever, 1969), as well as informal reports, indicate difficulty in replicating. There is some evidence that the systems may be more successfully distinguished by such central and autonomic components as hippocampal activity (Grastyhn, Karmos, Vereczkey, Martin, & Kellenyi, 1969, skin potential changes (Raskin er al., 1969), pupillary constriction or dilation (Sokolov, 1963), H R increase or decrease (Graham & Clifton, 1966), and by such motor responses as head turning, ear flicks and oculo-motor movements. The work in our laboratory has concentrated on HR change, which is a sensitive and reliable measure that can be easily recorded without disturbing the subject. Sokolov did not include direction of HR change among components that differentiate between an OR and a DR but Lacey (e-g., 1959) argued, on the basis of neurophysiological considerations and behavioral data, that HR deceleration occurs in situations of “stimulus intake” and H R acceleration occurs in situations of “stimulus rejection.” While Lacey was concerned with complex situations unlike the simple conditions in which orienting has been studied, Graham and Clifton (1966) hypothesized that, if Lacey’s reasoning were correct, HR deceleration should be a component of the OR, and HR acceleration a component of the DR. A review of the literature offered considerable support for the hypothesis, although the picture was complicated by some reports of a diphasic response of acceleration-deceleration in situations presumably appropriate for eliciting orienting. Graham and Clifton suggested that the initial, short latency, accelerative phase might be a consequence of a respiratory “startle” response and that this response might be due to the large onset transients produced by many methods of generating auditory signals. Subsequent work has provided additional support for the H R differentiation hypothesis. To distinguish an OR from a DR and thus to determine whether a component is differentiating, several criteria have been described by Sokolov. First, an OR is elicited by low-to-moderate intensity stimuli while a DR is elicited by high intensity stimuli. This is not an easily applied criterion, however, since there is no absolute definition of what constitutes “high” intensity, short of intensities producing tissue damage. While presence of a response difference as a function of stimulus intensity difference is evidence suggesting OR-DR differentiation, absence of a response difference may mean either that the particular

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type of response does not differentiate the systems or that the stimuli employed do not include stimuli both above and below the threshold for eliciting a DR. A second criterion is that the OR is elicited by change ir stimulation and thus habituates (diminishes) rapidly when the same stimulus is repeated. This criterion applies only to “non-signal” stimuli, i.e, stimuli which are not themselves reinforcing or associated with reinforcement. In contrast, a DR habituates slowly or may even be intensified by stimulus repetition. A third criterion also depends on the fact thal stimulus change is an effective stimulus for eliciting the OR. Since intensity decrease is as much a stimulus change as intensity increase, the response to offset of a sufficiently long-lasting stimulus should elicit an OR and could not elicit a DR. Consequently, if a response component is differentiating, onset and offset responses should be in the same direction when low-moderate intensity stimuli are used and should differ when high intensity stimuli are used. Differences in direction of HR change as a function of stimulus intensity have been shown in a number of studies (Graham & Clifton, 1966). The usual finding is HR deceleration with low intensity stimulation, and acceleration with high intensity stimuli such as painful shock and tones above 90 db. Between approximately 60 and 90 db, the diphasic acceleratory-deceleratory response has often been reported when rise time of tones is not controlled. Unpublished work from our laboratory (Hatton, Graham, & Berg, 1968) suggests that the initial acceleration of the diphasic response may be explained by onset characteristics.2 Using an electronic switch to control onset, even a 90 db re .0002 microbar tone elicited immediate deceleration when onset was gradual but elicited a diphasic response when the onset was sudden (300 ms versus <5 ps to peak intensity). This is illustrated in Fig. 1 for 1000 Hz tones of 2second duration. Curves are the average response of 24 undergraduate Ss on four non-consecutive trials. Differences in rate of habituation of HR accelerative and decelerative responses have also been shown in a number of studies. In addition to studies cited by Graham and Clifton (1 966), several more recent studies demonstrated very rapid habituation of deceleration (W. G. Chase & Graham, 1967; Meyers & Gullickson, 1967; D. B. D. Smith & Strawbridge, 1968). Meyers and Gullickson also found that the habituated deceleration reappeared with change of stimulation. Chase and Graham showed, further, that HR deceleration met the additional criterion of similar onset and offset responses (Fig. 2). The stimuli were tones varied 2Appreciation is expressed to Harry Ludwig for suggesting the possible importance of rise time functions.

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in frequency and in intensity (from 60 to 87 db) presented over 71 db white noise. This work with adult human Ss, as well as further animal work (Lynch, 1967; Newton & Perez-Cruet, 1967), generally supports the Graham-Clifton hypothesis that direction of HR change differentiates the OR and the DR. However, misinterpretations can arise from failure to consider certain factors which tend to complicate HR response in situations supposedly appropriate for eliciting a decelerative OR. These factors include (a) averaging across trials, (b) sudden onsets of stimuli, (c) instructions giving stimuli a signal character, and (d) situations requiring activity. Obviously, any averaging across trials can dilute or obscure a response which is very rapidly habituating. If a low intensity stimulus is used, the OR would be expected to disappear within a few trials and its magnitude will be underestimated if early trials are averaged with noresponse later trials. If a moderate or high intensity stimulus is used, the OR should be replaced within a few trials by an accelerative DR. Again, an average of ORs on early trials with DRs on later trials will not adequately describe the OR.

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I 1 I l I I 1 I I I I 1 1 1 1 1 1 1 I

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8.5

12.5

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Seconds

Fig. I . Second-by-second changes in mean adjusted H R f o r I second preceding and 20 seconds following onset of 90 db, 1000 H z tones of slow (300 ms) and fast (4 ps) rise time. Averages for 24 adult Ss on 4 trials @om Hatton et al., 1968).

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Frances K . Graham and Jan C . Jackson Onset

Seconds from onset Fig. 2 . Second-by-second H R response of 10 adult Ss to onset and offset of 18-second tones varying in frequency and intensity. Average of I0 trials (from W . G . Chase & Graham, 1967, with permission of the publisher).

It is also evident that rapid onsets, at least with moderately intense stimulation, produce a brief HR acceleratory phase. Whether this response should be considered the cardiac accompaniment of a D R or part of a “startle” reflex is uncertain. While both may be classified as protective reflexes, there are some grounds for believing that “startle” can be discriminated from “defense” both by latency and by peripheral neural mechanism. Another possible source of misinterpretation arises if supposedly nonsignal stimuli acquire signal properties by virtue of general laboratory conditions or instructions. This may only retard habituation, as in a recent study by Korn and Moyer (1968). They showed that small differences in the wording of instructions-addition of the phrase “pay attention to the tones you will hear” - significantly affected the amplitude and habituation of responses, in this case, G S R responses. Under some circumstances, the supposedly benign stimuli may elicit previously conditioned DRs. The naive S, connected to unfamiliar wires and electrodes,. may, for example, believe that he is in a situation where injury is possible despite assurances to the contrary. Other instructions, such as a request to count stimuli, affect not only the signal character of the stimuli, but may produce associated activity. Implicit speech movements and respiratory changes associated with counting would themselves influence HR response. Studies of H R change in signal situations do suggest that activity or preparation for activity produces HR acceleration which combines with orienting re-

Arousal Systems and Infant Heart Rate Responses

67

sponses of deceleration to yield more complex curves than are seen in the simpler non-signal conditions (W. G. Chase, Graham, & Graham, 1968; Headrick & Graham, 1969). While consideration of these adult studies is remote from the purposes of the present paper, it is appropriate to note that such research indicates the potential value of studying HR response in learning situations.

11. Procedure Certain specific procedures have been followed in all or most of the studies in our laboratory and these are described below. More general problems of measuring HR activity are also considered. A. INFANT SUBJECTS

Newborns have been obtained from the obstetrical services of University Hospitals and St. Mary’s Hospital, Madison, Wisconsin. Only fullterm infants meeting criteria of normal pregnancy, delivery, and postnatal condition are selected. The criteria include: birth weight greater than 5.5 Ib, normal spontaneous or low-forceps delivery, absence of risk factors in the maternal history (Graham, Ernhart, Thurston, & Craft, 1962), normal birth condition as judged by an Apgar score of 6.0-7.0 or higher (Apgar, 1953), and normal physical examination following birth. Age at the first testing has been restricted to the period between 30 and 62 postnatal hours. Permission to serve in experiments is given by the attending obstetricians and pediatricians and by the infant’s mother. Both physicians and parents are provided with a written description of the experiment’s purpose and procedures. Of 3 17 newborn infants selected for studies described in this paper, only 9% were lost through failure to obtain parental permission. An additional 9% of Ss were replaced because infant crying, regurgitation, or movement led to illegible records, and 16% were replaced because of equipment failures or procedural error. This tabulation does not include a recent study (Kantowitz & Graham, 1969) whose special selection criteria will be discussed in a later section. Older infants have been located through the maternity records at University and St. Mary’s Hospitals. The same criteria of normal birth and pregnancy are required as in the case of newborns; infants are also excluded if questioning of the mother reveals any current illness or any postnatal cardiovascular or central nervous system defect or disease. Permission to test the infant is sought by letter and a subsequent tele-

68

Frances K. Graham and Jan C. Jackson

phone call. Parents are asked to bring the infant to the laboratory and are reimbursed for any transportation or baby-sitting costs attendant on their cooperation. Of 210 parents contacted by letter, approximately 30% have been unwilling or unable to permit their infants to serve as subjects. Another 10-25% could not be reached by telephone. Of infants who began an experimental session, a larger percentage were replaced than was true with newborn subjects. In one study of 6- and 12-week-old infants, 36% were lost because of crying on more than one trial with any given stimulus. In a study of 16-week-old infants, it was necessary to replace 45% to meet the stricter criterion of no crying trials. B. LABORATORY ARRANGEMENTS

Sterile procedures are followed in the two laboratories in which infants are tested and safety checks of apparatus are made before each experimental session. Two experimenters are present throughout all sessions. One monitors equipment while the other monitors the infant and, when required, makes behavioral observations. With older infants, E remains out of sight and observes through a mirror. The mother is not in the room with the infant. Newborns are swaddled and tested while lying supine either in a copper-shielded incubator or in a crib placed in a sound-attenuated IAC chamber. In the latter case, equipment is located outside the subject room. Older infants are also tested in the IAC chamber. They are only minimally restrained and, depending on the mother’s preference, lie supine on a specially constructed, large platform or recline in an infant seat mounted on the platform. To reduce irritability, infants are usually fed shortly before an experimental session. Pacifiers are also offered when necessary, generally during the application of electrodes or during intertrial intervals. However, infants are permitted to retain the pacifier during stimulation if its removal evokes crying. It appeared preferable to maintain all infants in as nearly comparable a state as possible than either to exclude irritable infants or to test during states of irritability. Inspection of HR records did not suggest that there was any consistent effect of pacifier presence or absence independent of whether sucking increased or decreased in response to stimulation. Both types of sucking response occurred and, as with other movements, activity tended to be positively correlated with HR (cf. Section 111, A,3). An experimental session consists of presenting a series of single stimuli and recording heart rate and, in some cases, respiration and behavioral observations. The stimuli have been sound stimuli, presented in

Arousal Systems and Infant Heart Rate Responses

69

free field. Early experiments employed a tape-recorded 300 Hz rectangular wave, with on-off time approximately one to nine. This was qualitatively a rough-sounding buzz. In later experiments, pure tones, usually 1000 Hz, have been produced by a Hewlett-Packard sound system and rise and fall time have been controlled by a Wisconsin electronic switch (Olson & Ludwig, 1965). Electronic timing equipment determines stimulus duration and intertrial intervals. The stimulus artifact and physiological responses are recorded on a continuously operating, ink-writing polygraph, and, more recently, they have also been recorded on magnetic tape. Before introduction of the tape system, records were manually read but, with the tape system, data are automatically digitized off-line by a Laboratory Instrument Computer (LINC). Behavioral observations are typically made during the 10 seconds preceding stimulus onset. Eye position and movement, vocalizations, head and general movement, and muscular tension are recorded and a rating of General State is then made. General State has been categorized according to either an 8- or 9-class system. The latter system includes the categories asleep, drowsy, alert, fussy, crying, or in transition between any two states. Assuming an ordinal scale, interobserver reliability has been determined in three studies (H. Chase, 1965; Graham, Clifton, & Hatton, 1968; Hatton, 1969). Based on 94, 102, and 106 observations, respectively, we obtained reliability coefficients of .6 1 , .78, and .88, or agreement within one class of 90.4, 87.2, and 92.5%. C. H R RESPONSEMEASUREMENT

It is a simple matter to record an electrocardiogram but not as simple to measure a H R “response.” The response is not a discrete change whose presence or absence is easily identified, but a transient change in i continuous activity. The transient must be distinguished from a noisy Jackground which may include spontaneous fluctuations, sinus arrhythnia, and movement artifacts, and may affect response differently at diferent base levels. Further, if the direction and time course of the traniient are of concern, the response must be measured in detail. The early iterature employed various averages and indices of response that did lot preserve information about multiple changes in direction, or distin:uish changes in variability from changes in level. Even with more re:ently used response measures, three kinds of problems are encounered. These concern the units of measurement, the sampling period, and he prestimulus response level.

70

Frances K . Graham and Jan C . Jackson

1. Cardiac Units The first problem concerns the units of measurement. In the case of cardiac cycling activity, the smallest possible unit is the time to complete a single cardiac cycle. This may be expressed as time per cycle (cardiac period or RR interval) or as rate per unit time (HR in bpm), the reciprocal of time per cycle. Although it is frequently assumed that use of either measure is a matter of personal preference, Lacey (1962) and Lipton, Steinschneider, and Richmond (1961a) have pointed out that the measures are not identical and might yield differences of practical importance. For example, correlations of HR with another variable cannot be the same as the correlations of RR with that variable. Since the relationship of rate and period is non-linear by definition, they cannot have the same linear relation to a third variable. However, it can be observed by actually plotting the relation (cf. Lipton et al., 1961a, Fig. I), that deviation from non-linearity is moderate and, within the normal range of human adult or infant rates, might not have practical consequences. The two measures might also differ in the shape of their frequency distributions. Reciprocals are frequently used to normalize data, as in the familiar case of speed and latency, so it would not be surprising if one of the measures had a more normal distribution than the other. Unfortunately, there appear to be no published data on distributions, although Lipton, Steinschneider, and Richmond ( I96 1 bf examined scattergrams of newborn HR change plotted against prestimulus HR and recommended a log transformation. They did not comment on the RR distribution. To obtain empirical data relevant to this question, frequency distributions of HR, RR, and log HR were plotted for the 100 newborns studied by Clifton, Graham, and Hatton (1 968). Figure 3 shows the distributions based on a 1-second period occurring just before the first stimulus presentation; similar distributions were obtained for the 1 -second period occurring 4 seconds after stimulus onset. While it is obvious that all of the measures are skewed, their distributions did not differ significantly from one another by a chi-square test (Table 1,A). Heart rate was, if anything, the least skewed since its distribution did not depart significantly from the Gaussian, at least in this relatively insensitive test (Table 1,B). Similar findings have been obtained by M. A. Wenger, and T. D. Cullen, (personal communication) with several adult samples. They also concluded that there was little basis for choice among measures although, in their case, RR distributions were slightly more normal. Judging from this evidence, none of the measures has any major advantage and we have consequently chosen to employ the most familiar unit, rate in bpm.

Arousal Systems and Infant Heart Rate Responses

251

71

/,A

r:

5-

-3.0 Slow

-210

-110

0.0

Standard score

+1.0

+2.0

+3.0 Fast

Fig. 3. Frequency distributions of cardiac rate ( H R ) ,period ( R R ) ,and log of rate (log H R ) for a I-second sample from 100 newborns.

A different decision might be warranted in situations where recording or measurement error is substantial. Such error is usually constant for the time measure (RR) and, therefore, not constant for rate. In reading polygraph EKG records, for example, the seriousness of the variation in error will depend on polygraph speed and on the range of HR values. At a speed of 25 mm per second, a 0.5 mm reading error will equal i 2 0 ms whether a period is short or long but will be a 1-beat error when HR is 60 and a 7-beat error when the rate is 150. Under these circumstances, the period measure would be preferable.

2 . Sampling and Temporal Units The second problem concerns the sampling of cardiac activity. Two considerations are relevant in studies where multiple phases may occur. Activity should be sampled for as long as a response can be detected and it should be sampled in sufficient detail to detect inversions in the direction of change. In determining the detail with which responses should be measured, we have adopted a more conservative method than might be optimal under every condition. Because there is still a need for exploratory work and because automatic data processing makes it feasible to examine

Frances K . Graham and Jan C . Jackson

12

TABLE I CHI-SQUARE TESTSOF DIFFERENCES BETWEEN H R , RR, AND LOG H R DISTRIBUTIONS AND OF DIFFERENCES FROM A NORMAL DISTRIBUTION A . Comparison of empiricul distributions, using 8 intervals and 7 df Prestimulus sample Poststimulus sample

H R vs. R R R R vs. log H R H R vs. log H R

2.89 1.41 0.42

3.15 I .47 0.59

B . Comparison with normal distribution using 8 intervals and 5 df Prestimulus sample Poststimulus sample

HR RR

I8.54**

11.05 22.02**

Log

13.21*

14.65*

9.58

HR *p < .os.

* * p < .01.

large amounts of data, the smallest possible data unit (a cardiac cycle) was selected as the starting point.3 An interesting question then arises. In plotting the temporal course of the response, should the units of time be cardiac units, i.e. successive beats, or real-time units? This is the distinction between two commonly-used methods, beat-by-beat as compared with second-by-second analysis. In the one case, measurement is made in terms of an organismic (cardiac) clock and, in the other, in terms of a real-time clock. Responses obtained with the two methods will not be identical. If cardiac cycles are plotted, a smaller real-time sample will be obtained from individuals with rapid heart rates than from S s with slow heart rates. Conversely, if real-time is plotted, S s with rapid rates will have experienced more heart contractions during a given period of time than S s with slow HRs. Although both methods have been used, the reasons for choice have apparently not been discussed. We have used real-time units. They appear better suited to comparisons across age groups whose base heart rates differ markedly and to coordination with other concomitant activities. They also have an advantage in reaction time or conditioning studies where two stimuli are separated by fixed time intervals rather than by fixed numbers of cardiac cycles. Our procedure is to calculate a 1-second average of rate, based on all cardiac cycles and partial cycles, weighted proportionately, which occur within the second. This requires computer processing, both because of the calculation burden and because of the difficulty in accuearly work where records were manually read, a 3-beat unit was used.

Arousal Systems and Infant Heart Rate Responses

73

rately measuring partial cycles. Schachter, Williams, and Tobin ( I 967b) have used a shorter 100 ms time base which may prove valuable in studying the changes that occur within the first second or two. Since this time base is shorter than the average cycle, a single cycle will determine the HR of more than one time period. The degrees of freedom for evaluating changes across time will, therefore, be less than the usual N-1 time periods and suitable adjustment for the loss in &should be made. We have usually obtained the per-second averages for 1 second before and for varying numbers of seconds, most frequently 20, following stimulus onset. A 1-second sample of prestimulus was selected after analyses indicated that it accounted for as much of the variance in peak responses as the average of 5 prestimulus seconds (Clifton & Graham, 1968). The per-second values are then averaged across individuals for each trial separately or for blocks of trials. Although trial-blocking is widely used, experimenters rarely discuss the basis for deciding how many trials should constitute a block. Unfortunately, there does not seem to be any clearcut answer. Selection appears to involve such intuitive considerations as aesthetics (how many curves can be drawn on a single graph), convenience (what numbers divide equally the total number of trials), and inherent variability of the data (increasing the number of trials, like increasing the number of subjects, produces more reliable data). In the present case, we are concerned with responses that may habituate or change rapidly in the course of a few trials. Consequently, where habituation is directly of interest, we have used a design in which the same stimulus is repeated, ordinarily for 15 trials, and have selected the minimum number of trials which produce equal trial-blocks (in this example, three). When stimulus parameters have been the object of study, habituation has been reduced by interspersing stimuli and we have averaged all trials, usually four, with the same stimulus (e.g. Fig. 1). Our method thus results in a summary response curve showing average second-by-second HR for a group of Ss on a particular trial-block. A similar curve, based on organismic time, could be obtained by averaging beat-by-beat HR. Another method, which is best illustrated by Lipton et al. (1961a), also employs organismic time. This method produces summary response curves by averaging such important parameters of individual curves as accelerative slope, peak, and postpeak decelerative slope. Certain practical problems arise in applying the individual parameter method. It is not an easy task to define the parameters in such a way that they can be reliably and objectively identified. This is especially true with weak or complex responses. It is also a relatively inflexible

74

Frances K . Graham and Jan C . Jackson

method. If changed experimental conditions produce a different type of response, it is necessary to redefine the response parameters. There is a further problem in handling an individual response which is not characteristic. When parameters of a wave of acceleration are being sought, for example, a decelerative response must either be excluded or scored as 0.0. Exclusion is unsatisfactory if the occurrence of non-characteristic responses is associated with the variables being investigated and giving zero scores has the effect of weighting negative instances differently from positive instances. A brief comment should be made about the use of response indices. They may be efficient in reducing data if the characteristics of the response are known and indices are selected in such a way that the relevant characteristics are preserved. However, there are many pitfalls in devising indices. A common method is to measure X number of extreme beats, say the 3 fastest cycles, in a given period preceding and following stimulation. With this procedure, there will appear to be an increase or decrease in HR even if the only change is an increase or decrease in variability. A less obvious distortion can result if the X extreme beats are selected from periods of different durations. In this case, there will appear to be an increase or decrease in H R even if both means and variances of the two periods are equal. An accelerative “response” will be identified, for example, if the 3 fastest beats of a 5-second prestimulus period are compared to the 3 fastest beats of a 10-second poststimulus period which is, in fact, exactly identical with the prestimulus period. The fallacy can be easily illustrated by selecting any group of numbers, say 1, 2, 3 , 4 , 5 , and reproducing the group so that you have 1, 1, 2, 2, 3, 3 , 4 , 4, 5, 5. If you now select the 3 largest numbers from each group to represent the “response”, you will conclude that the second group has a larger response. Stated in more general terms, if a fixed number of extreme observations (e.g. 3) is selected from periods of unequal size (e.g. 5 and 10 observations), the selections will necessarily include different proportions of each period (e.g. 60 and 30%). Obviously, if the two periods have identical means and variances, values in the upper 30% of a period will be larger than values in the upper 60%. 3. Initial Level Efects The third problem concerns the effects of initial heart rate. There is good evidence that amplitude measures of poststimulus cardiac activity are reliably related to prestimulus cardiac activity and that this relationship generally follows the “law of initial values [Lacey, 1956; Wilder, 19671.” The ‘‘law’’ states that response to an excitatory stimulus decreases and

Arousal Systems and Infant Heart Rate Responses

75

response to an inhibitory stimulus increases as the level of activity before stimulation increases. This means that whether stimuli generally evoke H R acceleration or generally evoke H R deceleration, the change from high prestimulus levels will be relatively negative, i.e. a smaller increase or a larger decrease compared to the change from low prestimulus levels. Interestingly, not only do both infant and adult H R responses appear to follow the “law of initial values” but the actual regression coefficients fall within a narrow range. If the “law” holds, the regression of poststimulus H R on prestimulus H R should be positive but less than 1.0. Table I I lists coefficients for the poststimulus regression which were obtained in several adult and infant studies. The coefficients average 0.71 and, with three exceptions, lie between 0.63 and 0.92. They do not show any obvious difference as a function of age or sleep-wake state and they are approximately the same in studies yielding accelerative response as in those reporting deceleration. It is possible that slopes may be reduced with intense stimuli or with tactual-proprioceptive stimuli, but this has not been systematically investigated. That the regressions are highly significant is obvious from the percentages of variance ( 1 00 X P ) for which they account. Again with the exception of two unusually low coefficients, the respective r’s are significant at better than the .01 level. Since response is clearly related to prestimulus level, if the independent variable is also associated with prestimulus level, then control for prestimulus H R is necessary to determine whether any treatment effects exist that are not confounded with prestimulus differences. Even if treatment conditions do not differ in prestimulus level, control may be desirable to reduce error variance. Since experimental control of prestimulus cardiac activity is often impossible, statistical control must usually be employed. The goal is to convert measures that are dependent upon initial level into measures that are independent of initial level. This can be done by subtracting from each score that portion of it which is predicted by the relation with initial level. If the pre- and poststimulus relation is linear, the appropriate adjustment is to remove that portion of the score predicted by the linear regression of poststimulus level on prestimulus level. If the relation is better fitted by a lsecond-degree polynomial function (a form of curvilinear relation) thed, in a similar fashion, the portion of the score predicted by the curvilinear regression is removed. The basic procedure is, in any case, to determine empirically the nature of the relation between pre- and poststimulus scores and then to adjust for that relation. This method, by definition, leaves the adjusted or residual poststimulus

TABLE I1 COEFFICIENT OF REGRESSION OF POSTSTIMULUS H R ON PRESTIMULUS HR PERCENTOF VARIANCE DUETO REGRESSION

Groups

AND

Stimulusresponse"

Regression coefficient

Percent variance"

Airstream-A Auditory- A Auditory- A VisualA Olfactory- A Airstream-A Auditory- A

.I6 .74 .84d .92d .92d .42d .78

5.4' 70.0

Auditory- D Auditory- A Auditory- D

.92 .77 .85

83.6 88.2 78.2'

D

.73 .69 .7 I .76

52.3 42.9 62.5 87.0'

Auditory- D

.82

70.3

AuditoryAuditoryAuditoryAuditory-

D

.74 .63 .88 .78

96.8 87.0

Auditory- A Auditory- D ShockA

.07 .69 .88

2.4 73.8 97.8

I. Newborn (a) Bridger and Reiser ( 1 959) (b) Clifton et al. ( I 968) (c) C. M. Davis et al. (1965)

(d) Graham et (11. ( 1968)

-

83.7

11. Infants 1-6 months (a) K. M. Berg et ctl. ( 1968)

Alert Non-alert (b) Clifton and Meyers ( 1969) (c) Hatton ( 1969) 6-weeks awake 12-weeks awake Sleepy (d) Moffitt ( 1968) 111. Adults (a) Hatton er al. ( I 968) (b) Hord, Johnson, and Lubin ( 1964) Pilots Corpsmen Patients (c) Meyers ( 1969)' (d) Meyers and Gullickson ( 1967)' Peak Trough ( e ) Westcott and Huttenlocher (1961)

AuditoryAuditoryAuditoryAuditory-

D D A

A A A

54.7 66.8

"An A following the stimulus indicates that response was accelerative; D indicates a decelerative response. Response was measured, in studies from our laboratory, by H R on poststimulus second 4. I n studies from other laboratories, response was usually mean HR for several poststimulus seconds or an individually determined peak. See references for exact measures. "Percent of variance = 100 X i2,where r is the correlation of poststimulus HR(Y) and prestimulus HR(X). When studies reported correlations and regression coefficients (b) for change (D) and prestimulus HR, they were transformed via the equations: b,, = bd, 1.0 r:, = (bizr$,)/bir ra, b$, ( I .O -

+ +

a,)

'Computed from the average correlation, after transforming to z' the individual correlations in Bridger and Reiser ( 1959, Table I). dAverage of coefficients for presentations on two days or for within-modality variations in stimuli. 'Values supplied by authors in personal communication.

Arousal Systems and Infant Heart Rate Responses

71

score unrelated to initial level. For an authoritative discussion of some of the controversial questions related to initial level effects see Benjamin ( 1963, 1967). Adjustment for linear regression is a simpler procedure than adjusting for more complex relations, but it should be used only if ( 1 ) the relation between post- and prestimulus scores is, in fact, linear and (2) the regressions are homogeneous. We have found, in fairly extensive tests, that these assumptions are reasonably well satisfied. A tabulation of analyses performed on the five studies listed in Table I1 shows (a) only 17 significant F's of 347 within-treatment-group tests that compared regressions among trials for each poststimulus second, (b) only 2 significant F's of 19 within-treatment-group tests that compared per-second regressions among trials and among seconds, and (c) no significant F ' s for within-study tests of per-second regressions. There is more evidence for significant curvilinearity especially during the seconds of maximal response, but even when significant, the curvilinearity accounts for a small proportion of the variance. In the five studies noted above, linear and second-degree polynomial regressions were compared for each poststimulus second, within treatment-groups. There was significant curvilinearity in 45 of the 347 comparisons. Considering only the 45 significant curvilinear regressions, the increase in variance accounted for by curvilinearity amounted to a median 2.0%, a maximum 6.3%, and to less than 1 .O% in one third of the instances. The procedure is the same whether response is defined by a difference score or by poststimulus H R level. Differencing is a method frequently used to reduce the correlation between pre- and postmeasures but it will only do so completely if the regression of the difference on prestimulus level is zero (Benjamin, 1963). Since there is a fixed relation between the regression of differences (b,J and the regression of poststimulus values (bur),such that bds = bux-1.0, difference regressions will be zero only when poststimulus regressions equal 1.0. As Table 11 shows, this is not usually the case with H R data. In fact, the linear correlations between difference scores and prestimulus H R ranged from -0.12 to -0.89 in the listed studies of Table 11. If difference scores are to be completely independent of prestimulus levels, therefore, the empirically determined regression should be removed. The resulting adjusted difference score will be a linear transformation of the adjusted level score and analyses of variance and similar statistics will not be affected (W. G. Chase et al., 1968). In short, if the regression of poststimulus H R on prestimulus level is 1 .O, the regression of the difference is 0.0, and adjusting for the poststimulus regression effect will be the same as using difference scores. Both methods will produce identical scores that have no linear correlation

78

Frances K . G r a h a m and Jan C . Jackson

with prestimulus. However, the regression of poststimulus HR is not usually 1.0 and difference scores will therefore not be independent of prestimulus. They can be made independent only by adjusting for the regression of difference scores on prestimulus level which is equivalent to adjusting poststimulus HR level for the regression on prestimulus level. Adjustment for response amplitude, i.e. H R level or change, does not, of course, guarantee that temporal or trend characteristics of response are independent of prestimulus level. However, Steinschneider and Lipton (1 965) have reported that latency to peak response and other temporal measures are not related to prestimulus level and Clifton and Graham (1 968) have confirmed their findings. As regards response trend, which is of special interest for studies concerned with the form and direction of HR change, no data have been published. Consequently, we determined the relation between trend and prestimulus level in four studies involving different age groups. Tests were made separately for orthogonal linear, quadratic, and cubic trends across the first 10 poststimulus seconds. This includes the period of maximal and most reliable response. It was found, both within and across subgroups, that while regressions were sometimes significant, they accounted on the average for only 6% of the variance in trends, and at the most for 17% (Table 111). It appears, therefore, that where the only interest is in the direction of HR change, it will usually prove satisfactory to analyze trpnd variance using unadjusted scores. 'The slope of prestimulus HR may also affect response, according to Williams, Schachter, and Tobin (1 967). Using a hand-drawn line-of-bestfit to estimate prestimulus slope, they were able to account for 14 to 23% of the variance in HR response. The relation could be demonstrated even with prestimulus HR level held constant. Efforts to replicate this finding, using computer detection of slope, have been less successful but the work is still in progress (J. Schachter, personal communication). While the slope factor apparently does not account for enough response variance to be a serious source of confounding, adjusting for it may prove a useful method of increasing response reliability.

111. Developmental Studies of Evoked HR Response This section reviews, in rough chronological order, studies of infant HR response beginning with newborn studies in the late 1950s that employed electrocardiographic recording methods (Section 111, A). The

Arousal Systems and Infant Heart Rare Responses

T A B L E 111 PERCENTOF VARIANCE I N 10-SECOND TRENDS DUETO REGRESSION PRESTIMULUS LEVELS

79

ON

Percent variance due to regression" Groups

Linear

Quadratic

Cubic

4.7**

IS.O**

9.7"*

8. I 2.6 4. I

16.6** 4.3

I. Newborn Graham er al. ( 1968)

I I . Infants 1-4 months (a) K. M. Berg et a/. ( 1968) Alert Non-alert Pooled (b) Hatton ( 1969) 6-weeks Awake 12-weeks Awake Sleepy (6 & I ? weeks) Pooled

6.7 I l.3* 4.8 6.9**

1.1

I5.8* I .6 0.7

6.8 7.6 8.0 7,4;k*

3.5 2.4 4.4 0.0

10.5** 8.9'"

0.0 I .6 1 .0

111. Adults Hatton et ul. ( 1968)

Exp. I Exp. I I Pooled

I .4 0.2 0.7

9.3**

"Computed for pooled variance within trials and thus based on N s ranging from 43 to 224. * p < .05. * * p < .Ol.

newborn work generally agreed in finding a rnonophasic accelerative response to a variety of stimuli. With the advent of studies using older infants, it became evident that response of the older infant was partially or largely decelerative (Section 111, B). Section I l l , C discusses the possibility that this developmental change in response is due to non-developmental factors. A. NEWBORNHR RESPONSE

Early studies of newborn HR described an accelerative response but the measures that were used could not have detected a secondary phase of deceleration had one been present. However, subsequent studies, using more detailed analyses, also failed to reveal any deceleration below prestirnulus levels. The accelerative response was apparently not due to concomitant respiratory or motor responses and, within the range

80

Frances K . Graham and Jan C . Jackson

of behavioral states that were examined, was apparently not a function of state. Since newborns were rarely examined in a fully awake state or with low to moderately intense and non-sudden stimuli, the possibility exists that state or stimulus factors might account for the nature of the response. This possibility is considered further in Section 111, C. 1. Early Studies With the rekindling of interest in newborn research during the late 1950s, studies of newborn cardiac activity began to appear in the psychological literature (Bridger & Reiser, 1959; Richmond & Lipton, 1959). A pioneering series of papers from the Upstate Medical Center in Syracuse was especially promising (Lipton & Steinschneider, 1964; Lipton et al., 1961a, 1961b; Lipton, Steinschneider, & Richmond, 1960, 1964, 1965a, 1965b; Richmond, Lipton, & Steinschneider, 1962a, 1962b; Steinschneider, Lipton, & Richmond, 1964, 1965,1966). They suggested that a discrete HR response, closely time-locked to stimulation, could be obtained consistently from newborns, and that this response might offer a sensitive and objective method for investigating psychological processes in an organism not easily accessible to study through more traditional techniques. This early work, as well as most subsequent studies, was not primarily concerned with orienting behavior. Some writers hoped to use the cardiac response to investigate sensory-perceptual capacities of the newborn; others were interested in individual differences in autonomic responsivity and the implications that these might have for later personality or psychosomatic disease development. In general, the early research established that cardiac changes could be evoked by a variety of stimuli and that many characteristics of cardiac activity could distinguish among individual newborns. However, later work has been less optimistic about the possibility of identifying stable individual characteristics from newborn data. Clifton and Graham (1968) showed that 13 of 14 newborn cardiac measures were sufficiently reliable over a 5-day period to be useful in studying stimuli or group differences, but they did not demonstrate reliabilities high enough for use in predicting individual differences. Lipton, Steinschneider, and Richmond (1966) failed to find any significant reliability with retests at 2% months. From the present viewpoint, the early newborn work is of interest because it found, almost without exception, that discrete stimulation evoked HR acceleration. This was true of the series of Syracuse studies cited above and was confirmed by Bartoshuk (1962a, 1962b, 1964), Bridger (196 1, 1962), Bridger, Birns, and Blank (1963, Bridger and Reiser (1959), and Schachter, Bickman, Schachter, Jameson, Lituchy, and Williams (1966).

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The exceptions included a study of a single infant, by Beadle and Crowell (1962), which did not obtain any consistent pattern of response to low intensity tones, and a study by Vallbona, Desmond, Rudolph, Pap, Hill, Franklin, and Rush (1963) which investigated cardiac activity during the first few hours of life. The latter authors stated that HR response to an external stimulus (“thumping on the foot”) was “usually that of acceleration and rebound deceleration (p. 191).” This statement is difficult to evaluate, however, since the report did not note either the number of stimulations or the number and type of responses. A comment (p. 175) indicated that thumping on the foot elicited transient tachycardia in 13 of 15 infants with, “in some instances,” rebound deceleration (bradycardia) following the tachycardia. The illustrative recordings of spontaneous activity and of response to interoceptive stimuli did support the authors’ principal conclusion that there was marked cardiovascular instability for at least the first 6 hours after birth. Instability during this period was also evident in a study by Desmond, Franklin, Vallbona, Hill, Plumb, Arnold, and Watts (1963). If HR levels are sufficiently high preceding stimulation, the “law of initial values” also predicts an exception to the general rule of accelerative response. The level at which a decelerative “cross-over” should occur varies as a function of the regression an8 the magnitude of the response and, for newborns at least, may be beyond the physiological range. C. M. Davis, Crowell, and Chun (1965), in calculating “crossover” points for 12 stimuli, found only four instances in which the point would fall below 200 bpm. For two stimuli, the points were above 1000 bpm. In contrast, Bridger and Reiser ( 1 959) reported “cross-over” points for individual subjects ranging from 1 1 1 to 195 bpm with a mean of 142 bpm. As noted previously, they also obained extremely low regression coefficients (Table 11). This may be due, in part, to the use of relatively intense stimuli but may also be due to an unusual response measure. These investigators selected either the maximal HR increase or the maximal decrease, depending upon whether there were accompanying signs of increased or diminished behavioral response, respectively. This procedure would exaggerate HR response at low prestimulus levels where larger HR responses are expected, according to the law of initial level, and where greater behavioral response would also be expected since activity is positively associated with H R (Section 111, C, 3) and itself reflects the law of initial level (Schachter, Williams, Bennett, & Williams, 1967a). Similarly, the procedure would underestimate HR response at high prestimulus levels where smaller H R and behavioral changes are expected. The consequence would be to produce a steeper slope for the regression of HR change on prestimulus level and a flatter slope for the regression of HR level on prestimulus level.

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When these early newborn studies were published it had not yet been proposed that H R deceleration characterized adult orienting responses, although the typical adult response to simple, non-painful stimuli was clearly not the pronounced acceleration seen in newborns. The best evidence suggested that adult responses were diphasic with initial, brief acceleration followed by a larger deceleration (R. C. Davis et ul., 1955; Lang & Hnatiow, 1962). While it might have been concluded from this that cardiac response changed with age, there were weaknesses in the newborn evidence. Responses had either been measured by indices such as peak acceleration, which could not reveal a diphasic response, or HR activity had not been examined beyond the initial return to prestimulus level. I t remained possible, therefore, that a secondary deceleration might be detected by more detailed analyses. 2 . Studies of the Response Form The need for more detailed analyses was met by other, generally more recent, newborn studies which measured HR beat-by-beat or second-bysecond. Davis et uf. (1 965) followed the response for 25 beats after stimulus onset and Chase (1965) and Keen, Chase, and Graham (1965) observed H R for 5 1 post-onset beats. The response in all three studies was a monophasic acceleration which showed no significant deceleration below prestimulus levels. C. M. Davis et ul. were sufficiently impressed with the contrast between their newborn results and those reported for adults to construct idealized curves illustrating the difference (Fig. 4). Monophasic acceleration was also found in further studies from both of these laboratories (Clifton et al., 1968; Graham et al., 1968; Gray & Crowell, 1968). Graham et ul. repeated a 10-second 75 db sound, 15 times daily for 5 successive days, to determine whether or not secondary deceleration would develop during the course of stimulation. The response remained accelerative on every trial-block (3-trial averages) of each day. While there was some significant habituation over trial-blocks within a session (Fig. 5 ) , habituation did not occur more rapidly on subsequent days. On the fifth day, there was still no statistically significant deceleration although, as Fig. 6 shows, the average curve did fall below prestimulus on the final triak4 Measures of trend were not obtained in 4Not only did significant deceleration fail to develop but peak acceleration actually increased with age. This was also true in a newborn study by Bartoshuk (1962b). What, if any. theoretical importance should be attached to this finding is obscure. As Bartoshuk noted. it could be due to gradual disappearance of amniotic fluid from the middle ear with consequent increase in stimulus intensity. The finding is apparently not a function of increasing alertness since state did not vary significantly in the course of the Graham et al. experiment.

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-Neonate

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Pulses from origin Rig. 4 . Idealized curve illustrating adult and neonate H R response to briei sensory stimulation (from C . M . Davis et al., 1965. with permission of the authors).

this study and, because they are sometimes a more sensitive indicator of directional change, the data have been reanalyzed since publication. Reanalysis did show a significant change, at the p < .05 level, in the 20second linear response trend over days, but it was not a systematic change. Trends on Day 3 were relatively more accelerated than trends on Days 1 and 2. The study by Clifton et al. (1 968) also obtained monophasic acceleration in 5 groups of Ss each presented with a different duration of the same sound stimulus. Figure 7 shows the response curves on the first trial-block and Fig. 8 the response curves on the fifth and last trial-block. Again, there was habituation from the first to last trial-blocks, but no evidence that secondary deceleration was developing. However, HR response to the 30-second stimulus decreased significantly on the last seconds of the first, third, and fifth trial-blocks. This raised two further questions -whether response had been measured for a long enough period of time, and whether longer durations of stimula-

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Fig. 5. Newborn HR during 1 second preceding and 20 seconds following a 75 db, 10second auditory stimulus presented on three trial-blocks ( T B ) of Day I . Averages f o r I0 Ss (from Graham et al., 1968, with permission of the publisher).

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Fig. 6 . Newborn H R during I second preceding and 20 seconds following a 75 db, 10second auditory stimulus presented on three trial-blocks ( T B )of Day 5 . Averages f o r I0 Ss (from Graham et al.. 1968, with permission of the publisher).

Arousal Systems and Infant Heart Rate Responses

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tion might be more effective in eliciting decelerative responses from newborns. Both questions are reasonable in the light of what is known about the relatively slow neural processing in newborns (Scheibel & Scheibel, 1964). It might be argued, therefore, that a delayed secondary deceleration would have appeared had the response been followed for a longer period. While this seems unlikely in view of the relatively flat curves obtained during seconds 10 to 20 on later trials (Fig. 8), deceleration could have been missed on early trials where the acceleration had barely returned to prestimulus level by the end of 20 seconds (Fig. 7). If there were such an early, undetected deceleration and it habituated rapidly, the evidence of flat curves on late trials would be irrelevant. Other data make this possibility remote, however. In addition to findings with a 150-second stimulus, discussed below, the 1O-second stimulus of Keen, Chase, and Graham (1965) and the 18-second stimulus of Clifton et al. (1 968) were monitored for 90 and 30 seconds, respectively. The average

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Frances K . Graham and Jan C. Jackson

-

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Fig. 8 . Newborn HR response on the lust Ti3 (trials 13-I5) for auditory stimuli of varying durations. Averages for 20 Ss per duration-group (from Clifton et al., 1968, with permission of the publisher).

first-trial curves did not show a diphasic response in either case, nor did they suggest any other multiple response, such as a pattern of damped oscillations. The question regarding a decelerative effect with longer stimulus duration was answered, in part, by another study in which the sound stimulus was presented for 150 seconds (Hatton, Clifton, & Graham, unpublished data). While there had been some significant deceleration between 17 and 20 seconds with a 30-second presentation, there was no significant decrease with the 150-second presentation (Fig. 9). After an initial accelerative wave, HR neither increased nor decreased significantly from prestimulus although visual inspection suggested a gradual slowing over the last minute of the period. Such slowing might occur if there were gradually increasing drowsiness. A report by Brackbill, Adams, Crowell, and Gray ( 1 966) indicates that stimulation continued long enough to become “background” can induce both sleep and an accompanying decrease in HR. It appears, therefore, that the transient newborn response to stimulation does not have the secondary decelerative phase reported in adults,

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even when response is measured in detail and for a period long enough to ensure that it is complete. However, it may show an initial brief deceleration under some circumstances. Williams et al. ( 1 967) and Schachter et al. (1967b) reported a 3-beat deceleration with a trough at approximately 1-second, followed by immediate acceleration reaching a peak between 2 to 3 seconds. The possible significance of this finding is discussed in Section I l l , c, 1. 3. State and Bodily Movement E f e c t s Although, with the exceptions noted, both the early newborn studies and the more recent studies of second-by-second HR agreed in finding monophasic acceleration, it is necessary to consider whether the response might be an artifact of variables not under direct experimental control. Behavioral state should influence response, or at least response magnitude, since state and HR level are grossly correlated across individuals, and substantial within-individual correlations have been demonstrated in newborns (Bridger et ul., 1965; Schachter et ul., 1966). Consequently, adjusting for prestimulus HR should remove some of the variance associated with state. The more important question is whether state has an

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effect independent of HR level. Within newborn studies and within the range of states studied, the few data available suggest that any effect is not marked. H. Chase (1965), in a direct comparison of newborns rated Drowsy and those rated Alert, found no significant difference in latencies to peak acceleration, a measure which is independent of prestimulus level. There is also evidence that stimulus characteristics and repetitions have a significant effect on HR in the absence of significant changes in state (Graham et al., 1968, Keen et al., 1965). These findings suggest that state has not been a potent factor contributing to variance within newborn studies. However, it could be an important factor contributing to variance across age groups since most newborns have not been tested in a fully awake state. C. M. Davis et al. (1965) commented specifically that their subjects were “quiet with their eyes closed before every stimulus presentation except for three cases when the subjects’ eyes were open.” In a later study by Gray and Crowell (1968), the average state rating was 2.25 which is closer to State 2 (“irregular respiration, eyes closed, no movement”) than to State 3 (“eyes open, alert, but inactive”). The subjects in H. Chase’s study (1965) and in the Graham et al. study (1968) were also, on the average, in a state between irregular sleep and alert inactivity. Other investigators have not always described state except to note whether data from crying trials were or were not excluded. Gross motor activity is another possible source of variance in HR response. It is, of course, partially confounded with state and figures prominently in the criteria for behavioral rating scales that attempt to measure state (Bridger et al., 1965; H. Chase, 1965; Prechtl & Beintema, 1964; Wolff, 1966). Generally, newborn experimenters have tried to avoid movement effects. Some have done so by introducing stimuli only when the infant is quiet. Other experimenters have restrained the infant either through swaddling or by the ingenious device of an airsplint (Schachter et al., 1966). However, Li’pton et al. (1960) suggest that there is no marked difference between the HR responses of swaddled and unswaddled infants. While half of their 10 S s were more responsive when free to move, others showed no difference in response and one was more reactive when swaddled. The possible effects of movement are not limited to its role as a prestimulus factor. If a stimulus evokes both HR change and a change in motor activity, the HR changes may be due to feedback from the peripheral motor changes, as K. Smith (1954) suggested, or the two responses may be part of a single system evoked in parallel by a central event. It would also be possible for HR responses to include both centrally-initiated and peripherally-mediated changes. This question is not easily an-

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swered and the answer may vary depending upon experimental conditions. While there is good evidence from curarization studies (e.g., Black, 1965; Miller & DiCara, 1967) that conditioned HR responses can develop without skeletal responses, this does not indicate how the two systems are related when skeletal response is possible. In a series of studies with adult humans and other animals, Obrist and collaborators (e.g., Obrist, Webb, & Sutterer, 1969) have shown that there may be considerable, although not perfect, concomitance between H R and various measures of motor activity. There has been some similar work with newborns. Lipton et al. (1961a) reported a moderately high correlation of 0.59 between cardiac and motor change. Because motor restraint via swaddling “did not necessarily alter heart-rate responses,” they concluded that autonomic response does not “result” from motor activity per se. They also noted that the same “patterns” of response could occur in the absence of an overt motor response, although responses were likely to be of lower magnitude. However, Bridger and Reiser ( 1 959) felt that “only negligible, random heart rate changes (p. 268)” occurred on trials with no observable behavioral response and Bridger (1962) stated that “if one includes heart-rate data from stimuli that do not produce behavioral responses, one dilutes and distorts the possible meaningfulness of the experiment (p. 72).” This statement was apparently based on the assumption that behavioral response provides an independent measure of the infant’s “accessibility or receptivity to stimulation (Bridger & Reiser, 1959, p. 268).” Lipton et al. ( 196 1 a) also advocated segregation of “no-motor-change’’ trials, both to reduce variability and to eliminate individuals who might not have received the stimulus centrally. It is evident that neither set of investigators considered the H R response to be an artifact of the motor response, but whether their exclusion strategy is a good one would depend on the questions being investigated. In any case, it is important to note whether studies report data only for trials on which there is also a motor response. Such data clearly include a sample of responses different from a sample based on all trials. If the behavioral response is an increase in activity, relatively greater HR acceleration would be expected. If both increases or decreases in activity are called behavioral responses and the HR response is measured differently in the two cases (Bridger & Reiser, 1959), then it is difficult to make any comparison with other studies. Respiratory activity is a particular form of motor activity which is known to have feedback effects on HR although, again, the systems will not necessarily be related under all conditions. H. Chase (1 9 6 9 , in an unusually thorough examination of the relation between rate changes in

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the cardiac and respiratory systems, obtained suggestive evidence of a correlation only during the first 2 seconds following stimulus onset. However, these were correlations across subjects. Correlations within subjects, for changes across 20 seconds, varied widely with approximately as many correlations significantly negative as significantly positive. Similar results were obtained when tests were made for a delayed effect of respiration on HR, i.e. when correlations were computed with a I - or 2-second lag. These several analyses considered only the relation between rate changes, and Chase acknowledged that other measures, such as amplitude, might be more sensitive to concomitant or causal changes. It is worth pointing out, however, that there was a different pattern of response in the two systems. While HR response was the usual monophasic acceleration, respiration changes were diphasic, with an initial brief acceleration followed by a more prolonged and large deceleration. The comparison is shown in Fig. 10. Steinschneider (1968) has also failed to find any consistent intra- or interindividual correlations between cardiac and respiratory measures. His measures included several characteristics of the initial acceleratory phase of the respiration response. In summary, the monophasic acceleration of HR, reported in newborn studies, is apparently not an artifact of movement, respiration, or the method of measurement. Behavioral state also appears to have little

Seconds F i g . 10. Newborn respiration rate and H R responses on T B 1 (Trials 1-31 to a 10second auditory stimulus. Averages for 10 S s (from H . Chase, 1965).

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effect when the variance in common with prestimulus HR is removed. However, these observations apply only within the range of states and stimuli studied and only to the newborn. Most stimulation was relatively sudden and intense and it was usually presented to drowsy subjects. B. HR RESPONSE I N OLDERINFANTS

I n contrast to the newborn response, decelerative phases have been reported consistently in older infants. However, many studies were not concerned with H R change per se and, consequently, employed response indices such as a given number of the slowest beats (Kagan, Henker, Hen-Tov, Levine, & Lewis, 1966; Kagan & Lewis, 1965; Lewis, Kagan, Campbell, & Kalafat, 1966; McCall & Kagan, 1967a, 1967b; Meyers & Cantor, 1966). Since the indices were selected from variable periods of time (during a period of visual fixation) or from lengths of time different from the prestimulus indices to which they were compared, the data were biased in favor of deceleration (cf. Section 11, C , 2) and are not useful for the present purpose. I t should also be noted that selecting a given number of the slowest beats from fixation periods of variable duration biases in favor of a positive correlation between duration of visual fixation and magnitude of deceleration even when the true correlation is zero. Although reports of these studies did not describe form characteristics of the HR response and their response indices provide ambiguous evidence for deceleration, several of the authors commented specifically that they inspected individual records and rarely found any accelerations. More satisfactory evidence comes from other studies in which HR was measured beat by beat or second by second. Three studies obtained clear decelerative changes in 6-month-old infants. To a complex visual stimulus, Meyers and Cantor ( 1967) found a slight acceleration of 0.5 bpm or less, followed by a 2-beat decrease which peaked 3 seconds after stimulus onset. Lewis and Spaulding ( 1967) obtained decelerations without preceding acceleration, approximately 3 bpm to visual and 9 bpm to auditory stimuli. Moffitt ( I 968) found even more pronounced monophasic decelerations, as large as 20 beats, in response to speech sounds. Decelerations have also been obtained from still younger infants, using stimuli which produce monophasic accelerations in newborns. At 5 months, the tactual-pressure stimulus used by Lipton et al. (1966) produced a triphasic response of brief, initial deceleration, acceleration which was less than the newborn H R increase, and a subsequent decrease below prestimulus level. At 2% months, the initial deceleratory

Frances K . Graham and Jan

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phase was only questionably present. Two studies have shown marked, monophasic decelerations at 4 months. Figure 1 1 illustrates the effect of 2-second, 1000 Hz tones of 50 and 75 db re 0.0002 microbars (K. M. Berg, Berg, & Graham, 1968). Clifton and Meyers (1969) also reported large and longer-lasting deceleration in response to a 10-second auditory stimulus. The stimulus was similar to the 300 Hz sound used in Clifton et al. (1968). Finally, Gray and Crowell (1968) compared the effects of tactual-pressure, olfactory, and auditory stimuli on 2-day, 6-week, and 1 1-week-old infants. All stimuli elicited increasing deceleration with increasing age and, by 1 1 weeks, the response was primarily a wave of deceleration followed by some acceleration beyond prestimulus after approximately 10 seconds. There was no initial acceleration evident but the analysis by 2.5 second intervals might not have been able to detect a brief acceleratory phase. It appears, therefore, that HR response shifts from acceleration to deceleration sometime during the first few weeks or months of life. Soviet investigators have also described a developmental shift in the direction of HR response. One of the more detailed reports, by Polikanina 142 -

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and Probatova ( 1965), agrees with American studies. These authors described the response during early infancy as a generalized, diffuse motor reaction, accompanied by respiratory slowing and cardiac acceleration. Toward the end of the first month, there emerged a “getting-attentive, and ready” reaction of motor inhibition, accompanied in the majority of cases by cardiac deceleration. Although a graph summarized the changing percentages of accelerative and decelerative responses with age, the authors did not indicate how the HR response was measured, whether it included only one phase of cardiac change, how many subjects were represented at each age, nor the extent to which results were confounded by repetition effects. Fifty-nine premature infants were stimulated “almost daily” for “not more than” 10 trials a day, but they were apparently not all represented in every graph since one figure included a total of only 14 S s . However, even with possible confounding by repetition effects, there is some independent evidence of a maturity factor. Less mature S s (birth weight 900- 1200 gm) gave more accelerative than decelerative responses over a period from 15 to 105 days while more mature S s (birth weight 1600-2 100 gm) gave predominately decelerative responses from 30 days on. Polikanina and Probatova ( 1 965) cited two other Soviet studies which apparently found similar age changes in fullterm infants and one study which observed the same pattern in puppies. Lynn (1966, p. 80) also pointed out that the autonomic reactions of the newborn may be opposite in direction from those of adults but he proposed that HR slowing is found in newborn humans, monkeys, and dogs and acceleration in adults of these species. This description of the adult HR response conflicts with his conclusion (p. 4)that HR slowing is found in adult humans and dogs. Further, the references which he cited do not support his description of the newborn response, at least as regards the human newborn. They included Bridger and Reiser (1 959) and the study discussed above by Polikanina and Probatova ( 1965). C. FACTORS AFFECTING THE DEVELOPMENTAL SHIFT

While there is strong evidence for a developmental shift, it is not clear why the shift occurs. Maturation of higher nervous centers is a possible explanation but characteristics of stimulation, state of the subjects, and postnatal experience should also be considered. 1. Characteristics of Stimulation Although stimuli, identical in physical properties, have sometimes been presented to both newborn and older Ss, there is no assurance that

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stimuli are equally effective or have the same properties when applied to organisms at different points on the phylogenetic or ontogenetic scales. From the present point of view, the important question is whether newborns are incapable of decelerative H R responses to any non-signal stimuli, or respond only to a different o r restricted range of stimuli. In brief, have stimuli been used which have optimal attention-evoking properties for an immature organism with limited prior experience? At least three questions should be raised. First, on the assumption that direction of H R change is a non-monotonic function of intensity but that the point of inflection or threshold for acceleration might be lower in newborns, is there any intensity of stimulation which will not evoke acceleration in the newborn? Second, have stimuli been presented to sensory systems which are the most mature a t this stage? Third, have “preferred” or prepotent stimuli been presented, i.e., stimuli with characteristics to which the nervous system is innately sensitive, presumably by virtue of their adaptive significance? It is possible that newborns have a lower threshold for elicitation of protective reflexes than do older Ss. This is supported by behavioral studies of startle (Landis & Hunt, 1939) and appears reasonable from what is known about neural organization. Since the cortex of the newborn is relatively underdeveloped and cortical inhibitory effects are weak or absent, reflexes controlled by lower brain mechanisms may not only be enhanced but may also be more easily elicited by a wider range of stimuli. Whether there is an accelerative response to low intensity stimuli is not dearly answered by the newborn studies reviewed, most of which employed high intensity stimuli with sudden onsets. In the few studies that did employ low intensity stimuli, onset was not controlled and results were conflicting (Bartoshuk, 1964; Beadle & Crowell, 1962; C. M. Davis et al., 1965). Since adult studies in our laboratory indicated that rapid rise time interacted with stimulus intensity to produce a short-latency acceleration, it appeared desirable to reinvestigate neonatal response using stimuli with gradual onsets. Jackson ( 1968), therefore, replicated experiments that had been conducted with adult and with 4month-old subjects. Twenty-four newborns received I6 presentations of 1000 H z tones lasting 2 seconds from beginning of rise time to beginning of fall time. T w o variables, rise time (3 or 300 ms) and intensity (50 o r 75 db) were combined factorially to yield 4 stimuli. Each block of 4 stimuli, balanced across S s for order of presentation, was repeated 4 times. Unexpectedly, the two stimuli with rapid rise time had no clear effect on H R while the slowly rising stimuli yielded acceleration, but only after

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a delay of several seconds -a relatively long latency in comparison with earlier findings. I t was expected that control of rise time might reduce short latency acceleration and this expectation was met. However, a late acceleration with slowly rising but not with rapidly rising tones is difficult to explain on any grounds, except that it was a chance occurrence reflecting a change in state or motor activity randomly related to stimulus variables. The absence of any significant response to the rapidly rising tones suggests that control of rise time may not have been the critical factor in eliminating the usual accelerative response. It may have been due, instead, to the use of pure tones in place of the more complex auditory stimulus employed previously in our newborn work. There is some indication that pure tones may not be effective stimuli with newborns. C. M. Davis e l af. (1965) found more variable and prolonged latencies of HR acceleration following tones than following clicks and tactile stimuli, and tones are apparently less likely to evoke motor responses. Froeschels and Beebe (1946) reported that the sound of tuning forks did not evoke overt movement in any of the 10 newborns that they tested, although whistles (not explicitly equated for intensity) were effective in producing responses in 9 of these infants. Similarly, Riesen ( 1960) asserts that pure tones produce “little or no response of any kind” in neonates and speaks of a “consensus” among specialists that standard audiometric procedures are unsatisfactory for infants when they use tonal stimuli. Jackson’s results, therefore, failed to answer the question with which the study began, i.e. whether newborns have lower intensity and rise time thresholds for evocation of HR acceleration. They do suggest that certain kinds of stimulation may be relatively ineffective with newborns. Since Bartoshuk (1 964) reported significant accelerative responses to 1 second, 1000 Hz tones as low as 47.5 db, tones are apparently not always ineffective. It should be noted that rise time was not controlled in Bartoshuk’s study and there were other differences between the two experiments. In particular, Bartoshuk stimulated only when baseline HR was steady, while Jackson stimulated at predetermined intervals. A difference in state may have been associated with this procedural difference since prestimulus HR was approximately 16 bpm lower in Bartoshuk’s study. One other finding may be relevant to the question of possible intensity effects. Williams et af.( I 967) and Schachter, Williams, Khachaturian, Tobin, and Druger (1968) have reported an exception to the general finding of immediate acceleration in newborns. These authors found deceleration during the first three heart beats following stimulus onset, after which HR accelerated. In the first study, their stimulus was a pair

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of I ms clicks, separated by 500 ms. Stimulus intensities of 80, 85, 100, and 1 15 db were randomly presented over 75 db random “white” noise. The stimulus in the second study was a 112 db, 0.3 ms click presented over 5 5 db white noise, With clicks as brief as this, presented over masking white noise, the effective stimulus energies may have been relatively low, especially in comparison with other studies (Licklider, 195 1). Pilot studies apparently did suggest that the 85 db clicks were close to threshold (T. Williams, personal communication). This finding is interesting because of Sokolov’s report (1963, p. 179) that near-threshold stimuli are especially potent elicitors of the OR. Since the response is not the typical long-lasting deceleration seen in older subjects, and since it apparently does not habituate over many trials, it is probably not the mature orienting reaction which we are seeking. However, it may be the form which an OR takes when cortical components of the system are not functioning. Intensity and rise time characteristics may be less important than sensory modality in determining newborn response. Extensive morphological and histological studies indicate that primary sensory areas of human cortex are not equally mature at birth and during early infancy. At least up to 6 months, the somesthetic area is relatively advanced compared to the visual area, while the auditory area is the least developed (Conel, 1952). Electrophysiological studies show the same ordering (Ellingson, 1964; Hrbek, Hrbkova, & Lenard, 1968; Scheibel & Scheibel, 1964). Synchronous activity presumed to be alpha rhythms first appears over the sensory-motor Rolandic area in human infants. In addition, tactual-proprioceptive stimuli are the first to produce evoked potentials in several infrahuman species and, in human newborns, produce primary evoked potentials of a more mature waveform and latency than those evoked by visual stimuli. Acoustic stimuli evoke nonspecific responses in newborns but, thus far, a specific, primary, evoked potential has not been found. It might be expected, therefore, that the relative effectiveness in evoking ORs would order sensory modalities similarly. There are too few data from either newborns or young infants to test this hypothesis, although conditionability, as a function of the type of conditioned stimulus, may follow a different developmental sequence (Brackbill & Koltsova, 1967). While all three modalities have been employed in newborn work, tactual-proprioceptive stimulation has been limited to what may be a relatively intense stimulus -an airstream directed to the abdomen and visual stimulation (incandescent light) was used in only one study (C. M. Davis et al., 1965). It appears obvious that further work with both tactual-proprioceptive and visual stimuli is needed before we con-

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clude that decelerative responses cannot be elicited from newborns. Sameroff ( 1968) made this point explicit in pointing out that the kind of stimuli which have elicited visual fixation have not been employed in studies of newborn HR. Other qualitative differences in stimuli may also be important if, as seems probable, the higher nervous system is innately sensitive to certain relatively complex aspects of stimulation that have adaptive value for a species. Hubel and Wiesel’s classical demonstration (1 963) that there are striate cortex cells in the newborn kitten which are selectively responsive to movement and pattern challenged the idea that complex perception was necessarily built up from what analysis had identified as elementary characteristics. They point out, for example, that “diffuse light is at best a poor stimulus, and for cells in the area of central representation it is usually ineffective at any intensity [Hubel 8z Wiesel, 1962, p. 1461.” Fantz (1965), working with human newborns, found that patterned visual stimuli were “preferred” to plain surfaces. While less is known about selectivity in the auditory modality, a similar principle is suggested by recent work. Kiang, Peake, Siebert, Weiss, and Wiederhold ( 1968), investigating extracellular unit potentials in cat cortex, state that “in general . . . auditory cortical neurons are more responsive to complex stimuli and less responsive to simple ones [p. 3 191.” Eisenberg (1 965) has observed that the human newborn may be especially attentive to sounds within the speech frequency range and to speech-like patterns; Hutt, Hutt, Lenard, Bernuth, and MuntjeweriT ( 1 968) also report newborn electromyographic data suggesting that the most effective stimuli are patterned sounds, as compared to pure tones, and sounds whose fundamentals are within the range of the fundamentals of the human voice. Moffitt’s finding (1968) that HR responses of 5 - to 6-month-old infants discriminated between synthetic speech sounds, differing only in second formant transition, may be another example of such selectivity. Again, complex or patterned stimuli have rarely been used in newborn HR studies. Bartoshuk (1962a) did present an acoustic pattern, an ascending series of different frequencies, but obtained only H R acceleration. When response had habituated, the pattern was reversed and the habituated acceleration reappeared. This might be interpreted as evidence that H R acceleration rather than deceleration indicates orienting in newborns. Unfortunately, intensity of frequencies was not equated and the same ascending sequence was used with all Ss so that reversal of pattern constituted an increase in intensity of the initial frequency of the series. An intensity change rather than pattern discrimination might, therefore, account for the dishabituation. We also tried a complex acoustic stimulus in an experiment carried

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out during our preliminary work with newborns. The results were suggestive. While the usual HR accelerative response occurred on the first two trials with the stimulus (an 18-second excerpt from a recorded ballad singer), there was a period of deceleration on the two subsequent trials. Because 9 of 10 newborns showed the decelerative pattern, it seemed possible that the phenomenon was a reliable one, although it required the complicated assumption that orienting developed only after the stimulus had first evoked a DR. However, a subsequent replication failed to confirm the finding. Response in the music replication study appeared to be smaller and more variable than in earlier experiments with the 300 Hz rectangular wave, but H R increases provided the only significant changes (Harper, Gerlach, & Kantowitz, unpublished data). While the results from our laboratory and from others offer little encouragement for the idea that deceleratory ORs can be elicited from newborns, the equivocal results with tones and musical stimuli indicate, at least, that pronounced, short-latency accelerations do not always occur. Schachter’s work (Schachter et al., 1968; Williams et al., 1967) is also encouraging in suggesting that low effective stimulus energy may produce an initial brief deceleration even though large accelerations followed the deceleration. It is clear that further efforts to vary stimulus characteristics should be made. Most investigators have used “startling” stimuli and few have attempted to work with relatively mature sensory systems or with relatively complex, “interesting” stimuli. In addition to including a broader spectrum of stimuli, any further research should, as discussed below, also take into account the effects of behavioral state.

2 . Behavioral State The newborn accelerative response was apparently not affected by variations in behavioral state but it was pointed out (Section 111, A, 3) that newborns have usually been tested when drowsy or asleep. In contrast, older infants have usually been tested in a relatively alert state. There are both theoretical and empirical reasons for supposing that such a difference in state might account for the observed differences in HR response. Theoretical considerations suggest, in the first place, that a system facilitating information-processing and enhancing stimulation effects should be difficult to elicit during sleep, while a protective system, which limits stimulation effects, might be expected to have lower thresholds during sleep than during the waking state. If the functional distinction between OR and DR systems is correct, sleeping Ss should, therefore, be more likely to give DRs than ORs. In the second place, although Sokolov ( 1963) identifies the non-habituating reflex obtained in sleeping

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adults as an OR when it is elicited by stimuli that evoke an OR in the waking state, he does not provide any criteria which would distinguish sleep ORs from sleep DRs. The criterion of rapid habituation is not applicable, presumably due to the absence of cortical influence, and there are no data showing either non-monotonic relations with stimulus intensity or the occurrence of offset responses. Further, the sleep response is characterized by cephalic vasoconstriction (Sokolov, 1963. p. 122) which, in the waking state, indicates a DR. It follows that cephalic vasomotor responses are either not differentiating during sleep or that they are differentiating but DR thresholds are lowered during sleep. Lower DR thresholds are compatible with reports that behavioral startle is easier to elicit in sleeping than in awake newborns (Wolff, 1966). Finally, if the reflex occurring during sleep is usually a DR, and if Graham and Clifton ( 1 966) are correct in assuming that HR acceleration is a component of the DR, the “developmental shift” from acceleration to deceleration could be a function of confounding age change with state change. There is also empirical evidence that a state-dependent change in H R response does occur. Hord, Lubin, and Johnson (1966, Fig. I ) found that a 30 db stimulus elicited, from waking adults, an initial deceleration with little if any subsequent acceleration, but produced, in the sleeping state, a diphasic response of marked acceleration followed by deceleration below prestimulus. The difference in wake-sleep response was evident even though the waking response was averaged over 54 trials from 5 S s and had probably undergone considerable habituation. Lewis, Bartels, and Goldberg ( 1967) reported a similar sleep-wake difference in the response of 2- to 8-week-old infants. A tactile stimulus evoked H R acceleration during sleep, although it was not clearly demonstrated that the same stimulus elicited H R deceleration when S s were awake. Stronger evidence is available from two recent studies. In the K. M. Berg et al. ( 1968) study of 4-month-old infants, the mean response of 24 S s was a monophasic deceleration (Fig. I I). However, the picture was markedly changed when state of the infants was taken into account. Using the behavioral ratings obtained on each trial, the group was divided at the median into “alert” and “non-alert” subgroups according to the number of trials on which S s had been rated alert. The former subgroup was alert an average of 14.6 trials, ranging from 10 to 16, while the latter was alert for only 3.0 trials, ranging from 0 to 10. The same split obtained if the groups were divided according to average behavioral rating with Alert given a score of 2, Drowsy or Fussy a score of 1, and Sleepy a score of 0. Figures 12 and 13 show that large decelerations characterized the “alert” subgroup while response of the “non-alert”

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subgroup was mainly accelerative after brief initial deceleration. These differences in response trend were highly significant during the first 10 seconds. The F-ratios (df= 1,22) for quadratic, cubic, and quartic trends were, respectively, 40.2, 4.4, and 17.9, with associated p-values < .OO 1, < .05, and < .OO 1. Error terms were based on the respective individual4 trends. Only the quartic trend remained significantly different during the last 10 seconds ( F = 6.0, p < .05). Similar differences were found in a study of 24 six- and 24 twelveweek-old infants (Hatton, 1969). Again using behavioral ratings to classify Ss, Hatton identified at each age 12 infants who were awake on either the first or second presentations of each of four different stimuli and 6 other infants who were sleepy on those trials. “Awake” included infants rated, on a 9-point scale, as Inactive-alert, Active-alert, and Alertfussy, while “Sleepy” included infants rated Asleep, Irregular sleep, and Drowsy. The four stimuli, presented in blocks, included a 2-second and an 18-second 1000 Hz tone and a 2-second and an 18-second “complex” tone. Complexity was achieved by randomly interrupting the presentation of a combined tone of 1000 and 750 Hz. Intensity of all stimuli was 75 db over 30 db background noise and rise time was 30 ms. The characteristic response in both groups of Awake Ss was HR deceleration; Sleepy Ss showed acceleration of HR to most stimuli although frequently following a brief deceleration (Figs. 14 and 15). Both the quadratic and quartic response trends differed significantly as a function of state [ F (1,32) = 11.2 and 10.6, respectively; p < .01]. These studies demonstrate clearly that state is important in determining the nature of the infant HR response. As expected from theoretical considerations, the response is decelerative in the waking state and relatively accelerated during sleep. The Hatton (1 969) study showed, however, that there are also significant developmental changes in response, even with state controlled. The developmental change was one of relatively greater deceleration in older children in both waking and sleep states. While Awake 6-weekolds gave predominately decelerative responses to all stimuli, the responses were relatively small, brief, and variable, except to the 18second complex stimulus. This is congruent with the observation, made earlier, that patterned stimuli may be relatively more effective than simple stimuli with very young infants. In contrast, Awake 12-week-olds gave large, smooth decelerations to all four stimuli. The Sleepy response curves of 6-week Ss also differed from those of 12-week Ss. With the exception of response to the long, simple stimulus, 12-week Sleepy Ss gave a triphasic or diphasic response in which a sharply rising accelerative phase was followed by rapid deceleration below prestimulus -a re-

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sponse similar to the adult sleep response described by Hord et al. ( I 966). The full extent of secondary deceleration has been cut off by the shortened graphs. Six-week Sleepy S s did not make this response to any of the stimuli. To the complex stimuli, there was a largely decelerative but fluctuating response while the simple stimuli elicited large and prolonged accelerations reminiscent of the newborn response. These differences were reflected in significantly different quadratic and quartic trends as a function of the State by Age interaction [F(1,32) = 7.0 and

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10.0,p < .05 and < .01, respectively] and in differences in quartic trend as a function of the Age by Complexity interaction [F(1,32) = 6.5, p < .05]. Although state changes had not been related to response or to response habituation in the earlier newborn studies, the more recent evidence on state effects in older infants convinced us that studies of awake newborns should be instituted. A first study (Jackson, 1968) was carried out in which 12 newborns were presented with stimuli only when they

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Frances K . Graham and Jan C. Jackson

were behaviorally awake, i.e. when their eyes were open and they were not crying. Because periods of newborn wakefulness are brief and unpredictable, a design with fixed numbers of trials and intertrial intervals could not be used. Instead, a single stimulus was given for as many trials, up to 15, as could be obtained in the waking state and the intertrial interval was 45 seconds or longer, depending on infant state. If Ss fell asleep during the testing procedure, they were reawakened by gentle prodding. An observer judged when the appropriate state was reached and triggered stimulus onset. The stimulus was the slowly rising, 75 db tone which had produced long latency acceleration when newborn state was not controlled (Jackson, 1968). The same stimulus, except for an inconsequential difference in rise time, had produced deceleration in the Awake 6-weekolds of Hatton’s experiment ( 1 969). With awake newborns, the stimulus also evoked some deceleration but it was slight and was present only on early trials. A significant HR decrease occurred during the first poststimulus second of the first trial-block of a two trials per trial-block analysis [F(1,11) = 5.01; p < .05]; there was no significant change with blocks of three or four trials. While the occurrence of deceleration immediately following stimulus onset and its habituation on later trials is reasonable in view of the rapid habituation of an OR seen in adult subjects, a finding as ephemeral as this clearly needed to be replicated. Replication was attempted in a second experiment which presented the same stimulus to another group of 12 waking newborns (Kantowitz & Graham, 1969). There were several procedural changes. In the first awake newborn experiment, stimuli had been presented only when S was judged to be in the appropriate state. Unlike the procedure of presenting stimuli at predetermined intervals, this introduces the possibility that prestimulus condition will be systematically associated with subsequent activity, whether or not a stimulus is presented. The replication permitted measurement of such an effect by giving mock trials, randomly predesignated. When the observer indicated that S was in a satisfactory condition, trial onset was recorded on tape as usual, but no stimulus was given. The observer received a masking noise through earphones and did not know which were true and which were mock trials. A second procedural change was to retain only infants who were in an awake state in the nursery when selected and who remained awake throughout the two control and two stimulus trials. It was felt that the technique used in the previous experiment, of arousing S s and of attempting to keep them awake, might produce a less alert infant than one who was spontaneously awake. It proved extremely difficult to meet this criterion. To obtain 12 S s , 30 S s were tested of whom 17 were discarded because

Arousaf Systems and Infant Heart Rate Responses

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they changed state. The 30 had been selected from a much larger population. A record maintained after the first 3 S s had been completed showed that of 112 infants for whom parental permission was secured, only 2 I infants were quiet and awake when observed in the nursery. Results of this experiment are shown in Fig. 16, along with the response in the first awake experiment. All curves are averages of 2 trials and 12 S s . I t is evident that deceleration does not characterize the awake newborn response to a pure tone of moderate intensity. There were, in fact, no significant changes from prestimulus during any poststimulus second, nor were there any significant trends across the first 10, second 10, or all 20 seconds. On the basis of several studies, then, state appears to be an important variable in determining the H R response of older infants. Whether, even in an alert state, it is possible to obtain a decelerative H R response from newborns, remains uncertain. Awake newborns did not show any consistent response to a stimulus that elicited some acceleration in newborns whose state was not controlled, and that elicited definite deceleration in awake older infants.

3. Postnatal Experience While maturation of higher nervous centers occurs during the early months of life and might account for the “developmental shift” in H R

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response, any effect of neural change is confounded with the effects of environmental stimulation. Since stimulation is important in influencing neural change, and since any permanent effects of stimulation must be somehow recorded by a neural change, in a certain sense it is meaningless to ask about maturational effects independent of stimulation effects or vice versa. However, there are at least two questions which it may be instructive to pose and for which answers are at least possible. One question is whether conceptional age (age since conception) and postnatal age have different weights in determining response. The other is whether response can be affected by manipulations of stimulus experience. A comparison of premature and full-term infants of varying ages since conception and birth could provide an answer to the first question. The only published work along these lines is the previously cited study of Polikanina and Probatova ( I 965) which showed that conceptional age had an effect when postnatal age was held constant. This study did not indicate whether postnatal age also had an independent effect, i.e. whether with conceptional age constant, there would be an advantage to greater postnatal age. Unpublished work by Schulman (1968a, 1968b) suggests that this may be the case, although her findings are not easily reconciled with those from other studies. She reported a decelerative HR response in awake 36-week prematures to a 3-second, 80 db buzzer. Such a stimulus would not be expected, from our results, to elicit deceleration in awake full-term newborns. Since her infants were 3 weeks old when tested, the implication is that 3 weeks of postnatal experience can more than compensate for 4 weeks of prematurity. However, the premature response was a much more pronounced deceleration than has been reported in awake, full-term infants who were as old as 6 weeks (Hatton, 1969) or 2 to 8 weeks (Lewis et al., 1967). If Schulman’s results can be replicated, it would appear that there is not only a powerful effect of postnatal experience but that the particular experience of relative isolation in a premature nursery is important. Such isolation could conceivably heighten novelty effects although it would operate against the habituation of defensive reactions. It is also likely that stimuli have different effects when presented in the hospital environment in which an infant lives than when presented in a strange laboratory to which the S has been transported. The question is whether such differences in experience or in testing conditions can account for such major differences in findings. Further work is clearly needed. If naturally occurring postnatal experience should prove to be an important factor in the development of orienting, it might be possible to produce more rapid development of ORs by manipulating expefience.

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Familiarization with stimuli, without any apparent reinforcement, has been shown by the Gibsons to improve stimulus differentiation (Gibson & Gibson, 1955). This procedure might also be effective in developing orienting in the newborn, either by establishing the neural memory traces of past stimulation that are necessary before a stimulus can be perceived as novel, or by leading to extinction of startle or defense responses. Sameroff ( 1 968) suggests that the newborn’s initial reaction to most novel stimuli is “defensive” and that stimuli must be “dissociated from negative consequences” before an OR can appear. He believes that habituation is the most likely process by which this occurs. Similarly, Gray and Crowell (1968) suggest that the “neonate’s lack of experience with a n y form of sudden peripheral stimulation leads to an interpretation of abrupt changes in the environment as aversive.” As noted previously, Graham et al. ( 1 968) were unable to produce an OR, indexed by H R deceleration, in the course of habituating a stimulus over a 5-day period (Fig. 6). Nor did they find evidence of more rapid habituation on successive days, except for a change between Days 1 and 2 which was in the same direction as the significant change obtained in an earlier experiment (Keen et al., 1965). However, Graham et al. provided only 15 stimulations a day which was not sufficient to habituate the response completely on any one day and would, therefore, be a weak test of the familiarization or habituation hypothesis of O R development. Sontag (1960), in a much more extensive test, did obtain suggestive evidence of learned habituation. He reported progressive decrease in H R acceleration when a fetus received 625 vibratory stimulations distributed over a 9-week period before birth. Age controls did not show the decrease. Stimulation alone might be ineffective or less effective than stimulation associated with positively or negatively reinforcing conditions. Even in situations where the newborn has not exhibited successful conditioning or learning, it is possible that the conditioning procedure would lead to changes in the H R orienting response either to the conditioned or discriminative stimulus or to omission of reinforcement during extinction. Such studies have not been reported in this country. Soviet work with prematures (Polikanina, 1961) in which the development of conditioned cardiac, respiratory, and skeletal responses were compared may indicate that cardiac changes are slower to develop than those of other systems. However, only cardiac acceleratory changes appear to have been considered. While there is virtually no relevant experimental work, it is obvious that postnatal experience is confounded with maturation and might reasonably be expected to affect arousal systems through either a familiari-

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zation-habituation mechanism or through association with positive and negative reinforcements.

IV. Summary and Discussion Newborn HR studies have generally obtained prolonged, short-latency accelerative responses with no secondary decelerative phase. While this response differs from the diphasic or solely decelerative responses obtained from older infants, non-developmental factors have typically been confounded with the developmental variable. Newborns have usually been stimulated with intense and sudden stimuli and have rarely been presented with stimuli from relatively mature sensory systems or with prepotent stimuli. They have also been studied, in the main, while drowsy or sleepy. However, even when awake, they do not give decelerative responses to stimuli that evoke deceleration in older infants. It can be concluded, therefore, that decelerative H R responses are, at least, more difficult to elicit from newborns than from older infants, although it would be premature to assert that such responses could not be obtained from newborns under optimal conditions. It can also be concluded that deceleration increases with age, during both sleeping and waking states. In the waking state, deceleration begins at least by 6 weeks and increases at least up to 4 to 6 months. In the sleeping state, a diphasic response is not present at 6 weeks but is present at 12 weeks. On the assumption of two arousal systems, both developmental and state differences could reasonably be inferred. It would be expected that the system facilitating information-processing should t e relatively more difficult to elicit during the newborn period when limbic and cortical areas, presumed to control such a system, are less mature than older brain areas, presumed to control a protective-energizing system. For similar reasons, the facilitative system should also be difficult to elicit during sleep. These inferences are supported by the infant H R data if the further assumption is made that the facilitative system or O R is associated with HR deceleration, and the protective-energizing system with H R acceleration. The assumption that H R response differentiates arousal systems has been tested in a number of adult studies but there have been no direct tests with infants that direction of H R change meets the criteria for distinguishing an O R and a D R . While there is apparently relatively slow habituation of newborn cardiac accelerative responses, compared to other non-cardiac newborn response systems (Graham et al., 1968),

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there are no infant data showing that cardiac acceleration habituates more slowly than cardiac deceleration. The data of Clifton and Meyers ( I 969) would suggest, in fact, that cardiac deceleration may also habituate slowly in the infant. Neither is there any evidence showing a nonmonotonic relation between stimulus intensity and cardiac response in infants. N o studies with older infants have included intense stimuli. Some effort has been made to demonstrate an offset response but the results are not conclusive. Hatton ( 1969) found a decelerative offset response in 12-week Awake S s , to an 18-second simple stimulus, and Clifton and Meyers ( 1 969) found deceleration in 4-month-old infants at offset of a 10-second simple stimulus. In both studies, more complex interrupted stimuli failed to evoke any offset response. The effect of sleep-wake state on infant H R is also compatible with the assumption that H R differentiates between an OR and a DR, although it is not among the criteria proposed for establishing that a response component is differentiating. Sokolov has referred to the sleep response as an O R on the grounds that sleep abolishes cortical inhibition of the OR and thus reinstates a previously habituated OR. As noted earlier, it is not clear why Sokolov calls this “reinstated” response an OR since it meets criteria of a DR. Later writers have tended to accept Sokolov’s statement without further evaluation. In the present state of knowledge, it is not possible to state precisely the neural changes that might be related to a developmental shift in cardiac response. If Routtenberg (1968) is correct in identifying the structures that might be associated with the two arousal systems, the change in waking response may reflect increasing maturation of the limbic system and probably also increasing participation of cortical areas in controlling the response. Since the reticular system is relatively mature at birth, the change in sleep response may reflect primarily the maturation of a specific cardiovascular control system- the homeostatic baroreceptor reflex. Lipton et al. ( 1 966) have reviewed the evidence suggesting that capacity for rapid reflex bradycardia is relatively deficient in the newborn and matures during the early months of life. On the grounds that sleeping 2- to 3-month-olds showed HR responses like those of awake 5-month-olds, Lipton el al. (1966) rejected the idea that “higher centers or a maturing ‘orientation reflex’ [p. 141” could be responsible for the developmental change between birth and 2 % months. In reply to this, Clifton and Meyers (1969) argued, following Sokolov, that ORs could also be obtained during sleep. However, it is the thesis of the present authors that the sleep response is not usually an OR, in which there is monophasic deceleration, but a DR or startle reflex in which there is a diphasic or triphasic response including

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acceleration followed by a secondary deceleration. The fact that Lipton et al. (1966) obtained the diphasic response pattern in both waking and sleeping Ss is probably a function of using relatively intense stimuli with sudden onsets. As discussed in an earlier section, there is evidence that a diphasic response of acceleration-deceleration will occur, even in the awake S, when onsets are sudden and intensity is moderately high. This could be called a combined startle-OR response and we would speculate that the decelerative phase in this response of the awake S is controlled by neural mechanisms different from those producing a decelerative phase during sleep. In the waking S, the decelerative phase habituates rapidly while acceleration remains or is intensified. It follows that deceleration cannot be solely a homeostatic baroreceptor reflex, secondary to HR acceleration, and the rapid habituation suggests that it is an OR, presumably under cortical control. In contrast, the decelerative phase does not habituate during sleep and, since cortical control is absent or minimal, may well be a homeostatic reflex mediated at the medullary level. Data on correlations between accelerative and decelerative phases during sleep would be interesting in this connection. It should be emphasized that the present authors are not proposing that an OR is impossible to elicit during sleep, but only that it may be a less probable response than in the waking state, either because thresholds for startle-DR reflexes are lower, or because the response, not being subject to cortical control and thus to amplification, is more difficult to detect, We are also suggesting that a subcortical response might be expected to differ from the response obtained when cortical influences are present. It may be hypothesized that subcortical responses of both OR and startle-DR systems should resemble, in their initial direction of change, the response that is exhibited by the mature nervous system in the waking state. However, the later characteristics would not resemble the waking response since they would not be subject to cortical feedback effects. Thus, a subcortical OR might show a small, brief deceleration but not the prolonged, larger deceleration presumed due to amplification of the response by cortical feedback. Similarly, a subcortical startle-DR might show brief initial acceleration followed by baroreceptor-initiated deceleration rather than a relatively prolonged and larger acceleration. While decelerative responses increase during the first few months of life, in both waking and sleeping states, there have been no studies showing that accelerative responses can be elicited from awake newborns and, if so, whether stimulus thresholds and response characteristics change with age. Such information could be important in clarifying the physiological mechanisms underlying developmental change. It

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would be expected, for example, that changes in the waking DR would parallel changes in the sleep response by showing less prolonged and less marked acceleration as the accelerative phase becomes more effectively modulated by maturing baroreceptor reflexes. If developmental changes beyond the period of early infancy are considered, adult work suggests that there is a subsequent reduction in the magnitude of the OR, at least in response to pure tones. This curvilinear trend in OR with age can not be due to any simple relation with prestimulus H R level. The regressions of post on prestimulus HR are similar at all ages (Table 11) and, given the prestimulus levels associated with each age, would predict larger decelerative responses from newborns than from adults. A possible explanation is suggested by animal research on the effectiveness of sensory reinforcers. In a review of the literature, Kish ( 1966) found evidence that “a curvilinear relation exists between age and reactivity to sensory reinforcers with responsiveness increasing with maturational status to some maximal value and falling off with further increments in age [p. 1401.” If an increase in amplitude of decelerative responding during the first few months of infancy is influenced by exposure to environmental stimulation, a subsequent decline might also be expected due to generalized decrease in the novelty of stimulation provided by further experience. Kish offered such an explanation for the effects of sensory reinforcement, stating that “The drop-off in responsiveness in the later age ranges may be a function of increased experience with a variety of stimuli, which consequently tends to reduce the related novelty of the stimulus objects presented [p. 1401.” The gross outline of a theory relating H R response to basic arousal functions is thus visible. The data are internally consistent, on the whole, but many aspects of importance remain unexplored or inadequately explored by either adult or infant research. ACKNOWLEDGMENTS

The cooperation of the nurses and staff of the University Hospitals and St. Mary’s Hospital, Madison, Wisconsin was essential to our research and w e thank them for their patience and understanding. We also acknowledge our indebtedness to Harry Ludwig, Allan F. Puariea, and other staff of the Medical Electronics Laboratory for generous advice and assistance on technical problems; we are grateful to Leonard E. Ross and W. Keith Berg for a critical reading of the manuscript.

REFERENCES Apgar, V. A proposal for a new method of evaluation of the newborn infant. Current Research in Anesthesia and Analgesia, 1953, 32, 260-267.

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Bartoshuk, A. K. Human neonatal cardiac acceleration to sound: Habituation and dishabituation. Perceptual and Motor Skills, 1962, 15, 15-27. (a) Bartoshuk, A. K. Response decrement with repeated elicitation of human neonatal cardiac acceleration to sound. Journal of Comparative and Physiological Psychology, 1962, 55, 9-13. (b) Bartoshuk, A. K. Human neonatal cardiac responses to sound: A power function. Psychonomic Science, 1964, 1, 15 1 - 152. Beadle, K. R., & Crowell, D. H. Neonatal electrocardiographic responses to sound: Methodology. Journal of Speech and Hearing Research, 1962,5, 112- 123. Benjamin, L. S. Statistical treatment of the law of initial values (LIV) in autonomic research: A review and recommendation. Psychosomatic Medicine, 1963, 25, 556-566. Benjamin, L. S. Facts and artifacts in using analysis of covariance to “undo” the law of initial values. Psychophysiology, 1967.4, 187-206. Berg, K. M., Berg, W. K., & Graham, F. K. Infant heart rate response as a function of stimulus and state. Unpublished manuscript, University of Wisconsin, 1968. Berg, W. K. Vasomotor and HR response to non-signal auditory stimuli. Unpublished master’s thesis, University of Wisconsin, 1968. Berlyne, D. E. Arousal and reinforcement. In D. Levine (Ed.), Nebraska symposium on motivation. Lincoln, Neb.: University of Nebraska Press, 1967. Pp. I - 110. Black, A. H. Cardiac conditioning in curarized dogs: The relationship between heart rate and skeletal behavior. In W. F. Prokasy (Ed.), Classical conditioning: A symposium. New York: Appleton-Century-Crofts, 1965. Pp. 20-47. Brackbill, Y., Adams, G., Crowell, D. H., &Gray, M. L. Arousal level in neonates and preschool children under continuous auditory stimulation. Journal qfExperimental Child Psychology, 1966, 4. 178- 188. Brackbill, Y., & Koltsova, M. M. Conditioning and Learning. I n Y. Brackbill (Ed.), Infancy and early childhood. New York: Free Press, 1967. Pp. 207-288. Bridger, W. H. Sensory habituation and discrimination in the human neonate. American Journal of Psychiatry, 1961, 117,991-996. Bridger, W. H. Sensory discrimination and autonomic function in the newborn. American Academy of Child Psychiatry, Journal, 1962, 1, 67-82. Bridger, W. H., Birns, B. M., & Blank, M. A comparison of behavioral ratings and heart rate measurements in human neonates. Psychosomutic Medicine, 1965, 27, 123- 134. Bridger, W. H., & Reiser, M. Psychophysiologic studies of the neonate: An approach toward the methodological and theoretical problems involved. Psychosomatic Medicine, 1959,21,265-276. Chase, H. H. Habituation of an acceleratory cardiac response in neonates. Unpublished master’s thesis, University of Wisconsin, 1965. Chase, W. G., & Graham, F. K. Heart rate response to non-signal tones. Psychonomic Science, 1967, 9, 18 I - 182. Chase, W. G., Graham, F. K., & Graham, D. T. Components of HR response in anticipation of reaction time and exercise tasks. Journal of Experimental Psychology, 1968, 76,642-648. Clifton, R. K., & Graham, F. K. Stability of individual differences in heart rate activity during the newborn period. Psychophysiology, 1968,5, 37-50. Clifton, R. K., Graham, F. K., & Hatton, H. M. Newborn heart-rate response and response habituation as a function of stimulus duration. Journal of Experimental Child Psychology, 1968.6, 265-278. Clifton, R. K., & Meyers, W. J. The heart-rate response of four-month-old infants to auditory stimuli. Journal of Experimental Child Psychology, 1969, 7, 122- 135.

Arousal Systems and Infant Heart Rate Responses

113

Conel, J. L. Histologic development of the cerebral cortex. In The biology of mental health and disease. Twenty-seventh Annual Conference of the Milbank Memorial Fund. New York: Hoeber, 1952, Pp. 1-10, Davis, C. M., Crowell, D. H., & Chun, B. J. Monophasic heart rate acceleration in human infants to peripheral stimulation. American Psychologist, 1965, 20, 478. (Abstract) Davis, R. C., & Buchwald, A. M. An exploration of somatic response patterns: Stimulus and sex differences. Journal of Comparative and Physiological Psychology, 1957, 50, 44-52. Davis, R. C.. Buchwald, A. M., & Frankmann, R. W. Autonomic and muscular responses, and their relation to simple stimuli. Psychological Monographs, 1955, 69(20, Whole No. 405). Desmond, M. M., Franklin, R. R., Vallbona, C., Hill, R. M., Plumb, R., Arnold, H., & Watts, J. The clinical behavior of the newly born. 1. The term baby. Journal of Pediatrics, 1963, 62, 307-325. Eisenberg, R. B. Auditory behavior in the human neonate: 1 . Methodologic problems and the logical design of research procedures. Journal of Auditory Research, 1965, 5 , 159- 177. Ellingson. R. J. Cerebral electrical responses to auditory and visual stimuli in the infant (human and subhuman studies). In P. Kellaway & I. Petersen (Eds.), Neurological and electroencephalographic correlative studies in infancy. New York: Grune & Stratton, 1964. Pp. 78- 116. Fantz, R. L. Visual perception from birth as shown by pattern selectivity. Annals of the N e w York Academy of Sciences, 1965,118,793-814. Froeschels, E., & Beebe, H. Testing the hearing of newborn infants. A.M.A. Archives of Otolaryngology, I946,44, 7 10-7 14. Gibson, J. J., & Gibson, E. J. Perceptual learning: Differentiation or enrichment? Psychological Review, 1955.62, 32-41. Graham, F. K., & Clifton, R. K. Heart-rate change as a component of the orienting response. Psychological Bulletin, 1966, 65, 305-320. Graham, F. K., Clifton, R. K.. & Hatton, H. M. Habituation of heart rate response to repeated auditory stimulation during the first five days of life. Child Development, 1968, 39, 35-52. Graham, F. K., Ernhart, C. B., Thurston, D., & Craft, M. Development three years after perinatal anoxia and other potentially damaging newborn experiences. Psychological Monographs, 1962,76(3, Whole No. 522). Grastyan, E., Karmos, G., Vereczkey, L., Martin, J., & Kellenyi, L. Hypothalamic motivational processes as reflected by their hippocampal electrical correlates. Science, 1965, 149.91-93. Gray, M. L. & Crowell, D. H. Heart rate changes to sudden peripheral stimuli in the human during early infancy. Journal of Pediatrics, 1968,72, 807-8 14. Hatton, H. M. Developmental change in infant heart rate response during sleeping and waking states. Unpublished doctoral dissertation, University of Wisconsin, 1969. Hatton, H. M., Graham, F. K., & Berg, W. K. Effects of stimulus rise time and intensity on evoked heart rate response. Unpublished manuscript, University of Wisconsin, 1968. Headrick, M. W., & Graham, F. K. Multiple component heart rate responses conditioned under paced respiration. Journul of Experimental Psychology, 1969, 79, 486-494. Hord, D. J., Johnson, L. C., & Lubin, A. Differential effect of the law of initial value (LIV) on autonomic variables. Psychophysiology, 1964,1,79-87. Hord, D. J., Lubin, A., & Johnson, L. C. The evoked heart rate response during sleep. Psychophysiology, 1966,3,46-54.

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Frances K . Graham and Jan C . Jackson

Hrbek, A., Hrbkova, M., & Lenard, H. G . Somato-sensory evoked responses in newborn infants. Electroencephalography and Clinical Neurophysiology, 1968, 25,443-448. Hubel, D. H., & Wiesel, T. N. Receptive fields, binocular interaction and functional architecture in the cat’s visual cortex. Journal of Physiology (London), 1962, 160, 106- 154. Hubel, D. H., & Wiesel, T. N . Receptive fields of cells in striate cortex of very young, visually inexperienced kittens. Journal of Neurophysiology, 1963, 26,994- 1002. Hutt, S. J., Hutt, C., Lenard, H. G., Bernuth, H. v., & MuntjewerfF, W. J. Auditory responsivity in the human neonate. Nature, 1968, 218, 888-890. Jackson, J. C. Neonatal cardiac response as a function of stimulus rise time and subject state. Unpublished master’s thesis, University of Wisconsin, 1968. Kagan, J., Henker, B. A., Hen-Tov, A., Levine, J., & Lewis, M. Infants’ differential reactions to familiar and distorted faces. Child Development, 1966, 37, 5 19-532. Kagan, J., & Lewis, M. Studies of attention in the human infant. MerrilbPalmer Quarterly, 1965,11,95-128. Kantowitz, S., & Graham, F. K. Evoked heart rate response in awake newborns. Unpublished manuscript, University of Wisconsin, 1969. Keen, R. K., Chase, H. H., & Graham, F. K. Twenty-four hour retention by neonates of an habituated heart rate response. Psychonomic Science, 1965, 2,265-266. Kiang, N. Y. S., Peake, W. T., Siebert, W. M., Weiss, T. F., & Wiederhold, M. L. Research on the peripheral auditory system. Quarterly Progress Report No. 88, January, 1968, Research Laboratory of Electronics, Massachusetts lnsitute of Technology. Kish, G. B. Studies of sensory reinforcement. In W. K. Honig (Ed.), Operant behavior: Areas of research and application. New York: Appleton-Century-Crofts, 1966. Pp. 109- 159. Korn, J. H., & Moyer, K. E. Effects of set and sex on the electrodermal orienting response. Psychophysiology, 1968,4,453-459. Lacey, J . 1. The evaluation of autonomic responses: Toward a general solution. Annals of the New York Academy of Sciences, 1956,67, 123- 164. Lacey, J. I. Psychophysiological approaches to the evaluation of psychotherapeutic process and outcome. In E. A. Rubinstein & M. B. Parloff (Eds.), Research in psychotherapy. Washington, D. C.: American Psychological Association, 1959. Pp. 160-208. Lacey, J. 1. Of number and syntax in the psychophysiology of the heart. Presidential address, Society for Psychophysiological Research, Denver, October 2962. Lacey, J. I . Somatic response patterning and stress: Some revisions of activation theory. In M. H. Appley & R. Trumbull (Eds.). Psychological stress: Issues in research. New York: Appleton-Century-Crofts, 1967. Pp. 14-37. Landis, C., & Hunt, W. A. The startle pattern. New York: Farrar & Rinehart, 1939. Lang, P. J., & Hnatiow, M. Stimulus repetition and the heart rate response. Journal of Comparative and Physiological Psychology, 1962,55, 78 1-785. Lewis, M., Bartels, B., & Goldberg, S. State as a determinant of infants heart rate response to stimulation. Science, 1967, 155,486-488. Lewis, M., Kagan, J., Campbell, H., & Kalafat, J. The cardiac response as a correlate of attention in infants. Child Development, 1966, 37, 63-71. Lewis, M., & Spaulding, S. J. Differential cardiac response to visual and auditory stimulation in the young child. Psychophysiology, 1967,3, 229-237. Licklider, J. C. R. Basic correlates of the auditory stimulus. In S. S. Stevens (Ed.), Handbook of experimentalpsychology. New York: Wiley, 195 1. Pp. 985- 1039. Lipton, E. L., & Steinschneider, A. Studies on the psychophysiology of infancy. MerrillPalmer Quarterly, 1964, 10, 103- 117. Lipton, E. L. Steinschneider, A., & Richmond, J. B. Autonomic function in the neonate: 11. Physiologic effects of motor restraint. Psychosomatic Medicine, I960,22, 57-65.

Arousal Systems and Infant Heart Rate Responses

115

Lipton, L., Steinschneider, A,, & Richmond, J . B. Autonomic function in the neonate: 111. Methodological considerations. Psychosomatic Medicine, 196 1 , 23, 46 1-47 1. (a) Lipton, E. L., Steinschneider, A., & Richmond, J. B. Autonomic function in the neonate: IV. Individual differences in cardiac reactivity. Psychosomatic Medicine, 196 1, 23, 472-484. (b) Lipton, E. L., Steinschneider, A., & Richmond, J. B. Autonomic function in the neonate. VIII. Cardio-pulmonary observations. Pediatrics, 1964.33, 212-215. Lipton, E. L., Steinschneider, A., & Richmond, J. B. The autonomic nervous system in early life. New England Journal of Medicine, 1965, 273, 147-154, 201-208. (a) Lipton, E. L., Steinschneider, A., & Richmond, J. B. Swaddling, a child care practice: Historical, cultural and experimental observations. Pediatrics, 1965, 35 (Suppl.), 52 1-567. (b) Lipton, E. L., Steinschneider, A., & Richmond, J . B. Autonomic function in the neonate: VII. Maturational change in cardiac control. Child Development, 1966,37, 1- 16. Lynch, J. J . The cardiac orienting response and its relationship to the cardiac conditional response in dogs. Conditional Reflex. 1967, 2, 138-152. Lynn, R. Attention, arousal and the orienting reaction. New York: Macmillan (Pergamon), 1966. Malmo, R. B., & Belanger, D. Related physiological and behavioral changes: What are their determinants? Research Publications, Association for Research in Nervous and Mental Disease, 1967.45, 288-3 18. McCall, R. B., & Kagan, J. Attention in the infant: Effects of complexity, contour, perimeter, and familiarity. Child Development, 1967, 38,939-952. (a) McCall, R. B., & Kagan, J. Stimulus-schema discrepancy and attention in the infant. Journal of Experimental Child Psychology, 1967,5, 303-3 17. (b) Meyers, W. J . The influence of stimulus intensity and repetition on the mean evoked heart rate response. Psychophysiology, 1969, 6, 3 10-3 16. Meyers, W. J . , & Cantor, G. N . Infants’ observing and heart period responses as related to novelty of visual stimuli. fsychonomic Science, 1966,5,239-240. Meyers, W. J., & Cantor. G. N. Observing and cardiac responses of human infants to visual stimuli. Journal of Experimental Child Psychology, 1967,5, 16-25. Meyers, W. J., & Gullickson, G. R. The evoked heart rate response: The influence of auditory stimulus repetition, pattern reversal, and autonomic arousal level. fsychophysiology, 1967,4,56-66. Miller, N . E., & DiCara, L. V. Instrumental learning of heart rate changes in curarized rats: Shaping and specificity to discriminative stimulus. Journal of Comparative and Physiological Psychology, 1967,63, 12- 19. Moffitt, A. R. Speech perception by infants. Unpublished doctoral dissertation, University of Minnesota, 1968. Moruzzi, G., & Magoun, H. W. Brain stem reticular formation and activation of the EEG. Electroencephalography and Clinical Neurophysiology, 1949, 1, 455-473. Newton, J. E. O., & Perez-Cruet, J. Successive-beat analysis of cardiovascular orienting and conditional responses. Conditional Reflex, 1967, 2, 37-55. Obrist, P. A., Webb, R. A., & Sutterer, J. A. Heart rate and somatic changes during aversive conditioning and a simple reaction time test. Psychophysiology, 1969.5696-723. Olson, R. E., & Ludwig, H. A solid-state electronic switch for auditory research. ZEEE Transactions on Bio-Medical Engineering, 1965, 12, 193- 195. Polikanina. R. 1. The relationship between autonomic and somatic components during the development of a defensive conditioned reflex in premature children. Pavlov Journal ofHigher Nervous Activity, 1961,11,72-82. Polikanina, R. I., & Probatova, L. E. On the problem of formation of the orienting reflex in

116

Frances K . Graham and Jan C . Jackson

prematurely born children. In L. G. Voronin, A. N. Leontiev, A. R. Luria, E. N. Sokolov, & 0. S. Vinogradova (Eds), Orienting reflex and exploratory behavior. Washington, D. C.: American Institute of Biological Sciences, 1965. Pp. 330-340. Prechtl, H. F. R., & Beintema, D. J. The neurological exarninatioiz of t h e ~ u l l - r e rnewborn ~ infant. London: Spastics Society Medical Education and Information Unit, 1964. Raskin, D. C., Kotses, H., & Bever, J. Autonomic indicators of orienting and defensive reflexes. Journal of Experimental Psychology, 1969.80, 423-432. Richmond, J. B., & Lipton, E. L. Some aspects of the neurophysiology of the newborn and their implications for child development. In L. Jessner & E. Pavenstedt (Eds.), Dynamic psychopathology in childhood. New York: Grune & Stratton, 1959. Richmond, J. B., Lipton, E. L., & Steinschneider, A. Autonomic function in the neonate: V. Individual homeostatic capacity in cardiac response. Psychosomatic Medicine, 1962, 24, 66-74. (a) Richmond, J. B., Lipton, E. L., & Steinschneider, A. Observations on differences in autonomic nervous system function between and within individuals during early infancy. American Academy of Child Psychiatry, Journal, 1962, 1, 83-91. (b). Riesen, A. H. Receptor functions. In P. H. Mussen (Ed.), Handbook ofresearch methods in child development. New York: Wiley, 1960. Routtenberg, A. The two-arousal hypothesis: Reticular formation and limbic system. Psychological Review, 1968,75, 5 1-80. Royer, F. L. The “respiratory vasomotor reflex” in the forehead and finger. Psychophysiology, 1966,2,24 1-248. Sameroff, A. Can conditioned response be established in the newborn infant? Paper presented at the Eastern Regional Meeting of the Society for Research in Child Development, Worcester, Massachusetts, March 1968. Schachter, J., Bickman, L., Schachter, J. S., Jameson, J., Lituchy, S., & Williams, T. A. Behavioral and physiologic reactivity in human neonates. Mental Hygiene, 1966, 50, 5 16-52 1 . Schachter, J., Williams, T. A., Bennett, S., & Williams, J, D. Spontaneous and stimulusevoked behavioral variations in neonates. Paper presented at the meeting of the Society for Research in Child Development, New York, April 1967. (a) Schachter, J., Williams, T. A., Khachaturian, Z., Tobin, M., & Druger, R. The multiphasic heart rate response to auditory clicks in neonates. Paper presented at the meeting of the Society for Psychophysiological Research, Washington, D. C., October 1968. Schachter, J., Williams, T. A,, & Tobin, M. Neonatal heart rate response to auditory stimuli: Effect of prestimulus heart rate slope. Paper presented at the meeting of the Society for Psychophysiological Research, San Diego, October 1967. (b) Scheibel, M. E., & Scheibel, A. B. Some neural substrates of postnatal development. I n M. L. Hoffman & L. W. Hoffman (Eds.), Review of child development research. New York: Russell Sage Foundation, 1964. Pp. 48 1-5 19. Schneirla, T. C. An evolutionary and developmental theory of biphasic processes underlying approach and withdrawal. In M. R. Jones (Ed.), Current theory and research on motivation. Lincoln, Neb.: University of Nebraska Press, 1959. Pp. 1-42. Schulman, C. A. The development of heart rate deceleration in premature infants. Paper presented at the meeting of the Society for Psychophysiologic Research, Washington, D.C., October 1968. (a) Schulman, C. A. Differentiation in the neonatal period between infants at high risk and infants at low risk for subsequent severe mental retardation. Paper presented at the meeting of the Eastern Psychological Association, Washington, D.C., April 1968. (b)

Arciusal Systems and Infant Heart Rate Responses

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Smith. D. B. D.. & Strawbridge. P. J. Stimulus duration and the human heart rate response. Psychonomic Science, 1968. 10.71 -72. Smith, K. Conditioning as an artifact. Psychological Review, 1954, 61, 217-225. Sokolov. E. N. Perception and the condifioned reflex. New York: Macmillan, 1963. Sontag. L. W. The possible relationship of prenatal environment to schizophrenia. In D. D. Jackson (Ed.), The etiology of schizophrenia. New York: Basic Books, 1960. Pp. 175-187. Steinschneider, A. Sound intensity and respiratory response in the neonate: Comparison with cardiac rate responsiveness. Psychosomatic Medicine, 1968,30,534-541. Steinschneider, A., & Lipton, E. L. Individual differences in autonomic responsivity. Problems of measurement. Psychosomatic Medicine, 1965, 27.446-456. Steinschneider, A., Lipton. E. L., & Richmond, J. B. Autonomic function in the neonate: VI. Discriminability, consistency, and slope as measures of an individual’s cardiac responsivity. Journal of Genetic Psychology, 1964, 105,295-3 10. Steinschneider, A., Lipton, E. L.. & Richmond, J. B. Stimulus duration and cardiac responsivity in the neonate. Paper presented at the meeting of the Society for Research in Child Development, Minneapolis, March 1965. Steinschneider, A., Lipton, E. L., & Richmond, J. B. Auditory sensitivity in the infant: Effect of intensity on cardiac and motor responsivity. Child Development, 1966, 37, 233-252. Vallbona, C., Desmond, M. M., Rudolph. A. J., Pap, L. F., Hill, R. M., Franklin, R. R., & Rush, J. B. Cardiodynamic studies in the newborn 11. Regulation of the heart rate. Biologia Neonatorum, 1963, 5 , 159- 199. Westcott, M. R., & Huttenlocher. J. Cardiac conditioning: The effects and implications of controlled and uncontrolled respiration. Journal of Experimental Psychology, 196 1, 61. 353-359. Wilder, J. Stimulus and response. The law of initial value. Bristol, Eng.: Write, 1967. Williams, T. A,, Schachter, J., & Tobin, M. Spontaneous variation in heart rate: Relationship to the average evoked heart rate response to auditory stimuli in the neonate. Psychophysiology, 1967,4, 104- 1 I 1. Wolff, P. H. The causes, controls, and organization of behavior in the neonate. Psychological Issues, 1966, 5 (Monogr. 17).

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SPECIFIC AND DIVERSIVE EXPLORATION'

Corinne Hutt2 UNIVERSITY OF OXFORD

1. I N T R O D U C T I O N

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I I . COMPLEXITY AS A D E T E R M I N A N T O F A T T E N T I O N A N D EXPLORATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A . MULTIDIMENSIONAL COMPLEXITY .................... B. U N I D I M E N S I O N A L COMPLEXITY ....................... C . A COMPARISON O F F I V E DIMENSIONS OF COMPLEXITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D . REVIEW A N D C O M M E N T S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I l l . NOVELTY AS A D E T E R M I N A N T OF EXPLORATION . . . . . . . . A . SEPARATION OF NOVELTY A N D COMPLEXITY VARIABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B . SOME D E F I N I T I O N S O F NOVELTY ...................... C . NOVELTY IN A BIOLOGICAL C O N T E X T . . . . . . . . . . . . . . . . D . TWO-DIMENSIONAL N O V E L T Y ......................... E . HABITUATION T O NOVELTY ........................... F . SOURCES O F N O V E L T Y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G . WHAT IS FEAR O F NOVELTY? .......................... H . T H E APPROACH-AVOIDANCE C O N F L I C T . . . . . . . . . . . . . . .

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159 IV . SPECIFIC A N D D l V E R S l V E ACTIVITIES .................... A . CURIOSITY A N D BOREDOM T H E O R I E S . . . . . . . . . . . . . . . . . 159 B . INVESTIGATION A N D PLAY . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 C . CHARACTERISTICS O F S P E C I F I C A N D D l V E R S l V E ACTIVITIES ............................................. 167 'The preparation of this paper as well as the work of the author reported in it were most generously supported by the Nuffield Foundation . "ow at the Department of Psychology, University of Reading.

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V. SUMMARY A N D CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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REFERENCES

I. Introduction In the last decade and a half the area of exploratory behavior has seen a resurgence of interest and activity. One of the most notable aspects of this interest has been the change in emphasis from rodent behavior to primate behavior. The early fifties witnessed the formulation of several theories of exploratory behavior based almost exclusively upon data from the laboratory rat. Later in the fifties the work of Harlow and his colleagues at the Wisconsin Laboratory (see, e.g., Butler, 1965) provoked further interest in this area of behavior. These studies showed that mere visual and auditory incentives were adequate to maintain a high level of exploration in the monkey and furthermore that discrimination problems would be solved in the course of this exploratory activity. But it seems fair to say that it was not until the publication of Berlyne’s (1960) masterly exposition, based upon a remarkable collation of empirical data from many species and sources, that interest in the exploratory activities of humans became evident. Even so it seems disappointing to find a recent review of the area (Fowler, 1965) which again dwells largely upon rat behavior. Certainly both rodent and man are inveterate explorers, but their ecologies, habitats, selection pressures, and behavior repertoires differ so markedly that in this area perhaps more than any other in psychology, we do well to recall Beach’s (1950) cautionary tale. Many of the stimulus variables which are effective in eliciting exploration are related to a greater or lesser degree with one another, and G . N. Cantor (1 963) regarded the two variables of complexity and novelty as likely to be the least dependent. This is true insofar as they refer to different aspects of the environment-organism interaction. Complexity refers chiefly to the variety in the stimulus (G. N. Cantor, 1963), and novelty to the immediate, recent, or past experience of the organism. Moreover, by far the greatest number of studies of exploration in children have been concerned with the effect of one or other of these variables. For these reasons, discussion will be confined largely to those studies which have explicitly attempted to investigate the effects of complexity or novelty. This discussion of the important stimulus variables in exploration will be followed by an attempt to elucidate the pertinent response variables. These are economically grouped into two main categories- specific and

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diversive exploration - and consideration is given to the antecedent conditions of which they may be a function. A final attempt at synthesis seeks to reconcile two apparently opposed groups of theories of exploration by reference to differences in the conditions, nature, and effects of the phenomena they seek to explain. Traditionally it has been accepted that the young of most mammalian species manifest a high degree of curiosity, and yet the data from rats indicate that adult rats show more exploratory activity than preadolescent animals (Goodrick, 1966, 1967) and young chimpanzees exhibit greater caution toward novel objects than do adults of the species (Welker, 1956a). In humans, then, are children in general more curious than adults, or preschool children than school children, or infants than preschool children? The simple answer is that we do not know. The answer we obtain will depend upon the nature of our behavioral analysis and the particular measure we decide to adopt. Is curiosity a valid and meaningful concept-does it add anything to the description of the behavior? Is exploration a behavior that can be operationalfy defined and can it be identified with a unitary drive system? These are some of the questions that will be considered in the course of this paper but it will not be surprising to find that this area, particularly, but not exclusively, with respect to human subjects, is beset by problems of definition, methodology, and conceptual analysis.

11.

Complexity as a Determinant of Attention and Exploration

To many, complexity has seemed a variable preferable to deal with than novelty, since it can be described in terms of the physical attributes of a particular stimulus. G. N . Cantor (1963) felt that the lack of necessity to resort to information of past experience is in its favor. Moreover it permits quantification and parametric variation in a manner that novelty does not. Berlyne (1960), however, cautioned that complexity is the most impalpable of the collative variables. Certainly it appears to be a concept that has challenged the ingenuity of many, to judge by the prodigious effort expended upon its elucidation. The volume of research on this subject seems to have increased exponentially even since G . N . Cantor’s (1963) admirable review of the pioneering investigations in this area. But complexity seems to have lost little of its elusive character, as suggested by the variety of discrepant results the inquiry has yielded. The effects of stimulus complexity upon infant attention may be cited as an example: Berlyne (1958a) and Fantz

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(1961) found their subjects to look longest at, or to “prefer,” the most complex of a series of stimuli differing in complexity; Hershenson (1964) and Brennan, Ames, and Moore ( 1966) found most preference for least complex stimuli, the peak shifting with age. Hershenson, Munsinger, and Kessen ( 1965) and Thomas ( 1965) obtained preference for stimuli of intermediate complexity. In these studies a tacit assumption of a unitary and parametric scale of complexity did not include an acknowledgment of the difference, and hence incomparability, of the scales. In general, the studies concerned with the effects of stimulus complexity upon attention and exploration may be seen as of two kinds: (a) those that conceive of complexity as varying along a number of dimensions (asymmetry, heterogeneity, incongruity, etc.) which are not independent but which can be investigated individually and systematically though not necessarily parametrically; (b) those that are concerned primarily with the parametric variation of a particular attribute of patterns, and use randomly generated geometric figures to do so. Many of the latter group have been influenced by Attneave’s attempt to formulate rules based on information theory principles, for specifying the amount of complexity (variability) in a figure (Attneave, 1954; Attneave & Arnoult, 1956). A. MULTIDIMENSIONAL COMPLEXITY

Berlyne ( 1957) investigated the effects of incongruity, meaningfulness, surprise, and entropy variables upon the visual exploration of adults. Using a tachistoscopic exposure of 0.14 second, he allowed his subjects to view each pattern as often as they wished before proceeding to the next. He found that the response level for the incongruous pictures was much more than for the congruous one (means of 5.8 and 3.0 seconds, respectively). N o differences were obtained for the meaningful and random sequences, but significant effects were found for the surprise and entropy variables. Berlyne contrasted the overall level of response of adults (mean response per picture 2.8) with that of 5-year-old children (mean response 12.1) in a similar experiment carried out by Burgess, the details of which are recorded by Berlyne. Burgess used a considerably shorter exposure time, 0.0 14 second; but on the basis of a control experiment with adults using this shorter response time, Berlyne concluded that the greater responsiveness of the children could not be a function of the exposure time. Despite their greater “curiosity,” however, the children appeared to be insensitive to incongruity and surprise effects. Berlyne ( 1 958b, I958c, 1963a) demonstrated similar effects with longer exposure periods of 10 seconds and 2 minutes; in these cases the response measure was viewing time.

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Several investigations of children’s exploratory behavior have utilized material from Berlyne’s original studies. One such study was carried out by Smock and Holt (1962) and has already been commented upon by G. N. Cantor (1963). It will therefore not be described in detail here. Using 6- to 7E-year-old subjects, they investigated the effects of three stimulus variables: stimulus ambiguity, perceptual conflict, and conceptual conflict. These three variables were not sampled equally, nor did all the stimulus sets consist of pairs-in such cases presumably the series were dichotomized to form the simple and complex pictures. In all sets, those stimuli conventionally regarded as more complex were found to elicit significantly more responses than the less complex ones. This difference, however, varied in extent from one set to another; whereas the difference in the contour set was substantial, that in the sequence set appeared negligible. It is interesting that the familiar, congruous figures elicited the same level of responsiveness as the complex geometric figures and as the random sequence. In the case of the random meaningful sequences, mean response frequencies for each sequence were derived from response values for each of the six component pictures. The comparison between responses to single stimuli and to a series of stimuli seems a slightly dubious procedure. These authors also found marked sex differences in the degree and quality of the “curiosity motivation” of their subjects. Boys were generally far more responsive than girls, but particularly so under conditions of increase in figural contour and pattern incongruity; girls were more responsive only under conditions of pattern heterogeneity. This study raises a particularly perplexing conceptual issue. Despite the fact that the authors used stimuli previously used to investigate the attributes of stimulus complexity and also used traditional definitions of figural complexity, they nevertheless regarded their study as one of novelty parameters: “A major concern of this study was to determine the effect of qualitatively different types of environmental novelty on children’s tendency to maintain or seek perceptual contact with objects [p. 6361.” It is difficult to see what rationale would determine that 9 crosses in a random arrangement were more novel than the same crosses arranged in a 3 X 3 matrix or that 5 wavy and dotted lines were more novel than 5 straight lines. More conceptual clarity might perhaps have made the experimental design appear less arbitrary. In their study of perceptual curiosity in mental retardates, Hoats, Miller, and Spitz (1963) used stimulus material representing 6 dimensions including 5 previously investigated by Berlyne ( I 958b) with adults: Irregularity of Arrangement, Amount of Material, Heterogeneity of Elements, Irregularity of Shape, Incongruity, and Incongruous Juxtaposition (the last being the one omitted by Berlyne). These 6 dimensions were represented by 30 stimulus pairs, one member of each pair being

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more complex than the other. Each stimulus pair was exposed for 3 seconds after which the subject reprojected one of the pair by pressing the appropriate lever. He could view the reprojected picture as long as he wished up to a maximum of 39 seconds. The average age of the retarded subjects was 15% years. Two groups of normal subjects, of equivalent mental and chronological ages, respectively, were also included. The results were most surprising in that in all groups, choices of simple pictures far exceeded those of complex ones. Only in the case of the Amount of Material dimension was there a more even distribution of choices. More surprising still was the finding of a significant negative correlation between IQ and the number of “complex” choices within the retarded group. This raises some difficulties for protagonists of “optimal complexity” or “optimal level of stimulation” theories (Dember & Earl, 1957; Fiske & Maddi, 1961; Leuba, 1955), since the optimum is assumed to be a function of some capacity of the individual which in turn is dependent upon both intellectual and experiential factors. Although the use of two response measures was highly desirable, actual information regarding viewing time is unavailable-we are told only that the equal CA subjects viewed their complex choices longer than their simple choices; there were no significant differences in the equal MA or retardate groups. This very definite preference - here the term seems appropriate -for simple over complex visual patterns in groups of normal 16-year-olds and 8-year-olds, as well as in a group of retardates, certainly has developmental implications. These will be discussed subsequently when other corroborative data are reported. In a study of perceptual investigation in 4- to 5-year-old children, Clapp and Eichorn (1965) used some of Berlyne’s original material. Two of the variables studied - incongruity and redundancy (in geometrical figures)-were the same as Berlyne’s; to these Clapp and Eichorn added a series involving “redundancy of meaningful patterns,” consisting of pictures of a rake and a spade, an apple, horseshoe, magnet, and tacks, etc. The stimuli in this third category were of three types: (a) the objects represented in color; (b) the same drawings in black and white; and (c) black and white stick drawings of these objects. It was argued that the three types differed in the degree of redundancy since color reduced the similarity between parts of the figure in type (a), and redundancy was decreased by eliminating curvature in type (c). Although the authors did not say so, presumably the degree of redundancy was regarded as increasing from (c) to (a) to (b). Subjects individually viewed the 32 stimuli in the 3 series. The stimuli were presented tachistoscopically, each exposure lasting 0.14 second, and subjects were allowed as many viewings of each as they wished.

Unlike Berlyne’s procedure, however, the experimenter operated the tachistoscope in this experiment. This modification eliminated the audiotactile reinforcement resulting from operation of the tachistoscope, so that Clapp and Eichorn failed to obtain the significant temporal increase in responses per stimulus that Berlyne did. In general, responses were highest to the incongruity series and lowest to the geometric-redundancy series. Within the incongruity series the response to the incongruous stimuli (mean 8.1) was significantly higher than to the congruous ones (mean 6. I). However, no significant response differences attributable to stimulus characteristics were evident in the geometric-redundancy series. Moreover, the means were frequently not in the predicted order. Within the meaningful-redundancy series, the colored pictures elicited more response than the black and white ones. Interestingly, in this series an additional stimulus variable produced significant effects: the nature of the objects represented determined the level of response, the more common objects like apple and rake being looked at more frequently than less common ones like mushrooms and spilled-ink-bottle. The authors favored an explanation invoking novelty - on the assumption that familiar objects in an unfamiliar configuration or context result in maximum novelty. However, an alternative interpretation will be offered later in this section, in discussion of other similar results. A point of interest that emerges from a comparison of the studies mentioned hitherto is one relating to the response frequency per stimulus. On the assumption that briefer exposures would result in more responses so that the individual might obtain sufficient information to identify and categorize the stimulus, and o n the additional assumption that young children have a less adequate background of experience and information than older children and would therefore require more exposures to do so, the subjects of the Burgess study (cited by Berlyne) should have had a higher response level than those in the Clapp and Eichorn study, and both of these should have been considerably higher than in the Smock and Holt study. I n fact, the response levels were as follows: Burgess: mean response 12.1 and no congruity differences; Clapp and Eichorn: incongruous 8.1, congruous 6. I ; Smock and Holt: incongruous 16.0, congruous 13.0 (approximate figures derived from graph). These discrepancies suggest that details of experimental procedure were affecting the results as much as stimulus parameters. Testing hypotheses derived from the Dember and Early theory, May (1963) used an adaptation procedure whereby his nursery school subjects were given prior exposure to stimuli designated as having medium complexity value. Complexity varied according to the number of colored

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rectangles on a card, i.e., 2, 3, 5 , 8, or 12 rectangles, 10 cards in each set. In this series, therefore, the 5-rectangle cards were the adaptation stimuli. It was assumed that the adaptation procedure would have raised each subject’s complexity level to that of the adaptation stimulus, but it was not ascertained whether any of the subjects were already at or exceeded this adaptation level. After adaptation, subjects were allowed to choose, for closer viewing, a card from any one of the 6 packs. This procedure was repeated, but for how long is not certain. Nevertheless, the mean number of cards selected was 13.25. The comparison of greatest interest, however, concerned the first choice: 16 out of 21 subjects selected a card more complex than the adaptation one, and 18 subjects showed a subsequent overall preference for the more complex cards. In a more interesting variant of this experiment, May used manipulatable objects made up of sticks of different sizes and colors and connecting spools. The five constructed objects varied in shape, number of parts, and number of differently colored parts. Adaptation exposure was again given to the object of medium complexity value, the subject being asked to make an object like it. During testing, the subject was presented all five and told he could make one like any one of them. All but one subject, who had been able to make the adaptation object in the first place, chose a more complex object than the adaptation one. The inclusion of a problem which sampled another modality, and not just the visual, was a commendable addition. It must be emphasized, however, that these several attempts at assessing the effects of stimulus complexity upon visual exploration have manipulated the independent variable along many dimensions simultaneously. Since most often these dimensions are not subjected to any scaling procedure, quantitative variation is severely limited, and the most that is possible is a categorization such as “lesslmore” or one on an intuitive basis. In one study of complexity effects Berlyne, Craw, Salapatek, and Lewis (l963) used eight categories of stimuli; within each category a “less irregular” (LI) pattern was distinguished from a “more irregular” (MI) one. Berlyne admitted that “the variable that distinguishes MI from LI patterns differs from category to category,” but stated that “these variables are, nevertheless, alike in that (a) they are all . . . variables to which everyday language might well refer as differences in complexity, (b) they appear to have similar effects on exploratory behaviour [p. 5601.’’ The vernacular use of a term in scientific discourse has frequently led to just the kind of confusion “complexity” promises to lead to. Berlyne’s second argument, while verging on the tautologous, has also been shown to be invalid, at least in the case of children (C. Hutt, 1969a).

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B. UNIDIMENSIONAL COMPLEXITY

Since the adoption of communication theory by experimental psychologists, much attention has been devoted to attempts to specify stimulus complexity in terms of redundancy, variability, uncertainty, bits of information transmitted, and so on. The pioneering and prolific workers in this area have been Munsinger and Kessen who, adapting procedures suggested by Attneave (1954) and Attneave and Arnoult (1956), generated random polygons varying in their number of independent turns, this attribute bearing a logarithmic relation to amount of information transmitted (Munsinger & Kessen, 1964). These authors have been primarily concerned with the human organism’s preference for environmental complexity or variation, and with the factors that might affect it. Their theoretical formulation is based on three central tenets: (a) there is a limit upon the human organism’s capacity for processing variability; (b) this limit can be circumvented by the use of rules acquired from past experience; (c) preference is for a level of “cognitive uncertainty” which is congruent with the processing ability of a particular individual, cognitive uncertainty being the resultant of interaction between stimulus variability and the set of effective rules an individual possesses. These authors assumed that there could be little structuring of random patterns and hence that, in the case of their stimuli, cognitive uncertainty would be almost wholly ascribable to stimulus variability. An important prediction was then derived, which stated that there would be greatest preference for stimuli of intermediate variability (given a wide range of variabiiity), variability both below and above the congruent level of processing ability being rejected. Testing this prediction with adults, who were presented asymmetrical random shapes of varying numbers of turns in a paired-comparison design and asked to state which of the shapes they preferred, Munsinger and Kessen (1964) did indeed obtain a nonmonotonic function between scale values of preference and stimulus variability, but the precise nature of the function was not a simple parabola as had been predicted. Preference for 3-turn figures was as great as for 10-turn figures, preference for 5- and 6-turns (and to a lesser extent to 20-turns) was low, but preference for figures having over 20-turns was relatively high. The function relating the two variables thus seemed a higher order than a parabolic one. The authors were nevertheless concerned to demonstrate the simpler function, and did so by considering a restricted range of variability of 5- to 20-turns, on the argument that the high degree of preference for the extremes of the variability distribution “artifactually” depressed preference in the 5- and 20-turn ranges. But such an effect was hardly an artifactual one, nor was it specific to particular points in the range of that variable. Rather it was an inherent

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product of the paired-comparisons technique, where the response is a result of the properties of both stimuli being compared. The authors then proceeded to demonstrate that the high degree of preference at the low and high extremes of the variability continuum were due to structuring in terms of “good form” and meaningfulness, respectively. But this demonstration only tells us why they were preferred, and in no way alters the fact that they were preferred. The nonparabolic nature of the variability-preference function was in fact emphasized when the responses of different age groups were considered. Munsinger, Kessen, and Kessen ( 1964), repeating essentially the same experiment with different age groups of children, found a relationship which appeared to have a marked cubic component (see Fig. 1) over all age groups, and the younger children were found to prefer complex figures more than their older colleagues. Nevertheless these authors did succeed in demonstrating what appeared to be an age-invariant peak at 10-turns in the preference-variability curve. This is a surprising finding since a priori it would be expected that younger children are more limited in their processing ability than older children. In fact these

41 m2

3 4 5 6 8 10 13 16 2025 31 40 Independent turns

Fig. 1 . Scale scares of preference .far rundom shapes of wrying numbers of independent turns far grudes 2 , 4 , 8 .and young adults (from Munsinger et al., 1964).

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authors themselves provided empirical evidence in support of this when they showed that younger children were much less accurate in estimating variability than were older children and furthermore that their accuracy was reduced as variability increased (Munsinger & Kessen, 1966b). This paradox is very largely the result of the circularity of the argument relating to the construct processing ability: a limit on processing ability is both inferred from the empirically determined preference-variability function and used to explain it. Since no independent tests of processing ability are suggested it is difficult to see that it is a construct of any validity. As such its use leads to no more than a restatement of the facts, as illustrated by the following quotations: The younger children experience no differential difficulty with the 5-turn figures. However, they exhibit less ability to estimate the more variable figures accurately. The basis of such differential difficulty may be related to the suggestion made earlier (Munsinger, Kessen, and Kessen, 1964) that younger children sample figures of many turns and therefore cannot handle them nearly as well as can older children and adults [Munsinger & Kessen, 1966b. p. 251.

. . . it is our tentative conclusion that young children prefer high variability, and thus appear to be able to process high variability, largely because they select from figures of many turns that amount of variability which they can handle [Munsinger & Kessen, 1966a. pp. 177- 1781.

These workers repeatedly asserted the preference of an individual for a specific degree of cognitive uncertainty, which is a function both of stimulus variability and cognitive structure, and they emphasized the significance of such a model for theories of cognitive development as well as of curiosity and exploration. Primu fucie it is indeed a parsimonious and attractive model and we might do well to examine some of its implications as well as the empirical data adduced in support of it. It has already been mentioned that younger children were found to show a greater preference than older children, and older children than adults, for figures of many turns, a result which was contra-hypothesi. Munsinger and Kessen (1966a) accounted for this unexpected finding by assuming a difference in processing strategy between children (young ones in particular), and adults, i.e., young children tend to sample only parts of highly variable figures, whereas adults attend to the whole. They tested this interpretation by hypothesizing that in the event, young children would exhibit differential difficulty in categorization as compared with older individuals, this difficulty would be more manifest with figures of high rather than low complexity, and they would show less improvement with practice since they were responding on the basis of a part of the total figure. The results in fact revealed the predicted interaction, but the analysis failed to specify the precise nature of it. The

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younger children were poorer at this task than older children and adults but their performance on the 40-turn figures was no worse than on the 1 0-turn ones. Although the authors stressed the lack of effect of practice on improving such categorization in young children, by pointing to the similarity in scores on trials 1 and 3 for 40-turn figures, the corresponding scores for the 10-turn figures were even more similar (see Munsinger & Kessen, 1966a, Fig. 2, p. 170). Moreover, an interesting fact that emerged is that categorization of the 10-turn figures was consistently worst for all age groups. Is there a relationship, then, between inefficient processing strategy and preference? Whatever the conclusion, young children’s preference for high variability certainly could not be accounted for simply in terms of their differential attention to parts of complex figures. More recently, Munsinger and Weir (1967) claimed to have shown “preference” to be an increasing linear function of variability in 9- to 41month-old children. What they actually did demonstrate was that more variable figures were viewed longer than less variable ones. Although use of the term “preference” in this case is misleading, the departure from efforts to reiterate the curvilinearity of the relationship between “preference” and variability was significant. A number of anomalous results obtained in these studies are excused in terms of the task the subject is required to perform or the kind of strategy that may be involved, and the ad hoc nature of some of these interpretations is illustrated by the following statements: To be sure, the stimuli did vary minimally in complexity but the results indicated a preference for stimuli of intermediate complexity, and the overall preferences show that the least complex stimuli were the least preferred. This is in marked contrast to the complexity-preference function for newborns previously reported . . . and suggests that complexity was not a contributing variable in the present study [Hershenson er a/., 1965, p. 6301. Using looking time as a preference measure, [Hershenson, Munsinger, and Kessen] found evidence suggesting an inverted-U relation between complexity and preference with 10-turn figures preferred over both 5- and 20-turn figures. Since the only significant difference in preference was between 5- and 10-turn figures, however, considerable caution should be exercised in interpreting these findings as evidence for a curvilinear relationship between preference and stimulus complexity [Munsinger & Weir, 1967, p. 69, my italics].

The multiplicity of assumptions invoked to account for the various results seriously questions the validity of the theoretical constructs as well as the proposed model, and suggests that the attribute of stimulus variability may be neither the most adequate nor the most appropriate in investigating preference, exploration, curiosity, or cognitive change.

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The general equivocality of studies investigating the effects of this stimulus dimension adds strength to this dissuasive argument. Thomas (1966) sought to answer some questions arising from the ambiguous results of Munsinger and Kessen, in particular the decrease with age in preference for high Complexity. Accordingly, he used a formidable number of subjects (787), ranging from 6 to 19 years of age, and used pairs of randomly generated polygons of 3, 6, 10, 20, and 40 turns to obtain 2 measures of preference: (a) which stimulus of a pair was viewed longer when each was presented singly, and (b) which stimulus the subject said he ‘‘liked’’ better when the 2 stimuli were presented simultaneously. The first measure is not strictly a measure of pvefcrence, sincz, as Berlyne ( 1 9 5 8 ~has ) pointed out, figures with greater detail need more scanning for registration or identification. There were 4 stimuli at each complexity level. All complexity levels were paired. This first study used 5 age groups of mean ages 6, 7, 8, 9, and 12 years, although in the analysis the 3 middle groups were combined. Unfortunately, actual fixation scores were not utilized in the first measure -instead a scaled preference score was derived. “Preference” was found to be a linear function of complexity in all age groups, the 3-turn figures rating very low indeed. Interesting age effects were manifest in the differences in scaled scores for the individual members of a pair: the difference was insignificant in all pairs in the 6-year group, 6 of 10 pairs in the 7-year group were significant, as were 8 of I0 in the 12-year group. The function relating actual preference to variability was similar to that derived from viewing time -preference increased with complexity. Since the moot point is whether fixation time can be regarded as a valid indicator of preference, it is regrettable that the author did not obtain a measure of correlation between the 2 indices of preference. In his second study Thomas extended the age range to 19 years and utilized only measures of actual preference. Monotonic functions, similar to those in the first study, were obtained up to the age of 16; thereafter the function was characteristically nonmonotonic, with age-dependent shifts in the point of peak-preference: 17-year-olds preferred 20turn figures, 18-year-olds 10 turns, and 19-year-olds 6 turns. What was remarkable was that in neither of these experiments did any of the preference-variability functions resemble those obtained by Munsinger and Kessen. That this lack of agreement was not wholly accounted for b y the nature of the stimuli used (Thomas used white figures on black ground, Munsinger and Kessen vice versa) was shown by a third experiment carried out by Thomas in which he used both types of stimulus. Again he obtained very similar functions. He nevertheless did obtain a relationship approximating that of Munsinger and Kessen with a 19-year

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age group. Thomas used the transitivity of his preference scores (measured in terms of the number of circular triads) as evidence that a single dimension - complexity -was mediating the choices of his subjects. Yet the fact that he did obtain different functions for his 19-year group when he used two different types of stimuli questions this interpretation. Thomas concluded, however, that his results suggested an increasing preference for complexity until mid-adolescence, after which there was a systematic change in preference for less complex shapes. Clearly Thomas’ sanguinity regarding complexity is not shared by other workers in the field. McCall and Kagan (1967), for example, stated, “Although random shapes and checkerboards possess complexity in the information theory sense and these dimensions correlate with adult judged complexity . . . , these stimuli also vary on dimensions other than the number of turns or squares [p. 9401.” The dimension that was of primary interest to these workers was mean contour length, i.e., perimeter divided by number of sides. In a study of 4-month-old infants they used random figures of 5 - , lo-, and 20-turns, each of small, medium, or long contour. It was shown that this ordering was by no means shared by a number of other physical attributes of the stimuli. I n summary the results showed: (a) no turn-effect but a significant contour-effect upon number of visual fixations: and (b) no effects in raw scores upon either total or first fixations, but in both cases use of transformed scores revealed a contour by turns interaction which was generally unsystematic and manifested no peak at 10 turns. The authors then investigated the effect of the dimension relative perimeter on the simple grounds that this and another highly related dimension (relative area) provided a sufficient range of values to be evaluated. The function relating relative perimeter to both first and total fixations was found to be a quadratic one, which led the authors to conclude that the contour by turns interaction might more appropriately be interpreted in terms of relative perimeter. In a second study these random patterns were compared with more meaningful patterns. These latter were four achromatic pictures of human faces consisting of a regular photograph, an irregular photograph (the central features scrambled), and a regular and an irregular schematic face. The mean first fixation scores were as follows: regular photograph, 10.8; irregular photograph, 8.2; regular schematic face, 10.9; irregular schematic face, 8.1; and random shapes, 4.4. The scores for cardiac deceleration showed a similar ordering. These results suggested to the authors that by 4 months of age those events that have acquired some meaning or familiarity are more potent in attracting the child’s attention than stimuli that possess variability or complexity but are nevertheless

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unfamiliar. But this interpretation raises imponderable difficulties for those theories of exploration for which attributes like novelty, complexity, and incongruity are critical constructs. On the basis of any of these theories the pictures of scrambled features, because of their novelty, complexity, incongruity, or surprise, should have elicited more attention than the regular features. The fact that they did not suggests that meaningfulness is a neglected yet important variable. Surprisingly little attention appears to have been devoted to assessment of the extent to which apparent meaningfulness - as manifest in labeling, for instance - determines fixation and visual preference. Considering the general trend of their results, the authors were right to question the current psychological significance of the concept of complexity. Deriving hypotheses yet again from the Dember and Earl (1957) theory, Vitz ( 1966) attempted to demonstrate the curvilinearity of the preference-variability function in relation to a different type of randomly generated figure. These were random walk generated patterns as described by the author. Eight stimuli of increasing complexity were used: figures of 8, 16, 32, 64, 168, 384, 512, and 1024 steps. These figures were reproduced on 4” X 4” cards and each subject was asked to select the pattern he liked best from the pile of cards, the one he liked next, and so on until he had preferentially ranked all 8 figures. The stimuli were next presented in a paired-comparisons procedure, and the subject was asked to denote the preferred one of each pair. The response score derived from this procedure was a probability of preference, which turned out to be a parabolic function of complexity with a peak at stimulus 5 (168 steps). But this preference was very likely to have been simply an artifactual function of stimulus complexity, since the patterns differed in so many other and dominating aspects - orderliness, spread, resemblance to a pattern as such, etc. The 8 stimuli moreover did not vary in accordance with any kind of quantitative progression, rather they were selected from 12 original stimuli as representing approximately equal perceptual steps by 2 observers, thus confounding perceptual and physical variables at the outset. Vitz also failed to find an effect of previous experience upon the position of the preference-peak as tested in two ways: (a) students who had already experienced a considerable period of formal art training and also expressed a great interest in art showed no tendency to prefer more complex figures than those who both were uninterested in art and had no such training; and (b) exposure to and experience with such complexity did not shift the preference-peak toward greater complexity. Reversals in the preference curve occurred in a substantial proportion of cases, but these were dismissed as arising from “idiosyncratic,” “uncontrolled,” or “random” factors. The ad hoc

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nature of some of the explanations is exemplified in this statement: “Perceptually simple patterns may be preferred because at a more abstract or cognitive level they are quite complex [p. 1 1 11.” Finally, we may urge that some caution be exercised in the interpretation of results obtained from work on infants, particularly newborn ones. To say that a subject responds differentially is not to say how he does so nor on what basis he does so. Sackett (1963), for instance, has argued that a number of the selective visual responses in early infancy could be mediated at a peripheral level on the basis of intensity differences, and it is known that the optomotor reflex can be reliably elicited in the anencephalic, who is incapable of visual discrimination as such (Robinson, 1968). Moreover, a number of recent studies have raised pertinent methodological issues: Haynes, White, and Held ( I 965) demonstrated the young infant’s deficiency in accommodation; Salapatek (Salapatek, 1968; Salapatek & Kessen, 1966) found a tendency for infants to scan specific parts rather than the whole of a geometric figure; Wickelgren (1 967) failed to find an appreciable degree of convergence and a tendency for the right eye to fixate right portions of the visual field; and Lewis, Kagan, and Kalafat (1 966) found that several different measures of visual response were not always positively correlated. It appears that a great deal more empirical evidence is needed before we are able to specify precisely the stimulus parameters upon whose basis the infant is responding selectively. Nevertheless, the notion of the unidimensionality of visual complexity is one that dies hard. Attempts to quantify proceed apace and whether the parametric variation is done in terms of distinguishable elements (Berlyne, 1960), number of rectangles (May, 1963), number of independent turns (Munsinger & Kessen, 1964), number of different parts, their areas, and number of symmetrical axes (Terwilliger, 1963), turns, perimeter, variance of angles and “compactness” (Stenson, 1966), length of binary and ternary sequences (Payne, 1966), number of steps (Vitz, 1966), or mean contour length (McCall & Kagan, 1967), does little to reduce the ambiguity of the results. True, some kind of function may be derived to relate any one or set of these stimulus attributes to preference or to an exploratory response like viewing time, but the compatibility of these several functions may be very tenuous indeed. Can we reliably say that the preference-peaks on several differently determined variability scales are equivalent - that they are isomorphic to the degree that the same stimulus attributes determine the preference in each case? After all, Terwilliger ( 1 963) found that his painstakingly derived measure accounted for only 20% of the variance in judgments of pleasantness (and thus presumably of preference); McCall and Kagan (1967)

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found a negative correlation of .65 between number of turns and mean contour length; Clapp and Eichorn (1 965) were able to demonstrate only low and non-significant correlations between variables of congruity and redundancy; Rump ( I 968) obtained zero correlations between scores of preference for asymmetry, multiplicity, and heterogeneity of elements. Lack of agreement of this kind provoked a salutary warning from Rump: it follows that reports should specify the variable used instead of using the inappropriate concept preference-for-complexity. In addition, the use of ‘subjective complexity’ ratings to form an independent variable in studies of pattern evaluation, and perhaps also pattern discrimination, is controverted, for the ratings and their correlates would depend on the variable to which S gives most weight in his assessment [p. 3481.

c. A

COMPARISON OF

FIVE DIMENSIONS OF COMPLEXiTY

The necessity for this timely caution was underlined by some recent results of visual complexity effects obtained from young children (C. Hutt, 1969a; C. Hutt & McGrew, 1969a, 1969b). I n these experiments groups of 5-, 8-, and 1 1-year-old children were allowed to expose simple and complex patterns for themselves by pressing one of two buttons distinguished by color as discriminanda. For any one subject one color controlled all the pictures of one kind. Position preference was controlled for by changing the color to the opposite side on successive trials. The stimulus material consisted of five sets of figures representing (a) irregularity of arrangement, (b) amount of material, (c) heterogeneity of elements, (d) irregularity of shape, and (e) variability in random polygons. The first four sets each consisted of four pairs of patterns, all taken from Berlyne (1958b), one member in each pair being simpler than the other. The fifth set consisted of randomly generated figures of the kind used by Munsinger et al. (1 964); the complex members consisted of four figures each of 5 , 10, 15, and 20 independent turns and the simple members of this set consisted of symmetrical 5-, lo-, 1 5 , and 20-turn figures. On the assumption that “preference” should involve an element of choice, did such a preference exist it should manifest itself in differential responsiveness. In other words, since the two discriminanda controlled simple and complex pictures, respectively, a “preference-for-complexity” should selectively strengthen those responses upon which complexity was contingent. But in the first of these studies (C. Hutt & McGrew, 1969a) no significant differences were found in any age group in the number of simple and complex exposures. In fact, the youngest children employed a strict alternation strategy, and initially paid little attention to the stimuli appearing on the screen. This lack of selective re-

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sponse occurred despite the fact that almost all the older children were aware that the button had operated different kinds of pictures. In addition to the manipulatory measure, a measure of viewing-time for each picture was also obtained, since the subject was able to view a picture as long as he wished before pressing for the next one. The results for viewing time were unexpected: the 5-year-old children viewed the simple figures longer and the 1 1-year group vice versa (Fig. 2). There was no significant difference in viewing times of the two kinds of patterns in the 8-year group. T h e surprising reversal among the youngest subjects was largely accounted for by the fact that these children viewed those pictures they could identify or approximate to a known object, and these in general were the symmetrical and regular simple patterns. An even more surprising result emerged when the different sets of pictures were considered separately (C. Hutt & McGrew, 1969b). Viewing times for the simple and complex members within each set are plotted by age in Fig. 3. It can be seen that only in the amount-of-material set was there an unequivocal “preference” in all age groups for the more

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complex pictures. In every set the relative viewing-times were age-dependent, inasmuch as a clear increase in attention to complexity was evident only in the 1 1-year group. In this respect the %year group appeared to be at an equilibrium point of doubtful stability. From these results it was also evident that the exploration-eliciting potential of complex patterns depended to some extent on the dimension considered. Whatever attributes the amount-of-material dimension represented, the Complex members of this set consistently elicited most attention. This is of particular interest in view of the similar finding of Hoats ef al. (1963) with the same material. The failure of these authors to find a preference for Complex figures may partly be accounted for by the different effects between dimensions, at least in the younger subjects who were at the 8year level. However, Eisenman (Eisenman, 1967; Eisenman & Rappaport, 1967) has shown that college students prefer relatively simple and symmetrical figures to asymmetrical and complex ones. It will also be recalled that- Clapp and Eichorn ( 1965) found “preference” for more common than unusual objects in their subjects. In general it does appear that the young child has a preference for more orderly, regular, and symmetrical patterns, in particular for those he can label. This may be

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part of an accommodatory strategy necessary for effective assimilation of new information. D. REVIEW AND COMMENTS

In review, despite the effort expended, the concept of complexity seems as elusive as ever. It appears that we have a variety of empirical data but still lack the conceptual notation for organizing them into a harmonious and meaningful composition. Acknowledging that it is a useful short-hand term but no more, we may have to suspend, at least temporarily, the use of the term and discipline ourselves instead to specify exactly which dimension of the independent variable is being manipulated and how. Perhaps in a paper of this kind it is permissible to indulge in some general comments without the invidious obligation of specifying sources. The apparent discrepancies in this area would be appreciably reduced if authors would confine themselves to discussion of the specific parameters considered in the experimental test. Although a certain degree of generality is to be expected from research findings, hasty and premature generalizations and oversimplified conclusions can but be misleading. For example, effects of incongruity are at times interpreted in terms of “ novelty,” at others in terms of “complexity,” according to the author’s predilections. Measures of the dependent variable should be objectively rather than inferentially described, e.g., viewing time should be called just so and not termed “preference.” The tendency to treat discrete and arbitrarily selected (and varied) indices as equidistant points on a continuum is to be deplored. Finally, in an area where very small differences in response (e.g., fixation time) are often found to be statistically significant, there is much need of replication and demonstration of consistency so that such results might be deemed practically significant as well.

111. Novelty as a Determinant of Exploration Exploratory behavior is essentially stimulus selection behavior, and as such is a characteristically pervasive behavior of many young mammals. It thus has an immediate attraction for those interested in the activities of such organisms when they are not constrained, restricted, nor limited by the demands of the experimental situation. As Berlyne (1960) commented:

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Most of the standard experimental situations used by psychologists are designed to study the effects of one stimulus factor at a time; the stimulus of interest is made to predominate in determining behaviour, and the influence of other background stimuli is reduced to a minimum . . . . As soon as the experimental situation is made more complex by introducing several conspicuous stimuli at once or as soon as animals are studied in surroundings resembling their natural environments in which their receptors are inundated with an endless variety of stimuli coming from all directions. a new question arises: “To which stimulus will this animal respond’?’’ [pp. 6 & 71.

To which must be added an equally important question “And why?” A. SEPARATION OF NOVELTY A N D COMPLEXITY VARIABLES

From the studies reviewed in the previous section, however, it will be seen that despite the professed interest in exploration, curiosity, investigation, preference, and similar phenomena (which by any definition must involve a selective aspect) we have in fact confined ourselves to preisely those controlled and restrictive conditions Berlyne has described as characteristic of studies of response selection. We have become laced up in the traditional experimental psychologist’s straitjacket. Commendable though these efforts at elucidating the parameters of two-dimensional stimuli eliciting differential visual fixation may be, it has yet to be demonstrated that these same parameters are the effective ones which :licit active investigation and which result in commerce with that stimulus. It seems unlikely that such a demonstration is feasible since it is ;iiflicult to see how complexity variables could be manipulated while keeping novelty effects negligible. Even in visual patterns Eisenman : 1967) found that ratings of novelty were a linear function of degree of :omplexity. Perhaps it is for this reason that workers in the animal field have refrained from many attempts to use complexity factors as independent variables. Two notable exceptions with rats (Dember ef at., 1957; Walker & Walker, 1964) failed to reach completely concordant results, but Welker (1956a, 1956b), demonstrated greater approach toward and manipulation of the complex objects of a series in chimpantees. In the human species, too, it seems important to inquire whether many if the collative variables effective in eliciting exploration as described by Berlyne (1960) may not owe these effects to novelty. Incongruity, for :xample, is the juxtaposition of two (or more) improbable elements to ?orm a whole; this particular juxtaposition is unlikely ever to have been mcountered before and to that extent is novel. Similarly, surprisingness s nothing more than unexpectedness. These are precisely the forms of

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novelty that can be distinguished as relative novelty. Other than as two. dimensional patterns, therefore, it seems unlikely that complexity pa rameters can be manipulated independently of novelty. The admissior that the two variables may overlap to a very large degree has been im. plicit in many studies which have investigated jointly the effects of stim. ulus complexity and novelty; occasionally it has even been made ex plicit: “The difference in frequency of response to incongruous a: compared to nonincongruous pictures . . . was used as the index of pref. erence for novelty [Smock & Holt, 1962, p. 6351.” Berlyne’s complain that “novelty is all too often confused with other properties, such as change, surprisingness and incongruity [Berlyne & Parham, 1968, p 4151” is perplexing in view of the now classic model of the orienting reaction (Sokolov, 1963) which Berlyne himself has espoused. But what. ever the degree of overlap between the two variables, the notion thx complexity factors can account for novelty effects (Eisenman, 1968 could be entertained only in the case of two-dimensional patterns. The definition of stimulus complexity can be formulated simply ir terms of stimulus attributes. The definition of novelty, however, musl resort to data concerning the percipient’s experience. Novelty has reference to the individual’s past experience as well as to the total environ. mental constellation of which it characterizes a particular part. In othei words, a stimulus not encountered previously by an individual has now elty, but this novelty is reduced if it is one of an ensemble of equally novel stimuli (Berlyne et al., 1963). Conversely, the subjective novelty of a particular stimulus can increase with the familiarity of other stimul occurring at the same time (Berlyne & Parham, 1968). But whether this is equally true of stimulus objects other than two-dimensional patterns i$ yet to be ascertained. Unlike complexity, novelty is agreed to be a stimulus attribute prepo. tent in eliciting attention, orientation, and exploration. In this respect the literature appears unequivocal and any detailed review of it would be tedious. In this section, therefore, in contrast to the previous one, it is proposed to briefly mention relevant findings, but particularly so in questioning certain traditional assumptions, and to propose a classification of novelty effects, not as an alternative to Berlyne’s ( 1960) classification but as an adjunct to it. B. SOMEDEFINITIONS OF NOVELTY

Berlyne ( 1 960) has distinguished three categories of novelty along a temporal dimension: complete novelty, long-term novelty, and shortterm novelty. Two additional categories are those of absolute noveltj (when an aspect of a stimulus has not been encountered before) and rel.

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d i v e novelty (when otherwise familiar aspects of elements are combined in an unexpected manner). Whether these latter types of stimulus-change can properly be regarded as novel and thus different in kind from other, hardly distinguishable stimulus-changes involving incongruity, surprise, etc., is doubtful. These reservations increase with attempts to vary the degree of novelty of a stimulus. The most valid definition of novelty seems to be one in terms of a temporal dimension, within which complete novelty appears to have different behavioral consequences from long- and short-term novelty ( C . Hutt, 1966, 1967a). But even on this dimension a constraint upon its applicability seems desirable, namely that it should not be applied to relatively contemporaneous events, particularly if all these are ordinarily familiar and the novelty arises simply from its difference from a set-as in a sequence of tones. Such effects seem more appropriately attributable to stimulus-change, unless we accept that stimulus-change by definition is novel. In human studies, for instance, the case might be made for differentiating between short- and long-term novelty in terms of days and months. Although an attempt at such terminological precision may appear contrived, the application of colloquial terms in situations where a certain degree of specificity is implied, does lead to unnecessary confusion. The trichotomy of novelty to be proposed here is an attempt to reconcile at least some of the discrepant results in the literature in a manner that makes them biologically meaningful. It is proposed that novelty differs according to its source, and can be of three kinds: (a) object-novelty; (b) environment-novelty; and (c) conspecific-novelty, or in the human more simply stated as person-novelty. Much of the literature hitherto has confused novelty emanating from these three sources and it would be instructive to examine the more relevant animal and human results while attempting to partial out the effects due to the individual sources. This categorization of novelty is justified on several grounds: (a) there are species-specific and differential reactions to each type of novelty; (b) within a species, and particularly in the human, these reactions appear at different but nevertheless specific periods in ontogeny; (c) a good deal of empirical data already demonstrates the distinctive effects of each; and (d) the evolutionary significance of each is likely to differ according to the species. C. NOVELTYI N

A

BIOLOGICAL CONTEXT

Most theoretical formulations in psychology have erred in prematurely assuming a generality for their models that subsequent work has failed to substantiate. Those relating to exploratory behavior are no ex-

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ception. Just as Rattus norvegicus upheld or demolished a considerable body of learning theory for decades (Beach, 1950), so too was he the progenitor of exploratory theory. One of the features of this paro, chialism is that there is a tacit assumption that concepts like reward. novelty, complexity, have an equivalent valency for all species. Novelty is assumed to have similar effects upon all animals, in that moderate degrees elicit exploration and extreme degrees avoidance. And yet it woulc seem biologically nonsensical for a number of disparate species to reacl in the same way to certain situations, irrespective of their social organization, their ecology, their physical structure, and their neuromusculai organization. Laboratory rats, for example, react differently to novelty than do voles and wild rats (Barnett, 1958, 1963; Shillitoe, 1963). In an extensive study of 187 mammals and 20 reptiles, Glickman and Sroge! (1966) found very great variation in reactions to novel objects even within an order. These authors also demonstrated the differences in exploratory activities as a function of the habitat: the Colobus monkeys. for example, are tree-dwelling and leaf-eating and their exploration is predominantly visual; a Cercopethicus monkey like the baboon, in contrast, which is ground-dwelling and has to manipulate a number of obstacles like rocks and plants in searching for food, shows immediate approach toward, and very active manipulation of novel objects. From their analyses of exploratory patterns these authors concluded that “at least within an order, habitat will be a more potent predictor of quantity of response than some crude index of brain development [Glickman & Sroges, 1966, p. 1821.” Among the mammalian species, rats, macaques, baboons, chimpanzees, and humans seem generally exposed to the most varied habitats. Macaques live in geographically very distinct areas; baboons, under persistent predation from humans, have had to find new territory and food sources (Marais, 19391, chimpanzees need to obtain food from diverse sources and are able to improvise tools for some of their requirements (Lawick-Goodall, I968), and humans are the most widely distributed species of all. A measure of the success of these species is their ability to survive in such a variety of habitats. They are also notably exploratory animals. Hence it seems reasonable to suppose that their respective exploratory tendencies have conferred a distinct advantage. Man’s particular success in diversity can be ascribable to a “hypertrophy of curiosity.” It is suggested that selection pressures have acted upon man in a manner so as to favor those individuals with the greatest exploratory tendencies. Consequently we now find in man an “innate” attraction to novelty (object). To posit this, one requires only an elaborated form of the orienting reaction. In other words, it is postulated that novel objects

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elicit an orienting reaction which is immediately followed by approach and active exploration. Thus, fear of object-novelty per se, of whatever degree, would not be manifest. This will not necessarily be true of the other classes of novelty, but detailed discussion of these aspects may be suspended until experimental data have been reviewed. It would also follow that stimuli which did not elicit the orienting reaction would not elicit exploration.

D. TWO-DIMENSIONAL NOVELTY

Once again studies investigating the effects of novelty in children have predominantly used two-dimensional stimuli. Fantz ( 1964), for example, found greater visual fixation in newborn infants to novel stimuli than to familiar equivalents. Many other authors have utilized this increased attention to novelty to demonstrate habituation and sensory discrimination in various modalities in the newborn (Bartoshuk, 1962; Bridger, 1961 ; Engen, Lipsitt & Kaye, 1963). However, C. Hutt, Bernuth, Lenard, Hutt, and Prechtl ( 1968) failed to demonstrate habituation in the auditory modality, irrespective of changes of state in the newborn and found an increased reaction to a novel stimulus only if it was contemporaneous with an “upward” change of state (e.g., sleep to wakefulness). It was argued (S. J . Hutt, Lenard, & Prechtl, 1969) that in many of the studies just mentioned, the habituation and recovery effects could equally be due to spontaneous state-changes, since each state had its associated level of response (S. J. Hutt, Hutt, Lenard, Bernuth, & Muntjewerff, 1968). The failure to demonstrate habituation or response decrement in an organism that is asleep for much of its time was not particularly surprising since adults too failed to habituate during sleep (McDonald, Johnson, & Hord, 1964). But this raises the question of how workers dealing with the visual modality of the newborn keep their subjects awake sufficiently long to obtain reliable results. The difficulties incurred might account for the relatively high rejection rate of subjects in many of these experiments. Saayman, Ames, and Moffett ( 1964) demonstrated increased viewing time for a novel stimulus in 3-month-old infants, but only in cases where the stimulus differed from a familiar one in both form and color and not in cases where the difference was in one dimension. In view of some of the discriminations of which infants are reported to be capable, it is surprising that these authors failed to obtain a differential response to a color change, particularly after a familiarization period as protracted as the one they used. It is not clear whether from their results they inferred

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a failure to discriminate visual patterns on the basis of a single dimension at the age of 3 months. E. HABITUATION TO NOVELTY

There seems to be a surprising lack of agreement in results and interpretations concerning what Meyers and Cantor ( 1966) have called intrastimulus and interstimulus familiarization. The former refers to repeated presentation of the same stimulus and the latter to comparison of a new stimulus with an already familiarized one. Kagan and Lewis (1965) showed a decrement in fixation time over 4 and 5 trials, respectively, for both chromatic pictures and patterns of blinking lights. Although no significance tests were given, the practical differences, particularly in the latter set of patterns, were considerable. Similar decrements in cardiac deceleration were also demonstrated, though in the case of the pictures the graphic results appeared somewhat equivocal. The subjects of this study were 6-month-old infants, some of whom were tested again at 13 months. An inexplicable finding of this study was that infants who at 6 months showed no differential fixations with respect to three different patterns of lights (point source, row, and helix) nevertheless at 13 months showed a clear preference for the least complex pattern. Meyers and Cantor ( 1966), however, failed to find a similar decrease in fixation time with 16 presentations of the same stimulus, and more recently (Meyers & Cantor, 1967) have reported that Kagan and Lewis found “no significant decrease in the time infants spent observing either pictures or blinking lights [p. 171.” The puzzled reader can only infer that Meyers and Cantor did not regard the appreciable response decrement found by the latter authors to be statistically reliable. The failure of Meyers and Cantor ( 1967) to find any decrement in fixation time or cardiac deceleration in 6-month-old infants is nevertheless surprising, particularly in view of the results of Fantz and of Saayman et a / . with much younger subjects. However, as Meyers and Cantor pointed out, these studies used a paired-comparisons technique, in which, as mentioned earlier, fixation time is jointly determined by both stimuli- in other words it is a result of a comparison of the two patterns. But if no alternative sources of patterned stimulation are available in the case of the single presentation, it is unlikely that the infant will look elsewhere than at the stimulus. It is a pity that Meyers and Cantor did not provide a measure of response recovery to the non-familiarized stimulus in their test phase, since Lewis et a / . (1966) failed to demonstrate any increase in viewing time when infants between 3 and 18 months of age were presented with a different pattern after four or five exposures to another. It

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is likely that this lack of response recovery was due to the nature of the stimulus patterns since they were positional variants of a blinking light. With 3 %-year-old children and using pictures, Lewis, Goldberg, and Rausch ( 1967) and Lewis and Goldberg ( 1969) were able to demonstrate both decrement in fixation with repeated exposure, and increase in fixation when the picture was changed. J. H. Cantor and Cantor (l964a, 1964b, 1966) found that 3- to 5-year-old children viewed color cartoon pictures as well as black and white drawings that were novel longer than familiar ones and irrespective of the delay between familiarization and testing. An interesting finding was that a larger degree of familiarization resulted in a larger difference between viewing times for the novel and familiar stimuli, supporting the argument that the response resulting from a comparison technique is a function of both stimuli that are compared. F . SOURCES OF NOVELTY

Considering the significance of novelty in determining orienting, attention, and exploration, it is regrettable that studies of curiosity and exploration in young children are so few. Most young mammals, and primates in particular, acquire information about their environment through their exploratory activities. Curiosity in the human infant and child are only too characteristically manifest, as any caretaker will vouch, and yet we know relatively little about what stimulus attributes make a child direct his attention to one object from a host of possible alternatives, how he explores it, how effectively he processes the information (Fraser, 1966), and when he becomes satiated with it. Although much is known about the properties of random polygons that determine visual attention and preference, a similar knowledge of the effective parameters of commonplace and manipulatable objects is sadly lacking. The revolution in pedagogic theory in recent years, which has resulted in the substitution of “exploratory learning” for “teaching,” appears to have had little impact on the study of the basic motivational and cognitive processes of their subjects. I . Object-Novelty

a. lnfrahuman primate studies. Harlow and his colleagues showed that monkeys would readily manipulate puzzle-devices introduced into their cages and incidentally solve problems (Harlow, 1950; Harlow, Blazek, & McClearn, 1956; Harlow, Harlow, & Meyer, 1950) or learn a discriminant response (Harlow & McClearn, 1954). Carr and Brown (1959a, 1959b, 1 9 5 9 ~ similarly ) found approach and manipulation of objects of

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different materials by rhesus monkeys which waned after a period oi exposure to these objects. Mason, Harlow, and Rueping (1959) found that manipulation of a number of objects by infant monkeys increased steadily over the first few weeks of life, and they attributed this to maturational or reinforcement effects. Welker ( 1956b, 19.56~)demonstrated increased responsiveness to novel objects in chimpanzees, this responsiveness also decreasing with time. The chimpanzees showed “preferences” for those stimulus objects upon which their manipulations could effect changes and for those objects left inside as opposed to outside their cages: these animals also manipulated a heterogeneous set of objects more than an equivalent hut homogeneous set. Of these workers. only Welker ( I 956a) described a fear reaction to novelty: 1- to 2-yearold chimpanzees showed initial withdrawal or caution whereas 3- to 4year-olds approached and manipulated readily. I t is not clear whether this fear is specific to this age in most infrahuman primates. Certainly Glickman and Sroges found evidence of fear in only 19 out of 100 adult primates and in many of these cases the fear was due to idiosyncratic features of the object (e.g., to rope but not to block) or of the animal. Na evidence of age-specific fear reactions was observed in the subadult animals. b. Human studies. A human infant of 7 months was shown to grasp and manipulate novel objects with alacrity (Hutt, 1967a). In this case the object was presented to the child by a familiar adult; no signs of fear or caution were observed. The stimulus objects in this study were those which were completely novel, i.e., the child had not encountered them previously in his life. Attention spans were found to decrease with repeated presentation of an object, and reciprocally the frequency with which the child dropped the object increased. During any particular session the frequency of toy-dropping (of equally familiar toys) generally increased from beginning to end, but this trend was dramatically inhibited by the presentation of a new toy (Fig. 4). In a comparison of the social and exploratory responses of first-born children with later-born ones, Collard ( 1968) used 9- to 13-month-old infants; she found manipulatory latencies to be far greater in the firstborn than in the later-born. The first borns also appeared to be generally more inhibited in their exploration of the toy. But, as Collard has very nicely demonstrated, these children were also more wary of the stranger and manifested more negative reactions toward her, although they engaged in as much play and interaction with their mothers as the laterborns did. Hence, the first-born’s inhibition of exploration was more likely to have been due to fear-of-the-stranger (from whom he was required to take the toy) than fear-of-the-object.

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Mendel (1 965) familiarized kindergarten children on certain toys and then offered them a selection from sets containing different proportions of novel toys, on the assumption that an individual would prefer optimally an intermediate degree of novelty. The children showed a clear preference for the set offering 100% novelty. Harris ( I 965) found that young children when familiarized on one or two toys would subsequently show a preference for a novel toy even if it was damaged and for a novel toy over two familiar ones. In an investigation of developmental patterns in the exploration of a novel object, Schaffer and Parry (1969) compared 6- and 12-month-old infants. The subjects were presented with a “nonsense” object which was made out of plastic and which therefore had complete novelty for them. This object was presented on 7 successive 30-second trials, with intertrial intervals of 30 seconds. On the eighth trial a similar-shaped object, but of different colors, was presented, and on the ninth trial the original object was presented again. The objects were moved toward the subject on a mobile tray from behind a screen which occluded any view of the experimenters or observers. A familiar adult sat behind the sub-

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ject. The results for the two chief measures - total fixation and manipulative latency-are shown in Fig. 5 . The 6- and 12-month-old infants showed a very similar visual pattern, decrease in fixation with repeated exposure and increased fixation on appearance of the novel object. The two age-groups diverged, however, on the manipulation measure, the older group showing a considerable delay in grasping and handling the new object at first but doing so more readily thereafter. The younger group showed no such hesitation. The authors interpreted the behavior of the younger children in terms of a failure of perceptual recognition to exert control over overt action: “these infants registered the information received in terms of familiarity-unfamiliarity but did not act accordingly [p. 961.” But such an interpretation follows only on the assumption that there must be an avoidance of novelty. The “indiscriminate approach behavior” becomes simply approach-of-novelty if the hypothesis proposed earlier (of an innate attraction-to-novel-objects) is accepted. How then can the latency of the older group upon initial presentation of the object be explained? It was very likely to have been due to the experimental procedure, whereby the object moved forward toward the subject without the aid of a detectable agent. This would be a disconcerting procedure for a 12-month infant whose body of experience, and hence expectations, considerably exceeds that of the 6-month old. Moreover, other primates like monkeys have been shown to manifest persistent fear reactions to stimuli which apparently loomed at them (Schiff, Caviness, & Gibson, 1962). The latency of the older children is thus more likely to

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be a function of the manner of stimulus presentation than of the novelty of the object per se. The fact that after adaptation to the first object, the appearance of another novel object did not cause an increase in approach latency supports this interpretation, although SchaRer himself (personal communication) does not regard his method of presentation as comparable with “looming.” Exploration of a completely novel object by 3- to 5-year-old children was studied utilizing a procedure which permitted access to familiar alternative toys (Hutt, 1966). The subjects were familiarized with the playroom, which contained five commercially available toys. The novel object (see Fig. 8) was designed to allow one of several different kinds of feedback to be contingent upon manipulations of the lever: i. ii. iii. iv. v.

none -other than tactile simple visual -counters, which registered manipulations, exposed buzzer contingent upon two of the four manipulations sound -bell sound simple visual - bell and buzzer, and counters exposed complex visual-orange and green lights contingent upon 2 of the 4 manipulations vi. sound complex visual -(iii) and (v) combined.

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The terms “simple visual” and “complex visual” refer largely to the relative heterogeneity involved. Each child was individually familiarized with the playroom and other toys in two preexposure sessions. Then followed six experimental sessions of 10 minutes each at 48 hour intervals, on the first of which the novel toy had been introduced into the playroom. Cine recordings of the children’s behavior enabled a detailed analysis to be made of their approach and investigatory responses, their process of habituation to novelty, and any response classes that might be manifested. The different kinds of incentive had marked effects upon the level of manipulatory response (Fig. 6). Condition (vi) did not differ at all from Condition (iv) and hence is not illustrated in the graph. Despite the fact that the counters changed upon each manipulation, the incentive value was inadequate to maintain responsiveness. Lights and sounds were both effective in maintaining response but the sounds together with the counters were most effective. Nevertheless, all these curves reflected a response decrement in the sixth session. In this study, where practical considerations necessitated the presence of the observer in the same room as the child, it was found that the latency of approach toward the novel object was considerably less than if the child was alone in the room (Hutt, 1966). The results were interpreted in terms of the “fear of novelty” being reduced in the presence of

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Fig. 6 . Cumulative respcjnse curves obtained during exploration of a novel toy providing different incentives.

the adult. This, however, might not have been the most appropriate interpretation since there had been a difference in the degree of familiarity of the environment for the two groups, the room producing the shorter latency being more familiar to that group since it was often encountered outside the experimental situation as well. A subsequent experiment (unpublished) was thus carried out to test the relative validity of these interpretations. If response latency was due to fear-of-novelty, then the greater the novelty the greater the latency to be expected. Three groups of children were allowed to play in the same situation as already described (a) twice in the presence of the novel toy, (b) once in the presence of the novel toy, the preceding session being only with the other toys, or (c) twice with all the other toys except the novel one. Two weeks later they were tested with the same experimental design as be-

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fore. The mean latencies of approach were: (a) 45.6 seconds (SD 16.2), (b) 28.1 seconds (SD 12.41, (c) 12.8 seconds (SD 9.5). I n fact the results were entirely contrary to prediction, thus indicating that the more novel the object the more readily it was investigated. This suggested that the earlier finding was in fact partly due to the confounding of differences in environment-novelty for the two groups. There were of course signs of apprehension in certain children but these were peculiar to specific individuals rather than to particular points in the temporal course of exploration. Berlyne’s ( 1 955, 1960) prediction that exploration should wane with continued exposure to a novel stimulus was fulfilled only under Conditions (i) and (ii) in this series of experiments. When sound and light changes were made contingent upon manipulation, responsiveness continued to increase until the fifth session. That this unpredicted result was largely a matter of response definition and could still be encompassed within the terms of Berlyne’s theory will be demonstrated in a subsequent section. In an area where there seems to be a consensus of evidence that infants and children attend to and prefer novel stimuli more than familiar equivalents, a discordant result strikes a cautionary note. This result stems from an experiment carried out by Hunt and Uzgiris and described by Hunt (1965) in which infants were found to prefer mobiles with which they had previously been familiarized to novel ones. The infants were 4 weeks old a t the start of the familiarization period and at the time of testing they were 8 to 9 weeks old. Preference was evaluated in terms of differential fixation. The fact that preferential response for three-dimensional novelty could not be demonstrated at an age when that for two-dimensional novelty is manifest (Fantz, 1964), is disconcerting since more salient cues would have been available in the former situation. Whether infants younger than the age of three months can reliably discriminate novel features of their environment is clearly still a vexed question, Hunt explained the preference for familiarity in his study in terms of an ontogenetic phase in infancy characterized by attraction to recognitive familiurity. 2. Environment-Novelty a. Rat studies. Many of the studies of exploration in the rat have actually been concerned with environment-novelty. Changes of mazes o r maze arms involve relatively nonspecific alterations in the animal’s total available environment. The evidence in general does seem to support the notion that there is some initial fear of a completely new environ-

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ment, particularly if it happens to be an elevated maze. That it is imperative to clarify concepts and terminology in this area is no more clearly illustrated than in the interpretations of results obtained by A. B. Sheldon (1968). In these experiments, rats were put in a strange, and elevated Y-maze and offered the choice of an object with which they were already familiar ur of a novel object. The rats predominantly chose the familiar as opposed to the novel object and this preference increased with the degree of familiarity, In other words, where both visual and olfactory cues were familiar, preference was greater than when only one set of familiar cues was available. These results were interpreted in terms of a positive motivation toward familiarity, which was independent of a fear of novelty, and were seen (mistakenly) as support for Hunt’s ( I 965) postulation that, under certain conditions, familiarity elicits approach. Sheldon’s explanation, however, was no more than a redescription of her empirical evidence since she failed to specify the precise conditions under which the behavior was likely to recur or to indicate the mechanism whereby such a preference would be mediated and for which independent evidence might be obtained. An interpretation more consonant with a greater body of evidence would be that the experimental situation was one generative of fear (strange environment plus raised maze), and thus of increased arousal, which is precisely that state in which an animal is known to prefer familiar to novel objects (see Section 111,G). In a more recent paper (A. B. Sheldon, 1969) very similar results were attributed to the effects of “degrees-of-novelty,” since it was found that with adaptation to the unfamiliar environment the novel objects themselves became increasingly preferred. But this still leaves the additive nature of novelty (irrespective of source) to be demonstrated; a more parsimonious interpretation of all Sheldon’s results is simply that environment-novelty inhibits exploration in the laboratory rat. b. Primate studies. The literature is less explicit with respect to primates - human and infrahuman. Perhaps the earliest systematic account of children’s reactions to an unfamiliar environment is that given by Arsenian ( 1943), although it is a commonplace observation that children are extraordinarily distressed by a new environment unless reassured by an adult. Arsenian’s subjects were 24 children between 1 and 24 years of age. Sixteen of these children were introduced to a novel situation (room with toys) by themselves, and 8 were accompanied by their mothers or substitutes. The children who were exposed to the strange situation alone exhibited intense distress reactions- crying, screaming, attempts to escape, autistic gestures-which showed some abatement only after 4

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or 5 trials. Their approaches to the toys at this time were characterized by conflict. The children accompanied by their mothers also manifested some emotional behavior initially but this disappeared almost completely after the fourth trial. In general this group’s behavior consisted mainly of “adaptive” reactions such as play, locomotion, and talk. The departure of the mother on the sixth trial caused distress reactions in some, but not all subjects. Cox and Campbell (1968) investigated the effect of the mother’s temporary departure from an unfamiliar situation upon the behavior of 1 year and 2- to 3-year-old children. During a 12-minute exposure to a strange situation, the mother remained with the child during the first 4 minutes, left the room for 4 minutes, and returned to it for the final 4 minutes. Mothers of the control group remained with their children throughout the 12-minute period. There was a pronounced decrease in play activity, general movement, and talking in both older and younger children of the experimental group; the majority of the younger children also cried throughout the period the mother was away, whereas none of those in the control group uttered distress vocalizations. In the l-yearold children return of the mother resulted in only a partial recovery of their earlier activities. Unfortunately, much information that might have been of greater significance than rigorous statistical comparisons between control and experimental groups does not appear to have been obtained in this study. For example, what were the reactions of the children on initial exposure to the new situation? Did the reactions of the older children differ from the younger? How did they react to the return of the mother since they showed less interest in their former activities? In this experimental design, the effects of environment-novelty may well have been confounded with those of “separation-anxiety”: while, in such a situation, the distinction may be largely a semantic one, this remains to be demonstrated. Rosenthal ( 1967) investigated the frequency of two forms of dependency behavior- attention-seeking and proximity-seeking- when 3- to 5-year-old children were exposed to a novel situation with their mothers or mother-substitutes. She found that in a situation which was deliberately designed to be anxiety-provoking, proximity-seeking increased over a 30-minute period. More significant still was the finding that even in a pleasant playroom, not designed to evoke any anxiety, proximityseeking did not decrease over the 30-minute period, thus indicating that despite the presence of mother or substitute the new situation was evocative of anxiety. In an investigation of the “fear of visual novelty,” Bronson (1970) concerned himself with children’s reactions to strange situations and

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strange adults. Various response categories relating to “sensitivity,” “shyness,” and “fear” were sampled from 1 month to 84 years of age in 30 boys and 30 girls. The sampling was more frequent at the earlier ages. It was found that in boys, precocity in fear of strangeness (i.e., first manifest at 4 to 6 months) was highly predictive of increased fearfulness and shyness up to early school years. The possibility that this early onset and increased intensity of fear were due to a general hypersensitivity was eliminated. The girls, however, were not found to show this continuity in fear and shyness with age: in their case an early expression of fear of novelty was indeed due to a general hyperexcitability, i.e., they tended to cry when confronted with novelty, but also cried in many other situations. Unfortunately, Bronson did not specify the kind of novelty he was considering and has tended to regard visual novelty as a uniform category ( 1968a, 1968b). This seems unwarranted, particularly in view of his earlier statements, that “Strange persons produce the earliest fear reactions reported for human subjects,” and again . . . for most infants a fear of strange persons appears at around 7-9 months of age. Experimental studies of fear reactions to novel situations or strange objects during this age range have not been found, but anecdotal evidence suggests that such reactions develop along with fear of strange persons [Bronson, 1968a, pp. 4 10 & 4 1 1 , respectively].” Regrettably, anecdotal evidence can be adduced in support of any position. The most systematic and detailed account of infant reaction to environment-novelty has recently been given by Rheingold (1969). She seems to have been the only worker to have isolated the effects of environment-novelty from other kinds of novelty and related effects. In an elegant study she systematically investigated the effects of a simple but novel environment on the child alone and with its mother, and the modification of these effects by the introduction of toys and of a stranger. The subjects of her study were 10 infants approximately 10 months of age. Her results showed quite unequivocally that exposure to a novel environment caused great distress to the child and almost wholly inhibited any exploratory activity. The presence of attractive toys and of a stranger in that environment did little to ameliorate the child’s distress or encourage exploration. I n contrast, those infants first exposed to this strange situation in the presence of their mothers showed no distress and explored fairly freely. A most interesting fact that emerged concerned the persistent effects of this fear-of-novelty: those infants who had initially been exposed to the situation alone continued to show some distress reactions and inhibition of exploratory activity even when their mothers were subsequently present and despite the fact that they had spent some time in the room, in contrast to those infants who were initially exposed to the strange situation with their mothers. In other “

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words, the fear of environment-novelty appears to have been so intense that it had a proactive effect on a potentially unalarming situation. This fear was minimized by the presence of the mother or substitute. Rheingold is to be congratulated on her timely clarification of a confused issue by her diligent separation of effects attributable to different agents. 3. Conspecijic-Novelty Conspecific-novelty will not be considered here in any detail since, due to its peripheral relevance to exploratory behavior as such, it does not fall properly within the terms of reference of this paper. Nevertheless it must be emphasized that in humans it is the most dramatic form of fearof-novelty. Recognition of pattern or object novelty has been demonstrated in the first few weeks of life (see Section III,F,I). It thus antecedes by a considerable interval the recognition of strangers at approximately 4 months (Ambrose, 1961; Polak, Emde, & Spitz, 1964). Nevertheless, while there seems to be no fear of novel patterns or objects, fear of strangers, as Bronson remarked, is one of the earliest manifest fear reactions, appearing between 7 and 9 months of age (Freedman, 1961 ; Morgan & Ricciuti, 1969; Schaffer & Emerson, 1964; Spitz, 1950; Tennes & Lampl, 1964). Conspecific-novelty, certainly for the human, clearly has a very special significance, being dependent as it is on the formation of adequate affectional bonds. G. WHAT Is FEAR OF NOVELTY?

A number of theories of exploratory behavior assume that novelty evokes both approach and investigation as well as fear (e.g., Berlyne, 1960, 1964; Fowler, 1965; McReynolds, 1962). To avoid difficulties arising from this obvious contradiction, the qualification is generally made that only extreme or intense degrees of novelty evoke avoidance, moderate degrees evoking ambivalence and eventually approach. The lack of independent measures of degree-of-novelty, apart from the behavior under investigation, makes this a particularly unprofitable tautology. More recently the intimate relation between fear and exploration has been emphasized to the extent of providing a fear-motivated basis for exploration (Halliday, 1966; Lester, 1967, 1968). This theoretical formulation states that mild increases in fear enhance exploratory activities while high levels of fear result in avoidance. Tests of this theory, however, are largely based on the extent of locomotor activity in elevated mazes, which appear to present the rat with a very special problem since on a n y raised platform the animal looks for an opportunity to step down. Therefore the results might simply mean that the animals are searching

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more actively for a way out. Moreover, as M. H. Sheldon (1968) has pointed out, to demonstrate that some experimental manipulation has affected locomotor activity is not to show that it has affected exploration directed toward specific environmental features. Where Halliday succeeded in demonstrating greater exploration of the complex arm of a maze by shocked than nonshocked rats, this arm also happened to be the more familiar of the alternatives since the experimental animals had been shocked in a similarly patterned box. Thus, a formidable array of evidence demonstrates that only in those cases where arousal level has been experimentally altered (by administration of stimulant drugs, electric shock, or noise) do the animals choose to explore the less novel alternatives presented (Thompson & Higgins, 1958; Berlyne, Koenig, & Hirota, 1966; Haywood & Wachs, 1967; A. B. Sheldon, 1968, 1969; Thompson & Higgins, 1958). Haywood and Wachs, furthermore, emphasized that their results showed a reduction in novelty-preference rather than novelty-avoidance. Thus, the already slender evidence adduced in support of fear-motivated exploration becomes very tenuous indeed when appropriate measures of exploration are considered. This raises a further thorny problem, that of adequate measures of exploratory activity. In general, locomotor activity is used as the principal measure of exploration, though studies which have used multiple measures have not found locomotion to correlate highly with others like sniffing (Bindra & Spinner, 1958; Goodrick, 1966). Very few of the studies on rats have maintained their experimental situation in such a manner as to allow the separation of object-novelty and environmentnovelty effects. That it is important to do so is suggested by the fact that the domesticated rat, for instance, shows no fear or avoidance of novel objects, while under other conditions it may well show an increased latency to explore a new situation. Apart from elevated mazes, to what degree novelty evokes fear in rats is still an open question. In the case of monkeys and chimpanzees the inevitable examples offered, of fear evoked by intense novelty, are the almost hysterical reactions released by the sight of an anesthetized chimpanzee, a snake, or a model of a monkey head (Hebb, 1946). It is indeed debatable whether these stimuli a priori are novel, but more pertinent perhaps is the fact that these reactions are very specific to these particular stimuli. In other words, it is their biological significance rather than their novelty that results in the negative reaction. More important, Butler (1964), using stimuli similar to those discussed by Hebb (snake, rubber coil, anesthetized monkey, etc.) found that they did not in any way suppress an instrumental response upon which they were contingent. The monkeys’ exploratory behavior was no more diminished by these supposedly fear-

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provoking stimuli than by others. Similar results were reported by Wolin, Ordy, and Dillman (1963). A comparable and often cited example in humans is the finding by Buhler and her colleagues and described by Berlyne (1960, p. 176) that children showed more fear and distress to partially “novel” stimuli - like a distorted voice emanating from a familiar face or a mask covering the face of a person who was talking in his familiar voice - than to completely novel stimuli -like the distorted voice, or the mask alone. This finding. suggests that it was the violation of a strong and emotive expectancy which resulted in fear. Often, extraneous parameters of the experimental situation, e.g., sudden movement or gross distortion of the familiar (as just described), may evoke avoidance, but these effects must be distinguished from the effects of novelty per se, since they introduce a qualitative rather than a quantitative change. In other words, we should be clear whether we are attributing novelty effects to the stimulus presented, to the mode of presentation, or to an interaction of the two. When unconfounded with the effects of environment- and/or strangernovelty, the effect of object-novelty appears to be to elicit approach and investigation. Although the evidence from rats and, to a certain extent, from monkeys and chimpanzees, seems less supportive than the data for humans, it is likely that selection pressures acting differentially on species will militate against uniform reactions to particular attributes of stimuli. Certainly in humans there is no reliable empirical evidence which supports the notion of fear of novelty in any substantial sense. Where a deliberate attempt has been made to create novel but fear- or anxiety-provoking pictures, children manifested not aversion but greater visual exploration (Faw & Nunnally, 1968). Degree of novelty has not been defined adequately nor has it been shown to have systematic effects. A reduction in preference-for-novelty has been demonstrated in cases where the internal parameters (the state) of the animal were experimentally increased by stimulant drugs (e.g., Berlyne et al., 1966; Stretch, 1963) and in autistic children (C. Hutt, 1969b; S. J. Hutt & Hutt, 1968) in whom, it is suggested, the level of arousal is abnormally and chronically high. Moreover, the precise extent of this internal change may be important in view of Gilmore’s (1966) demonstration that while “anxious” children approached novel toys as readily as non-anxious children, “very anxious” children did not.

H. THEAPPROACH-AVOIDANCE CONFLICT

Few conceptualizations in this area have been able to specify what

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motivates or energizes the animal when he proceeds to encounter new and complex stimuli. If these stimuli really were fear-arousing, would not the most adaptive response be flight and avoidance of further encounter with them? Otherwise, it has to be postulated that an animal will continue to approach a novel object despite the progressive increase in fear as it approaches, it being axiomatic that the gradient of fear becomes steeper with approach. To circumvent this impasse, Berlyne (1 960, 1964, 1966) has used the construct curiosity: “the condition of discomfort, due to inadequate information, that motivates specific exploration is what we call ‘curiosity’ [ 1966, p. 251,” or again, “novel stimulation, either directly or by producing uncertainty and conflict, occasions a rise in arousal (drive) which corresponds to what everyday parlance calls ‘curiosity’ [ 1964, p. 241.” Although the first definition seems satisfactory, the second, which exemplifies Berlyne’s more commonly expressed theoretical position, causes some difficulty, as does his more general statement: “what underlies all the collative properties and gives them their common motivational effects is conflict, by which we mean a condition in which incompatible, mutually interfering patterns of behavior are simultaneously mobilized [ 1964, p. 231.” Whatever these several response tendencies may be, it is difficult to see why they should not possess some commonality unless they are conceived of as resolving around a bipolar approach-avoidance axis. In most cases of ambivalence the situation can be resolved by manipulation of some variable which will reduce (or increase) one of the competing motivational systems. In the exploratory antithesis, however, this is impossible since the very features of the stimulus that are supposed to evoke avoidance (fear) are those that elicit approach (investigation), so that prolonged exposure to the novel object is likely to reduce fear but due to reduction of “novelty” it is also likely to reduce exploration. In summary, several points may be made: (a) there is no evidence of fear of object-novelty per se in humans, despite a very early recognition of it in ontogeny. Rather, object-novelty appears to be maximally effective in releasing exploratory responses, but this potency also wanes relatively quickly upon repeated exposure; (b) There is no clear evidence of when environment-novelty can first be recognized, but certainly fear of it is manifest at the age of 10 months, and it also effectively inhibits exploration. These effects can be minimized by the presence of a “security base” though the negative reactions show some resistance to habituation. (c) Conspecific novelty is recognized relatively late in ontogeny but evokes fear early; its effects are primarily of an emotional nature and its influence on exploration is indirect but nevertheless inhibitory.

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Specific and Diversive Activities A. CURIOSITY A N D BOREDOMTHEORIES

In his admirable review of the subject, Fowler (1965) has described the historical and conceptual development of formulations in the domain of exploratory behavior. Proceeding from the stage where exploration was “the behavior without a definition,” we have reached a point where both increasing specificity in conceptualization and increasing generality in terms of empirical findings are possible. As Fowler has said: Collectively, the early studies on exploration achieved two ends: first, through the variety of measures and test procedures that they employed, the general and initially vague term of exploration was given specific reference to such behaviours as orienting or locomoting toward. investigating, sniffing, and manipulating particular objects or patterns; secondly, the findings of these studies demonstrated that an animal would explore a stimulus object or pattern to the extent that it was novel, unfamiliar, complex, or provided a change in the animal’s present or recent pattern of stimulation. These findings are not limited in their generality by the fact that the specific investigations used visual forms of stimulation primarily or dealt with rats as subjects [Fowler, 1965, p. 281.

Perhaps this optimism is somewhat premature. To what degree the second end has been achieved has already been questioned. That the first question is far from resolved is illustrated by the frequency with which exploration and play are either confused with each other or identified with each other. For example, in his earlier series of papers Welker (1 956a, 1956b, 1 9 5 6 ~made ) no attempt to draw any distinction between the two categories. In a later review, acknowledging that “the term play is often used in conjunction with, or in place of, the term exploration,” and that “in some cases, no differentiation is made between play and exploration [ 1961, p. 2221,’’ h e nevertheless did attempt to categorize the two behaviors descriptively. Not so Hayes (1958), Thorpe (1963), Marler and Hamilton ( 1966), nor Burgers ( 1966). The failure to record, identify, and classify these behavior categories accurately has resulted in unnecessary conceptual disarray, since similar determinants and functions are ascribed to both. This confusion is particularly surprising in view of Berlyne’s ( 1960) effort to distinguish between specijic and diversive exploration. But the point failed to be taken even after his subsequent exposition upon the subject (Berlyne, 1966), as illustrated by a reply which emphasized “play” as a predominant method for processing information (Burgers, 1966). Fowler ( 1965) described two groups of theories which are in apparent

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antithesis, namely the “curiosity” group and the “boredom” group. The protagonists of the “curiosity” group are notably Berlyne (whose original statement was made in 1950), Montgomery (1951, 1953) and Harlow (1950, 1953). T o oversimplify, this group postulated that novel stimuli would evoke an exploratory drive, the strength of which would wane with continued exposure to the stimulus. In contrast, the “boredom” theorists (e.g., Glanzer, 1953; Myers & Miller, 1954) proposed that continued exposure to the same stimuli would result in satiation to these stimuli (boredom) and subjects would consequently attend to or explore any change in the stimulus configuration. Fowler conceded that aspects of both these theories might be applicable, presumably to the same set of empirical data. But the difference in emphases of the two theories does in fact generate rather different predictions: in terms of the “curiosity” theory, strength of exploratory drive and hence response strength should be a direct function of the novelty, complexity, etc., of the stimulus, degree of familiarity of the rest of the situation having little effect; on the basis of the “boredom” theory, exploratory strength would be primarily a function of the familiarity of the situation and relatively little of the degree of stimulus change provided it was a stimulus change. These predictions are being tested by investigating the responses of groups of children who are familiarized to different degrees with a situation and are then exposed to objects of greater and lesser novelty. Irrespective of the result, it seems that both these theories are valid insofar as they apply to different sets of antecedent conditions. This distinction will become more apparent if we consider results pertaining to the temporal course of exploration. Certain workers have predicted, and many more have demonstrated, a progressive decrement in exploratory activity with continued exposure to the source of stimulation. This decrement has been interpreted severally in terms of Hullian principles of response inhibition (Berlyne, 1950, 1955), in terms of stimulus satiation (Glanzer, 1958), and in terms of decrease in drive strength (Montgomery, 1953). Workers from the Wisconsin Laboratory, however, emphasized the prepotency of exploration and “curiosity drive” in interpreting the persistent and nondecremental temporal pattern of exploratory activities (Butler & Alexander, 1955; Butler & Harlow, 1954; Harlow et al., 1956). The interpretation of the latter set of results needs some qualification in view of the nature of the experimental situation utilized. In these studies the animals were typically restrained in small bare cages with no alternative source of stimulation. Thus, the character of the response elicited is vastly different-in the case of the “curiosity” studies it is a consummatory response to a stimulus change: in the “boredom” studies it is an instrumental response for a stimulus change (Fowler, 1965). Confusion is worse confounded by the frequent failure

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to describe accurately the subjects’ responses-we are more often told how much the animal did rather than what he did. For example, in the Butler and Harlow study the monkey was said to be visually exploring when the trap door was held open for relatively long periods of time. Symmes ( 1959), however, reported that in a similar situation, the monkeys “very commonly sat near the door holding it open with one hand, and moving it against the spring resistance, and only occasionally turning to look through the opening.” The animals continued to do this even if there was complete darkness outside the door. Monkeys free to operate two levers at either end of a room, only one of which brought on sound reinforcement, were found to rush across the room to press one lever while the sound for the other was actually on (Butler, 1957), and monkeys will on occasion open the door but look toward the rear of the cage (Butler, 1965). Thus, there is no equivalence in the responses, qua responses, of the “curious” animals and the “boredom-alleviating” animals. Apart from differences in antecedent conditions, we are also concerned in the one case (specific) with those stimulus attributes that elicit attention and in the other (diversive) with those attributes that maintain attention, and they are very unlikely to be the same. Many workers have shown that stimulus changes that are made contingent upon such instrumental responses are able to reinforce them (Barnes & Kish, 196 1 ; Butler, 1953, 1954, 1957; Harlow & McClearn, 1954; Kish & Antonitis, 1956; Moon & Lodahl, 1956), but whereas specific exploration is greater the greater the stimulus change, instrumental responses seem best reinforced by moderate stimulus changes (see Fowler, 1965; Leuba & Friedlander, 1968). Audio-visual incentives were shown to differentially increase the responsiveness of human infants (Rheingold, Stanley, & Doyle, 1964; Friedlander, McCarthy, & Soforenko, 1967). But even here, apparently the investigative or specific exploratory activities could be distinguished from the responses-for-change. Leuba and Friedlander, for example, drew attention to the fact that during the first three trials, both manipulanda were more or less equally responded to, although the audiovisual feedback was contingent upon only one. Furthermore, as the studies of Kagan and Lewis (1965) and Friedlander (1965) showed, the stimulus attributes that are able to maintain selective attention are not necessarily as effective in eliciting it.

B. INVESTIGATIONA N D PLAY

In the study of exploration in young children already mentioned (C. Hutt, 1966), one of the hypotheses tested was that the nondecremental

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temporal pattern of response upon repeated exposure was largely a function of the properties of the experimental situation, in which case provision of alternative sources of stimulation should result in a decline in exploration even though specific stimulus changes were made contingent upon the exploratory responses. In fact, under certain conditions [(i) and (ii), as described in Section 111, F, 1, b] this hypothesis was borne out. The failure to find support for the hypothesis when sound or light incentives were available was only apparent, since it was dependent upon the level of response classification used. Two morphologically distinct behavioral categories were delineated (from detailed analysis of cine records) and the functions relating these categories to time were by no means similar. The easier behavioral category to designate, because of its largely stereotypic character, was “investigation;” the other category consisted of a variety of responses which most observers would commonly class as “play.” As no satisfactory definition of play is available, in the context of the argument to be developed here, the use of this term might seem to beg the question, but it is emphasized that it is used merely as a convenient shorthand. Typical patterns of investigation and play are illustrated in Figs. 7 and 8.

Fig. 7 . Characteristic investigatory response.

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Fig. 8. Posture and expression characteristic of "play."

The patterns of overall response toward a novel object under four different incentive conditions [(i), (ii), (iii), (iv)] are shown in Fig. 9. Exploration showed an exponential decline with time under the simple incentive conditions; when auditory feedback was available, exploration manifested a nonmonotonic increase with time. I n the first two of these conditions, playful activities hardly occurred at all. When the two behavior categories were considered separately, the pattern changed markedly. While investigation or specific exploration showed a nonmonotonic linear decrease with time, playful responses were essentially a quadratic function of time. Thus, there were clearly two separable decremental processes - one attributable to response inhibition and the other to stimulus satiation. Nevertheless, R. F. Thompson and Spencer ( 1966) argued that the contradictions between predictions derived from stimulus satiation theory and those derived from response-inhibition theory were more apparent than real, and concluded that "insofar as behavioural responses are concerned, the formal properties of stimulus satiation and response habituation are the same." If this were so, then any manipulation of independent variables should affect the two processes equally. I n other words, children would be expected to tire of a novel object at the

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same rate as they cease investigation of it, though the two decremental functions may not be superimposable under all conditions. For instance, under certain incentive conditions no distinction between the two constructs might be demonstrable in terms of observable effects. “Boredom” or “stimulus satiation” theory, in emphasizing the perceptual or input aspect of the stimulus-response constellation, says nothing about the response classes involved. Thus, those conditions which elicited more than one response class would be the most likely to reflect differential decremental effects ascribable to response repetition and stimulus satiation, respectively. Since exploratory activity had been shown to be sensitive to temporal effects (C. Hutt, 1967b) it was decided to vary the intersession interval between successive presentations of the novel toy. Both response-inhi-

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bition and satiation theory predict greater decrement with smaller intertrial intervals, and a differential effect upon the two processes would be expected under the more complex rather than the simple incentive conditions. Hence, the effects of three temporal schedules-48-, 24-, and 12-hour intertrial intervals- were examined (C. Hutt, 1967b) under conditions (i) and (iv). The results for condition (i) are illustrated in Fig. 10. No significant differences were found between the three curves. As Fig. 11 shows, overall responsiveness toward the novel toy under the sound-incentive condition was selectively affected by the nature of the temporal schedule. When, however, response classes were considered separately, no significant differences were obtained in the rates of decrement in “investigation” under the three temporal conditions (Fig. 12). This result contrasted with the appreciable and significant differences obtained in the amounts of “playful” activity directed to the toy (Fig. 13). These results indicate that the rate at which investigation of a particular novel stimulus declines is not affected by massed versus spaced exposures, but is affected by the complexity of the object, since the decrement was exponential when no feedback was available and was linear when sounds were contingent upon the responses. In terms of more generality, the rate at which specific exploration declines appears to be more a function of stimulus complexity and novelty than of temporal factors. Investigation or specific exploration is aimed at information

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acquisition. Hence, after such information is obtained the rate at which the organism “tires” of it, or conversely the extent of its diversive exploration, depends on (a) how much the organism can do with it, (b) temporal factors, and (c) the alternative sources of stimulation. The further separation of these two decremental processes emphasizes the fact that “curiosity” theories and “boredom” theories are both applicable but to different response classes, and are concerned with fundamentally different mediating processes. C. CHARACTERISTICS OF SPECIFIC A N D DIVERSIVE ACTIVITIES

The strict dependence of specific exploration upon very definite features of the stimulus situation, and the more variable dependence of diversive exploration on several environmental features, underscore the relative biological significance of these two categories of behavior. But before development of this point it might be useful to characterize these categories further. Investigative and “play” responses were initially distinguished on strictly behavioral criteria. As the illustrations (Figs. 8 & 9) demonstrate, during investigation visual inspection always accompanied manipulation and the facial expression was one of concentration. In “play,”

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however, the facial expression was relaxed and vision and manipulation were no longer simultaneously directed toward the object or were only briefly so. Subsequently, other features were to distinguish these two categories further. For instance the response sequence in investigation was typically stereotyped (see Fig. 14A).

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The designation of the various behavior categories was in terms of observable events; precise and clear definitions were provided for each (see S. J . Hutt & Hutt, 1970). Manipulatec, for instance, referred to “conventional” manipulation, which consisted of grasping the top of the lever in one hand and moving it in one of the four possible directions, as opposed to hitting it with an open palm, jogging it with an elbow, or butting it with head. Where the predicates omitted an object, it was assumed that the response was directed to the novel toy. The features that characterized the two behavior categories are summarized in Table 1, A. That these features embody most of the distinctive characteristics of specific and diversive exploration as enumerated by Berlyne ( 1960, 1966) can be seen from inspection of Table I, B. From these features it is apparent that specific exploratory responses are essential for the survival of the organism in that they most effectively obtain information for the animal from its particular habitat. Variability

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in the sequence of these responses is minimal and thus it is clearly distinct from appetitive behaviors. Diversive exploration, one form of which is play, is expendable and serves no specific function for the organism vis a vis its environment, insofar as an organism resorts to it only when alternative inputs are lacking; the particular source of the stimulation may be determined by any one or more capricious factors. When deer, for instance, were prevented from playing, they were found to dissipate their energy in other ways (Muller-Schwarze, 1968). If the intensity and availability of specific exploratory responses are a measure of an animal’s ability to survive in an environment subject to frequent change, the extent and variety of its diversive activities is a measure of its flexibility and adaptability. TABLE I CHARACTERISTICS OF INVESTIGATION A N D PLAY, AND MORE GENERALLY OF SPECIFIC AND DIVERSIVE EXPLORATION A.

Investigation

I . Synchrony of visual and tactile receptors 2. Intent facial expression 3. Stereotyped sequence of behavioral elements 4. Elements of relatively long duration 5 . Elicited by novel stimuli

6. Implicit query: “What does this object do?” 7. Shows linear decrement with time B.

Specific exploration

I . Concerns those inspective, investigative responses directed to a particular source of stimulation, i.e. stimulusoriented. 2. Occurs in presence of highly stimulating (by virtue of novelty, complexity etc.) set of environmental factors 3. Consists of consummatory response to stimulus -change 4. Extrinsically motivated 5 . Characterized by response stereotypy 6. Occupies superordinate position in motivational hierarchy in that it can inhibit most tissue-preserving activities

Play Desynchrony, or only transient synchrony of receptors Relaxed facial expression Variable and idiosyncratic sequence of elements Elements essentially brief Never manifest in the presence of novel stimuli Implicit query: “What can I do with this object?’ Is quadratic function of time Diversive exploration Concerns those activities which seem to increase stimulation irrespective of source, i.e., response-oriented Occurs in absence of specific environmental stimulation Consists of instrumental response for stimulus change Intrinsically motivated Characterized by response variability o r entropy Low in motivational hierarchy and can be inhibited by almost any other drive state

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Diversive exploration in young children is most likely to take the form of play, both since they are physically more active than adults and since their lack of linguistic proficiency would limit their symbolic activities. Nevertheless, these play activities have been considered to be as related to aspects of creativity as are their literary counterparts (Lieberman, 1965; Torrance, 1963). In this respect, the present series of studies revealed a particularly interesting result: boys, irrespective of IQ, age, or social class, engaged more frequently and with greater variety in diversive activities incorporating the once-novel object than did girls (Hutt, 1970).That is, boys saw a far greater potential in the object and realized it in a variety of ways-it was ridden like a horse, it was used to “shoot” at an imaginary enemy, as a gear lever, etc. The argument that this particular object had intrinsically more potential for boys than girls is not supported by the facts. Not all the “play” activities in which it was incorporated were those conventionally regarded as male activities-for example making the panda ring the bell while the child himself buzzed the buzzer, or running round and hitting the lever to make the bell ring on each excursion. This argument moreover is post hoc, with no particular suggestions for a more “neutral” toy. On the other hand, on a number of measures applied to these play activities - unusual uses (Torrance, 1962), uniqueness of responses (Wallach & Kogan, 1965), originality of the production of unusual and statistically infrequent responses (Guilford, 196 1 ) -the performance of the boys qualified as being more creative. Such sex differences however are usually attributed to cultural and social factors (see, e.g., Arasteh, 1968). But such an explanation ignores analogous sex differences in a number of other mammalian species (Goy, 1968; Hamburg & Lunde, 1966; Broverman, Klaiber, Kobayashi, & Vogel, 1968). Moreover, behavioral sex differences have been shown to be manifest in very early human development: Kagan and Lewis (1 965) and Moss ( 1 967) demonstrated sex differences in infants in their visual attention to patterns and to the mother respectively. Goldberg and Lewis (1969) found that at 13 months girls were more dependent on their mothers and engaged in relatively quiet play activities whereas boys were independent, more exploratory, and more vigorous. It still remains to be seen whether the “creativity” as manifest at the age of 4 or 5 years will continue to be characteristic of the individual. We hope in due course to have this answer. It is possible that because of their advance in left hemisphere maturation (Taylor, 1969) as reflected in the accelerated acquisition of hemispheric specificity for speech (Kimura, 1963) and in their general verbal competence (Maccoby, 1966), girls are less creatively exploratory than boys. Their creativity appears to be confined to the

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literary fields. I t is of some interest that even male academics were found to be more creative than their equally intelligent and equally qualified female colleagues (see Maccoby, 1966, p. 24). The two dimensions of exploration in man clearly reflect his adaptive and inventive commerce with his environment. There is some evidence that his efficiency in one may be related to his proficiency in the other. To say this is to oversimplify; its justification rests in the efforts it may stimulate.

V. Summary and Conclusions In attempting to stress the complexity of the concepts and variables in the area of exploratory behavior it may appear that an integration of the available evidence into a coherent theoretical formulation has been sacrificed. If so, two arguments in defense of this error of omission may be offered: (a) more competent integrative accounts of the field are already available (Berlyne, 1963a, 1966); and (b) the main purpose of this paper has been to clarify, or at least attempt to clarify, some of the issues relating to behavioral definition and analysis, stimulus variables, and theoretical constructs common in this area. Although most of the collative stimulus properties can conveniently be subsumed under novelty and complexity, the precise classification of any particular variable seems open to conjecture. This is most manifest in the attempts to elucidate the parameters of stimulus-complexity effective in eliciting exploration. Complexity, and to a certain extent some of its constituents, were seen to vary along a multiplicity of dimensions. The difficulty in ascertaining the critical features on occasion seems insurmountable. The response measures (fixation, number of exposures, statement of preference or interestingness) moreover do not necessarily show a high degree of correlation (e.g., Berlyne, Ogilvie, & Parham, 1968; Day, 1966, 1967; Kagan & Lewis, 1965). Although the evidence regarding the effective attributes of complexity in infants and adults is still equivocal, there seems some measure of agreement that immature organisms (young children and retardates) in general show greater fixation of and preference for the more simple and symmetrical figures of a series. With respect to stimulus novelty the picture is much less confused, but even greater clarity may be achieved by distinguishing not only the temporal dimension but also the source from which the novelty emanates, viz. object-novelty , environment-novelty, and conspecific-novelty. Man has no fear of object-novelty as such and this seems to be a feature

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of his evolutionary emancipation. There is clearly an association between an animal’s adaptability to a diversity of physical conditions and the intensity of its exploratory activities. Environment- and conspecific-novelty, in contrast to object-novelty, do elicit fear and distress. Although the impact of environment-novelty is maximal in that there is no familiar frame of reference, an explanation of the reaction in terms of “degree-of-novelty” is a misleading oversimplification, since it certainly does not account for what is very often a more intense reaction to strangers. The evidence suggests that fear of strangers precedes fear of environment-novelty in time of onset. It may be argued that such a classification unnecessarily proliferates conceptual categories which could more parsimoniously be subsumed under some such dimension as “degree-of-novelty” or “stimulus-intensity.” But parsimony may often be misleading; it would moreover need to await a definition of such dimensions independent of the behavior in question. In this area, not only stimulus variables but response variables too need more precise definition. Discrepancies in the literature relating to the eliciting properties or temporal course of exploration may be resolved with appropriate definition of stimulus conditions and response classes, thus also enabling a more formal distinction between specific and diversive exploratory activities. Thus, apparently incongruent formulations accounting for the energizing and directional aspects of exploratory activity may be equally applicable, with the proviso that they apply to different sets of response classes with different antecedent conditions. The formulations regarding complexity, novelty, and exploration which have been put forward in this paper resulted primarily from an attempt to find consistency in the very large volume of empirical data, but were also influenced by considerations of biological and psychological relevance. They owe little to any entrenched theoretical position. If they succeed in provoking good experiments to invalidate them, the attempt will have been vindicated. REFERENCES Ambrose, J . A. The development of the smiling response in early infancy. In B. M. Foss (Ed.), Determinanfs of infant behaviour. Vol. 1. London: Methuen, 196 I . Arasteh, J . D. Creativity and related processes in the young child: A review of the literature. Journal of Genetic Psychology, 1968, 112, 77-108. Arsenian, J. M. Young children in an insecure situation. Journal of Abnormal and Social Psychology, 1943,38,225-249. Attneave, F. Some informational aspects of visual perception. Psychological Review, l954,61, 183-193.

Speci’jic cind Diversive Exploration

173

Attneave, F., & Arnoult, M. D. The quantitative study of shape and pattern perception. Psychological Bulletin, 1956, 53, 452-47 I . Barnes, G. W., & Kish, G. B. Reinforcing properties of the onset of auditory stimulation. Journal of Experimental Psychology, 196 I . 62, 164- 170. Barnett, S. A. Experiments on “neophobia” in wild and laboratory rats. British Journal of Psychology, 1958.49, Part 3, 195-201. Barnett, S . A. A study in behaviour. London: Methuen, 1963. Bartoshuk. A. K. Response decrement with repeated elicitation of human neonatal cardiac acceleration to sound. Journal of Comparative and Physiological Psychology, 1962, 55, 9- 13. Beach, F. A. The Snark was a Boojum. American Psychologist, 1950,5, I 15- 124. Berlyne, D. E. Novelty and curiosity as determinants of exploratory behaviour. British Journal of Psychology, I950,41,68-80. Berlyne, D. E. The arousal and satiation of perceptual curiosity in the rat. Journal of Comparative and Physiological Psychology, 1955. 48, 238-246. Berlyne, D. E. Conflict and information-theory variables as determinants of human perceptual curiosity. Journal of Experimental Psychology, 1957,53,399-404. Berlyne, D. E. The influence of the albedo and complexity of stimuli on visual fixation in the human infant. British Journalof Psychology, 1958.49, 3 15-3 18. (a) Berlyne, D. E. The influence of complexity and novelty in visual figures on orienting responses. Journal of Experimental Psychology, 1958.55, 289-296. (b) Berlyne, D. E. Supplementary report: complexity and novelty responses with longer exposures. Journal ofExperinienta1 Psychology, 1958, 56, 183. (c) Berlyne, D. E. Conjict, arousal and curiosity. New York: McGraw-Hill, 1960. Berlyne, D. E. Motivational problems raised by exploratory and epistemic behavior. In S. Koch (Ed.), Psychology: A study of a science. Vol. 5 . New York: McGraw-Hill, 1963. (a) Berlyne, D. E. Supplementary report: complexity and novelty responses with longer exposures. Canadian Journal of Psychology, 1963, 17, 274-290. (b) Berlyne, D. E. Novelty. New Society, 1964, No. 87, 23-24. Berlyne, D. E. Curiosity and exploration. Science, 1966, 153, 25-33. Berlyne, D. E., Craw, M. A., Salapatek, P. H., & Lewis, J . L. Novelty, complexity, incongruity, extrinsic motivation, and the G.S.R. Journal of Experimental Psychology, 1963,66,560-567. Berlyne, D. E., Koenig, I. D., & Hirota, T. Novelty, arousal and the reinforcement of diversive exploration in the rat. Journal of Comparative and Physiological Psychology, 1966,62, 222-226. Berlyne, D. E., Ogilvie, J. C., & Parham, L. C. C. The dimensionality of visual complexity, interestingness, and pleasingness. Canadian Journal of Psychology, 1968, 22, 376-381. Berlyne, D. E., & Parham, L. C. C. Determinants of subjective novelty. Perception & Psychophysics, 1968.3.41 5-423. Bindra, D., & Spinner, N. Response to different degrees of novelty: the incidence of various activities. Journal of the Experimental Analysis of Behavior, 1958, 1, 341-350. Brennan, W. M., Ames, E. W., & Moore, R. W. Age differences in infants’ attention to patterns of different complexities. Science, 1966,151,354--356. Bridger, W. H. Sensory habituation and discrimination in the human neonate. American JournalofPsychiatry, 1961,117,991-996. Bronson, G . W. The development of fear in man and other animals. Child Development, 1968,39, 409-43 I . (a) Bronson, G. W. The fear of novelty. Psychological Bulletin, 1968.69, 350-358. (b)

174

Corinne Hurt

Bronson, G. W. Fear of visual novelty: developmental patterns in males and females. Developmental Psychology, 1970. in press. Broverman, D. M., Klaiber, E. L., Kobayashi, Y.. & Vogel. W. Roles of activation and inhibition in sex differences in cognitive abilities. Psychological Review, 1968. 75, 23-50. Burgers, J. M. Curiosity and play: basic factors in the development of life. Science, 1966, 154. 1680- I68 I . Butler, R. A. Discrimination learning by rhesus monkeys to visual-exploration motivation. Journal of Comparative and Physiological Psychology, 1953.46.95-98. Butler, R. A. Incentive conditions which influence visual exploration. Journal of Experimental Psychology, 1954.48, 19-23. Butler, R. A. Discrimination learning by rhesus monkeys to auditory incentives. Journal of Comparative and Physiological Psychology, 1957,50,239-24 I . Butler, R . A. The reactions of rhesus monkeys to fear-provoking stimuli. Journal of Genetic Psychology, 1964, 104, 32 1-330. Butler, R. A. Investigative behavior. In A. M. Schrier, H. F. Harlow. & H. Stollnitz (Eds.), Behavior of nonhuman primates. Vol. 2. New York: Academic Press, 1965. Butler, R. A., & Alexander, H. M. Daily patterns of visual exploratory behavior in the monkey. Journal of Comparative and Physiological Psychology, 1955,48.247-249. Butler, R. A., & Harlow, H. F. Persistence of visual exploration in monkeys. Journal of Comparative and Physiological Psychology, 1954, 47, 258-263. Cantor. G. N. Responses of infants and children to complex and novel stimulation. Advances in child development and behavior, 1963.1. 1-29. Cantor, J . H.. & Cantor. G. N. Children’s observing behavior as related to amount and recency of stimulus familiarization. Journal of Experimental Child Psychology, 1964, 1. 241 -247. (a) Cantor, J . H.. & Cantor. G. N . Observing behavior in children as a function of stimulus novelty. Child Development, 1964, 35, I 19- 128. (b) Cantor, J. H., & Cantor, G. N. Functions relating children’s observing behavior to amount and recency of stimulus familiarization. Journal of Experimental Psychology, 1966, 72.859-863. Carr, R. M., & Brown. W. L. The effect of the introduction of novel stimuli upon manipulation in rhesus monkeys. Journal of Genetic Psychology, 1959.94, 107-1 1 I . (a) Carr. R. M., & Brown. W. L. The effect of sustained novelty upon manipulation in rhesus monkeys. Journal of General Psychology, 1959,61, 121 -125. (b) Carr, R. M.. & Brown, W. L. Manipulation of visually homogeneous stimulus objects. Journal of Genetic Psychology, 1959,95, 245-249. (c) Clapp, W. F.. & Eichorn, D. H. Some determinants of perceptual investigatory response in children. Journal of Experimental Child Psychology, 1965.2, 37 1-388. Collard, R. R. Social and play responses of first-born and later-born infants in an unfamiliar situation. Child Development, 1968, 39, 325-334. Cox, F. N.. & Campbell, D. Young children in a new situation with and without their mothers. Child Development, 1968, 39, 123- 13 I . Day, H. Looking time as a function of stimulus variables and individual differences. Perceptual and Motor Skills, 1966. 22. 423-428. Day, H. Evaluations of subjective complexity, pleasingness and interestingness for a series of random polygons varying in complexity. Perception & Psychophysics, 1967, 2, 28 1-286. Dember. W. N., & Earl, R. W. Analysis of exploratory, manipulatory and curiosity behaviors. Psychological Review, 1957,64,91-96.

Specific and Diversive Exploration

175

Dember. W. N., Earl. R. W., & Paradise, N . Response by rats to differential stimulus complexity. Journal of Comparative and Physiological Psychology, 1957, 50, 5 14-5 18. Eisenman, R. Complexity-simplicity: 1. Preference for symmetry and rejection of complexity. Psychonomic Science, 1967. 8, 169- 170. Eisenman, R . Novelty ratings of simple and complex shapes. Journal of General Psychology, I968,78,275-278. Eisenman. R..& Rappaport, J. Complexity preference and semantic differential ratings of complexity-simplicity and symmetry-asymmetry. Psychonomic Science, 1967, 7, 147-148. Engen, T.. Lipsitt, L. P., & Kaye, H. Olfactory responses and adaptation in the human neonate. Journal of Comparative and Physiological Psychology, 1963, 56, 73-77. Fantz. R. L. The origin of form perception. Scientific American. 1961, 204, 66-72. Fantz, R. L. Visual experience in infants: decreased attention to familiar patterns relative to novel ones. Science, 1964, 146,668-670. Faw, T. T., & Nunnally, J. C. The influence of stimulus complexity, novelty and affective value on children’s visual fixations. Journal of Experimental Child Psychology, 1968, 6, 141-153. Fiske, D. W.. & Maddi, S. R. (Eds.) Functions of vuried experience. Homewood, 111.: Dorsey, 196 I . Fowler, H . Curiosity and exploratory behavior. New York: Macmillan. 1965. Frdser, D. C. Satiation and exploratory activity. Nature. 1966, 212, I61 3- 16 14. Freedman, D. G. The infant’s fear of strangers and the flight response. Journal of Child Psychology and Psychiotrv. 196 I , 4. 242-248. Friedlander. B. Z. Performance differentiation in a child’s incidental play for perceptual reinforcement. Paper presented at the meeting of the American Psychological Association, Chicago, 1965. Friedlander, B. Z., McCarthy, J. J., & Soforenko, A. Z. Automated psychological evaluation with severely retarded institutionalized infants. American Journal of Menral D e f ciency, 1967. 71, 909-919. Gilmore. J . B. Play: a special behavior. In R. N. Haber (Ed.), Current research in motivation. New York: Holt, Rinehart & Winston. 1966. Glanzer, M . Stimulus satiation: an explanation of spontaneous alternation and related phenomena. Psychological Review, 1953.60. 257-268. Glanzer, M . Curiosity, exploratory drive, and stimulus satiation. Psychological Bulletin, 1958,55.3O2-3 15. Glickman, S. E., & Sroges, R.W. Curiosity in zoo animals. Behavior, 1966, 26, 15 1 - 188. Goldberg. S., & Lewis, M. Play behavior in the year-old infant: early sex differences. Child Development, 1969.40.2 1- 3 1 . Goodrick, C. L. Activity and exploration as a function of age and deprivation. Journal of Genetic Psychology, 1966,108,239-252. Goodrick, C . L. Exploration of nondeprived male. Sprague-Dawley rats as a function of age. Psychological Reports, 1967.20, 159- 163. Goy, R. W. Organising effects of androgen on the behaviour of rhesus monkeys. In R. P. Michael (Ed.), Endocrinology & human behaviour. London and New York: Oxford University Press. 1968. Guilford, J . P. Factors that aid and hinder creativity. Teachers College Record, 63, 380392, 1962. Halliday, M . S. Exploration and fear in the rat. Symposium of the Zoological Society of London. 1966,18,45-59.

176

Corinne Hutt

Hamburg, D. A,, & Lunde, D. T. Sex hormones in the development of sex differences in human behaviour. In E. Maccoby (Ed.), The development of sex differences. London: Tavistock Publications, 1966. Harlow, H. F. Learning and satiation of response in intrinsically motivated complex puzzle performance by monkeys. Journal of Comparative and Physiological Psychology, 1950,43,289-294. Harlow, H. F. Mice, men, monkeys and motives. Psychological Review, 1953,60, 23-32. Harlow, H. F., Blazek, N. C., & McClearn, G. E. Manipulatory motivation in infant rhesus monkeys. Journal of Comparative and Physiological Psychology, 1956, 49, 444-448. Harlow, H F., Harlow, M. K.. & Meyer, D. R. Learning motivated by a manipulatory drive. Journal of Experimental Psychology, 1950,40,228-234. Harlow, H. F., & McClearn, G. E. Object discrimination learned by monkeys on the basis of manipulation motives. Journal of Comparative and Physiological Psychology, 1954,47,73-76. Harris, L. The effects of relative novelty on children's choice behavior. Journal of Experimental Child Psychology, 1965,2, 297-305. Hayes, J . R. The maintenance of play in young children. Journal of Comparative and Physiological Psychology, 1958, 51, 788-790. Haynes, H., White, B. L., & Held, R. Visual accommodation in human infants. Science, 1965,148,528-530. Haywood, H. C., & Wachs, T. D. Effects of arousing stimulation upon novelty preference in rats. British Journal of Psychology, 1967, 58, 77-84. Hebb, D. 0. On the nature of fear. Psychological Review, 1946,53,259-302. Hershenson, M. Visual discrimination in the human newborn. Journal of Comparative and Physiological Psychology, 1964,58.270-276. Hershenson, M., Munsinger, H., & Kessen, W. Preference for shapes of intermediate variability in the newborn human. Science, 1965, 147,630-631. Hoats, D. L., Miller, M. B., & Spitz, H. H. Experiments on perceptual curiosity in mental retardates and normals. American Journal of Mental Deficiency, 1963, 68, 386-395. Hunt, J. McV. Intrinsic motivation and its role in psychological development. In D. Levine (Ed.), Nebraska symposium on motivation. Lincoln, Neb.: University of Nebraska Press, 1965. Hutt, C. Exploration and play in children. Symposium of the Zoological Society of London, 1966,18,6 1-8 I . Hutt, C. Effects of stimulus novelty on manipulatory exploration in an infant. Journal of Child Psychology and Psychiatry, 1967, 8, 241-247. (a) Hutt, C. Temporal effects on response decrement and stimulus satiation in exploration. British Journal of Psychology, 1967,58,365-373. (b) Hutt, C. Complexity, curiosity and development. Proceedings of the XIXth International Congress of Psychology, London, 1969. (a) Hutt, C. Exploration, arousal and autism. Psychologische Forschung, 1969,33, 1-8. (b) Hutt, C. How children explore. Science Journal, 6 , 68-71, 1970. Hutt, C., Bernuth, H. v., Lenard, H. G., Hutt, S. J., & Prechtl, H. F. R. Habituation in relation to state in the human neonate. Nature, 1968, 220, 618-620. Hutt, C., & McGrew, P. L. Do children really prefer complexity? Psychonomic Science, 1969, 17, 113-1 14. (a) Hutt, C., & McGrew, P. L. The multidimensionality of visual complexity: effects on children's preferences and fixations. Paper presented at the London Conference of the British Psychological Society, December 1969. (b)

Specific and Diversive Exploration

I77

Hutt, S. J., & Hutt, C. Stereotypy, arousal and autism. Human Development, 1968, 11, 277-286. Hutt, S. J., & Hutt, C. Direct observation and measurement of behavior. Springfield, Illinois: C. C. Thomas, 1970. Hutt, S. J., Hutt, C., Lenard, H . G., Bernuth, H. v., & Muntjewerf€, W. J. Auditory responsivity in the human neonate. Nature, 1968, 218, 888-890. Hutt, S. J., Lenard, H. G., & Prechtl, H. F. R. Psychophysiology of the newborn. Advances in child development and behavior, 1969.4, 128- 172. Kagan, J., & Lewis, M. Studies of attention in the human infant. Merrill-Palmer Quarterly, 1965, 11,95-127. Kimura, D. Speech lateralization in young children as determined by an auditory test. Journal of Comparative and Physiological Psychology, 1963,56,899-902. Kish, G. B., & Antonitis, J. J. Unconditioned operant behaviour in two homozygous strains of mice. Journal ofGenetic Psychology, 1956, 88, 121-129. Lawick-Goodall, J . V. The behaviour of free-living chimpanzees in the Gombe Stream Reserve. Animal Behaviour Monograph, 1968,1, 161-3 11. Lester, D. Sex differences in exploration: towards a theory of exploration. Psychological Record, 1967,17,55-62. Lester, D. Two tests of a fear-motivated theory of exploration. Psychonomic Science, 1968, 10,385-386. Leuba, C. Toward some integration of learning theories: the concept of optimal stimulation. Psychological Reports, 1955, 1 , 27-33. Leuba, C., & Friedlander, B. Z. Effects of controlled audio-visual reinforcement on infants manipulative play in the home. Journal of Experimental Child Psychology, 1968, 6, 87-99. Lewis, M., & Goldberg, S. The acquisition and violation of expectancy: an experimental paradigm. Journal of Experimental Child Psychology, 1969,7,70-80. Lewis, M., Goldberg, S., & Rausch, M. Attention distribution as a function of novelty and familiarity. Psychonomic Science, 1967, 7, 327-328. Lewis, M., Kagan, J., & Kalafat, J. Patterns of fixation in infants. Child Development, 1966. 37,331-341. Lieberman, J. N. Playfulness and divergent thinking: an investigation of their relationship at the kindergarten level. Journal of Genetic Psychology, 1965, 107, 219-224. Maccoby, E. E. Sex differences in intellectual functioning. In E. E. Maccoby (Ed.), The development of sex differences. London: Tavistock, 1966. Marais, F. N . My friends the Baboons. London: Methuen, 1939. Marler, P. J., & Hamilton, W. J. Mechanisms of animal behavior. New York: Wiley, 1966. Mason, W. A., Harlow, H. F., & Rueping, R. R. The development of manipulatory responsiveness in the infant rhesus monkey. Journal of Comparative and Physiological Psychology, 1959,52,555-558. May, R. B. Stimulus selection in preschool children under conditions of free choice. Perceptual and Motor Skills, 1963, 16,203-206. McCall, R. B., & Kagan, J. Attention in the infant: effects of complexity, contour, perimeter and familiarity. Child Development, 1967,38, 939-952. McDonald, D. G., Johnson, L. C., & Hord, D. J. Habituation of the orienting response in alert and drowsy subjects. Psychophysiology, 1964, 1, 163- 173. McReynolds, P. Exploratory behaviour: a theoretical interpretation. Psychological Reports, 1962, 11, 311-318. Mendel, G . Children’s preferences for differing degrees of novelty. Child Development, 1965,36,453-465.

178

Corinne Hutt

Meyers, W. J., & Cantor, G. N. Infants’ observing and heart period responses as related to novelty of visual stimuli. Psychonomic Science, 1966, 5, 239-240. Meyers, W. J., & Cantor, G. N . Observing and cardiac responses of human infants to visual stimuli. Journal of Experimental Child Psychology, 1967. 5. 16-25. Montgomery, K. C. The relationship between exploratory behavior and spontaneous alternation in the white rat. Journal of Comparative and Physiological Psychology, I95 I , 44, 582-589. Montgomery, K. C. Exploratory behaviours as a function of “similarity” of stimulus situations. Journal of Comparative and Physiological Psychology, 1953, 46. 129- 133. Moon, L. E., & Lodahl, T. M. The reinforcing effect of changes in illumination on leverpressing in the monkey. American Journal ofPsychology, 1956.69, 288-290. Morgan, G. A., & Ricciuti, H. N. Infants’ responses to strangers during the first year. In B. M. Foss (Ed.), Determinants of infant behaviour. Vol. IV. London: Methuen, 1969. Moss, H. Sex, age and state as determinants of mother-infant interaction. Merrill-Pnlmer Quarterly, 1967, 13, 19-36. Muller-Schwarze. D. Play deprivation in deer. Eehaviour, 1968,31, 1-2. Munsinger, H ., & Kessen, W. Uncertainty, structure and preference. Psychological Monographs, 1964, 78, (Whole No. 596), 1-24. Munsinger, H., & Kessen, W. Stimulus variability and cognitive change. Psychological Review, 1966.73, 164- 178. (a) Munsinger, H., & Kessen, W. Structure, variability and development, Journal of Experimental Child Psychology, 1966.4, 20-49. (b) Munsinger, H., Kessen, W., & Kessen, M. L. Age and uncertainty: developmental variation in preference for variability. Journal of Experimental Child Psychology, 1964, 1, 1-15.

Munsinger, H., & Weir, M. W. Infants’ and young children’s preference for complexity. Journal of Experimental Child Psychology, 1967,5, 69-73. Myers, A. K., & Miller, N. E. Failure to find a learned drive based on hunger: evidence for learning motivated by “exploration.” Journal of Comparative and Physiological Psyc‘hology, 1954,47,428-436. Payne, B. The relationship between a measure of organization for visual patterns and their judged complexity. Journal of Verbal Learning and Verbal Behavior, 1966, 5, 338-343. Polak, P. R., Emde, R. N., & Spitz, R. A. The smiling response. 11. Visual discrimination and the onset of depth perception. Journal of Nervous and Mental Disease, 1964, 139, 407-415. Rheingold, H. L. The effect of a strange environment on the behaviour of infants. In B. M. Foss (Ed.), Determinants of infant behaviour. Vol. 1V. London: Methuen, 1969. Rheingold, H. L., Stanley, W. C., & Doyle, G. A. Visual and auditory reinforcement of a manipulatory response in the young child. Journal of Experimental Child Psychology. 1964.1.316-326. Robinson, R. Visual performance in the newborn. Paper read to the Spastics International Study Group, Oxford, England, September 1968. Rosenthal, M. K. Effects of a novel situation and of anxiety on two groups of dependency behaviours. British Journal of Psychology, 1967,58, 357-364. Rump, E. E. Is there a general factor of preference for complexity? Perception di Psychophysics, 1968, 3, 346-348. Saayman, G . . Ames, E. W., & Moffett, A. Response to novelty as an indicator of visual discrimination in the human infant. Journal of Experimental Child Psychology, 1964, 1. 189-198.

SpeciJc and Diversive Exploration

I79

Sackett, G. P. A neural mechanism underlying unlearned, critical period, and developmental aspects of visually controlled behavior. Psychological Review, 1963, 70, 40-50. Salapatek, P. Visual scanning of geometric figures by the human newborn. Journal of Comparative and Physiological Psychology, 1968, 66, 247-258. Salapatek. P., & Kessen, W. Visual scanning of triangles by the human newborn. Journal of Experimental Child Psychology, 1966.3, 155- 167. Schaffer, H. R., & Emerson, P. E. The development of social attachments in infancy. Monographs of the Society for Research in Child Development, 1964, 29, Serial No. 94, 1-77. Schaffer, H. R., & Parry, M. P. Perceptual-motor behaviour in infancy as a function of age and stimulus familiarity. British Journal of Psychology, 1969, 60, 1 - 10. Schiff, W., Caviness, J . A., & Gibson, J. J. Persistent fear responses in rhesus monkeys to the optical stimulus of “looming.” Science, 1962, 136, 982-983. Sheldon, A. B. Preference for familiar situation independent of fear of novelty. PsychonomicScience, 1968,13, 173-174. Sheldon, A. B. Preference for familiar versus novel stimuli as a function of the familiarity of the environment. Journal of Comparative and Physiological Psychology, 1969, 67, 5 16-521. Sheldon, M. H. The effect of electric shock on rats choice between familiar and nonfamiliar maze arms: a replication. Quarterly Journal of Experimental Psychology, 1968, 20,400-404. Shillitoe, E. E. Exploratory behaviour in the short-tailed vole Microtus agrestis. Behaviour, l963,21, 145-154. Smock, C. D., & Holt, B. G. Children’s reactions to novelty: an experimental study of “curiosity motivation.” Child Development, 1962,33,63 1-642. Sokolov, E. N. Higher nervous functions: the orienting reflex. Annual Review of Physiology, 1963,25,545-580. Spitz, R. A. Anxiety in infancy: a study of its manifestations in the first year of life. International Journal of Psycho-analysis, 1950, 31, 138- 143. Stenson, H. H. The physical factor structure of random forms and their judged complexity. Perception & Psychophysics, 1966.1, 303-3 10. Stretch, R. Effects of amphetamine and pentobarbitone on exploratory behaviour in rats. Nature, 1963,199,787-789. Symmes, D. Anxiety reduction and novelty as goals of visual exploration by monkeys. Journal ofGenetic Psychology, 1959,94, 18 1-198. Taylor, D. C. Differential rates of cerebral maturation between sexes and between hemispheres: evidence from epilepsy. Lancet, 1969, July 19, 140-1 42. Tennes, K. H., & Lampl, E. E. Stranger and separation anxiety. Journal of Nervous and Mental Disease, 1964,139,247-254. Terwilliger, R. F. Pattern complexity and affective arousal. Perceptual and Motor Skills, 1963, 17,387-395. Thomas, H . Visual-fixation responses of infants to stimuli of varying complexity. Child Development, 1965,36629-638. Thomas, H. Preferences for random shapes: ages six through nineteen years. Child Development, 1966,37,843-859. Thompson, R. F., & Spencer, W. A. Habituation: a model phenomenon for the study of neuronal substrates of behaviour. Psychological Review, 1966,73, 16-43. Thompson, W. R., & Higgins, W. H. Emotion and organisation behaviour: expenmental data bearing on the Leeper-Young controversy. Canadian Journal of Psychology, 1958, 12,61-68.

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Thorpe, W. H. Learning and instinct in animals. (2nd ed.) London: Methuen, 1963. Torrance, E. P. Guiding creative talent. Englewood Cliffs, N . J.: Prentice-Hall, 1962. Torrance, E. P. Education and the creative potential. Minneapolis: University of Minnesota Press, 1963. Vitz, P. C. Preference for different amounts of visual complexity. Behavioral Science, 1966, 11, 105-1 14. Walker, E. L., & Walker, B. E. Response to stimulus complexity in the rat. Psychological Records, 1964, 14,489-497. Wallach, M. A., & Kogan, H. Modes of thinking in young children: A study of the creativity-intelligence distinction. New York: Holt, Rinehart & Winston, 1965. Welker, W. 1. Effects of age and experience on play and exploration of young chimpanzees. Journal of Comparative and Physiological Psychology, 1956,49, 223-226. (a) Welker, W. I. Some determinants of play and exploration in chimpanzees. Journal of Comparative and Physiological Psychology. 1956.49, 84-89. (b) Welker, W. 1. Variability of play and exploratory behaviour in chimpanzees. Journal of Comparative and Physiological Psychology, 1956.49, 18I - 185. (c) Wickelgren, L. W. Convergence in the human newborn. Journal of Experimental Child Psychology, 1967, 5, 14-85. Wolin, L. R., Ordy, J. M., & Dillman, A. Monkeys’ fear of snakes: a study of its basis and generality. Journal of Genetic Psychology, 1963,103,207-226.

DEVELOPMENTAL STUDIES OF MEDIATED MEMORY'

John H . Flavell UNIVERSITY OF MINNESOTA

1.

INTRODUCTION

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I I . T H E STUDIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 A . FLAVELL. BEACH. A N D CHINSKY ...................... 182 B. KEENEY. CANNIZZO. A N D FLAVELL . . . . . . . . . . . . . . . . . . . 184 C . MOELY. OLSON. HALWES. A N D FLAVELL . . . . . . . . . . . . . . 186 D . CORSINI. PICK. A N D FLAVELL ......................... 189 E . DAEHLER. HOROWITZ. WYNNS. A N D FLAVELL . . . . . . . . 191 111. SOME IMPRESSIONS REGARDING T H E NATURE A N D

DEVELOPMENT O F MEDIATED MEMORY . . . . . . . . . . . . . . . . . . . 193 A . T H E NATURE O F MNEMONIC MEDIATION . . . . . . . . . . . . . 193 B . PRODUCTION A N D MEDIATIONAL DEFICIENCIES IN CHILDREN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 C . IMPLICATIONS FOR FURTHER RESEARCH . . . . . . . . . . . . . . 207

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IV . SUMMARY

'Most of the research described in this paper was supported by a research grant from the National Institute of Child Health and Human Development (HD01888) and by grants to the University of Minnesota's Center for Research in Human Learning from the National Science Foundation (GS541). from the National Institute of Child Health and Human Development (HDOI 136). and from the Graduate School of the University .

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I. Introduction It has been repeatedly suggested over the past decade that young children may have difficulty in using verbal symbols as mediators in various task situations (e.g., T. S. Kendler, 1963; Luria, 1961; Reese, 1962). Although in possession of the relevant words, the young child is said to be somehow unable to utilize them as a mediative bridge to task solution. Following a suggestion by Maccoby (1 964), the author and his students have distinguished two possible sources of the child’s difficulty (Flavell, Beach, & Chinsky, 1966). On the one hand, the appropriate word or phrase might be produced at the appropriate moment but then fail to stimulate any subsequent adaptive responses; that is, the wouldbe mediator might be generated but yet unaccountably fail to mediate anything. On the other hand, the nonmediated task performance might simply be a consequence of the child’s failure to generate the mediator at all. The term “mediational deficiency” had been coined initially as a general characterization of the young child’s apparent failure to show mediated task performance (Reese, 1962). Flavell et al. have proposed that the term be restricted to only the first of the above-mentioned possibilities: the hypothetical case where potential mediators are produced but do not mediate. The rubric “production deficiency” was then offered as a description of the second possibility: the hypothetical case where potential mediators are not produced and hence cannot mediate. The child might of course be prone to both types of deficiency in a task situation, failing to produce mediators on many trials and also failing to mediate with them on the trials where they are produced. This paper has two objectives. The first is to summarize five developmental studies of mediational, and especially, production deficiencies with respect to children’s performance on memory tasks (Corsini, Pick, & Flavell, 1968; Daehler, Horowitz, Wynns, & Flavell, 1969; Flavell et al., 1966; Keeney, Cannizzo, & Flavell, 1967; Moely, Olson, Halwes, & Flavell, 1969). These will be presented in an informal fashion, with only the important details given. The second objective is to propose some generalizations about the nature and development of mediational activity and related topics. Support for these generalizations will be drawn from our five major studies, from other research carried out under the author’s aegis, and from the literature at large.

11. The Studies A. FLAVELL, BEACH, AND CHINSKY

The major purpose of this initial investigation was to find out if at least a verbal production deficiency would be detected in the task perform-

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ance of younger versus older children, whether or not accompanied by a mediational deficiency. The first research step was to find a task that would be virtually certain to elicit verbal-mediational efforts in the mature human responder, for the reason that such efforts would likely be adaptive. Our guess (since shown to be correct) was that a task which required S to hold a particular sequence of depicted objects in memory for a short time would meet this requirement, since verbal rehearsal of the names of the objects could facilitate retention of both the objects themselves and also the order in which they were presented. Thus it was that, originally interested in the development of verbal mediation in general, without regard to task, we came to narrow the arena of its investigation to recall situations (as will be seen, this has been balanced by a compensatory broadening of the definition of “mediation” to include nonverbal behavior). The second step was to select objects for recall which the youngest S s in the study could easily name, thus insuring that mediational activity in the form of verbal rehearsal would at least not be denied them on purely linguistic-competence grounds. The last step was to find a method of measuring (or more accurately, “sounding”) any spontaneous verbal-mediational activity the child might undertake. Accordingly, objects were selected the pronunciation of whose names entailed rather large and conspicuous mouth movements (“pipe,” “flag,” etc.), and one E trained himself to lip-read semi-covert verbalizations of these particular names. A way was found for him to observe the child’s mouth quite closely and yet unobtrusively, and his observations provided the principal basis for inferences regarding the production/nonproduction of verbal mediators in this study. The S s were 20 kindergarteners, 20 second-graders, and 20 fifthgraders. Following some pretraining on the concept of order, seven object pictures were spread before S, and E slowly pointed in turn to a given subset of them (e.g., three). Either immediately thereafter or following a 15-second delay period, S’s task was to try to point to the same subset of objects and in the same order that E had pointed to them, the spatial distribution of the entire set of seven pictures having been randomly rearranged in the meantime. There was a series of such immediate-recall and delayed-recall trials, with ordered subsets of various sizes to be remembered. Subsequently, E asked the child how he had gone about trying to remember the pictures (in order to supplement the lip reading data), verified his ability to name each of the seven objects, and administered a supplementary series of delayed-recall trials under the instruction to name aloud each object when E pointed to it (stimulus presentation) and again when he pointed to it (recall). We had predicted that the amount of observed verbal rehearsal would be an inverted-U type function of age across Grades K, 2, and 5. The

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principal hypothesis was that, relative to the older children, the kindergarteners would tend not to engage in verbal rehearsal as a means of amplifying their serial recall, i.e., that children of this age group would show a production deficiency with respect to this particular form of verbal mediation. A secondary hypothesis was that verbal rehearsal in the fifth-grade group would be less observable to a lip reader as a consequence of a Vygotsky-type (Vygotsky, 1962) internalization-of-nonsocial-speech development. Thus, both the oldest and the youngest S s were expected to show less detectable rehearsal than those of intermediate age: the oldest, because their rehearsal would be more covert (internalization); the youngest, because they would tend not to rehearse at all (production deficiency). The first hypothesis was clearly supported but the second was not (and thereby, as it turned out, lending some added support for the first). The numbers of S s who showed any detectable verbalization during the main series of trials (i.e., those prior to the inquiry) were 2, 12, and 17 for Grades K, 2, and 5, respectively. If one adds the S s who reported having rehearsed but were not “seen” to do so by the observer, the corresponding figures were 2, 16, and a unanimous 20. Having to name the objects aloud at the stimulus-presentation and recall ends of a trial sequence (the above-mentioned supplementary series) may serve to stimulate or “prime” delay-period rehearsal, even in chronic nonrehearsers: the number of kindergarten Ss showing it increased from 2 to 7 under this experimental condition. While there were hints in the data that verbal rehearsal is in fact a mediator of effective recall in this task situation, the study provided no convincing test of this basic assumption. Likewise, it was unfortunately not possible to obtain any evidence at all as to whether mediational as well as production deficiencies beset the younger children’s management of this particular memory task. Clearer evidence on both of these points was obtained in the next study to be described. B.

KEENEY,CANNIZZO, AND

FLAVELL

This experiment was designed to answer four questions concerning children’s production and utilization of verbal mediators in the service of recall. 1 . Do children who spontaneously rehearse sequences of recall items (i.e., producers) retain them better than children of the same age who do not rehearse (i.e., nonproducers)? 2. Can nonproducers quickly and easily be trained to rehearse, i.e., can they readily adopt a verbal-rehearsal strategy when instructed to do so?

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3. Assuming an affirmative answer to Questions 1 and 2, does the experimentally induced rehearsal of a nonproducer mediate recall as effectively as does the spontaneous rehearsal of his producing peer, or is his production deficiency also coupled with a mediational deficiency? 4. When no longer required by E to rehearse, would the nonproducer tend to maintain or to abandon his newly acquired mnemonic aid? The basic testing procedure used was essentially the same as in the previous study, except that all of the trials entailed a 15-second delay between item presentation and recall. There were 2 testing sessions, separated by an interval of about 6 weeks. In the first, 89 first-graders were given a series of 10 delayed-recall trials, with one of the Es carefully monitoring lip movements as in the preceding study. Two extreme groups of S s were then constituted on the basis of their performance in this session: a group of producers ( N = 24), consisting of S s who were observed to rehearse on at least 9 of the 10 trials; a group of nonproducers ( N = 17), who were observed to rehearse on no more than 1 trial ( 1 2 of the 17 showed no detectable rehearsal at all) and who also failed on posttest inquiry to report having rehearsed. Only these 4 1 S s were retested in the second session. The group of 24 producers was further subdivided into two subgroups of 12 S s each, matched on first-session recall scores (number of trials on which S recalled in correct sequence all of the items presented). For one subgroup (control), the second session was simply a repetition of the first. For the nonproducers and the other subgroup (experimental) of producers, the second session began with one delayed-recall trial to assess the stability, over the 6-week period, of s’s production-nonproduction tendencies. Following this, nonproducers and experimental producers alike were given a brief period of instruction and practice in verbal rehearsal (they were induced to whisper audibly the sequence of object names over and over during each delay period). The next phase was a repetition of the 10 trials of the first session, but with S instructed at the outset to rehearse on all trials and subsequently reminded to do so whenever necessary. Finally, 3 more trials were administered in which S was explicitly given the option of continuing or not continuing to rehearse. The recall data from the initial session gave a clearly affirmative answer to the first of our four questions: the recall scores of the 24 producers were significantly higher than those of the 17 nonproducers. The answer to the second question was also positive. Most of the nonproducers quickly and easily learned to rehearse in the manner requested; there was, in fact, essentially no difference between nonproducers and experimental producers in their ability to comply with the rehearsal instructions of the second session. There were no significant differences in

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second-session recall scores among nonproducers, control producers, and experimental producers. All three groups improved their recall scores on the second-session retest: the improvement was zero-order in the case of the two producer groups; it was, however, quite substantial in the case of the nonproducers, and significantly greater than that of the other two groups. These data clearly indicate that the production-deficient S s in this study were not also mediationally deficient (Question 3); once induced to rehearse, their recall rose to a level essentially indistinguishable from that of their producing age mates. In addition, these same data serve to confirm our initial assumption that verbal rehearsal would be an effective mediator of recall on this sort of task; like the issue of mediational deficiency, this had been unresolved in the previous investigation. Somewhat to our surprise (Question 4),no fewer than 10 of the 17 nonproducers completely abandoned the whispered-rehearsal strategy on the final three, free-choice trials (none of the experimental producers did); the result was a noticeable but statistically nonsignificant drop in their recall level, in comparison with that of the experimental producers. Whether they would have persisted in rehearsal if given adequate feedback as to its beneficial effects on their recall remains an open question. And finally, the overall pattern of results served to increase our confidence in the reality of the production-nonproduction distinction and in our lip reading method of indexing it. For instance, the control producers were observed to rehearse spontaneously in the second session just about as much as they had in the first. Similarly, on the initial trial of the second session (prior to rehearsal instruction), most of the nonproducers and experimental producers behaved in accordance with their original diagnoses. Add to this their first-session differences in recall level, the washing out of these differences in the second session, and their subsequent differential reaction to the removal of the rehearsal requirement, and we begin to believe that the lip reading procedure must have tracked with fair fidelity a genuine, moderately stable response dimension. C. MOELY, OLSON,HALWES,A N D FLAVELL

The major purpose of this experiment was to determine whether young children would also exhibit a production deficiency with respect to verbal-conceptual skills of a ssomewhat higher order than those previously studied. As in the two earlier investigations, the goal (mediated) activity was recall, but the instrumental (mediator) activity of primary interest was that of grouping or Clustering items by conceptual category rather than simply rote-rehearsing them in the order presented. In the

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present study, S was given a 2-minute period of solitary study prior to each test of recall, during which he had the opportunity to show observable manifestations of pre-recall clustering activity, e.g., physically sorting the items (pictures of objects) into groups according to their class membership. The S s were 48 kindergarteners, 48 first-graders, 48 third-graders, and 16 fifth-graders. The S s in the three lower grades were assigned in equal numbers to one control and two experimental groups; the fifth-graders served in the control condition only. The recall items consisted of 24 2 X 2 inch pictures of common objects belonging to four conceptual categories: animals, furniture, vehicles, and clothing. Four, five, and six of the six items of each category comprised the recall sets for Grades K-1 , 3, and 5 , respectively. Following a practice trial with different items, the control S s were presented with the test set of pictures, arranged in an irregular circle on the table with no two members of the same category adjacent. After having named the pictures, S was told that he would be left alone for 2 minutes to memorize them in preparation for subsequent verbal recall, and that he was free to move or rearrange the pictures if he wished. The procedure for one of the experimental conditions (Naming) was identical, except that E initially labeled each category in an age-appropriate way (e.g., “Things to ride in”) and pointed to its members in the circular array. In the other experimental condition (Teaching), S was induced to sort the items manually, label the resulting categories, and count the items in each category, with E providing assistance as needed. The S was further told that he might aid his recall by first trying to remember each category and then its individual members. All S s were given three trials with the same pictures, each trial consisting of stimulus presentation (always the same circular array), 2 minutes of solitary study (with an E observing via a one-way mirror), and an untimed oral recall test. Following the third trial, S s in the control condition who had not manually clustered the pictures perfectly during previous study periods were asked to group together the pictures “that go together or are alike” (sorting task). A clustering index was used to score manual clustering during study periods (S’s spontaneous item rearrangements were photographed) and on the sorting task, as well as verbal clustering during recall. The observer also recorded other behavior of interest during the study periods: off-task, distracted behavior; moving the pictures about (for clustering purposes or not); verbalization (audible or lip-movement level stimulus naming, principally); self-testing (looking away from the pictures and trying to reproduce them from memory).

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The ratio of study period to sorting task clustering scores within the four control groups could provide evidence for a production deficiency in pre-recall clustering, since this ratio is at least a crude estimate of the extent to which S s of different ages are spontaneously using as a mnemonic mediator (study period scores) whatever categorization ability they possess (sorting task scores). These ratios were .07, .16, .19, and .60 for Grades K, 1, 3; and 5 , respectively, suggesting that, in comparison with the oldest Ss, the three younger groups were in fact production-deficient for this genre of mediational activity. The relations between recall clustering and sorting task clustering yielded similar results. The data also permitted a second test for production deficiency. One kindergarten, 5 first-grade, 9 third-grade, and 14 fifth-grade control S s demonstrated the ability to categorize the items without error (sorting task). Nonetheless, the mean study period clustering score of the 14 fifth-graders proved to be almost triple that of the 15 younger Ss, a highly significant difference. Although appearing to be about equally production-deficient vis-a-vis the fifth-graders under the control procedure, the three younger groups were clearly different from one another in “production threshold,” as revealed by the experimental procedures. For the kindergarteners and first-graders, only the strong Teaching condition sufficed to elicit production; the study period clustering scores of the Teaching groups were dramatically higher than those of both Naming and control groups at these two age levels. In contrast, the Naming procedure was quite as effective in eliciting study period clustering as was the Teaching procedure at the third-grade level. There was no evidence at all that the Ss in the younger groups were deficient in mediation as well as in production on this particular task. The above-mentioned increases in pre-recall clustering activity engendered by the Teaching condition (and also, for third-graders, by the Naming condition) were in each instance neatly paralleled by increases in mean recall score; there was thus a highly significant main effect of experimental condition on recall, but no significant age by condition interaction, as would have been expected had the younger Ss been unable to make effective use of the clustering activity engendered by the experimental treatments. If any age group had been prone to mediational deficits in this study, it would surely have been the youngest, K group. However, it was found that those kindergarteners who (regardless of condition) received study period clustering scores of .60 or higher recalled the object pictures significantly better than those with scores lower than .60. It was possible to make a developmental analysis of S s study period

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activity in terms of a distinction between generic and specific (selective and focalized) behaviors. Thus, most of the S s moved the pictures to some extent (generic), but as we have seen, only the older ones tended without special prompting to move them into groups based upon shared class membership (specific). Similarly, virtually all of the S s did at least some detectable verbalizing of object labels during the study periods (generic), but again only the older ones tended to verbalize these labels within the context of a spontaneous, and to us, highly interesting selftesting operation, entailing a deliberate turning away from the pictures (specific). D. CORSINI, PICK, A N D FLAVELL

While all verbalization is potentially symbolic, it is obvious that not all symbolization need be verbal in nature. Correspondingly, production and mediational deficiencies might be found in the young child’s cognitive management of nonverbal as well as verbal symbols. The present study was designed to test this possibility. The child’s task was to reproduce a linear, ordered pattern of six colored wooden forms after the pattern had been destroyed. He had continuously available a set of small paper replicas of the forms and was told that he might utilize them to help himself remember the pattern. It was consequently possible for the child to make an exact paper-form copy of the wooden-form pattern - a nonverbal, “ikonic” representation (Bruner, Olver, & Greenfield, 1966) of it-from which the pattern could subsequently be reconstructed. As in the previous study, experimental treatment as well as age was included as an independent variable, to see whether production and utilization of nonverbal mediators could be induced when they did not occur spontaneously. The Ss were 40 kindergarten and 40 first-grade children. Twenty from each grade level were randomly assigned to each of two conditions, an experimental and a control. The recall items were wooden forms (triangles, circles, and squares) of three colors (red, yellow, and blue) which were about 2% inches in diameter. Their paper-form duplicates were 1 inch in diameter. There were two pretraining trials to insure that S understood the following basic procedure. The E presented a linear pattern (of three wooden forms only, during pretraining) and asked S to study it. The pattern was then removed from sight and S attempted to reconstruct it exactly, selecting from a large duplicate set consisting of two wooden forms of each form-color combination. The test series consisted of nine patterns (trials), each containing six forms. As the first pattern was presented, E placed a pile of the paper replicas before S and

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said: “Here, you can use these papers to help yourself remember.” This suggestion was repeated to the control S s on the fourth and seventh trials. The experimental Ss received the same three hints plus two other, stronger ones: (1) before the fourth trial E presented a pattern of wooden forms and asked S to make a paper-form copy of it; (2) prior to the seventh trial E made a paper-form pattern and requested S to make a wooden-form copy of it. In order that the basic capacity for production (wooden-to-paper) and utilization (paper-to-wooden) of these nonverbal mediators could be assessed for all S s , any control S who had not spontaneously made and used a paper copy during the experiment proper was also given instructions (1) and (2) above after his last test trial. As expected, all 80 children did in fact demonstrate this basic capacity, experiencing very little difficulty in reproducing patterns in either direction when explicitly requested to do so. There were clear age differences, however, in their spontaneous utilization of this capacity in the service of recall. We categorized Ss’ behavior on the nine test trials as follows: early models-S began making paper-form copies during the first three trials: late models-S showed this behavior on at least one of the last six trials (i.e., after additional hints and suggestions) but not on any of the first three; no models-none was made on any of the nine trials. Of the 20 control first-graders, 12 fell into the first category, 8 into the second, and none into the third. The corresponding figures for the control kindergarteners were 5 , 3, and 12. As in the Moely et al. study just described, the experimental manipulation had different effects at the two age levels. The experimental first-graders were distributed across the three categories in much the same way as the control first-graders: 1 1, 7, and 2. In contrast, the experimental-group procedures resulted in a considerable increase in mediator production at the kindergarten level: 5 , 12, and 3-thus 17 experimental “producers” (sooner or later) as against 8 controls. It can be concluded, therefore, that the kindergarteners in this investigation showed deficiencies in the production of a nonverbal mediator that seem exactly parallel to the verbal production deficiencies exhibited by children of the same age in our previous studies. While clearly capable of making, in isolation and on demand, the specific responses which define “production” here, they nonetheless tend not to use this capability for mnemonic purposes unless the prompts and suggestions to do so are made quite compelling. It became apparent that model-building was in fact a most effective mediator of recall in this task situation: with rare exceptions, correct reproduction of a six-item test pattern occurred only if S had previously built a paper-form replica of that pattern. One first-grader and four kindergarteners made correct models on at least one trial and then de-

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stroyed them before they could be used to mediate recall, thus exhibiting what could be defined as a mediational deficiency (i-e.,production but no subsequent mediation). As in previous investigations, however, the much more typical response was to utilize effectively whatever was produced. For most S s on most trials, to build a paper model at all was to build it correctly and then to use it correctly. In the few cases (usually first attempts) where the child had incorrectly encoded a wooden-form pattern (“inefficient production”), he almost invariable decoded (i.e., mediated) correctly from whatever he had encoded. It could generally be said, then, that for the great majority of S s at both age levels, modelbuilding was a sufficient condition for model-utilization. While spontaneous production problems abounded, particularly in the younger group, mediational ones appeared to be quite rare at both age levels. E. DAEHLER, HOROWITZ,WYNNS,A N D FLAVELL

The purpose of this experiment was to obtain developmental information about two distinct forms of symbolic-mediational behavior within a common task setting (delayed serial recall). One of them was verbal labeling and rehearsal, familiar from the Flavell et al. and Keeney et d . studies. The other was gesturing-pointing, a non-verbal form of representation but rather different from that investigated by Corsini et af. Colored lights having distinct spatial locations were illuminated sequentially. All S s were in the course of the experiment required to recall only the sequence of colors illuminated, only the sequence of spatial positions at which the lights appeared, or both color sequence and position sequence. Ranken ( 1 963) has shown that different modes of encoding information for mnemonic purposes may be differentially effective as a function of the kind of information to be retained. It seemed intuitively plausible, therefore, that verbal rehearsal of color names would be the more adaptive mediational strategy when storage of color information was required, whereas gestural rehearsal (repeated pointing at the sequence of positions where the lights had appeared) might be more effective when this kind of spatio-temporal information had to be retained. Our expectations were: (1) that older children would spontaneously select that form of rehearsal (verbal or gestural) which seemed best suited to the particular recall task at hand; (2) that younger children would tend to be deficient as regards the spontaneous production of both forms of rehearsal; ( 3 ) that congruent with previous results, their production deficiency would not be accompanied by any significant mediational incapacity. The S s were 20 children from each of Grades K, 1, 2, and 4. After

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having determined in pretest that all S s understood the concept of serial order, E administered a series of 12 test trials: 3 on which only the color sequence was to be remembered followed by 3 position-only trials (for half of each age group), or conversely (the other half); the final 6 for all S s were color-plus-position recall trials. During the stimulus-presentation portion of each trial, S sat alone in an experimental room facing a one-way mirror on which were displayed, one in each quadrant of an imaginary square, four black semi-circles indicating possible light-onset positions. The S knew that a given number of different-colored lights would be successively illuminated ( 5 seconds of Light 1, Light 1 offset, immediate onset for 5 seconds of Light 2, Light 2 offset, etc.) at the various semi-circles, and he knew whether he had to remember the sequence of onset loci, of colors illuminated, or of both. Fifteen seconds after the offset of the last light, E entered the room to administer a nonverbal test of recall. The S demonstrated recall of the light locations by putting magnetized white chips at the correct spatial positions and in the correct temporal sequence on a vertically placed response board, recall of the colors by correctly seriating colored chips in a straight line, and recall of both by performing the first-mentioned responses using colored rather than white chips. Any detectable pointing or color-naming which occurred during the presentation or delay periods of the 12 trials was recorded by observers on the other side of the one-way glass. The data on spontaneous verbalization accorded fairly well with our preexperimental expectations. First, color-name rehearsal did occur almost exclusively in response to instructions to remember color sequences. For instance, of the 40 S s whose first three trials were coloronly, 3 1 were observed to rehearse verbally during the delay period of at least one trial; in marked contrast, only 3 of the 40 Ss whose first three trials were position-only did the same-despite the fact that the actual visual input was of course identical for both groups (i.e., sequentially illuminated colored lights). Second, spontaneous verbal rehearsal during both color-only and color-plus-position trials was positively and significantly related to age, reflecting the anticipated production deficiency of the younger Ss. The deficiency was far from absolute in this task situation, however. Almost all of the younger children at least occasionally named the color of a light at the moment it was illuminated, and more than half engaged in one or more trial’s worth of spontaneous, delay-period rehearsal. As in the Keeney et al. experiment, our impression was that relatively little training or prompting would have been necessary to activate production in the younger nonproducers of our sample, at least on a temporary basis. And finally, while the data did suggest that re-

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hearsal of color names generally had a favorable influence on color-sequence recall, there was no evidence that it was less effective in this respect for younger than for older children (i.e., there was no evidence for an age-related mediational deficiency). Much to our surprise, the data on pointing rehearsal turned out to be completely at variance with the verbalization findings. First, it was much less strongly task-specific: while 22 of the 40 Ss whose initial three trials were position-only showed delay-period gestural rehearsal on at least one of these trials, the corresponding figure for the remaining, coloronly-initial-trials Ss was a substantial 16 out of 40. Second, delay-period gestural rehearsal was about equally common among older and younger Ss. Finally and most tellingly, there was no evidence whatever that the use of pointing rehearsal was at any age level associated with superior recall of position sequences. For reasons which remain unclear, overt gestural rehearsal was apparently just not an effective mnemonic strategy in this particular position-sequence recall task, our expectations (and seemingly, many of our Ss’) notwithstanding. And for “mediators” that do not in fact mediate at any age level, it obviously becomes meaningless to talk about either production or mediational “deficiencies” at the younger age levels.

111. Some Impressions Regarding the Nature and

Development of Mediated Memory It is obvious that the five studies just described could hardly form the empirical base for any substantive theory of mnemonic mediation and its ontogenesis; still less, of course, could they support anything resembling a general theory of the nature and development of “memory” in the broad sense. Taken in conjunction with other studies, however, they have led us to some scientific opinions about certain aspects of this domain of human functioning- opinions rather different in many cases from those we had held at the outset of our research endeavors. A. THENATURE OF MNEMONICMEDIATION

In the present context, “mnemonic mediation” will be somewhat arbitrarily restricted to refer to those cognitive activities which could be deliberately undertaken for the purpose of storing and retrieving input. One must assume that some mnemonic processes -no less “mediational” in the literal sense-are not ordinarily subject to voluntary control; it

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would be such processes which presumably insure, for example, that the most passive of young nonrehearsers is almost certain to recall at least something of the item series presented to him. Present evidence suggests that even within this narrow definition, “mnemonic mediation” may encompass an unexpectedly large and varied assortment of different cognitive activities, an assortment for which the classical schematization r--s (e?g.,H. H. Kendler & Kendler, 1962) somehow seems an inadequate rubric. I n the first place, mnemonic mediators are not confined to any single symbolic vehicle or modality. As our studies have shown, even immature human S s may variously engage in spontaneous verbal, ikonic, or enactive forms of representational activity in their efforts to retain information. Posner (1967) also speaks of visual and kinesthetic “memory codes” (and even of “visual rehearsal”) as alternatives to verbal mediation. In the second place, the nature of the mediational activity can also vary considerably within any given modality. The evidence from our own and other investigations indicates that verbal mediation may be particularly multiform in this regard. In the Daehler et al. study, for example, some children were observed to name the color of a given light just once, as soon as it was illuminated; some to repeat its color name several times over during its 5-second period of illumination; some to rehearse, once or repeatedly, whatever sequence of light colors had been presented up to that point (a sort of “cumulative rehearsal” strategy); and some, of course, to rehearse the entire sequence during the delay period, after all stimulus input had terminated. The spontaneous self-testing and classificatory (manual clustering) operations recorded in the Moely et al. experiment represent additional varieties of verbal-mnemonic mediation. Supplementary evidence can be found in the literature on paired-associate learning. For instance, Martin ( 1 967) had college students learn a paired-associate list comprised of low-meaningfulness paralogs (e.g., meardon-zumap) and afterwards describe how they had attempted to retain each pair. These adult S s reported a whole potpourri of spontaneously-generated mediational tricks, ranging from humdrum rote rehearsal to the creation of all manner of complicated orthographic and semantic-conceptual linkages between the items. For further illustration of verbal-mediational variety, see Adams (1 967). It is also our impression that, in keeping with its above-defined deliberate, intentional character, mediation in memory tasks is frequently a highly selective affair, with particular mediators called into service to suit particular mnemonic demands. The data from the Daehler et al. study gave clear evidence for such selectivity. The colors of the lights were in this particular experimental setting clearly more amenable to

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rapid and discriminative verbal coding than were their spatial positions. Correspondingly, spontaneous attempts at verbal mediation were frequently in evidence when color sequences were to be recalled but very rarely observed when position sequences were to be remembered, despite the fact that the stimulus input included both color and positional information in each instance. In our view, a memory task can profitably be regarded as a type of problem-solving situation in which efforts at mnemonic mediation constitute the means or problem-solving strategy, and recall the goal or problem solution. So viewed, it is hardly surprising to find that mnemonic mediation subsumes a large and heterogenous assortment of cognitive-representational activities and also that these activities are purposefully and selectively employed in accordance with the nature of the recall problem. Underwood appears to be expressing much the same point of view in the following passage ( 1 964, p. 52). The image of a subject in a verbal learning experiment as being a tabula rasa upon which the investigator simply chisels associations. and quite against the S’s wishes. is archaic. The S is far from passive and the tablet has already impressed upon it an immense network of verbal habits. Some of these habits are simple and direct and some are conceptual in their inclusiveness, i.e., t h e y are second-order habits. A more accurate description of the verbal-learning experiment is one in which the S actively “calls upon” all the repertoire of habits and skills to outwit the investigator

Should “mediation” ever be dropped from t h e psychological lexicon, “thinking” or one of its numerous synonyms might well replace it. Mnemonic mediation has a further parallel with problem solving. The mere fact that S deliberately selects some problem-solving approach or strategy when faced with a given problem may reassure you that the problem has indeed engaged his attention and energies, but it hardly tells you that that particular strategy will be a successful one, either absolutely or relative to others he might have tried. Likewise, the spontaneous utilization of a particular mnemonic strategy says nothing about its effectiveness in assisting recall -for this specific recall task and for this specific S. I t is clear that we know very little about mediational effectiveness or efficiency taken as a function of Mediator X Task X S , in either mnemonic or non-mnemonic task contexts. For the Mediator X Task portion of t h e triad and with respect to recall tasks, it is immediately apparent that the conceivable forms of mediation will not likely be even approximately equal in mediational effectiveness for any given task. Of particular note, mediators of the verbal type would not be expected invariably to win out against nonverbal competitors in this regard, despite their almost monopolistic status in the current mediation

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literature and despite their undeniable versatility as storage devices. For example, Ranken (1963) has shown that efforts at visual imagery may prove to be superior to verbal coding when the formal details of novel shapes have to be recalled. Similarly, verbal rehearsal would surely have been an inefficient alternative to model-building (a kind of externalized imagery) in the Corsini er al. task, and its apparent unsuitability for coding positional information in the Daehler er al. task has already been noted. There are some data to support the generalization that the development of mnemonic-mediational activity is partly a matter of progressively “homing in” on the more effective mediator-task pairings. In all five of our studies, evidence that a given mediational strategy is relatively adaptive for a given memory problem has invariably been accompanied by evidence that its spontaneous utilization in that problem is a positive function of age. Martin ( 1 967) has likewise shown that certain types of spontaneously devised mediational strategies lead to better paired-associate learning than others in both younger and older children, and also that the more effective ones tend to replace the less effective ones with increasing age. The generalization appears to have some rough edges, however. On the one hand, it may well be that the typical adult does not utilize what would for him be the most efficacious possible recall strategies in all (or perhaps even any) recall situations (a kind of permanent “production deficiency” for certain mediators). One thinks here of the esoteric but supposedly effective mnemonic techniques used by “memory experts,” some of which have recently been submitted to critical experimental study (e.g., Smith & Noble, 1965). On the other hand, even the oldest children in the Daehler er al. experiment used a plausible, but apparently quite ineffective gestural mnemonic; as indicated earlier, we think that we would have used it too, had we been the S s . Thus, while it does appear that effective mediators become more frequently exploited as the child grows older, some of the ineffective ones may only very slowly, if ever, get extinguished in the course of development. For any specific mediational activity, there may likewise be developmental changes with respect to the manner in which it is executed. There is some evidence, for example, which suggests that verbal-mediational responses normally diminish in amplitude or intensity in the course of ontogenesis. Recall that in the Flavell et al. study we had incorrectly predicted that fifth-graders would show less detectable verbal rehearsal than second-graders, congruent with Vygotsky’s ( 1962) notions about the progressive internalization of nonsocial, cognitive

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speech. It now appears that we may have had the right hypothesis but the wrong age group. R. N . Haber, D. R. Beach, and M. Gross (personal communication) subsequently tested 24 college students at the University of Rochester using virtually the same procedure and exactly the same lip reader (Beach). Although all S s reported having engaged in rehearsal or some other verbal mnemonic in an effort to retain the item sequence, only one showed readable lip movements. A recent study by Murray ( 1967) suggests that they may have done well to verbalize at low amplitude. College students instructed to rehearse silently a series of letters recalled them significantly better than those instructed to do their rehearsing aloud. Murray also made some plausible speculations about this finding. Voicing takes longer, leaving more time for the forgetting of items yet to be rehearsed: the attention devoted to the speaking-act may itself prevent rapid subvocal rehearsal; voiced items might set up more proactive or retroactive inhibition [p. 3641.

Rosenbaum ( 1967) and Hagen and Kingsley ( 1968a) have also reported data suggesting that overt verbalization has its shortcomings as a mnemonic mediator. We suspect that development generally brings with it, not only a better knowledge of just what it may be adaptive to d o when confronted with a specific type of memory task, but also a better knowledge of the more adaptive ways to do it. Finally, it is very probable that, either independently of, o r in interaction with the above-mentioned developmental changes, there are substantial individual differences both in the type of mediational activity favored for any given recall task and in its preferred manner of execution. Kuhlman ( 1960), for example, has found that children with high visual-imagery skills are better than their low-imagery peers at reproducing a visual stimulus from memory. It is not implausible to suppose that such children may lean more heavily on imaginal-ikonic versus, say, verbal forms of mnemonic mediation in a variety of recall situations. As to manner of execution, data from both the Flavell et al. and Keeney et al. studies attest to the likelihood that some child producers “prefer” to rehearse stimulus names at higher response amplitudes (audible naming, visible articulatory movements) than other producers. At the present time, however, there are simply too few facts concerning individual variation in mnemonic-mediational behavior to warrant any speculation as to either its origins or its possible functional significance.

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B. PRODUCTION

AND MEDIATIONAL DEFICIENCIES IN CHILDREN

We shall now offer some tentative conclusions regarding the development of mnemonic-mediational skills, and this implies an examination of the meaning and validity of the production deficiency and mediational deficiency hypotheses. The initial question in the former case is whether, for any symbolic activity likely to facilitate recall, one can in fact expect to find a developmental period during which that activity, although seemingly within the child’s cognitive reach, is nonetheless not spontaneously employed on appropriate memory tasks. That question can now be answered in the affirmative. Developmental transitions from nonproduction to production for several kinds of mediational activities have been consistently observed in our own studies, and suggestive evidence for such transitions can be found in a number of other recent investigations (e.g., Bernbach, 1967; Coates & Hartup, 1969; Gratch, 1966; Hagen & Kingsley, 1968a, 1968b; Jensen & Rohwer, 1965; Kingsley & Hagen, 1969; Martin, 1967; Moely, 1968). Gratch (1966) also reported a developmental increase in detectable verbal rehearsal between 5 and 7 years of age, using a memory task very similar to the one devised by Flavell et al., and several recall studies by Hagen and his co-workers have led them to believe that “spontaneous use of rehearsal strategies is seldom employed by children under 6 years [Hagen & Kingsley, 1968a, p. 61.” The concept of production deficiency has likewise been invoked to explain age differences in children’s performance on other (nonmemory) tasks (Silverman, 1966; Silverman & Craig, 1967), and has even been suggested as a possible explanation for retardates’ deficiencies in pairedassociate learning (Jensen, 1965; Jensen & Rohwer, 1963; Martin, 1967; Milgram, 1967, 1968a). There are, however, complexities and ambiguities in the notion of production deficiency that might not be predicted from the ease with which it can be demonstrated in young children’s task performance. Two will be mentioned here, with others appearing and reappearing throughout the remainder of this section. First, a production-deficiency versus some other characterization of the child’s performance seems warranted in direct proportion to one’s conviction that this particular child really could have produced the target mediator spontaneously, and that his failure to emit it is virtually all one can find to differentiate him from a producing child. The first-grade nonproducers in the Keeney et al. study would be cases in point. Although able to assume and execute an E-induced rehearsal set with apparent ease, when later given the opportunity they quickly reverted to what had previously been established as a stable and persistent pattern of nonrehearsal for them. Would

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one as readily characterize as “production deficiency” the nonrehearsal pattern of, say, a group of 4-year-olds in the same task situation, even if it could be shown that they “knew” the stimulus names? We would certainly be less confident that they were really capable of continuously maintaining a recall set, or really capable of sustained rehearsalin the absence of the stimuli (as opposed to one-shot labeling in their presence) on those occasions when the set was maintained.* We had originally coined the term “production deficiency” to describe a (then) hypothetical situation wherein S “doesn’t” but “could have”; it is now clear that its full explication will eventually demand a tighter specification of the “could have”-in addition, of course, to an explanation of why it is ever coupled with a “doesn’t” rather than a “does.” The second point is closely related to the first. It now seems certain that production itself, like the underlying capability for production just discussed, is not an all or nothing affair, and that there can be a whole gamut of intermediaries between a smooth and flawless execution of some mediational response pattern and no attempt to execute it at all. For instance, Kingsley and Hagen ( 1 969) tried to induce a group of nursery school Ss (barely 5 years of age) to rehearse aloud the names of a series of objects as the series was progressively constituted (what Daehler et af. had described as “cumulative rehearsal”). To quote the authors: Most of the . . . subjects understood in principle what was required of them, but only a few actually had much success in consistently and correctly rehearsing. Often S s rehearsed the first two or three items relatively well but found rehearsal of four and five items difficult [p. 451.

Recall also that Corsini et af. found instances of inaccurately-constructed paper-form models, i.e., where the child failed to make a correct ikonic encoding of the wooden-form pattern. Such “production inefficiencies,” as Corsini et af. christened them, were even more clearly evident in a just-completed study by Ryan, Hegion, and Flavell (1970). The major purpose of the study was to investigate the early beginnings of the ability to utilize Corsini el al. type ikonic mediators as a recall aid, and hence the task materials and procedures were carefully designed to maximize the likelihood that any budding ability of this kind would be realized in S’s task performance. The Ss were 50 preschoolers, approximately 10 at each half-year interval between 3.0 and 5.5 years. A small number of lifelike toy animals were inserted in a series of adjacent “zoo cages,” one of each species in each %See the quotation from the Kingsley and Hagen (1969) study in the following paragraph.

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cage. The cages were bisected by sliding doors such that, with the door in the closed,>osition and the animal in the rear half of its cage, it was no longer visible to S. The S was shown a duplicate set of animals and was told that each one “wanted” to be placed in the cage that contained his “friend” (i.e., a conspecific), and that he would be “unhappy” if mistakenly caged with an animal of a different species. Also available was a set of color photographs of each animal. After the first set of animals (R, = referent,) had been placed in the rear of each cage, S was told that the partitioning doors would shortly be closed and that as soon as they were, he would be given the second set of animals (R2) and would have to put them in their correct cages. It was suggested that he might do something with the pictures (S = symbol) now, while the doors were open and the R,s were visible, which would later assist him in making accurate R2 placements. In analogy with the Corsini et al. task, “production” was defined as placing each S in optical correspondence with its R, referent (e.g., at the base of its cage), and “mediation” as using the location of the Ss to guide the subsequent (with the R,s now nonvisible) placement of the corresponding R,s. Five trials were given, followed by either the first or both of two E-modeling trials, depending upon S’s performance; the first was wholly nonverbal, E silently demonstrating the above mentioned production-mediation sequence, whereas the second consisted of demonstration-plus-verbal-explanation. The data clearly showed that a number of these preschool children were quite capable of spontaneously and deliberately utilizing pictures as ikonic symbols to mediate their recall, given a facilitative, “cooperative” task setting; as would be expected, this capability was significantly age dependent across the 3 to 5% year age range. Thus, no fewer than 28 of the 50 S s produced and mediated perfectly on two successive trials during the initial five-trial sequence, and only 8 Ss never performed correctly, i.e., following two demonstrations by E. Of particular interest for the present discussion was the fact that putative production inefficiencies were about as common as outright production deficiencies on those trials where performance was not fully correct. The S might not touch the pictures at all, or merely finger or sort them (production deficiency). Alternatively, however, he might put only one S in correspondence with one R, (and later use it correctly to mediate that one R2 placement); he might put one S inside the cage, adjacent to its R1, so that it too was later screened from sight by the door; he might try to place S in correct position after, rather than before, the cage door was closed, and so on. We feel sure that at least some of these various behaviors reflected an intuition of the possible mediating function of the pictures coupled with some uncertainty or lack of skill (usually

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temporary) as to just how they should be made to perform that function. Our suspicion, then, is that production inefficiency may be a fairly frequent developmental precursor to efficient production, both where production is left to occur more or less spontaneously (our studies) and where it is experimentally induced at some ontogenetic remove from its normal age of spontaneous acquisition (the Kingsley and Hagen study). Assuming the production of a mnemonic mediator of proven effectiveness in older Ss, is there also a developmental period during which it fails to mediate (mediational deficiency)? There was certainly very little evidence for such periods in our initial five studies. Only one S in the aforementioned Ryan, Hegion, and Flavell study completely failed to utilize established S-R, contiguities to guide his subsequent placement of the R,s (mediational deficiency), and he only did so on one trial; a somewhat larger number of Ss made performance errors in attempting to utilize them (“rnediational inefficiency”). Despite the chronological immaturity of the S s in the Ryan et al. study, the predominant errors were clearly on the production side. Boat and Clifton (1968) also obtained clear-cut evidence of mediational abilities in preschool children (4-yearolds), using three paired-associate lists embodying a simple chaining paradigm (A-B, B-C, A-C). The evidence for mediational deficiencies is also meagre in studies by others, for instance, most of those cited earlier in this chapter. In fact, an investigator’s inference that his younger Ss are production-deficient is often based on data suggesting that they are not mediation-deficient. Suppose that it is found that E‘s provision of mediators to his older Ss does not significantly improve their performance, relative to that of a control group of the same age. The normal inference would be that children of this age produce and use these mediators spontaneously, and hence E‘s intervention was superfluous; these Ss would then be described as neither production-deficient nor mediation-deficient. Suppose that it is also found that provision of these mediators does significantly benefit the performance of the younger ss, again relative to that of their same-age controls. This finding-that they are not mediation-deficient - permits the inference that they are production-deficient, i.e., the poorer performance of the control Ss is attributable to the fact that they were not spontaneously producing the mediators. A recent study by Coates and Hartup (1969) is a case in point. Four-year-old and seven-year-old children observed a filmed model perform relatively novel and unexpected actions under one of three conditions: (1) induced verbalization (IV group), with S repeating aloud E’s standardized verbal description of each observed action as it occurred; (2) free verbalization (FV group), with S instructed to describe each action aloud in his own words; (3) passive observation (PO group), with no

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verbalization instructions given. For the older Ss, the recall levels were IV PO > FV, suggesting that the PO Ss had been spontaneously verbalizing the model’s actions covertly (IV PO), and perhaps thatrecall our earlier discussion of Murray’s ( 1967) findings -covert or semicovert self-codings may have been somewhat more effective mediators of recall than fully overt self-codings (PO > FV). For the younger Ss, the recall levels were IV > FV > PO, all differences highly significant, suggesting both the presence of a production deficiency (FV > PO and IV >PO) and the absence of a mediational deficiency; the IV > FV difference presumably reflects the greater precision (and hence, greater mnemonic-mediational potential) of E’s verses S’s verbal codings of the model’s actions. While it can thus be concluded from the existing evidence that mediational deficiency is a far less frequent and important determinant of nonmediated recall performance than is the production one, task conditions that might yield such a deficiency can at least be imagined. Our present guess is that the likelihood of finding a mediational deficiencyor, in analogy with the production case, a “mediational inefficiency” will be markedly dependent upon the precise conditions attending the production of that mediator. If one assumes, as we have been doing, that the production of mnemonic mediators is akin to attempts at problemsolving, then the provenance of that production might well affect its functional efficacy. As a general rule, E-induced mediator production ought to be less certain to have the expected mediational consequences than production of the spontaneous variety, since we can be surer in the latter case, as with self-generated problem-solving activities, that S really understands what he has done and sees its relevance to the recall test. “Marat-Sade” would not likely be an effective mediator for an 8year-old who is trying to remember “revolution,” “drama,” and “lunacy,” although he might humor you by producing it on command. Similarly, there probably exist mnemonic mediators which I could use but you could not, and conversely. This is, of course, not to imply that all induced production should be mediationally ineffective, even in those instances where S may have no conscious inkling of why he is being made to engage in it. Unlike the “Marat-Sade” example, enforced repetition of the names of familiar objects would likely have a positive effect on object recall for any S who knew their referents: the mediational link is maximally direct, preexperimentally overlearned, and should hence be virtually automatic for even very young Ss. It is noteworthy in this connection that the recall level of Kingsley and Hagen’s (1969) nursery school children actually did benefit from induced rehearsal, despite their aforementioned difficulties in complying with E’s rehearsal instructions.

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If it is really the case that spontaneous production, being intentional and goal-directed, almost always yields its expected quantum of mnemonicmediational effectiveness, and also that induced - even mindless - production may frequently do the same, it is not to be wondered at that mediational deficiencies are much more often sought than found. We need hardly add that if those which can be found really owe their existence solely to S’s incomprehension of the meaning and purpose of the mediational activity under study, that is, to the fact that S’s production is mindless, then mediational deficiency would have to be regarded as a theoretically trivial as well as empirically rare developmental datum. Assuming, then, that it is the transitions from nonproduction to production that comprise the significant developmental phenomena in this area, what additional conclusions can be tentatively made concerning these transitions? In analogy with most other developmental acquisitions (Flavell & Wohlwill, 1969), it can be surmised that the age of transition will be a joint function of both the nature of the mnemonic mediator considered and the nature of its eliciting task setting. There exists, as we have seen, a variety of possible mnemonic mediators. Neither common sense nor the existing evidence would lead one to believe that they are all acquired at the same mean age. For example, there are at least hints from Kingsley and Hagen’s (1969) study and from three of our own (Flavell et al., Daehler et al., and Moely et a/.) that genuine verbal rehearsal may be a later-developing mediational tactic than simple, unrepeated stimulus-naming. In turn, spontaneous and deliberate efforts at finding conceptual and associative linkages among items to be recalled probably emerges later in ontogenesis than does verbal rehearsal (Jensen & Rohwer, 1965; Martin, 1967; Moely et al., 1969). And finally, the results of the Ryan et al. study suggest that the capability for some forms of ikonic mediation may appear very early, prior to verbal rehearsal and possibly in rough synchrony with simple stimulus-naming. The analogy with problem solving comes once again to mind: some mnemonic-mediational strategies (problem-solving strategies) require more cognitive maturity than others, and their acquisitions are correspondingly ordered in ontogenesis. For any one of these mediators, however, the age of transition from nonproduction to production should also depend very heavily upon the specifics of the task conditions under which it is assessed. One class of specifics includes the nature of Es behavior toward S. H e may do nothing in the way of prompting S’s production; he may provide weak and indirect suggestion; or he may provide explicit instruction, direction, or modeling. Such variations in Es behavior have already been shown to have very powerful effects on mediator production and utilization in the

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Keeney et al., Corsini et al., and Moely et al. studies; similarly, Es modeling of the S-R1 and S-R, linkages in the recently completed Ryan et al. investigation was for 14 Ss a necessary but sufficient condition for production (recall that it was not sufficient for 9 others, however). An input from E that is sufficient to elicit production will not necessarily be sufficient to sustain it, as the post-input behavior of the nonproducers in the Keeney et al. study demonstrates; similar findings have also been reported by Milgram (1967, 1968b). The physical aspects of the task setting are also likely to be important variables. The gap in age for ikonicmediator production in the Ryan et al. versus Corsini et al. investigations must have been largely explainable on this basis (e.g., the use of animals versus abstract geometrical forms, of photographs versus paper replicas, etc.). Subtle differences in both mediational activity and task conditions may have been responsible for the following putative developmental sequence, constructed from the Flavell et al., Keeney et al, and Moely et al. data: (1) verbalization of stimulus names during the study periods of the Moely et al. task (very frequent among kindergarten Ss); (2) verbalization of stimulus names during the brief delay periods between stimulus offset and recall testing in the Flavell et al. and Keeney et al. task (infrequent prior to Grades 1-2); (3) self-testing, i.e., deliberately averting one’s head from the stimuli during the study periods of the Moely et al. procedure and verbalizing their names, presumably for purposes of rehearsal and/or monitoring of progress (infrequent prior to Grade 3). Consider first the sequence (1) + (2). In the Moely et al. task, the object pictures were continuously visible for a full 2 minutes on each trial, whereas they were of course out of the child’s sight during the delay periods of the Flavell et al. and Keeney et al. procedure. Whether one prefers to characterize this as a difference in the type of mediator used (stimulus-naming versus rehearsal) or a difference in task conditions (stimuli present versus absent), it is plausible that it could help account for the observed sequence. Moreover, the Ss in the Moely et al. experiment had to indicate their recall of the objects by naming them, not merely by pointing to them in sequence as was the case in the other two studies. This difference, more clearly of the taskconditions variety, may also have played a causal role, i.e., with naming during recall “priming” naming during stimulus presentation or something of the sort. Recall that having to name the stimuli at stimulus presentation and at test in the Flavell et al. study (supplementary series) increased delay-period rehearsal in the kindergarten group. (3), one again takes his choice between As for the sequence (2) mediator and task variables. Delay-period rehearsal is a subject-pro-

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duced activity made in response to an experimenter-produced physical isolation from the objects whose names are rehearsed. In contrast, selftesting is a subject-produced activity made in response to a subject-produced isolation (averting the eyes, etc.). Thus, the first-grade producer in the Keeney et al. study rehearsed despite the absence of the stimuli; in contrast, the third- and fifth-grade self-testers in the Moely et al. study did the same despite their presence, a much more subtle and maturelooking mnemonic tactic but, like both (2) and ( l ) , no less a form of “verbal mediation.” Although some suggestions have just been made about factors that may affect the developmental timing of nonproduction-production transitions, the basic fact that such transitions exist is not thereby fully explained. While the author is frankly uncertain as to exactly what a “full explanation” of any cognitive-developmental phenomenon ought in principle to look like (an uncertainty probably shared by many other developmental psychologists), he is at least sure that none is yet at hand regarding production deficiency and its remediation. For whatever it may be worth, our current belief is that these transitions may reflect underlying cognitive-developmental changes of two types, specific and general. The specific ones would refer to the particular cognitive activities which underlie the use of particular mnemonic mediators, each form of mediational activity being assumed to comprise its own unique constellation of skills. In the case of verbal rehearsal, for example, we could suppose that the growing child increasingly overlearns verbal-label responses to object stimuli, becomes increasingly skillful at rapid, subovert articulation of a string of labels, becomes better attuned to the sequencing and recycling (starting again at the first word) “rules” of repeated rehearsal, and the like. As these component skills mature, verbal rehearsal becomes a more serviceable and hence more readily elicitable response pattern in a variety of appropriate situations, including those in which it could serve to mediate recall. One supposes further that, for this mediator especially, formal schooling with its heavy emphasis on verbal skills may play a powerful acquisition-fostering role. The general change might consist of an increasing propensity, both in recall tasks and in many others which have a similar means-to-ends structure, to search the repertoire for activities to perform now, the performance of which has no immediate relevance but will facilitate some other activity subsequently (in this case, recall). This propensity - we have recently come to term it “planfulness” or “planning ability” -is not the exclusive skill-component property of any one specific mnemonic mediator; rather, it could be viewed as a kind of cognitive “executive

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routine” which tells S that the search for a mnemonic mediator is in order when faced with a recall task. Thus, an explanation of some instances of nonproduction - nonrehearsal, say - might simply be s’s inability to rehearse easily and efficiently (a specific factor). An explanation of other (or the same) instances, however, might be S’s failure to keep the goal continuously in mind, and to recognize fully that he ought to be doing something of a planful nature now to make its subsequent attainment more probable (a general factor). Actually, the transition from nonproduction to production for any given mediator would probably entail an interplay or interaction between both kinds of developmental change. It is perhaps easiest to imagine such an interaction as proceeding from the general to the specific: with increasing cognitive maturity, the child is more and more likely to think of acting planfully in recall situations, and thus to look for some mnemonic; if, say, skill at verbal rehearsal is also sufficiently advanced at that point in his ontogenesis (and if, of course, this recall task lends itself to verbal-rehearsal management), the child will then likely find and use that particular mnemonic. A flow in the opposite direction is also conceivable, however: with the child sufficiently mature for verbal rehearsal to have a low threshold as a response in this particular situation (given that the stimuli to be recalled have familiar, one-word labels, etc.), rehearsal may occur initially in an almost reflexive fashion; its usefulness as a mediator may then become only gradually apparent, perhaps as a consequence of feedback as to its effects on recall. It may even be that the sense of planfulness of which we have been speaking develops in part as a consequence of the maturation and repeated (initially nonplanful) utilization of potentially mediative actions, a notion reminiscent of Mandler’s ( 1962) “association-to-structure” conception and of Piaget’s (1 952) theory of the early genesis of intentionality. Although we of course cannot be sure, it was our impression that the microgenesis of ikonic mediation in the Ryan et al. task went from a sense of planfulness to picture-utilization in some S s and from picture-utilization to a sense of planfulness in others. Thus, one child might simply stare at the pictures, apparently aware that he ought to do something with them to assist subsequent R1-R2matchings, and then suddenly intuit the whole solution. In contrast, another might idly bring the pictures up next to their animal referents on one or more trials (a prepotent, high-probability response to these particular task materials for young children, we think, even without a recall set) and, seemingly, induce a means-to-ends, planning set in the course of going from S to R2.In summary, the hypothesis is that many of the observed developmental changes in children’s behavior in recall settings may be joint consequences of an increasing sensitivity

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to the need for planful and preparatory activity, to be carried out prior to the recall test, coupled with an increasingly varied repertoire of serviceable mediators from which to select for this purpose.

c. IMPLICATIONS

FOR

FURTHER RESEARCH

Many of the conclusions we have proffered concerning mnemonic mediation and its development are very speculative, perhaps excessively so. There is, therefore, an obvious need for more and better research evidence to confirm them or, where incorrect, to suggest alternatives. Rather than try to sketch out specific research designs for specific points of interpretative insecurity, however, we shall conclude by simply offering two general recommendations for future research. Although they are closely related, one is methodological and the other substantive. The methodological suggestion is to investigate the occurrence-nonoccurrence and the structure of ordinarily covert mediational activities by rendering them observable, insofar as present research technology, the investigator’s imagination, and the nature of the activity studied will permit. While it is true that inferences about mediational activity can and often have been made from indirect evidence (e.g., from S’s recall performance), direct, observational data are surely better when and where they can be had. We believe that our conclusions regarding production versus mediational deficiencies are far more secure for the fact that we attempted to observe rather than infer the presence-absence of phenomena such as rehearsal (Flavell et ul., Keeney et ul., Daehler et ul.), ikonic mediation (Corsini et af.,Ryan et ul.), and clustering (Moely er ul.), Furthermore, whereas direct, observational methods may be merely preferable for a diagnosis of production versus nonproduction, they are probably indispensable if one wants to learn anything about the structure and developmental status of whatever mediational activity was produced. Ikonic mediation is the best illustration at hand: the encoding and decoding activities elicited by the Corsini et al. and Ryan et al. tasks are fully externalized and must by their very nature proceed at a pace easily monitored by an observer (one picture placed next to one animal, then another, etc.). As such, the investigator can detect and classify S’s errors and false steps (production and mediational inefficiencies), and from these hopefully make good inferences about the psychological structure of this simple-looking form of symbolic-mediational activity. The substantive suggestion is as follows. The mnemonic-mediational behaviors we have been studying bear a close relationship to a real-life activity to which many, many childhood hours are devoted, namely, studying. Very little is known concerning just how children of different

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ages set about trying to commit information of various sorts to memory. The research described in this paper suggests that there would be significant developmental changes in children’s “operant studying behavior,” that is, in what they do when left alone with material they are to learn, e.g., when doing homework. In keeping with the methodological point made above, ways might be found to gain observational access to this private-looking behavioral preserve. How do children of different ages spontaneously order and organize data which are to be learned? How do they assess their own progress in mastering them (recall the curious selftesting procedures devised by the older children in the Moely et al. experiment)? Answers to such questions might have important educational as well as scientific theoretical uses. We have yet to appraise thoroughly the variables for teaching effective mediators, but the practical implications of this method are large. There is no reason why schoolteachers of future generations should not show students ways of learning materials that will result in their high recall. At present, students are given materials for learning and are left to their own memory devices. How much better it would be if an instructor told the students about proved mnemonic devices and saw that they used them in systematic ways [Adams, 1967, p. 1341.

IV. Summary This paper reports and interprets recent studies dealing with the development of mnemonic-mediational skills in children, e.g., verbal rehearsal. The following were among the major conclusions suggested by the available evidence. ( 1) There are many different types of mnemonic-mediational activities, even within a single system of symbolic representation such as the verbal one. Mnemonic mediation is best conceived as a planful, instrumental, cognitive act, akin to problem-solving behavior. (2) Descriptively, the developmental course of acquisition of any given mnemonic mediator typically consists of an age-dependent increase in the likelihood of its spontaneous occurrence in appropriate recall situations (production deficiency + production), rather than an age-dependent increase in the likelihood that, given its occurrence, it will mediate recall effectively (mediational deficiency + mediation). Mediator production is not an all or nothing affair, however; developmental intermediaries (“production inefficiencies”) between nonproduction and efficient production are probably the rule rather than the exception. (3) The average age of transition from nonproduction to production varies both with the particular mediator studied and with the particular

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task conditions (stimuli used, testing procedure, E's instructions, etc.) which elicit it. (4) The passage from nonproduction to production of any mnemonic mediator may be the joint resultant of cognitive-developmental changes at two levels: (a) a general, mediator-nonspecific ontogenetic movement toward greater planfulness (tendency to look for present means to the attainment of future ends): (b) the gradual acquisition and perfection of the specific cognitive skills which underlie, or constitute the components of, specific mnemonic -mediational activities.

ACKNOWLEDGMENTS The author is grateful to Marilyn Rea for her assistance in gathering and processing data, to Mervyn 0. Bergman for his technical assistance, to the personnel of the schools from which the Ss were obtained, and to the many students and colleagues who made invaluable contributions to the research project.

REFERENCES Adams, J . A. Human memory. New York: McGraw-Hill, 1967. Bernbach, H. A. The effect of labels on short-term memory for colors with nursery school children. Psychonornic Science, 1967,7, 149- 150. Boat, B. M., & Clifton, C., Jr. Verbal mediation in four-year-old children. Child Development, 1968,39,505-514. Bruner, J . S., Olver, R. R., & Greenfield, P. M. (with others). Studies in cognitive growth. New York: Wiley, 1966. Coates, B., & Hartup, W. W. Age and verbalization in observational learning. Developmental Psychology, 1969, 1, 556-562. Corsini, D. A., Pick, A. D., & Flavell, J. H. Production of nonverbal mediators in young children. Child Development, 1968, 39,53-58. Daehler, M. W., Horowitz, A. B., Wynns, F. C., & Flavell, J. H. Verbal and nonverbal rehearsal in children's recall. Child Development, 1969, 40, 443-452. Flavell, J . H., Beach, D. H., & Chinsky, J. M. Spontaneous verbal rehearsal in a memory task as a function of age. Child Development. 1966,37,283-299. Flavell, J. H., & Wohlwill, J. F. Formal and functional aspects of cognitive development. In D. Elkind & J. H. Flavell (Eds.), Studies in cognitive development: Essays in honor ofJean Piaget. London & New York: Oxford University Press, 1969. Pp. 67-120. Gratch, G. The use of private speech by Head Start and middle class preschoolers: An investigation of the mediating function of language in a non-linguistic memory task. Paper presented at the meeting of the Southwestern Psychological Association, Arlington, Texas, April, 1966. Hagen, J. W., & Kingsley, P. R. Developmental studies of verbal labelling effects on memory. Paper presented at the meeting of the Midwestern Psychological Association, Chicago, May 1968. (a)

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Hagen, J. W., & Kingsley, P. R. Labelling effects in short-term memory. Child Development, 1968.39, 113-121. (b) Jensen, A. R. Rote learning in retarded adults and normal children. American Journal of Mental Deficiency, 1965, 69, 828-834. Jensen, A. R., & Rohwer, W. D., Jr. The effect of verbal mediation on the learning and retention of paired associates by retarded adults. American Journal of Mental D e j ciency, 1963, 68, 80-84. Jensen, A. R., & Rohwer, W. D.. Jr. Syntactic mediation of serial and paired-associate learning as a function of age. Child Development. 1965,36,601-608. Keeney, T. J., Cannizzo, S . R., & Flavell, J . H. Spontaneous and induced verbal rehearsal in a recall task. Child Development, 1967,38,953-966. Kendler, H . H., & Kendler, T. S . Vertical and horizontal processes in problem solving. Psychologicul Review, 1962, 69, 1- 16. Kendler, T. S. Development of mediating responses in children. In J. C. Wright & J. Kagan (Eds.), Basic cognitive processes in children. Monographs ofthe Societyfor Research in Child Development, 1963, 28(2), 33-52. Kingsley, P. R., & Hagen, J. W. Induced versus spontaneous rehearsal in short-term memory in nursery school children. Developmental Psychology, 1969,1,40-46. Kuhlman, C. K. Visual imagery in children. Unpublished doctoral dissertation, Radcliffe College. 1960. Luria, A. R. The genesis of voluntary movements. In N. O’Connor (Ed.), Recent Soviet psychology. New York: Macrnillan (Pergamon), 1961. Pp. 165-185. Maccoby, E. E. Developmental psychology. Annual Review of Psychology, 1964, 15, 203-250. Mandler, G. From association to structure. Psychological Review, 1962, 69,415-426. Martin, C. J. Associative learning strategies employed by deaf, blind, retarded and normal children. Final Report, 1967, Office of Education Grant No. 5-0405-4-1 1-3. Milgram, N. A. Retention of mediation set in paired-associate learning of normal children and retardates. Journal of Experimental Child Psychology, 1967,5, 341 -349. Milgram, N. A. The effect of verbal mediation in paired-associate learning in trainable retardates. American Journal of Mental Dejciency, 1968, 72, 5 18-524. (a) Milgram, N . A. The effects of MA and IQ on verbal mediation in paired associate learning. Journal ofGenetic Psychology, 1968, 113, 129-143. (b) Moely, B. E. Children’s retention of conceptually related items under varying presentation and recall conditions. Unpublished doctoral dissertation, University of Minnesota, 1968. Moely, B. E., Olson, F. A., Halwes, T. G., & Flavell, J. H. Production deficiency in young children’s clustered recall. Developmental Psychology, 1969, 1, 26-34. Murray, D. J. Overt versus covert rehearsal in short-term memory. Psychonomic Science, 1967, 7, 363-364. Piaget. J. The origins of intelligence in children. New York: International Universities Press, 1952. Posner, M. I . Characteristics of visual and kinesthetic memory codes. Journal of Experimental Psychology, 1967,75, 103-107. Ranken, H . B. Language and thinking: Positive and negative effects of learning. Science, 1963,141,48-50. Reese, H. W. Verbal mediation as a function of age level. Psychological Bulletin, 1962,59, 502- 5 09. Rosenbaum, M. E. The effect of verbalization of correct responses by performers and observers on retention. Child Development, 1967,38, 614-622.

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Ryan, S. M., Hegion, A. G . , and Flavell, J. H. Nonverbal mnemonic mediation in preschool children. Child Development, 1970, 40, in press. Silverman. I. W. Effect of verbalization on reversal shifts in children: Additional data. Journal of Experimental Child Psychology, 1966, 4, 1-8. Silverman, I. W., & Craig, J . G . The roles of encoding practice and enforced decoding in verbal mediation: A developmental study. Paper presented at the meeting of the Society for Research in Child Development, New York, March 1967. Smith, R. K.. & Noble. C. E. Effects of a mnemonic technique applied to verbal learning and memory. Percepfual and Motor Skills, 1965.21. 123-134. Underwood, B. J. The representativeness of rote verbal learning. In A. W. Melton (Ed.), Categories of human learning. New York: Academic Press, 1964. Pp. 47-78. Vygotsky, L. S. Thought and Language. Cambridge, Mass.: M.I.T. Press and New York: Wiley, 1962.

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DEVELOPMENT AND CHOICE BEHAVIOR IN PROBABILISTIC AND PROBLEM-SOLVING TASKS

L . R . Goulet' and Kathryn S. Goodwin WEST VIRGINIA UNIVERSITY

I . INTRODUCTION

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I1. PROBABILITY LEARNING

A . DEFINITIONS AND METHODS .......................... B EARLY RESEARCH ...................................... C . DESCRIPTIVE DEVELOPMENTAL CHANGES IN PROBABILITY LEARNING ............................... D VARIABLES INFLUENCING PROBABILITY LEARNING: TASK VARIABLES ......................................... E TRANSFER O F TRAINING ................................ F . THEORETICAL INTERPRETATIONS O F AGECHANGES IN PROBABILITY LEARNING .................. G INCENTIVE ............................................... H COMMUNALITY OF RESPONSE PATTERNS ACROSS TASKS AND SUBJECTS ....................................

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GUESSING BEHAVIOR .................................. ALTERNATION BEHAVIOR .............................. STUDIES O F T H E DEVELOPMENT O F THE PROBABILITY CONCEPT ............................................... 248

OVERVIEW

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REFERENCES

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I. Introduction The study of children’s performance in probability-learning tasks is of recent vintage but nevertheless occupies much current interest. This interest apparently stems from the rather striking developmental changes that have been observed when these tasks are used, and from the current view that these tasks represent an approach to the study of problemsolving and, as such, have utility in the assessment of developmental changes in problem-solving strategies. Furthermore, probability-learning paradigms have more-than-apparent similarity to discrimination learning tasks, the multiple-choice tasks used to study response preferences, gambling behavior, etc. In addition, there is a considerable body of research and theory related to other similar problems, e.g., the development of the concept of probability and “spontaneous alternation” behavior, most of which has just recently been seen as related to the probability learning literature. The present purpose is to provide a general review of the research related to probability learning and similar tasks, with an emphasis on data collected using children as subjects. More specifically, an attempt will be made to provide some degree of integration of the literature related to developmental changes in choice behavior. There are recent reviews focusing on response preferences (Tune, 1964a, 1964b), spontaneous alternation behavior (Dember, 1961; Schultz, 1964), and probability learning (e.g., Atkinson, Bower, & Crothers, 1965; Estes, 1964) in young adult subjects. This research will be cited only as it relates to the focus of this paper. In addition, Gerjuoy and Winters ( 1968) have summarized the literature related to response preferences and choice behavior of retardates; the work cited therein will also be discussed only as it assists in the elaboration of the present data.

11. Probability Learning A. DEFINITION AND METHODS

1. .Nature and Utility of the Tasks The difficulty in specifying just what tasks or experimental situations should be included in a review of probability learning is made evident by Estes (1964), who noted that “probability learning is easier to identify than to define [p. 891.” However, probability learning like many familiar types of learning classifies as a “type” because of the communality of problems and procedures around which research activity is centered.

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Although it is rather easy to distinguish the studies that are relevant to this problem, it can be noted just how close the study of probability learning is to other areas of interest. In fact, the oldest variant of the probability-learning designs was devised by Humphreys ( 1 939) as a verbal analogue to Pavlovian conditioning (Atkinson et af., 1965). Moreover, in some instances, probability learning seems to be simply a special case of discrimination learning. If one considers a simple discrimination problem with partial reinforcement of a position discrimination, one finds exactly the same task often used in probability learning. The research in probability learning is generally concerned with two types of behavior. Some research is designed to assess the subject’s understanding of the nature of probability events (e.g., Yost, Siegel, & Andrews, 1962), while other research involves the use of the probability-learning tasks for evaluating problem-solving behavior (e.g., Weir, 1964). Although it is of interest to see how concepts of probability are developed, it appears more likely that the study of problem solving will be more productive for learning theory in general. As Brunswik (1939, 1943) has argued, the probability-learning paradigm, where partial reinforcement is the rule, is more representative of everyday life than the classical learning situations which involve 100% reinforcement. Typically, means to a goal are rarely absolutely reliable or absolutely wrong. The tasks most commonly used in the study of probability learning have been those where subjects are reinforced on some specified (in most cases experimenter-determined) partial reinforcement schedule for choosing or responding to one or a combination of stimuli from a finite array. The two-choice problem best exemplifies the nature of the task. In this case, subjects are instructed to predict which of the two events will occur on each of a series of trials. The schedule of partial reinforcement is typically determined such that one of the available stimuli is presented at a level considerably above chance but below unity and the other stimulus is presented on the remaining trials. For example, in a 70:30 task the fixed proportions of occurrence of two events over a block of trials are 70 and 30%, respectively. However, even though the events are presented in fixed proportions over the total number of trials, each occurs in a random (nonpredictable) sequence, limited only by the partial reinforcement schedule. There are a number of variations of the task and these will be specified in detail at a later point in the paper. However, it may be fruitful to specify just what can be “learned” in a task of this nature. First, subjects can obtain information regarding the percentage of occurrence of each event over the block of trials. Second, subjects can “learn” or deduce the optimum strategy for maximizing the number of “hits” (correct predictions). In the example cited above, the number of hits can be maxi-

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mized by predicting the most frequently occurring event on every trial. Third, subjects can “learn” which strategies do not maximize hits; i.e., nonefficient (incorrect) strategies can be inhibited. The last statement may be merely rephrasing what was said above, but its inclusion immediately makes apparent the possibility of the reinforcement and maintenance of “superstitious” behavior in tasks of a probabilistic nature. To the extent that subjects are reinforced (albeit on a partial-reinforcement schedule) for predicting the least frequently reinforced event, or for sequential behavior involving response patterns, the probability of occurrence of these behaviors can increase and be maintained. Each of the above problems is discussed in detail below. Why are these tasks used in developmental research? (a) Perhaps the most apparent reason is that performance measures can be obtained from a wide variety of subjects, i.e., the ability to perform on these tasks is, for the most part, independent of language skills, intellectual ability, etc. (b) Furthermore, the data obtained seldom suffer from “ceiling” or “floor” effects, which prevent statistical comparisons when tasks are too easy or too difficult for some or all of the subjects tested. (c) A wide variety of independent variables can be manipulated without modifying the essential nature of the task. For example, performance comparisons have been made under varying levels of incentives, both material and social, and sociopsychological variables such as social class (Odom, 1967; Rosenhan, 1966), sex of the experimenter (Odom, 1966), social deprivation (e.g., Lewis, 1965), reward and/or punishment (Das & Panda, 1963; Gruen & Weir, 1964; Offenbach, 1964), have been used. (d) Finally, the behavior manifested in tasks of this nature has been considered to reflect strategies of problem-solving characteristic of the age groups being studied. Indeed, much of the recent research has been oriented to the discovery of such strategies. The tasks involving choice behavior provide the opportunity for subjects to utilize widely variable “strategies” under identical conditions. Such strategies may be those which subjects bring to the laboratory, i.e., preexperimental strategies which are a function of maturational and/or experiential factors. Such strategies should be reflected in the performance in the early stages of practice. In contrast, asymptotic performance, i.e., behavior manifested in the later stages of practice, after which the subjects’ responding has reached a steady state, at least theoretically reflects a strategy which has been adopted as a result of the reinforcement of certain patterns of behavior and/or nonreinforcement of other patterns. The change and rate of change in performance from the early stages to later stages of practice, therefore, reflect the systematic elimination of inefficient strategies and/or acquisition of efficient strategies.

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2 . Methods In a manner similar to discrimination learning (e.g., Lipsitt, 1961; Spiker & Lubker, 1965), the tasks may be presented according to simultaneous or successive methods. With the simultaneous method of presentation, each of the stimuli is available to the subjects for selection on every trial; in the successive method only a warning signal or warning stimulus is presented and the subject must designate which stimulus of the array is to appear following his response. This distinction is important because, in addition to differences in method of presentation, another variable, information feedback, is typically confounded. That is, the successive method conveys information as to the reinforced stimulus on every trial whether or not the subjects choose or predict correctly. The typical procedure of simultaneous presentation conveys information regarding the correct response only if the subject chooses correctly or if the experimental procedure is such that the reinforced stimulus is identified whether or not the correct response is chosen. Providing information feedback on every trial has been called a noncontingent information feedback because such feedback is not dependent on the subject’s response. Similarly, contingent information feedback provides information regarding the correct response or incorrect response depending on whether the subject chooses correctly on that trial. As mentioned above, the use of the simultaneous method of presentation permits the experimenter’s choice of the use of either a contingent or noncontingent procedure of information feedback, but only the noncontingent procedure is possible when the successive method of presentation is used (e.g., Offenbach, 1965). There have been three basic types of reinforcement schedules used in probabilistic tasks, each of which may vary along the continuum from partial to continuous reinforcement. One of the schedules is that used for the typical probability-learning task. The basic requisite with this schedule is that the correct stimulus on each trial is determined by the experimenter prior to the initiation of practice within the limitations of the chosen level of reinforcement. In this case, the subject is reinforced on a specific trial only if he chooses the stimulus designated “correct” on that trial. We may call this type of schedule a trial-defined schedule. A second type of reinforcement schedule has been used by Stevenson (Stevenson & Hoving, 1964; Stevenson & Weir, 1959; Stevenson & Zigler, 1958), Weir (Weir, 1967, 1968; Weir & Gruen, 1965), Odom (1966, 1967), and others. This schedule, which may be called a response-defined schedule, involves reinforcing a fixed percentage (e.g., 66%) of the subject’s responses to a particular stimulus, independently of the trial on which they are made. However, the trial on which the sub-

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jects can be reinforced for choosing a particular stimulus is not determined prior to practice as it is with the trial-defined schedule. It should be mentioned that the use of a response-defined schedule precludes the use of the noncontingent information feedback procedure. A third type of schedule may be designated as a “random” reinforcement schedule, where the specific trials on which the subject is to be reinforced are predetermined and reinforcement is provided independently of the stimulus to which he responds (e.g., Goulet & Barclay, 1967; Jeffrey & Cohen, 1965; Rieber, 1966). It is apparent that there is no optimal strategy of responding when random reinforcement schedules are used. In fact, the number of times reinforcement is provided over a block of trials is invariant no matter which strategies, response patterns, etc., are used. However, one of the intriguing aspects of random reinforcement is that it can be used to reinforce-and maintain-the strategies that subjects bring to the laboratory. There are a number of other ways in which the tasks for the study of choice behavior can vary. As has already been mentioned, the number of stimuli can vary from two to many, although two- and three-choice tasks have been most commonly used. In addition, both response-defined and trial-defined schedules can be modified such that responses to one or more of the stimuli are reinforced. For example, with a twochoice task, either 75:25 or 75:O schedules of partial reinforcement could be used. In other words, the level of reinforcement for each stimulus is experimenter-determined, can be programmed independently for each of the stimuli in the task, and can take values ranging from 100 to 0%. As is apparent, whenever the reinforcement is 100:0,the distinction between a discrimination-learning task and probability-learning task (using a trial-defined or response-defined schedule) disappears. At the other extreme, when the schedule is 100: 100, there is considerable disparity between the two schedules and the discrimination-learning task; however, the schedules are now identical to one generated using a 100% random reinforcement schedule. B. EARLYRESEARCH

The widely diverse group of studies related to the behavior of children in probabilistic tasks has not been systematically reviewed. As mentioned above, one of the purposes of the present paper is to attempt such a review of both the results and the general interpretations proffered for the obtained effects of age, schedule, task, etc. It is also of interest to highlight some of the reasons for the initiation of the first studies. Messick and Solley (1957) were interested in a number of general problems, whether children’s (CA = 3-8 years) behavior in a two-choice

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task (successive procedure, noncontingent information feedback, trialdefined schedule) was best characterized by “maximizing” or “probability matching,” whether the subjects’ choice behavior in a 60:40 schedule deviated systematically from that expected by chance (choosing the two stimuli with equal frequencies), and whether incentive (candy) reinforcement for correct choices affected choice behavior. Unfortunately, the samples used were extremely small (N = 1-3) and each of the children was tested under all of the permutations of schedule, incentive, etc., used in the study. The results indicated a trend toward probability matching (choosing the stimuli at the level each is reinforced) under 100:0, 90: 10, 75:25, and 60:40 schedules, independent of age. Furthermore, the probability matching under the 60:40 schedule suggested that even 3- and 4-year-olds could discriminate between a 60:40 and a 50:50 task. When a material incentive was provided for correct predictions in a 75:25 task, the older subjects (CA = 7-8 years) maximized, the youngest subjects’ (CA = 3-4 years) behavior was still characterized by probability matching, and the terminal level of performance of the 5-year-olds reached an asymptote intermediate to maximizing and matching. In another early study, Stevenson and Zigler (1958), using a threechoice task (simultaneous procedure, contingent information feedback, response-defined schedule), found that the asymptotic performance of nursery school children varied directly with the schedule of reinforcement (100:0:0, 66:0:0, 33:0:0), the asymptotes after 80 trials being approximately .90, .80, and 3 0 for the three schedules, respectively. In contrast, the asymptotic performance of groups of MA-matched retardates (mean CA = 12.8 years) on the same task and schedules approximated .90, .90, and .65, respectively. The normal-retardate differences were attributed to differential expectancies of continuous reinforcement between the groups of children. That is, normal children were assumed to have learned through everyday experiences to expect a high degree of success in problem-solving tasks. Such an expectancy would not lead to maximizing behavior with a partial reinforcement schedule since the children would search for a sequence or pattern of responses which would yield continuous reinforcement. In Experiment 111, Stevenson and Zigler (1958) tested the hypothesis that the subjective expectancies of success for the children could be modified by pretraining involving either partial or continuous reinforcement. The three pretraining tasks were games structured to yield either partial (33%) or continuous (100%)reinforcement for different groups of nursery school children (mean CA = 5.9 years). Subsequent performance on the 66:O:O task was better following pretraining on the partial schedule than following pretraining on the continuous schedule.

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The absence of a no-pretraining control group made it impossible to determine whether the differences in performance as a function of pretraining were due to interfering effects of pretraining on the continuous reinforcement schedule, facilitative effects of pretrainhg on the partial reinforcement schedule, or both. However, it is possible to compare the performance of the subjects from Experiment I (who had no pretraining) to those from Experiment 111. These data are presented in Fig. 1. As can be seen in Fig. 1, pretraining interfered with performance on the early trials; however, in line with Stevenson and Zigler’s hypotheses, subjects pretrained on a partial reinforcement schedule had a higher terminal level of performance than the “control” group, and the performance of subjects pretrained on a continuous reinforcement schedule was depressed below that for the control group throughout practice. The initial inhibitory effects are unexplained. An experiment by Stevenson and Weir (1 959) provided further evidence that performance varies with the level of success that subjects will accept in the task. Reasoning that older children would seek a solution that would provide them with continuous reinforcement, Stevenson and Weir compared subjects (CA = 3, 5,7, and 9 years) on 100:0:0,66:0:0, and 33:O:O tasks. The number of choices of the reinforced stimulus varied inversely with age on each of the three schedules. However, the age-differences were attributable primarily to the greater number of 98 7 -

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Fig. 1 . Mean number of correct responses in blocks of 10 trials for the control, partial reidorcement (33%). and continuous reinforcement (100%) groups. [Adapted from Stevenson and Zigler (1958) wirh the permission of the authors and the American Psychological Association.]

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choices of the reinforced stimulus by the younger subjects on the early trials. In other words, a pronounced trend toward maximizing was apparent in the 3-year-olds even in the first block of 10 trials. This was true for each of the schedules of reinforcement. In addition, although performance varied directly with the reinforcement schedule in all agegroups, the performance differences among schedules increased with age. The early research and the obtained results highlight many of the theoretical issues and problems related to development that may be investigated with probability-learning tasks. Stevenson and Zigler (1958) and Stevenson and Weir ( 1 959) have suggested that the greater trend toward maximizing found in younger subjects and in retarded subjects is a function of experiential rather than maturational factors related to development. In this regard, comparisons of performance in probability learning among children of different ages may be considered as studies of transfer of training where performance on the task is a function of differential experience with expectancies of success in problem-solving situations. This interpretation points to the importance of transfer studies where the subjects’ subjective expectancies of success are experimentally manipulated by laboratory practice on tasks of a probabilistic nature. This work is discussed in detail in the section on transfer of training. Alternatively, the age differences found may be attributable to systematic, developmental changes in characteristic patterns of choice behavior. These characteristic patterns of behavior may indeed reflect “strategies” of problem-solving based on the subjects’ hypothesis that the task has a solution; i.e., that a certain “to be discovered” pattern of responding will yield continuous reinforcement. However, it is possible that performance of very young children e.g., 3-year-olds, is not a function of strategies per se, but rather a pattern of responding based on reinforcement. In other words, the choice behavior of very young children may be characterized by perseveration to a reinforced stimulus. This hypothesis is consonant with the data obtained by Stevenson and Weir (1959) since only one stimulus was reinforced in their tasks; i.e., either 100:0:0, 66:0:0,or 33:O:O schedules were used. Older subjects may systematically formulate, test, and reject hypotheses (based on the assumption that the task can be solved). Maximizing behavior will not be found if the strategies or hypotheses formulated deviate from perseveration. This, of course, would account for the trend toward decreased maximizing behavior with increasing age. This trend was also found with two-choice tasks by Jones and Liverant (1960). They used 70:30 and 90: 10 schedules (simultaneous procedure, contingent information feedback, trial-defined schedule) and found that the performance of young children (CA = 4-6 years) was better

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than that of older children (CA = 9-10 years). These data contradict those of Messick and Solley (1957). Apparently, the latter data are biased because of the small number of subjects, the multiple conditions under which each subject was tested, or both. C. DESCRIPTIVE DEVELOPMENTAL CHANGES IN PROBABILITY LEARNING

Much interest has been generated by a recent paper by Weir (1964). He consolidated the data from a number of previous studies (Gruen & Weir, 1964; Stevenson & Weir, 1959, 1963) in which subjects (CA = 3-20 years) had performed on the same task, apparatus, procedure, instructions, etc. The subjects were tested for 80 trials under 66:O:O or 33:O:O schedules of partial reinforcement (simultaneous procedure, contingent information feedback, response-defined schedule). When the percentage of choices of the reinforced stimulus during the last block of 20 trials was plotted as a function of age, a U-function was obtained; i.e., the 3-year-olds, 5-year-olds, and college students showed similar terminal levels of performance, but the performance of 7-, 9-, 1 1-, and 15-yearolds was depressed below that of the others. Similar functions were obtained for both the 33:O:O and 66:O:O schedules except that the terminal level of performance was lower for the 33:O:O schedule. An analysis of the learning curves provided additional information regarding the developmental changes in choice behavior. The trend toward maximizing was apparent for the 3- and 5-year-olds even in the first block of 10 trials (cf. Jones & Liverant, 1960) and they rapidly approached an asymptote approximating 80% choice of the reinforced stimulus. In contrast, the performance of the college students, even while reaching the same asymptote, approximated 35% choices of the reinforced stimulus for the first block of 10 trials. The responses of 7-, 9-, 11-, and 15-year-olds were best characterized by left, middle, right (LMR) or RML response patterns, presumably indicative of systematic, redundant search strategies involving the three stimuli. The youngest and college subjects’ behavior was best characterized by perseveration to the reinforced stimulus, whether or not the response had been reinforced on the preceding trial. It should be noted here that Crandall, Solomon, and Kellaway (1961) also found no differences over 80 trials between the performance of adolescents (CA = 15-17 years) and younger (CA = 6-8 years) children on an 80:20 two-choice task (simultaneous procedure, noncontingent information feedback, trial-defined schedule). In addition, Lewis, Wall, and Aronfreed (1 963) found no differences in performance between first- and sixth-grade children on a 70: 30 task (simultaneous procedure, contingent information feedback, trial-defined schedule).

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Kessen and Kessen (1961) using 70:30 and 50:50 schedules (successive procedure, noncontingent information feedback, trial-defined schedule) found no differences between groups of 3.6- and 4.4-year-old children in probability learning. Lewis (1966) also found greater trends toward maximizing for nursery school (CA = 3-5 years) than for firstand second-grade children on a two-choice 70:30 task (successive procedure, noncontingent information feedback, trial-defined schedule). Apparently, the data described by Weir (1964) are highly reliable and can be generalized across a variety of tasks, procedures, reinforcement schedules, etc. Similar results have been obtained when tasks involving random reinforcement have been used. Although only a few sets of data are available, alternation or systematic search behavior is found in normal children above the age of four (Goulet & Barclay, 1967; Jeffrey & Cohen, 1965; Rieber, 1966) and perseveration is found in subjects who are younger than four (Jeffrey & Cohen, 1965). This developmental trend from perseveration to alternation is also apparent in retarded children when MA rather than CA serves as the index for differentiating the subjects (Goulet, 1969). It is of interest to note that Schusterman (1964) and Metzger (1960) also found a trend toward alternation in the probability learning of retardates with MA’s between 5 and 6 years. Gerjuoy and Winters (1 968) have documented further evidence for this conclusion. Two additional studies (Derks & Paclisanu, 1967; Goodwin, 1969) also relate to the same general problem and provide data on probability learning across a wide age-range. Derks and Paclisanu compared nursery (mean CA = 4.3 years), kindergarten (mean = 6.6 years), first-grade (mean CA = 6.9 years), second-grade (mean = 8.0 years), fifth-grade (mean CA = 11.1 years), seventh-grade (mean CA = 12.9 years), and college (mean CA = 21.3 years) subjects over 200 trials on a two-choice 75: 25 task (simultaneous procedure, noncontingent information feedback, trial-defined schedule) and again found that selection of the more frequent event varied as a U-function of age. This was true whether performance was compared over the first 100 trials or the second 100 trials, and even though all groups were responding at a higher terminal level on Trials 101-200. The nursery school children manifested strong “positive recency” effects (increased probability of predicting an event as that event continues to occur) on Trials 1-100, with a switch to maximizing on Trials 101-200. The behavior of kindergarten children was best characterized by alternation, although positive recency effects were also manifested in the first block of 100 trials. The third-, fifth-, and seventh-grade children, for the most part, were not characterized by any apparent, general perseveration strategy. The college subjects

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showed an increasing trend toward perseveration with increasing practice. The one disparity between the results of Weir (1 964) and of Derks and Paclisanu relates to the kindergarten children. Weir found that the behavior of these subjects was similar to that of the nursery school (i.e., maximizing) children. Derks and Paclisanu found that the performance of the kindergarten children was depressed below that of the nursery school subjects and was more like that of the first-grade subjects over the number of trials used by Weir ( 1 964). In addition, Weir’s kindergarten subjects tended toward perseveration to the most frequently reinforced stimulus, but those of Derks and Paclisanu showed alternation behavior. There were a number of differences between the studies, including the number of choices [three (Weir) versus two (Derks and Paclisanu)], type of feedback [contingent (Weir) versus noncontingent (Derks and Paclisanu)], and type of schedule [response-defined (Weir) versus trial-defined (Derks and Paclisanu)]. Any of these differences could account for the disparities in results. However, it is useful to note that alternation behavior in children approximately 5 years of age has been found by Craig and Myers (1963), who used both 80:20 and 60:40 reinforcement schedules (simultaneous procedure, noncontingent information feedback, trial-defined schedule), and by Jeffrey and Cohen (1969, who manipulated random reinforcement (loo%, 50%, 33%) in a two-choice task. In fact, Craig and Myers found that the performance of kindergarten children was similar to that of fourth-grade children (but displaced below that of eighth-grade children) on Trials 1-120 but was strikingly below that of the fourth-and eighth-grade subjects on Trials 12 1-200 (a finding very similar to that of Derks and Paclisanu). A detailed consideration of the effects of task differences is contained elsewhere in the paper. However, recent data collected at West Virginia University (Goodwin, 1969) do provide some information regarding task- and age-differences across the same age-span considered by Weir (1 964) and Derks and Paclisanu. Goodwin (1 969) compared performance in probability learning as a function of the number of choices (two, three) and type of information feedback (contingent, noncontingent) across much the same age-range used by Weir (1964) and Derks and Paclisanu ( 1 967). The subjects were kindergarten (mean CA = 5.1 years), second-grade (mean CA = 7.6 years), and fifth-grade (mean CA = 10.9 years) children and college students. The reinforcement schedule (trial-defined)was 75:25 for the twochoice and 75: 12.5:12.5 for the three-choice task. Information feedback as to the reinforced stimulus on each trial was either contingent on choosing the stimulus that was keyed “correct” on that trial or was provided independently of the response made (noncontingent condition).

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Figure 2 provides summary data for responses to the most frequently reinforced stimulus in each of 6 blocks of 16 trials for the 4 age groups. These data (pooled over type of information feedback and number of choices) are remarkably similar to those of Weir ( 1 964). That is, on the first block of trials, the performance of college, fifth-grade and secondgrade subjects was similar and depressed below that of the kindergarten subjects. However, the terminal performance of the kindergarten and college subjects approached maximizing, and that of the second-grade and fifth-grade subjects was below the other two groups. Overall performance and performance in the last block of trials varied as a U-function of age, again in line with the results of Weir. As Weir suggested, markedly different processes are involved in probability learning in the different age-groups and this is reflected in the slopes of the learning curves of the four groups of subjects. In addition, similar U-functions were found whether performance was obtained with a two-choice or a three-choice task and whether information feedback was contingent or noncontingent. In an analysis of the effects of reinforcement or nonreinforcement of responses to the most frequently reinforced stimulus, Goodwin (1 969) found that the percentage of “win-stay” and the percentage of “lose-

Fig. 2. Mean percentage correct responses per block of 16 trials for kindergarten (K), second-grade (2), fifth-grade (5), and college (CON.)subjects (adapted from Goodwin, 1969).

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stay” responses vaned as a U-function of age, again in line with the results described by Weir ( 1964). In a sequential analysis of her data, Goodwin (1969) used the Index of Behavioral Stereotypy developed by Miller and Frick (1949). This measure, adapted from information theory, provides an index of the percentage stereotypy (or redundancy) of response sequences varying in length. That is, the first order of approximation (C,) provides a percentage estimate of perseveration -the degree to which the subjects choose certain stimuli with disproportionate frequencies. The second order of approximation (C,) involves successive sequences of two responses. Again, to the extent that subjects choose successive stimuli in an orderly (i.e., non-chance) fashion, C , will exceed zero. The third order of approximation (C,) provides a similar estimate except that it reflects the stereotypy of patterns three responses in length. The differences in stereotypy between successive orders of approximation (e.g., C, and C,) reflects the additional redundancy accounted for by the analysis of more complex response patterns. Figure 3 provides summary data on the Index of Behavioral Stereotypy for each of the age-groups used by Goodwin. The data reflect stereotypy measures for data pooled over 96 trials and over the other treatments. The stereotypy of the kindergarten was reflected primarily at C, (indicating strong perseverative behavior). The college subjects also had greater stereotyped behavior at C,; however, the stereotypy at C , and C , for these subjects did not differ from that of the second- and fifthgrade children. In other words, even though strong perseverative behavior was found for the college subjects, their sequential responding was still quite variable relative to the kindergarten children. This function for the college subjects most likely reflects a search for a response pattern involving 100% reinforcement (Weir, 1964) and which, nevertheless, involves disproportionate choice of the most frequently reinforced stimulus. The behavior of second- and fifth-grade subjects, in contrast, was less stereotyped than the kindergarten and college subjects even at C1.

D. VARIABLES

INFLUENCING PROBABILITY LEARNING:

TASKVARIABLES

1. Schedule of Partial Reinforcement The studies concerned with the probability learning of children have, for the most part, compared the performance of subjects under more than one schedule of partial reinforcement even though there has been little direct theoretical interest in this variable. Brunswik (1939) has suggested that the task can be used to obtain children’s “thresholds”

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Fig. 3 . Mean response stereotypy for kindergarten ( K ) , second-grade (2). jiifth-grade ( 5 ) , and college (Coll.)subjects pooled over 96 trials (adapted from Goodwin, 1969).

for discriminating a deviation from chance probability. However, the probability-learning task has not been used with children specifically for this purpose. Terminal performance has been found to vary directly with the level of reinforcement for the most frequent event (e.g., Little, Brackbill, Isaacs, & Smelkinson, 1963) and no exceptions have been found. In addition, even nursery school children can discriminate a 60:40 schedule from a 50:50 schedule. [Brunswik ( 1 939) has suggested that the “probability threshold” for rats is near .70.] However, for purposes of determining thresholds, it is perhaps of interest to note that the event schedules can be programmed independently for each stimulus. For example, schedules of 60:50, 90:80, 20:10, etc., can be used. And, if a simultaneous procedure is used and contingent information feedback is provided, subjects do not have to be made aware that any (or no) stimuli will be reinforced on any particular trial.

2. Number of Choices Two studies (Goodwin, 1969; Weir & Gruen, 1965) have dealt with the probability learning of children as a function of the number of choices in the task. Weir and Gruen (1965) compared preschool children (mean CA = 4.4 years in Exp. I, 4.7 years in Exp. 11) on 75:25 and 75:12.5: 12.5

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tasks (simultaneous procedure, contingent information feedback, trialdefined schedule) and found that terminal performance (after 96 trials) was higher tor the two-choice than for the three-choice task. This was true whether the task involved button pushing (Exp. 11) or involved guessing which of two toy milk bottles contained a prize. These findings contrast with the results of a number of other studies using young adult subjects. For example, Gardner (e.g., 1957, 1958) and Cotton and Rechtschaffen (1958) have found that terminal performance is higher in young adults as the number of alternatives is increased. Weir and Gruen suggested that the apparent disparity in results is a function of the type of information feedback (i.e., terminal performance is higher for a three-choice task with noncontingent feedback but lower with contingent feedback) rather than age differences. However, Neimark (1956), again using young adult subjects, has found that terminal performance was equal for two- and three-choice tasks whether contingent or noncontingent information feedback was provided. Goodwin (1969) compared the probability learning of subjects from kindergarten through college age and varied both the number of alternatives (two, three) and type of information feedback (contingent, noncontingent). Therefore, some additional information is available relative to the interaction of age, number of alternatives, and type of information feedback. Figure 4 shows mean responses to the reinforced stimulus pooled over 96 trials for Goodwin’s four age levels. The data are provided for treatments involving contingent and noncontingent information feedback. As Fig. 4 indicates, there is little regularity across the age groups regarding the effects of type of information feedback. Weir and Gruen’s ( 1965) results indicating higher performance for five-year-olds on a twochoice task were replicated under conditions of contingent information feedback. Performance was also better on the two-choice task for fifthgrade children under contingent reinforcement. Gardner (1 957) has suggested that performance in a three-choice task increases relative to a two-choice task with an increasing number of trials (e.g., 450 trials) for young adults. However, the effect of increasing the number of trials remains to be explored in children.

3. Apparatus and Procedural Digerences Extremely little research has been directed to the study of task and procedural differences as they affect children’s probability learning. Offenbach (1 965) has compared the performance of kindergarten (mean CA = 5.5 years) and fourth-grade (mean CA = 9.6 years) children on a two-choice task with 90: 10, 75:25, and 60:40 reinforcement schedules

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(noncontingent information feedback, trial-defined schedule) as a function of method of presentation (simultaneous or successive). No task differences were found except for a trend toward higher terminal performance under the simultaneous procedure for the 75:25 schedule. No interactions with age were found. Weir and Gruen (1965) used preschool subjects (mean CA = 4.5 years) and tasks involving button pushing or predicting which of two (or three) milk bottles contained a prize, and found that children performing on the latter task made significantly fewer correct responses. They speculated that the milk-bottle task was much more boring and thereby resulted in more response variability in these subjects. No interactions with type of incentive or number of response alternatives were found. However, the small amount of research related to these problems makes any generalization tenuous. 4. Instructional Effects A basic assumption in probability learning experiments is that subjects

enter the task with the belief that a solution is possible and that there is a method of obtaining reinforcement on every trial. It follows that instructions to the contrary (e.g., telling subjects that there is no solution or that it is impossible to be correct on every trial) will increase

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the frequency of predicting the most frequently reinforced stimulus. Similarly, instructing subjects that 100% success is possible should increase the variability of responding and thereby reduce the number of choices of the correct stimulus. Goodnow (1955) has found that young adult subjects with a “gambling’’ (no solution) set more closely approximated maximizing than did subjects with a “problem-solving” (solution) set. However, similar studies with children (Gruen & Weir, 1964; Weir, 1962) have had little success in modifying their choice behavior. This is true even though Stevenson and Weir ( 1 963) found that children (CA = 12- 18 years) entered the task with a strong expectancy that the task had a solution. Weir (1962) used a three-choice task and a 50:O:O reinforcement schedule (simultaneous procedure, contingent information feedback, response-defined schedule), and found that terminal performance of 5- to 7- and 9- to 13-year-olds was unaffected by instructions implying that the problem did not have a solution. Gruen and Weir (1 964) noted that the effects of a gambling set may be due to the “risk” aspects of the gambling task (penalizing subjects for an incorrect choice) rather than due to a “set” not to expect 100% success. With a 66:O:O reinforcement schedule and children approximating 7.6 and 13.5 years and college subjects, they factorially manipulated instructional set (solution, no solution, or neutral instructions) and penalty/no penalty for incorrect choices. Penalty for incorrect choices increased the selection of the correct stimulus for all subjects, but instructions had an effect only for the college subjects. The “no solution” and “solution” sets increased and decreased the selection of the reinforced stimulus, respectively, for the college subjects. E. TRANSFER OF TRAINING

The use of transfer tasks typically represents an extremely sensitive method for determining the effects of past experience. When applied to probability learning, a variety of transfer designs can be constructed. For example, subjects can be trained on one reinforcement schedule and can then be switched to another schedule varying in any of a number of ways from the first. The second schedule (task) may involve the same solution (most efficient strategy) as that required (or learned) in the first task, in which case performance in the second task should be facilitated as a function of first-task practice. For example, practice on a 66:O:O schedule - involving reinforcement for responding to the left (L) stimulus and no reinforcement to the right (R) and middle (M) stimuli-requires a “strategy” of maximizing. The second task may be identical in all respects to the first except that a 33:O:O schedule is

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used. Here, subjects can transfer both the solution (maximizing) and the response to be chosen (L). This design may be called a solution identical, response identical paradigm. Two sources of positive transfer are apparent; i.e., transfer of the solution and transfer of the response from Task 1 to Task 2. Transfer paradigms may also be generated such that one or more aspects of the second task are interfered with as a function of practice on the first; e.g., a solution identical, response different paradigm can be constructed. In this case, subjects could transfer the solution (e.g., maximizing) but optimal performance on the second task would require a change of the response (e.g., L to M) to which the subjects maximized. In this paradigm, a source of positive transfer (solution transfer) and a source of negative transfer (response transfer) would be present. Alternatively, solution different, response identical and solution different, response different paradigms could be constructed. It is apparent that a large number of different transfer tasks could be devised depending upon the solution, number of stimuli, and reinforcement schedules used. Extremely little research has been conducted within the framework of a transfer design. However, the transfer task can be useful in developmental research on probability learning. As an example, Weir (1 964) has suggested that very young children (e.g., CA = 3 years) do not respond in probabilistic tasks by formulating strategies and testing hypotheses. Rather, he suggested that they respond only on the basis of a simple reinforcement notion. If this is true, their performance on solution different, response identical and solution identical, response identical transfer tasks should be similar (given that other factors are held constant). As is the case with transfer studies, the tasks would be designed such that Task 2 is identical for all subjects and Task 1 would be varied. Similarly, strong negative transfer would be expected for these subjects if a change in response was required from Task 1 to Task 2. The sources of negative transfer as a result of switching the task solution from Task 1 to Task 2 would be expected to be greatest at the age when strategies are first formulated (e.g., CA = 5- 10 years) after which the negative transfer resulting from changing solution from Task 1 to Task 2 should decrease. Stevenson and Weir (1959) did compare transfer in children (CA = 7.5- 10.3 years) in a solution-identical, response-identical paradigm as a function of the first- and second-task schedule of reinforcement (factorially manipulated) and found that performance on Task 2 varied as a function of the first-task schedule (100:0:0,66:0:0, 33:0:0, and 0 : O : O ) and second-task schedule. Performance on Task 2 under 66:O:O and 33:O:O schedules was ordered as a direct function of the schedule on Task 1, a result that could be predicted from a view that considers

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learning to be a direct function of the number of reinforced trials. However, the ordering of performance was inconsistent under 0:O:O and 1OO:O:O schedules on Task 2, an indication that the transfer of the solution was an important factor in terms of Task 2 performance. Whether the same results would be found had the reinforced stimulus been changed on Task 2 is unknown. Jones and Liverant (1960) compared nursery school (CA = 4-6 years) and elementary school (CA = 9-1 1 years) children on an 80:20 transfer task (solution identical, response different paradigm) after training on either 70:30 or 90: 10 schedules. Consistent with the present hypothesis, initial performance on the transfer task for the nursery school children was depressed considerably below that of the elementary school children. In other words, the younger children had considerable difficulty in changing their response on the transfer task. However, this was true only during the initial trials on Task 2. During the later stages of practice similar terminal performance was evident for both groups of children. Similar results were found for both schedules of reinforcement on Task 1. In another early study, Kessen and Kessen (1961) compared young children (Median CA = 3.6 and 4.5 years) under a solution-identical, response-identical paradigm. The subjects were trained on 70:30 or 50:50 reinforcement schedules on Task 1 and were either maintained on the same schedule or were switched to the alternate schedule. The younger subjects continued to respond in the transfer task as if there had been no switch of reinforcement schedule, while the older subjects modified their choice behavior to conform to the schedule of the second task. Crandall et al. (1961) compared adolescents (CA = 16-18 years) and young children (CA = 7-9 years) on two probability-learning tasks involving “patterned” schedules of partial reinforcement. Task 1 involved an 80:20 schedule where the most frequent stimulus occurred 4 times, followed by one occurrence of the least frequently occurring stimulus in each block of 5 trials. Thus, it was possible to predict the occurrence of the 2 stimuli with 100% success. Task 2 (5050 schedule) involved 5 successive presentations of each stimulus in alternate blocks of 5 trials. While both groups of subjects responded to each stimulus with equal frequency on the transfer test, the “apparent” probability matching in the older subjects was accounted for, in large part, by correctly anticipating the response pattern present in the task. In contrast, most of the younger subjects did not anticipate the pattern and responded to the two stimuli in an unpatterned fashion in each block of 10 trials. Goodnow and Pettigrew (1955, 1956) have conducted transfer studies with college students and the results are of interest here. Goodnow and Pettigrew (1955) devised an interesting variant of the typical trial-defined reinforcement schedule. In these variant schedules each stimulus

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was keyed correct according to a predefined level (e.g., 50:50) over a larger block (long run) of trials. However, within each of a number of subblocks the reinforcement contingencies were varied around the longrun schedule. For example, the reinforcement schedule over 70 trials was 50:50 but within each block of 10 trials the schedules were 80:20, 70:30, 60:40, 5 0 5 0 , 40:60, 30:70, and 20:80. It is emphasized that in the usual procedures, the schedules over subblocks of trials and over the entire series of trials are identical, or in Goodnow and Pettigrew’s (1955) terminology the reinforcement schedule is defined over the short run. As Goodnow and Pettigrew (1955) have indicated, the long-run 50:50 schedule reinforces a win-stay, lose-shift strategy, but in the shortrun 50:50 schedule subjects develop a win- ?, lose-stay strategy because they try to operate on the basis of the probable length of a run of payoffs to a particular stimulus. Conceived in another way, the long-run schedules may be seen as a series of transfer tasks involving the same solution or strategy (maximizing) with the reinforced response being identical or shifting depending on the way the schedule changes between the blocks of trials. As Goodnow and Pettigrew (1955) have found, college students do adopt a win-stay, lose-shift strategy when practicing on a long-run schedule. Furthermore, and consistent with the present hypotheses, these subjects change response very easily in a transfer task as long as the schedule changes are discriminable (Goodnow & Pettigrew, 1955, 1956) and the solutions are similar between the two tasks (Goodnow & Pettigrew, 1956). Schusterman (1963, 1964) has found that young, normal children (CA = 3-5 years) and retardates of comparable MA were not sensitive to changes in the reinforcement schedule when it was defined in a long run manner. Rather, the children responded in a consistent fashion over the block of trials independent of the reinforcement schedule within each block. Ten-year-olds, in contrast, performed in much the same manner as had Goodnow and Pettigrew’s (1955) college students. A final series of transfer studies by Bogartz ( 1966) provides additional evidence that 4- and 5-year-old children have difficulty in changing solutions between two tasks involving binary prediction. In Experiment I, 5year-olds practiced on a task involving alternation (i.e., predicting 1 ,O,l ,O,l . . . sequences) and then were shifted to a task involving recurrent ( 1 ,O,O or 1 ,O,O,O) sequences. The children quickly learned the alternation problem, but the transfer tasks were not learned. In addition, performance on the simple alternation problem was negatively affected if the subjects had previous practice on recurrent sequences (even though the children did not “learn” or master the first task prior to the initiation of practice on Task 2). In Experiment 11, Bogartz found that transfer to

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an alternation problem was similar whether the children had practiced on a Task 1 where repetitive, alternation, or random choice behavior was reinforced. The transfer tasks in Experiment I1 conformed to solution different, response identical paradigms according to the terminology adopted in this paper. Performance in probability-learning tasks may also be considered to be a function of preexperimental learning or different levels of cognitive development. Thus, performance in probabilistic tasks may be considered to reflect strategies for hypothesis testing that subjects bring to the laboratory. As such, the probabilistic tasks may be designed to capitalize on or interfere with these preexperimental strategies. Weir (1 964) has noted that children older than 5 years can generate complex hypotheses and that these are reflected in a large number of LMR and RML response patterns in a three-choice task. College subjects can test and reject hypotheses, but younger subjects are assumed to be limited in the ability to generate more complex hypotheses or in the ability to process confirming or disconfirming information in the probability-learning task. Odom and Coon ( 1966) compared the performance of 6-, 11-,and 19year-old subjects in a three-choice task where the solution involved generating LMR or RML sequences. Fewer of the youngest subjects (45%) were able to master the task in 90 trials than were the 1 1- (60%) and 19year-olds (80%). Of the subjects who had mastered the task, 11- and 19year-olds quickly rejected the LMR and RML patterns on extinction trials when they were no longer reinforced; but no extinction of the LMR and RML patterns was evident for the 6-year-olds, again suggesting that a change in solution is difficult for children in this age-range. F. THEORETICAL INTERPRETATIONS OF AGECHANGES IN PROBABILITY LEARNING

The consistency of results across variations in tasks, procedures, reinforcement schedules, etc., has already been documented. Furthermore, the notable absence of interactions with age for the experimental variables most frequently manipulated makes it more simple to concentrate on the general processes involved in probability learning and the changes in these processes that are associated with age. That is not to say that selected experimental variables (e.g., penalty, level of reinforcement) do not affect children’s performance in probability learning. However, the effects of these variables are apparently consistent across a fairly wide age-range. A number of investigators (e.g., Stevenson & Weir, 1959; Stevenson & Zigler, 1958; Weir, 1964) have noted that subjects enter the proba-

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bility-learning task with strong expectancies that the task has a solution and that prediction with 100% success is possible. In addition, subjects enter the task with hypotheses or strategies either general or specific in nature and then systematically reject these strategies when they do not provide a “solution” that meets or approximates the level of success they expect. These conclusions highlight two general problems concerned with (a) the developmental changes in the complexity of the strategies that subjects bring to the task, and (b) the developmental changes related to the systematic elimination of strategies that have been rejected. Even a cursory look at the learning curves taken from Goodwin’s (1969) study (Fig. 2) reveals the striking age-differences found. The performance of the youngest children (i.e., 5-years) was characterized by a rapid rise to an asymptote approximating maximizing, and this was reflected even in the first block of trials. In contrast, the initial performance of second- and fifth-grade children and college students was much more variable and depressed below that of the kindergarten children. The asymptotic performance for the college students, however, approached that of the kindergarten children; less performance change over trials was found in the second- and fifth-grade children. As mentioned earlier, strikingly similar results were obtained by Weir (1 964). The differences in performance on the initial trials reflect different characteristic and replicable (Derks & Paclisanu, 1967; Weir, 1964) patterns of responding (strategies) among the age-groups. The college subjects enter the task with complex strategies or hypotheses, but systematically reject them and, according to Weir (1964), finally arrive at a solution approximating that of maximizing to the most frequently reinforced stimulus. The low initial performance of the second- and fifthgrade children does reflect the capacity to generate complex hypotheses (any of which will depress performance); however, the small performance change across trials reflects either an inability to generate alternative hypotheses when they fail, or an inability to reject an hypothesis or strategy when it does not lead to the expected level of success (Weir, 1964). Weir ( 1 967) has suggested that the inability of children between 7 and 10 years of age to reject simple strategies is due to inadequate memory of past events and outcomes. To test this hypothesis, he provided 9year-old subjects with a memory aid (which provided them with an accurate record of past responses and outcomes) in a 66:O:O task (simultaneous procedure, contingent information feedback, responsedefined schedule). Consistent with his hypotheses, better performance was found with the memory aid than when it was not provided. The per-

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formance of college students (who can process information about and recall past events and outcomes) was similar whether or not the memory aid was provided. The presence of the memory aid retarded the performance of 6-year-old children (who were not expected to profit by its presence). While the above results appeared extremely promising, Weir was later unable to replicate the finding for the 9-year-olds (Weir, 1968). Weir (1964) has also suggested that the capacity to process information and to reject hypotheses should vary with the number of alternatives in the probability-learning task. That is, Weir suggested that the age for maximum variability in responding should be found at younger ages (i.e., 6-9 years) for two-choice tasks than for three-choice tasks, in which he estimated the apex to occur between 9 and 11 years of age. In other words, the increased complexity of the three-choice task was assumed to require an increased capacity to store and process information. Thus, at an age when young children would be able to reject alternation as a strategy in two-choice tasks, they may not be able to reject R M L or LMR strategies in a three-choice task. The data provided by Goodwin (Fig. 4) give some evidence for this contention especially under conditions of contingent information feedback, typically used by Weir ( 1 964). The present analysis of the probability-learning task in terms of transfer mechanisms (discussed in Section 11, E) can be extended to account for the developmental changes in performance. It can be assumed (e.g., Weir, 1964) that very young children (e.g., 3-4 years) do not formulate and test strategies in probability learning, but that their performance is a direct function of responding to the reinforced stimulus. With increasing age, the data suggest that complex patterns of responding are generated, denoting a shift in process away from responding on the basis of a simple reinforcement notion and toward one which can be labeled problem-solving. The adoption of a problem-solving set necessarily leads to an increase in the variability of responding in probability learning and, directly correlated, a decrease in responding to the maximally reinforced stimulus. The very fact of variable responding implies that different patterns of responses (varying as to type and length of response sequence) will be reinforced (on a partial reinforcement schedule) across trials. The youngest children capable of generating complex strategies should thus have difficulty in filtering out response patterns that are differentially reinforced; however, older children should have less difficulty in doing so. The above interpretation is similar to that provided for transfer tasks except that in the case of probability learning on a single task, the solution is subject-generated and the source of negative transfer is attributable to intratask solution interference. In a transfer paradigm, the solu-

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tion is experimenter-defined and the source of solution transfer is an inter-task variable. For the most part, however, these hypotheses can best be tested in a transfer design. As stated previously, performance on a second task can provide much information related to the manner in which subjects were responding on the first task. G. INCENTIVE

The primary concern here is to determine whether magnitude of reward or type of incentive interacts with age in probability learning. It is important to note that the provision of incentives (reward) plays a dual role in probability learning tasks, that of providing information feedback for correct prediction and that of rewarding these choices. N o studies have systematically manipulated contingent/noncontingent information feedback and incentive level to determine the separate effects of each variable. For the most part, studies varying incentive level provide reward (typically candy or a small toy) or information feedback (instead of the reward) if correct predictions are made. The effects of reward for correct predictions have also been studied in conjunction with penalty for incorrect choices (Das RC Panda, 1963; Gruen & Weir, 1964; Offenbach, 1964). In these studies correct predictions result in obtaining reward and incorrect predictions result in giving up a reward object. Again, it is possible to manipulate factorially the reward and penalty variables. One additional consideration in the investigation of the effects of penalty should be mentioned. In probability learning tasks involving penalty treatments, subjects are punished for making both incorrect and correct responses. For example, consider a 66:O task. The subjects will be penalized for one third of the responses to the reinforced stimulus and will be rewarded for the remaining twothirds of their responses to this stimulus. Thus it is apparent that maximizing will be adopted as a strategy only if the cumulative effects of reward are greater than those of penalty. The problem becomes more complex if the reinforcement schedules used provide for reward and punishment of alternative responses (e.g., a 75:25 schedule). 1. Tangible Reward The effects of varying incentive level have been consistent for all age levels except for 3- to 5-year-olds. Brackbill, Kappy, and Starr (1962), using second-grade children (mean CA = 8.0 years) and a two-choice task (75:25 reinforcement schedule, successive procedure, noncontingent information feedback, and a trial-defined schedule), found that one, three, or five marbles (which could be turned in for a toy) as reinforcers

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for correct predictions led to higher terminal performance than providing information feedback alone. However, there were no differences between the one-, three-, and five-unit groups. Bisett and Rieber (1966) scaled incentives for children (CA = 6-7 and 10-1 1 years) and then varied the reward (most vs. least preferred in a two-choice probability-learning task (3 3 :O schedule, simultaneous procedure, contingent information feedback, response-defined schedule) and again found that performance with high incentive reinforcers was better than that with low incentive reinforcers. However, the performance differences between the high- and low-incentive treatments could have been due to the facilitative effects of high incentive or to interfering effects of low incentives (or both) relative to providing information feedback alone. Similarly, Stevenson and Hoving (1964), using children (mean CA = 9.4 and 13.7 years), found that reinforcement with incentives of high value (nickels) led to higher asymptotic levels of response than did incentives of low value (metal washers). This was true for both 66:O:O and 3 3 :O:O schedules (simultaneous procedure, contingent information feedback, response-defined schedule). However, opposite results occurred for preschool children (mean CA = 4.6 years). With college students, no differences in performance were found as a function of incentive-level. Stevenson and Weir (1959) have also found higher terminal levels of performance for 5-year-olds when low (marbles) relative to high (trinkets) incentives were used. Siegel and Andrews (1962), also using young subjects (CA = 3.8-5.0 years) and a 75:25 task (simultaneous procedure, noncontingent information feedback, trial-defined schedule), found that reinforcement with small toys (high incentive) facilitated performance relative to the provision of information feedback alone. Weir and Gruen (1965) attempted to reconcile the disparate findings of Siegel and Andrews ( 1 962) with those of Stevenson and Weir ( 1 959) and Stevenson and Hoving (1964) with 4- and 5-year-olds. They varied the task and number of response alternatives (two vs. three). With twochoice tasks the reinforcement schedule was 75:25, and with threechoice tasks the schedule was 75: 12.5:12.5. With a two-choice task which replicated the procedure of Siegel and Andrews (except that contingent information feedback was used), high incentive (small toys) led to higher terminal performance. With a three-choice task no differences in performance between the incentive treatments were found. Furthermore, when the incentive-level was switched after 96 trials (highjlow or low+high) these groups showed a marked increase in the number or choices to the most frequently reinforced stimulus. No such change was apparent for subjects who were maintained on the same (highjhigh, low+low) incentive level for 192 trials. The increase in terminal per-

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formance for the incentive-switch groups was apparent for both two- and three-choice tasks. When a task similar to that of Stevenson and Weir (1 959) and Stevenson and Hoving (1 964) was used, lower terminal performance was found for the high incentive treatment. This was the case for both two- and three-choice tasks.

2. Penalty Das and Panda (1963), Offenbach (1964), and Gruen and Weir (1964) have compared children’s probability learning under what may be called reward-penalty conditions (where subjects are rewarded for correct predictions and forfeit rewards for incorrect predictions). Again, the data across studies are inconsistent. Das and Panda (1963), used a 75:25 reinforcement schedule (successive procedure, noncontingent information feedback, trial-defined schedule) and 5- to 7- and 13- to 14-year-old children, and found that a reward-penalty treatment led to inferior performance relative to a treatment involving information feedback alone. Offenbach (1964) also used a 75:25 schedule (successive procedure, noncontingent information feedback, trial-defined schedule), with kindergarten (CA = 4.4-6.4 years) and fourth-grade (CA = 9.3-1 1.8 years) subjects, but found higher terminal performance under reward-penalty conditions relative to information feedback alone. The reasons for the disparate results of Offenbach ( 1964) and Das and Panda (1963) are not apparent. Gruen and Weir (1 964) did find that a rewardpenalty treatment resulted in superior performance for 7- and 13-yearolds and for college subjects relative to reward (marbles) alone. 3 . Social Reinforcement For the most part, studies of probability learning have provided information feedback alone for correct responses. In some cases, a reinforcer (e.g., marbles) was provided for correct responses and these could be traded in for “prizes” at the termination of the task. Another group of studies of probability learning have investigated the effects of social reinforcers (e.g., approval, disapproval) alone or in conjunction with the effects of other sociopsychological variables. Lewis et al. ( 1 963) found that positive social reinforcers provided by the experimenter (statements of “Good,” “Fine,” for correct responses) were much more effective than information feedback alone for firstgrade children performing on a 70:30 probability-learning task (simultaneous procedure, contingent information feedback, trial-defined schedule). No differences in performance were apparent in the effects of social and nonsocial reinforcement when sixth-grade children served as subjects. However, this effect is apparently restricted to conditions in which the experimenter maintains an aloof relationship with the child

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(Dorwart,Ezerman, Lewis, & Rosenhan, 1965), or when the child has been socially deprived (left alone) for a short period of time (Lewis, 1965; Lewis & Richman, 1964) or has a somewhat negative social encounter with the experimenter (Lewis & Richman, 1964). Furthermore, Stevenson and Weir (1963) found that children’s performance in a probability-learning task was unaffected by the presence or absence of the experimenter or a peer in the experimental situation. In addition, McCullers and Stevenson (1960) found that verbal reinforcement was an effective reinforcer for 3- and 4-year-old children but not for 8- and 9year-old children. Rosenhan ( 1 966) has also found that social approval was more effective than social disapproval for lower-class white and black children in a task similar to that of Lewis et al. ( 1 963). Social approval and disapproval were equally effective for middle-class white children. Unfortunately, there is a paucity of data relating to the interaction of age with type of social reinforcement. Lewis et al. (1963) did find that the facilitative effects of a positive social reinforcer were not apparent for sixth-grade children. And, the data taken together suggest that with the possible exception of first-grade and younger children, similar strategies are used in probability-learning tasks independently of the type of reinforcer provided. In addition, disapproval apparently has similar effects to penalty (penalizing subjects for incorrect choices) for first-grade children. Whether the same is true for older subjects is an empirical question needing investigation. However, as noted above, penalty conditions result in superior performance for subjects across a wide age range, but the data of Lewis et al. (1963) suggest that social reinforcers may become less effective with increased age. H. COMMUNALITY OF RESPONSEPATTERNS ACROSS TASKS AND SUBJECTS

The generality of results among the studies concerned with probability learning has already been discussed. Indeed, almost without exception the choice behavior of very young children (e.g., CA = 3-4 years) in probability-learningtasks has been characterized by perseveration independently of the reinforcement schedule, method, procedure, etc. In contrast, strong preferences for alternation (on two-choice tasks) or systematic search strategies (LMR or RML patterns on three-choice tasks), and again independent of the response-reinforcement contingencies, are found for children ranging in age from 6 to at least 1 1 or 12. Some disparate results are found for 5-year-olds. For example, Weir (1964) and Goodwin (1 969) found pronounced trends toward perseveration for these subjects, but Derks and Paclisanu ( 1 967) found that alternation best described their behavior. Presumably, differences in the sample characteristics between the groups of studies are responsible for the dis-

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parate results. Differences in task characteristics are apparently not responsible for the disparate findings.

111. Other Tasks A. HIDE-AND-SEEK BEHAVIOR

Stevenson and Odom (1964) devised an interesting variant of the probability-learning task -one in which the experimenter and subject alternated hiding and searching for small prizes. The experimenter hid prizes among three boxes according to a 75:25:0 schedule (simultaneous procedure, contingent information feedback, trial-defined schedule) and this aspect of the task was identical to the typical probability-learning situation. However, the subjects (CA = 3-5, 7-8, 10-12 years) alternated with the experimenter in hiding prizes; the experimenter, when the child hid the prize, searched randomly or according to a prearranged 75:25:0 schedule. Of primary interest is the subjects’ hiding behavior. When the experimenter was searching according to the 75:25:0 schedule, the subjects could minimize their losses by hiding the trinkets in the 0% box, but there was no best strategy when the experimenter was searching in a random manner. Although all subjects hid the trinket in the 0% box most frequently when the experimenter was searching according to a 75:25:0 schedule, the youngest children did not improve over the three blocks of 20 trials for hiding. Interestingly, the 7- and 8year-olds’ performance improved most over the three blocks of trials. When the experimenter was searching according to a random schedule, the 7- to 8- and 10- to 12-year-olds distributed their choices equally among the three alternatives. The youngest children showed a strong position preference for hiding the trinket in the middle box. The hide-and-seek task is an interesting one and has promise for the investigation of problem-solving strategies in children. A first line of inquiry, investigated by Stevenson and Odom (1964) and by Odom (1966) is directed to the determination of how children’s searching behavior is affected by the experimenter’s systematic (or unsystematic) pattern of searching. The evidence here suggests strong effects in the direction of superior performance if the experimenter is of the opposite sex (Odom, 1966). A second question is whether the processes involved in children’s hiding and searching are the same. Stevenson and Odom found no statistically significant correlations between children’s tendencies to maximize reinforcement in searching and to minimize loss in hiding. However, the correlation was low negative (r = -.34)for children with CA’s of 3 to 5 and low positive for children with CA’s of 7 to 8 ( r = .33) and 10 to 12 (r

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= .26), leading Stevenson and Odom to suggest the possibility of the

operation of a different process in the youngest group as compared to the two oldest groups. It should be mentioned that the data related to hiding and searching which were collected by Stevenson and Odom (1964) are not independent since the children alternated these activities. Hiding behavior can be investigated independently of searching. With data such as these, the similarity of the strategies in searching and hiding can be compared under treatments in which maximizing, alternation, etc., are the most efficient strategies. Furthermore, both searching (probability learning) and hiding can be compared under penalty conditions. As is apparent, failure to hide appropriately results in losing a trinket for the child-a condition which is similar to that in probability learning when the child fails to search appropriately and is penalized for his incorrect choice. In fact, the functional dissimilarity in the effects of searching and hiding in terms of reward and penalty may be the reason why no strong correlation was found between the efficiency of hiding and that of searching. However, Gratch (1964) has found similar age trends in searching and hiding behavior. Children (CA = 2-8 years) guessed (10 trials) in which hand the experimenter had hidden a marble and then hid the marble from the experimenter for a series of trials. With increasing age, the children shifted from stereotyped to less stereotyped guessing patterns and hid the marble in a less regular and thus more deceptive and competitive manner. Gratch interpreted his results as indicating that with increasing age, children have a greater ability to vary their behavior in an uncertain situation.

B. GUESSING BEHAVIOR A number of studies (Goulet, 1969; Goulet & Barclay, 1967; Jeffrey & Cohen, 1965; Rieber, 1966) have examined developmental changes in choice behavior using random reinforcement rather than reinforcement based on an experimenter-defined correct response (as in probabilitylearning tasks). When random reinforcement schedules are used, subjects are reinforced on prearranged trials, independently of which choice is made. The levels of random reinforcement selected may vary from continuous through any degree of partial reinforcement. As an example, Jeffrey and Cohen (1965) compared the alternation and perseveration behavior of children (mean CA = 3.3 and 4.6 years) in a two-choice task in which subjects were reinforced according to 100, 50, or 33 % schedules. Pronounced differences in alternation and perseveration behavior were found among the age-groups. The 3-year-olds perseverated on one response, and the 4%-year-olds alternated. These dif-

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ferences were especially apparent under the 100% schedule of random reinforcement and to a lesser degree under the 50% schedule. However, under the 33% schedule no differences were apparent between the 3and 41/-year-olds. These data suggest an interaction between level of random reinforcement and age. Additional children (mean CA = 4.1 years) were run under the 100% schedule and were found to divide themselves into two groups - those who perseverated and those who alternated - suggesting some transition in the characteristic pattern of responding in multiple-choice tasks. Rieber ( 1966) compared children (CA = 7-9 years) under random reinforcement conditions and found a strong tendency for alternation in these subjects. However, Schusterman ( 1963) used 100% random reinforcement and a two-choice task, and found that 10-year-olds showed no preference for either alternation or perseveration, while 3-year-olds again showed perseveration and 5-year-olds alternation. McCullers and Stevenson ( 1960), using a reinforcement schedule similar to random reinforcement (66:66:66 or 33:33:33 schedules; i.e., with no stimulus maximally reinforced), also found greater response perseveration for 3and 4-year-olds than for 8- and 9-year-olds. Two additional studies (Goulet, 1969; Goulet & Barclay, 1967) were also concerned with choice behavior of children under random reinforcement. Goulet and Barclay ( 1967) compared the characteristic patterns of responses over 200 trials for noninstitutionalized retardates (MA = 6-8 years, IQ = 50-70) and MA-matched normal children. A four-choice task with either 10 or 25% random reinforcement was used. Figure 5 presents summary data for the groups of subjects. The data are expressed in terms of the Index of Behavioral Stereotypy (discussed earlier). As can be seen from Fig. 5, no trend toward position perseveration was found for either the normal or the retarded children; i.e., the response stereotypy at C, approximates 0% for all treatments, implying that both groups of subjects selected the response alternatives with equal frequency over the 200 trials. Furthermore, in accord with the results of Weir (1 964) and Derks and Paclisanu (1967), who used probability-learning tasks, and Rieber ( 1966) and Jeffrey and Cohen (1963, who varied random reinforcement, the predominant response pattern when considering sequences of two responses was the selection of adjacent alternatives on successive trials. In other words, responses of (1,2), (2,3), (3,4), (4,3), etc., predominated when a frequency count of different patterns of consecutive responses was considered. When the stereotypy of sequences of three consecutive responses was considered, pronounced differences in the behavior of retardates and normals were evident. For the retardates, the third response in a sequence of three was more likely to be a response different from the pre-

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Fig. 5 . Mean response stereotypy for normal ( N ) and retarded ( R ) children at two levels of random reinforcement. [Adapted from Goulet and Barclay (1967) with the permission of the Society for Research in Child Development.]

ceding two. The normal subjects did not select adjacent alternatives, but the third response in a sequence of three was as likely to be any of the three remaining alternatives. Thus, the functional pool of alternative responses for normal children was three for the third response in a sequence of three, while that for the retardates was essentially reduced to two. A further finding by Goulet and Barclay (1967) was that response stereotypy was greater under the 25 % level of random reinforcement than under the 10%level for both groups, although the differences were small. Goulet (1969) also investigated the effects of random reinforcement (lo%, 33%) on the choice behavior of institutionalized retardates in a four-choice task. The MA levels were chosen to include one group (i.e., MA = 4 years) in which strong response perseveration was expected and a second group in which choice behavior was not expected to be characterized primarily by perseveration (MA = 6 years). Jeffrey and Cohen (1965), Weir (1964), and others (e.g., Derks & Paclisanu, 1967) have found that the choice behavior of normal children approximately 4 years of age is characterized by perseveration, and the behavior of older children is characterized by more complex patterns (e.g., alternation). Whether the same trend toward response perseveration can be found for retardates with MA’s approximating 4 years is of much interest. In addition, Goulet (1969) used a level of partial reinforcement much lower than those used by others. Figure 6 provides a comparison of the degree of behavioral stereotypy of response patterns as a function of MA and level of random reinforce-

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ment over the entire block of 210 trials. As can be seen, the degree of stereotypy was greater for low-MA than for high-MA retardates. In addition, the interaction of MA with length of the response pattern, although not pronounced, was statistically significant. In general, the predominant response pattern for low-MA retardates was perseveration to a particular stimulus; i.e., 1,2,3, or 4. However, no position preference was present across subjects. In other words, the greatest degree of stereotypy for these S s was at C1, with small increments in stereotypy present for the C , and C 3patterns (Fig. 6). For the high-MA retardates, the redundancy (stereotypy) in performance was much less pronounced but increased regularly from C, to C3. The interaction of MA with level of random reinforcement is also apparent in Fig. 6. The degree of stereotypy was much more pronounced under the 33 % level of random reinforcement for the low-MA subjects. Again, the effect of the level of random reinforcement was manifest primarily at C,. For the high-MA retardates, no differences in stereotypy were apparent as a function of level of random reinforcement.

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Fig. 6 . Mean response stereotypy for retarded children under two levels of random reinforcement (adaptedfrom Goulet, 1969).

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Identical results were found when the data were analyzed in blocks of 50 trials (omitting the last 10 trials). In addition, the degree of stereotypy for C, and C, patterns increased over blocks of trials for both low- and high-MA retardates. Furthermore, there was a trend toward increasing perseveration over blocks of trials for the low-MA subjects. This trend was much less pronounced for the high-MA subjects. As can be seen in Fig. 6, the low-MA retardates’ choice behavior was characterized by perseveration (greater stereotypy at C,) under both levels or random reinforcement. These data support those obtained by Jeffrey and Cohen (1969, who used random reinforcement, and those of others (e.g., Derks & Paclisanu, 1967; Weir, 1964), who used probability-learning tasks and normal children as subjects. However, the interaction of level of random reinforcement with MA-level found by Gouiet (1969) and that with CA and level of random reinforcement found by Jeffrey and Cohen (1965) suggest that the tasks involving random reinforcement may be somewhat more sensitive to developmental changes in choice behavior than those involving probability learning. In addition, the use of tasks involving random reinforcement has merit because subjects are reinforced for response patterns or strategies that they bring with them to the task. Thus, the characteristic response patterns (strategies) of all subjects, independent of age, are reinforced and presumably maintained. This is especially true for the 100% level of random reinforcement, where nonreinforcement cannot occur, as noted by Gerjuoy and Winters (1 968). However, partial random reinforcement schedules should also maintain these characteristic response patterns. C. ALTERNATION BEHAVIOR

The evidence relating to the spontaneous occurrence of alternation behavior of young children in probability learning has been amply documented. Earlier, Tolman (1925) and Wingfield and Dennis (1934) demonstrated the presence of spontaneous alternation behavior in rats performing in tasks involving two-choice mazes. Wingfield ( 1 938) also found strong alternation behavior in children with similar mazes modified for these subjects. However, alternation behavior was not as pronounced for adults in such tasks (Wingfield, 1943). The studies by Wingfield were concerned with preferences between two alternate pathways subjects could traverse to a goal. It is interesting to note that alternation behavior is found in tasks other than those involving probability learning and, furthermore, that similar developmental trends are found with these tasks. Baumeister (1966) has also documented this for normal (mean CA = 7.9 years) and retarded children on a three-choice discrimination task.

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The attempt to account for the presence and persistence of alternation behavior has prompted several theorists to specify the conditions under which alternation behavior will occur. For example, Skinner (1942) has suggested that through conditioning in childhood, a tendency is set up which opposes repetition in guessing behavior. Thus, with two-choice tasks alternation is generated because each successive response is under the control of the immediately preceding response. Similarly, Hull’s (1943) concept of reactive inhibition (Ir) was used to explain the decreased tendency to repeat a response. More recently, Glanzer (1953) has postulated a “stimulus satiation” theory, in which, with repeated exposure to the same stimuli, the subject’s tendency to respond to the stimuli is reduced. Thus, the result of stimulus satiation is “spontaneous” alternation behavior. In other theoretical accounts, Dember and Earl (1 957) have suggested that spontaneous alternation behavior is a function of a motive to optimize stimulus change, and Walker’s (1958) “action decrement” theory has considered alternation to be a function of a lowered capacity for rearousal of the same response after it has occurred. The primary purpose here is not to review these theories since thorough reviews are available in the articles cited above or in the general review by Dember (1961). Nor does the present description of the theories adequately differentiate between them in terms of their postulates or central assumptions. The above theories were not developed to account for the behavior of children, much less to account for developmental changes in alternation behavior. However, recent research with children has been stimulated by these theories and, of course, by the recurrent finding of “spontaneous” alternation behavior. Ellis and Arnoult ( 1965) have found that 4- and 5-year-old children do show decreased alternation on a simple motor task if external stimulus cues are changed from trial-to-trial, and suggested that the alternation behavior reflected a search for novelty or stimulus change. The introduction of new stimulus cues between successive trials apparently provided this novelty, whereas the novelty was response-produced (alternation) when the task stimuli were identical between trials. Croll (1966) and Ellis and Arnoult both found that spontaneous alternation decreased over practice trials and this has been observed by Jeffrey and Cohen (1965) and Bogartz and Pederson (1966) with other tasks. These findings are consistent with Glanzer’s (1953) theory. Rabinowitz and Cantor (1967), using a six-choice task with subjects instructed only to push the button to see “what lights come on,” found that 6-year-olds showed more circular behavior (pressing adjacent buttons in a systematic fashion) than did 7- or 8-year-olds and, further, that

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stimulus alternation (alternating responses which activated different stimuli) decreased over blocks of trials. Glanzer's (1953) theory apparently has some import for the study of alternation behavior. However, neither it nor any other theory relating to spontaneous alternation has been extended to account for developmental changes in choice behavior. D. STUDIES OF

THE

DEVELOPMENT OF THE PROBABILITY CONCEPT

A series of studies which received their original impetus from the results of Yost et al. (1962) was concerned with the objective assessment of the development of the probability concept in children. Yost, Siegel, and Andrews noted that Piaget (1950) had stated that children (ages 5-7) do not make predictions in probabilistic situations on the basis of quantitative proportions of elements and that they do not understand the idea of randomness nor possess a system of numerical and combinatorial operations. They questioned this assumption and devised a task in which young children (CA = 4.8-5.7 years) made decisions on the basis of objectively defined probabilities. The children saw two containers each of which contained plastic chips of two different colors in a specified proportion of one color to another. The two containers, however, contained different proportions of the two types of chips; e.g., the ratio of blue to white chips was '/3 or V5. The children were told that they were to try to draw a chip of a specified color (e.g., blue) and that they would win a prize if they drew this chip. Furthermore, they could choose the container from which to draw the chip and were fully informed of the different numbers of colored chips in the two containers. The results indicated that the children did choose the container which would maximize the opportunity to draw the payoff chip, thus suggesting that these children do have some understanding of the concept of probability. In a similar study, Goldberg (1966) found that preschool children (CA = 3.8-5.1 years) had greater difficulty in predicting which chip would be drawn as the proportion of chips of the two colors approached 5 0 . Ross (1966) obtained similar results for elementary school children in the second through eighth grades. Apparently, children in this age-range do not utilize a maximizing strategy in tasks of this nature. In other results, Ross (1 966) found that the performance of deaf children lagged behind that of hearing children in this task. This was true for 1 1-year-olds but not for older children. Finally, Ross found that children through the age of 9 did not consider the implications of choosing from the container without replacement when successive choices were made. These children demonstrated a strong tendency to alternate in predicting which of two colored balls would be drawn even though the proportion of the balls of each color changed with each successive choice. All children at

Probabilistic and Problem-Solving Tasks

249

age 6 and above solved the problem (i.e., chose the maximal payoff alternative) when verbalization of the probability concept was not required, but it was not until the age of 9 that all could both choose the correct alternative and verbalize the correct solution. Davies (1965) also used a task similar to that of Yost et al. (1962) and found that the selection of an alternative which maximized the probability of payoff varied directly with age from 3 to 9 years. An increasing percentage of children from 3 to 6 years of age selected the maximal payoff choice when the criterion for success did not involve verbalization of the probability concept. When such verbalization was required, a similar developmental trend was found except that criterion performance lagged behind that when no verbalization was required.

IV. Overview The series of studies reviewed all lead to the discussion of the same general problem -that of developmental changes in information-processing capacity. In probability-learning tasks, the issue takes the form of subjects systematically editing both strategies for “solution” of the task and the meaning of reinforcement or nonreinforcement of single responses or response patterns based on these strategies. A second theoretical issue, however, must not be overlooked- the change with age in the complexity of strategies that can be generated. In probability-learning tasks, this problem takes the form of identifying the number and type of strategies that are characteristic of subjects of different ages. With regard to this problem the evidence is most clear. These characteristic patterns change from perseveration (CA = 4 years) to alternation for children between 5 and 6 to 9 years, and to more complex search behavior through college age. Young children between 5 and 9 show strong tendencies to alternate in a wide variety of tasks (see Derks & Paclisanu, 1967; Ellis & Arnoult, 1965, Jeffery & Cohen, 1965; Ross, 1966). In transfer tasks, these same subjects have difficulty in modifying their behavior to conform to the new schedule (e.g., Crandall et al., 1961; Jones & Liverant, 1960; Kessen & Kessen, 1961) whether the transfer task involves a change in the response or responses to be made (Jones & Liverant, 1960) or in the solution to the task (Crandall et al., 1961). Apparently, the inability to conform to a new schedule is due to difficulty in rejecting a well-learned strategy (Odom & Coon, 1966). It is important to note that this difficulty is not as apparent by the age of 1 1 (Odom & Coon, 1966). The failure to find maximizing behavior in probability learning for chil-

250

L. R . Coulet and Kathryn S . Coodwin

dren between the ages of 6 and 15 years is probably not so much due to the inability to generate complex hypotheses or strategies for solution. Weir (1964, 1967) has suggested that it is likely due to inadequate memory for past events and their outcomes. Again, the likely factor responsible here is not so much the possibility of an inadequate short-term memory store as it is the possibility of interference among competing, partially reinforced response patterns generated during the subjects’ search behavior. There is direct evidence that children at least between the ages of 6 and 9 have difficulty in processing and deducing the meaning of information based on sequential events (Ross, 1966). Although extensive research has been conducted using probabilitylearning tasks, much of the work has been exploratory, parametric, or descriptive in nature. It would now be fruitful to change direction somewhat and to generate a series of studies oriented specifically to investigating the process or processes that covary with the developmental changes in choice behavior. For example, it is possible to modify the probability-learning task such that it capitalizes on (or is inconsistent with) the characteristic behavior shown by children on these tasks. For example, the identification of characteristic patterns of responding for young children provides interesting implications which relate to the rate of learning in discrimination problems. That is, 3- and 4-year-old children should learn a two-choice position discrimination task faster than older children (e.g., CA = 6 years) because perseveration is a characteristic pre-experimental habit which younger subjects bring with them to the task. In contrast, 6-year-olds should learn a simple alternation problem much more quickly. Some support for the former prediction has been provided by Schusterman ( 1964). Along similar lines, Bogartz (1 966) and Bogartz and Pederson (1 966) have investigated some of the parameters of alternation behavior with tasks that capitalize on this response pattern or require alternation behavior as a solution to the problem. Odom and Coon (1 966) have initiated similar work. Weir (1967, 1968) has concerned himself with the identification of the mechanisms responsible for the inadequate information processing in young children. Further research along these lines should prove immensely profitable.

REFERENCES Atkinson, R. C., Bower, G . H., & Crothers, E. J. A n introduction to mathematical learning theory. New York: Wiley, 1965.

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25 1

Baumeister, A. A. Analysis of errors in the discrimination learning of normal and retarded children. Psychonomic Science, 1966, 6, 5 15-5 16. Bisett, B., & Rieber, M. The effects of age and incentive value on discrimination learning. Journal of Experimental Child Psychology, 1966,3, 199-206. Bogartz. R. S. Variables influencing alternation prediction by preschool children: 1. Previous recurrent, dependent, and repetitive sequences. Journal of Experimental Child Psychology, 1966.3, 40-56. Bogartz, R. S., & Pederson, D. R. Variables influencing alternation prediction by preschool children: 11. Redundant cue value and intertrial interval duration. Journal of Experimental Child Psychology, 1966,4,21 1-2 16. Brackbill, Y.,Kappy, M. S.. & Starr, R. H. Magnitude of reward and probability learning. Journal of Experimental Psychology, 1962, 63, 32-35. Brunswik, E. Probability as a determiner of rat behavior. Journal of Experimental Psychology, 1939, 25, 175-197. Brunswik, E. Organismic achievement and environmental probability. Psychological R e view, 1943,50, 255-272. Cotton, J . W., & Rechtschaffen, A. Two- and three-choice verbal conditioning phenomena. Journal of Experimental Psychology, 1958, 56, 96. Craig, G. J . , & Myers, J. L. A developmental study of sequential two-choice decision making. Child Development, 1963, 34, 483-493. Crandall, V. J., Solomon, D., & Kellaway, R. A comparison of the patterned and non-patterned probability learning of adolescent and early grade shool-age children. Journal of Genetic Psychology, 1961,99, 29-39. Croll, W. L. Children’s response alternation as a function of stimulus duration, intertrial interval, and trials. Psychonomic Science, 1966, 6, 247-248. Das, J. P., & Panda, K. C. Two-choice learning in children and adolescents under reward and nonreward conditions. Journal of Genetic Psychology, 1963, 68, 203-21 I . Davies, C. M. Development of the probability concept in children. Child Development, 1965.36.779-788. Demaer, W. N. Alternation behavior. In D. W. Fiske & S. R. Maddi (Eds.). Functions of varied experience. Homewood, Ill.: Dorsey Press, 1961. Pp. 227-252. Dember, W. N., & Earl, R. W. Analysis of exploratory, manipulatory, and curiosity behavior. Psychological Bulletin, 1957.64,91-96. Derks, P. L., & Paclisanu, M. Simple strategies in binary prediction by children and adults. Journal of Experimental Psychology, 1967, 73, 278-285. Donvart, W., Ezerman, R., Lewis, M., & Rosenhan, D. The effect of brief social deprivation on social and nonsocial reinforcement. Journal of Personality and Social Psychology, 1965.2, 1 1 1 - 1 15. Ellis. N. C., & Amoult, M. D. Novelty as a determinant of spontaneous alternation in children. Psychonomic Science, 1965,2, 163-164. Estes. W. K. Probability learning. In A. W. Melton (Ed.), Categories of human learning. New York: Academic Press, 1964. Pp. 98- 129. Gardner, R. A. Probability learning with two and three choices. American Journal of Psychology, 1957, 70. 174-185. Gardner, R. A. Multiple-choice decision behavior. American Journal of Psychology, 1958, 71,710-717. Gerjuoy, 1. R., & Winters, J. J., Jr. Development of lateral and choice-sequence preferences. international Review of Research in Mental Retardation, 1968, 3, 3 1-63, Glanzer, M. Stimulus satiation: An explanation of spontaneous alternation and related phenomena. Psychological Review, 1953.60.257-268.

25 2

L. R . Goulet and Kathryn S.Goodwin

Goldberg, S. Probability judgments by preschool children: Task conditions and performance. Child Development, 1966,37, 157-167. Goodnow, J . J. Determinants of choice-distribution in two-choice situations. American Journal of Psychology, 1955.68, 106- 1 16. Goodnow, J . J., & Pettigrew, T. F. Effect of prior patterns of experience upon strategies and learning sets. Journal of Experimental Psychology, 1955,49, 38 1-389. Goodnow, J . J., & Pettigrew, T. F. Some sources of difficulty in solving simple problems. Journal of Experimental Psychology, 1956,51, 385-392. Goodwin. K. Changes in probability learning as a function of age, number of choices, and information procedure. Unpublished master’s thesis, West Virginia University, 1969. Goulet, L. R. Choice-behavior of retardates in a multiple-choice task under varying conditions of random reinforcement. Unpublished manuscript, West Virginia University, 1969. Goulet, L. R., & Barclay, A. Guessing behavior of normal and retarded children under two random reinforcement conditions. Child Development, 1967,38,545-553. Gratch, G. Response alternation in children: A developmental study of orientations to uncertainty. Vita Humana, 1964,7,49-60. Gruen, G . E., & Weir, M. W. Effect of instructions, penalty, and age on probability learning. Child Development, 1964, 35, 265-273. Hull, C. L. Principles of behavior. New York: Appleton-Century-Crofts, 1943. Humphreys, L. G . Acquisition and extinction of verbal expectations in a situation analogous to conditioning. Journal of Experimental Psychology, 1939,25294-301. Jeffrey, W. E., & Cohen, L. B. Response tendencies of children in a two-choice situation. Journal of Experimental Child Psychology, 1965,2, 248-254. Jones, M. H., & Liverant, S. Effects of age differences on choice behavior. Child Development, 1960,31,673-680. Kessen, W., & Kessen, M. L. Behavior of young children in a two-choice guessing problem. Child Development, 1961.32, 779-788. Lewis, M. Social isolation: A parametric study of its effect on social reinforcement. Journal of Experimental Child Psychology, 1965,2, 205-2 18. Lewis, M. Probability learning in young children: The binary choice paradigm. Journal of Genetic Psychology, 1966, 108,43-48. Lewis, M., & Richman, A. Social encounters and their effect on subsequent social reinforcement. Journal of Abnormal and Social Psychology, 1964,69, 253-257. Lewis, M., Wall, A. M., & Aronfreed, J. Developmental change in the relative values of social and nonsocial reinforcement. Journal-of Experimental Psychology, 1963, 66, 133- 137. Lipsitt, L. P. Simultaneous and successive discrimination learning in children. Child Development, 1961,32,337-348. Little, K. B., Brackbill, Y.,Isaacs, R. B., & Smelkinson, N. A further test of a general utility model for probability learning. Journal of Experimental Psychology. 1963, 66, 107- 108. McCullers, J. C., & Stevenson, H. W. Effects of verbal reinforcement in a probability learning situation. Psychological Reports, 1960, 7 , 439-445. Messick, S. J., & Solley, G. M. Probability learning in children: Some exploratory studies. Journal of Genetic Psychology, 1957,90,23-32. Metzger, R. Probability learning in children and aments. American Journal of Mental DeJiciency, 1960,64, 869-874. Miller, G. A., & Frick, F. C. Statistical behavioristics and sequences of responses. Psychological Review, 1949.56.3 1 1-324.

Probabilistic and Problem-Solving Tasks

253

Neimark, E. D. Effects of type of nonreinforcement and number of alternative responses in two verbal conditioning situations. Journal of Experimental Psychology, 1956, 52, 209-220. Odom, R. D. Children’s probability learning as a function of the cross-sex effect. Psychonomic Science, I966,4, 305-306. Odom, R. D. Problem-solving strategies as a function of age and socioeconomic level. Child Development, 1967,38, 747-752. Odom, R. D., & Coon, R. C. The development of hypothesis testing. Journal of Experimental Child Psychology, 1966.4, 285-29 1. Offenbach, S. I. Studies of children’s probability learning behavior: I. Effect of reward and punishment at two age levels. Child Development, t964,35, 709-7 15. Offenbach, S. I. Studies of children’s probability learning behavior: 11. Effect of method and event frequency at two age levels. Child Development, 1965.36,95 1-962. Piaget, J. Une expkrience sur la psychologie du hasard chez I’enfant: le tirage au sort des couples. Acta Psychologica, 1950, I , 323-336. Rabinowitz, F. M., & Cantor, G. N. Children’s stimulus alternation, response repetition, and circular behavior as a function of age and stimulus conditions. Child Development, 1967,38,661-672. Rieber, M. Response alternation in children under different schedules of reinforcement. Psychonomic Science, 1966.4, 145- 150. Rosenhan, D. L. Effects of social class and race on responsiveness to approval and disapproval. Journal of Personality and Social Psychology, 1966.4, 253-259. ROSS,B. N. Probability concepts in deaf and hearing children. Child Development. 1966, 37,9 17-927. Schultz, D. P. Spontaneous alternation behavior in humans: Implications for psychological research. Psychological Bulletin, 1964, 62, 394-400. Schusterman, R. J. The use of strategies in two-choice behavior of children and chimpanzees. Journal of Comparative and Physiological Psychology, 1963,56,96- 100. Schusterman, R. J. Strategies of normal and mentally retarded children under conditions of uncertain outcome. American Journal of Mental Dejciency, 1964, 69,66-75. Siegel, S., & Andrews, J. M. Magnitude of reinforcement and choice behavior in children. Journal of Experimental Psychology, 1962,63,337-341. Skinner, B. F. The processes involved in the repeated guessing of alternatives. Journal of Experimental Psychology, 1942,30,495-503. Spiker, C. C., & Lubker, B. J. The relative difficulty of the successive and simultaneous discrimination problems. Child Development, 1965, 36, 109 1 - 1101. Stevenson, H. W., & Hoving, K. L. Probability learning as a function of age and incentive. Journal of Experimental Child Psychology, 1964, I, 64-70. Stevenson, H. W., & Odom, R. D. Children’s behavior in a probabilistic situation. Journal of Experimental Psychology, 1964,68, 260-268. Stevenson, H. W., & Weir, M. W. Variables affecting children’s performance in a probability learning task. Journal of Experimental Psychology, 1959,57,403-4 12. Stevenson, H. W., & Weir, M. W. The role of age and verbalization in probability learning. American Journal of Psychology, 1963,76, 299-305. Stevenson, H. W., & Zigler, E. F. Probability learning in children. Journal of Experimental Psychology, 1958, 56, 185- 192. Tolman, E. C. Purpose and cognition: The determiners of animal learning. Psychological Review, 1925,32,285-297. Tune, G . S. A brief survey of variables that influence random-generation. Perceptual and Motor Skills, 1964, 18,705-710. (a)

L. R . Goulet and Kathryn S . Coodwin

254

Tune, G. S. Response preferences: A review of some relevant literature. Psychological Bulletin, 1964, 61, 286-302. (b) Walker, E. L. Action decrement and its relation to learning. Psychological Review, 1958, 65, 129-142. Weir, M. W. Effects of age and instructions on children’s probability learning. Child Development, 1962,33,729-735. Weir, M. W. Developmental changes in problem-solving strategies. Psychological Review, 1964.71.473-490.

Weir, M. W. Age and memory as factors in problem solving. Journal of Experimental Psychology, 1967,73,78-84. Weir, M. W. Memory and problem solving: A failure to replicate. Journal of Experimental Psychology, 1968,78, 166- 168. Weir, M. W., & Gruen, G. E. Role of incentive level, number of choices, and type of task in children’s probability learning. Journal of Experimental Child Psychology, 1965, 2, 121-134.

Wingfield, R. C. A study in alternation using children on a two-way maze. Journal of Comparative Psychology, I938,25,439-443. Wingfield, R. C. Some factors influencing spontaneous alternation in human subjects. Journal of Comparative Psychology, 1943,35, 237-243. Wingfield, R. C., & Dennis, W. The dependence of the rat’s choice of pathways upon the length of the daily trial series. Journal of comparative Psychology, 1934, 18, 135-147. Yost, P. A., Siegel, A. E., & Andrews, J. M. Nonverbal probability judgments by young children. Child Development, 1962,33, 769-780.

Author Index Numbers in italics refer to the pages on which the complete references are listed.

A Adams, G., 86,112 Adams, J. A,, 194,208,209 Alexander, H. M., 160, 174 Ambrose, J. A., 155, 172 Ames, E. W., 122, 143, 173, 178 Andrews, J. M., 215, 238,248, 249,253, 254 Angulo y Gonzalez, A. W.,6.9, 1 1, 12,34, 43, 45,SI Anokhin, P. K., 7,51 Antonitis, J. J., 161, 177 Apgar, V., 67, 11 I Arasteh, J. D., 170, 172 Arnold, H., 81, 113 Arnoult, M. D., 122, 127, 173,247, 249, 251 Aronfreed, J., 222, 239, 240,252 Arsenian, J. M., 152, 172 Arshavskiy, I. A., 35,51 Artom, G . , 4,52 Atkinson, R. C., 214,215,250 Attneave, F., 122, 127, 172, I73 Austin, M. F., 6, 57

B Badgley, C. E., 35,51 Balaban, M., 7, 9,44,45,53 Banker, B. Q., 35,52 Barclay, A., 2 18,223, 242, 243, 244,252 Barcroft, J., 6, 10, 38, 42, 45, 51 Barnes, G . W., 161, 173 Barnett, S.A., 142, 173 Barron, D. H., 6, 10, 38, 42, 45, 47,51

Bartels, B., 99, 106, 114 Bartoshuk, A. K., 80, 82,94,95,97, 112, 143, 173 Bauer, J. A., Jr., 33,53 Baumeister, A. A., 246, 251 Beach, D. H., 182,209 Beach, F. A., 120, 142,173 Beadle, K. R.,81, 94,112 Becker, R. F., 4,5, I I , 57 Beebe, H., 95,113 Beintema, D. J., 88, 116 BBlanger, D., 60, 115 Bellairs, A. d’A., 9,44, 45,54 Benjamin, L. S., 77, 112 Bennett, E. L., 33,55 Bennett, S., 81, 116 Berg, K. M., 76, 79, 92, 99, 100, 112 Berg, W. K., 63, 64, 65, 76, 79, 92, 99, 100, 112,113 Berlyne, D. E., 61, 112, 120, 121, 122, 123, 126, 131, 134, 135, 138, 139, 140, 151, 155, 156, 157, 158, 159, 160, 168, 171,173 Bernbach, H. A., 198,209 Bernuth,H.v.,97,114, 143,176,177 Bever, J., 63,116 Bickman, L., 80, 87,88, 116 Bindra, D., 156, I73 Birns, B. M.,80, 87, 88, I12 Bisett, B., 238,251 Black, A. H., 89,112 Blank, M., 80, 87, 88, 112 Blazek, N. C., 145, 160,176 Boat, B. M., 201,209 Bodian, D., 5,9,34, 36,45,46,51 Bogartz, R. S., 233,247,250,251 255

256

Author Index

Bolaffio, M., 4,52 Bot, A. P. C., 44,52 Bower, G. H., 214,215,250 Boyd, E., 52 Boyd, J. D., 35,53 Brackbill, Y., 86, 96, 112, 227, 237,251, 252 Brennan, W. M., 122,173 Bridger, W. H., 76,80,81,87,88,89,93, 112, 143,173 Bronson,G. W., 153, 154, 173, 174 Broverman, D. M., 170,174 Brown, W. L., 145, 174 Bruner, J. S . , 189,209 Brunswik, E., 215, 226, 227, 251 Bryant, S. V., 9,44,45,54 Buchwald, A. M., 63.82, 113 Burgers, J. M., 159, 174 Butler, R. A., 120, 156, 160, 161, 174

C Campbell, D., 153, 174 Campbell, H., 91, 114 Cannizzo, S . R., 182,210 Cantor, G. N., 91, 115, 120, 121, 123, 144, 145,174,178,247,253 Cantor, J. H., 145, 174 Carmichael, L., 3, 6,43,52 Carr, R. M., 145, 174 Caviness, J. A., 148, 179 Chase, H., 69, 82, 88, 89, 90, 112 Chase, H. H., 69,82,85,88,89,90,107, 112,114 Chase, W. G., 64,66,67, 77,112 Chinsky, J. M., 182, 209 Chun, B. J., 76, 81, 82, 83, 88,94, 95, 96, 113 Clapp, W. F., 124, 135, 137,174 Clifton, C., Jr., 201, 209 Clifton, R. K., 63, 64, 69, 70, 73, 76, 78, 79, 80, 82, 83, 84, 85, 86, 88, 92, 99, 107, 108, 109, 112, 113 Coates, B., 198, 20 I , 209 Coghill, G. E., 2, 3, 5 , 9, 12, 43, 52 Cohen, L. B., 218, 223, 224,242, 243, 244, 246,247,249,252 Collard, R. R., 146, 174 Conel, J. L., 96, 113

Coon, R. C., 234,249,250,253 Corner, M. A., 44,52 Coronios, J. D., 6, 9,45,52 Corsini, D. A., 182,209 Cotton, J. W., 228,251 Coulombre, A. J., 35, 52 Cox, F. N., 153, 174 Craft, M., 67, 113 Craig, G. J., 224, 251 Craig, J. G., 198, 211 Crandall, V. J., 223,232,249,251 Craw, M. A., 126, 140,173 Croll, W. L., 247,251 Crothers, E. J., 214,215,250 Crowell, D. H., 76, 81, 82, 83, 86, 88, 92, 94, 95, 96, 107,112, 113 Cuajunco, F., 48,52

D Daehler, M. W., 182,209 Daniel, R. S., 9, 56 Das, J. P., 216, 237, 239,251 Davies, C. M., 249,251 Davis, C. M., 76, 81, 82, 83, 88, 94, 95, 96, 113 Davis, M. E., 33,52 Davis, R. C., 63, 82, I13 Day, H., 171, 174 Dember, W. N., 124, 133, 139,174, 175, 214,247,251 Dennis, W., 246, 254 Derks, P. L., 223, 224, 235, 240, 243, 244, 246,249,251 Derr, J. E., 34,56 Desmond, M. M., 81,113, 117 Diamond, M. C., 33,52,56 DiCara, L. V., 89, 115 Dillman, A., 157, 180 240, 251 Dorwart, W., Doyle, G. A., 161, 178 Drachman, D. B., 35,52 Druger, R., 95,98, 116

E Earl, R. W.,124, 133, 139, 174, 175, 247, 25 I Eichorn, D. H., 124, 135, 137,174

Author Index

Eisenberg, R. B., 97, 113 Eisenman, R., 137, 139, 140, 175 Elligson, R. J., 96, 113 Ellis, N . C., 247, 249, 251 Emde, R. N., 155, 178 Emerson, P. E., 155, 179 Engen, T., 143, 175 Ernhart, C. B., 67, I13 Estes, W. K., 214,251 Ezerman, R.,240, 251

F Fantz, R. L.,97, 113, 122, 143, 151, 175 Faw, T. T., 157,175 Fish, M. W., 42, 57 Fiske, D. W., 124, 175 Fitzgerald, J. E., 4, 7, 9, 10, 12, 13, 16, 33, 34.4 I , 42,45,47,52, 57 Flavell, J. H., 182, 199, 203,209, 210, 211 Fourment, A., 33,56 Fowler, H., 120, 155, 159, 160, 161,175 Franklin, R. R.,81, 113. 117 Frankmann, R.W., 63,82,113 Fraser, D. C., 145, 175 Freedman, D. G., 155, 175 Frick, F. C., 226,252 Friedlander, B. Z., 161, 175, 177 Froeschels, E., 107, 113

G Gardner, R.A., 228,251 Gasser, R. F., 17, 52 Gejuoy, 1. R.,214, 223, 246,251 Gibson, E. J., 107, 113 Gibson, J. J., 107, 113, 148, 179 Gilman, A., I 1,52 Gilmore, J. B., 157, 175 Glanzer, M., 160, 175, 247, 248, 251 Glasshagle, E. E., 6, 43, 45, 5 7 Glickman, S . E., 142, 175 Goldberg, S., 99, 106, 114, 145, 170, 175, 177,248,252 Golubewa, E. L., 4, 7, 22, 52 Goodman, L. S., 11,52 Goodnow, J. J., 230, 232,233,252 Goodrick, C. L., 12i, 156,175 Goodwin, K., 223, 224, 225, 226, 227, 228, 229,235,252

257

Gottlieb, G., 3,9, 33,42,43,45, 52,53 Goulet, L. R.,218, 223, 240, 242, 243, 244,245,246, 252 Goy, R.W., 170, 175 Graham, F. K., 63,64,65,66, 67,69, 70, 73, 76, 77.78.79, 80, 82, 83, 84, 85, 86, 88, 92, 99, 100, 104, 105, 107, 108, 112,113,114 Grastyin, E., 63, 113 Gratch, G., 198,209, 242, 252 Gray, M. L., 82, 86, 88, 92, 107, 112, 113 Greenfield, P. M., 189, 209 Griffin, A. M., 6, 9,42,43,45,57 Gruen, G. E., 216,217,222,227,228,229, 230,237,238,239,252,254 Guilford, J. P., 170, 175 Gullickson, G. R.,64, 76, 115

H Hagen, J. W., 197, 198, 199, 202, 203,209, 210 Halliday, M. S., 155, 175 Halwes, T. G., 182, 203, 210 Hamburg, D. A., 170, 176 Hamburger, V., 3,7, 9, 30, 35,43,44,45, 47,53 Hamilton, W. J., 35, 53, 159, 177 Harlow, H. F., 145, 146, 160, 161, 174, 176, I77 Harlow, M. K., 145, 176 Harris, L., 147, 176 Harrison, R.G., 3 I , 53 Hartup, W. W., 198, 201,209 Hatton, H. M., 69,70,76, 79, 82, 84.85, 86, 88, 92, 101, 102, 103, 104, 106, 107, 108, 109,112,113 Hayes, J. R., 159, 176 Haynes, H., 134, 176 Haywood, H. C., 156,176 Headrick, M. W., 67,113 Hebb, D. O., 156,176 Hegion, A. G., 199, 211 Held, R.,33,53, 134, 176 Henker, B. A., 91,114 Hen-Tov, A., 91, 114 Hershenson, M., 122, 130, I76 Hewer, E. E., 48,53 Higgins, W. H., 156, 179

258

Author Index

Hill, R. M., 81, 113, 117 Hirota, T., 156, 157, 173 His, W., 34, 53 Hnatiow, M.,82, 114 Hoats, D. L., 123, 137,176 Hogg, I. D., 9, 41.48, 53 Holt, B. G., 123, 140, 179 Hooker, D., 3, 4, 9, 10, 11, 12, 14, 16, 17, 18, 19,20,21, 22,26,27,28,29, 31, 33, 34, 35, 37, 38,41, 42,43,45,46, 53,54 H0rd.D. J., 76, 99, 102, 113, 143, 177 Horowitz. A. B., 182, 209 Hoving, K. L., 217, 238, 239, 253 Hrbek, A., 96,114 Hrbkova, M.,96,114 Hubel, D. H., 97,114 Hughes, A., 9,44,45,54 Hull, C. L., 247,252 Humphrey, T., 6, 9, 10, 11, 12, 13, 15, 16, 17,18,19,20,21,22,23,26, 27,28, 29,31, 34, 35, 36,40,41,42,43,47, 48,54 Humphreys, L. G., 215,252 Hunt,J. McV., 151, 152,176 Hunt, W.A,, 94, 114 Hutt,C., 97, 114, 126, 135, 136, 141, 143, 146, 147, 149, 157, 161, 164, 165, 167, 168, 170,176,177 Hutt, S. J., 97, 114, 143, 157, 168, 177 Huttenlocher, J., 76, I I 7

I Isaacs, R. B., 227,252

J Jackson, J. C., 94, 103, 104, 105, 114 Jacobs, M. J., 40,55 Jacobson, M., 3, 30,55 Jameson, J., 80, 87, 88, 116 Jeffrey, W. E., 218, 223, 224,242,243, 244,246,247,249,252 Jensen, A. R., 198,203,210 Johnson, L. E., 76.99, 102,113, 143,177 Jones, M. H., 221,222,232,249,252

K Kagan, J., 91, 114, 115, 132, 134, 144, 161, 170, 171,177 Kalafat, J . , 91, 114, 134, 144, 177 Kantowitz, S., 67, 104, 105, 114 Kappy, M. S., 237,251 Karmos, G., 63,113 Kaye, H., 143, 175 Keen, R. K., 82,85, 88, 107, 114 Keeney, T. J., 182,210 Kellaway, R., 222, 232, 249, 251 Kellenyi, L., 63, 113 Kendler, H. H., 194, 210 Kendler, T. S., 182, 194,210 Kessen, M. L., 128, 129, 135, 178, 223, 232,249,252 Kessen, W., 122, 127, 128, 129, 130, 134, 135,176, 178,179,223,232,249,252 Khachaturian, Z., 95, 98, 116 Kiang, N. Y. S., 97,114 Kimura, D., 170,177 King, T. G., 34,56 Kingsbury, B. F., 40,55 Kingsley, P. R., 198, 199,202, 203,209, 210 Kish,G. B., 111,114, 161, 173, 177 Klaiber, E. L., 170, I74 Kobayashi, Y.,170,174 Koenig, I. D., 156, 157,173 Kogan, H., 170,180 Koltsova, M. M., 96, 112 Korn, J. H., 66, 114 Kotses, H., 63, 116 Krech, D., 33,55 Kuhlman, C. K., 197,210 7, 9, 39, 43, 45, 53, 55 KUO,Z.-Y.,

L Lacey, J. I., 60,63,70, 74,114 Lampl, E. E., 155,179 Landis, C., 94, I14 Lang, P.J., 82,114 Langley, A. L., 43,55 Lawick-Goodall, J. V.,142,177 Lenard,H.G.,96,97,:14, 143,176, 177 Lester, D., 155,177

259

Author Index

Leuba, C., 124, 161,177 Levine, J., 91, 114 Lewis, J. L., 126, 140, 173 Lewis, M., 91, 99, 106, 114, 134, 144, 145, 161, 170, 171, 175, 177, 216, 222, 223, 239, 240,251,252 Licklider, J. C. R., 96, 114 Lieberman, J. N., 170, 177 Lind, J., 39,56 Lindner, B., 33, 52 Lipsitt, L. P., 143, 175, 217, 252 Lipton, E. L.,70,78,80, 88,91, 110, 114, 115. 116, 117 Little, K. B., 227, 252 Lituchy, S., 80, 87, 88, 116 Liverant, S., 221, 222, 232, 249,252 Lodah1,T. M., 161, 178 Lubin, A., 76, 99, 102, 113 Lubker, B. J., 217,253 Ludwig, H., 69, 115 Lunde, D. T., 170, 176 Luria, A. R., 182, 210 Lynch, J. J., 65, 115 Lynn, R., 61,93, 115

M McCall, R. B.,91, 115, 132, 134, 177 McCarthy, J. J., 161, 175 McClearn, G. E., 145, 160, 161,176 Maccoby, E. E., 170, 171, 177, 182, 210 McCullers, J. C., 240, 243,252 McDonald, D. G., 143,177 McGrew, P. L., 135, 136, 176 McReynolds, P., 155,177 Maddi, S. R.,124, 175 Magoun, H. W., 36,55,61,115 Mall, F. P., 55 Malmo, R. B., 60,115 Mandler, G., 206,210 Marais, F. N., 142, 177 Marler, P. J., 159, I77 Martin, C. J., 194, 196, 198, 203,210 Martin, J., 63, 113 Mavrinskaya, L. F., 4,55 May, R. B.,125, 134, 177 Mendel, G., 147,177 Messick, S.J., 218, 222,252 Metzger, R.,223,252

Meyer, D. R.,145,176 Meyers, W. J., 64, 76, 91, 92, 109, 112, 115, 144, 178 Milgram. N. A., 198, 204, 210 Miller, G. A., 226, 252 Miller, M. B., 123, 137, 176 Miller, N. E., 89, 115, 160,178 Minear, W. L., 6, 57 Minkowski, M., 3.4, 5,42,43,45,55 Moely, B. E., 182, 198, 203, 210 Moffett, A., 143, 178 Moffitt, A. R., 76, 91, 97,115 Montgomery, K. C., 160, 178 Moon, L. E., 161, 178 Moore, R. W., 122, 173 Morgan, G. A., 155,178 Moruzzi, G., 61, 115 Moss, H., 170, 178 Mossman, H. W., 35,53 Moyer, K. E., 66,114 Muller-Schwarze, D., 169, 178 Munsinger, H., 122, 127, 128, 129, 130, 134, 135, 176, 178 Muntjewerff, W. J., 97, 114, 143, 177 Murphy, W. F., 43,55 Murray, D. J., 197, 202, 210 Myers, A. K., 160, 178 Myers, J. L., 224,251

N Neimark, E. D., 228, 253 Newton, J. E. O., 65, 115 Nilsson, L., 43,55 Noble, C. E., 196, 211 Nunnally, J. C., 157,175

0 Obrist, P. A., 89, 115 Odom, R. D., 216,217,234,241,242,249, 250,253 O’Donnell, J. E., 6, 43,45,57 Offenbach, S. I., 216, 217, 228, 237,239, 253 Ogilvie, J. C., 171, 173 Olson, F. A., 182,203,210 Olson, R. E., 69, I15

260

Author Index

Oppenheim, R., 7,9,43,44,45,53 Ordy, J. M., 157,180 Orr, D. W.,6, 9, 43,45,52,57

P Paclisanu, M., 223,224, 235, 240, 243, 244,246,249,251 Panda, K. C., 216,237, 239,251 Pap, L. F., 81, 117 Paradise, N., 139, 175 Parham,L.C.C., 140, 171,173 Parry, M. P., 147, 148, 179 Partanen, T., 39,56 Patten, B. M., 35,55 Patton, H. D., 36,56 Payne, B., 134,178 Peake, W. T., 97,114 Pederson, D. R., 247,250,251 Perez-Cruet, J., 65, 115 Pettigrew, T. F., 232, 233,252 Piaget, J., 206,210, 248,253 Pick, A. D., 182, 203, 209 Plumb, R., 81,113 Polak, P. R., 155, 178 Polikanina, R. I., 93, 106, 107, 115 Posner, M. I., 194,210 Potter, E. L., 35, 52 Prechtl, H. F. R., 43,55, 88, 116, 143, 176, 177 Prestige, M. D., 44,54 Preyer, W.,35,55 Pritchard, J. A., 35,55 Probatova, L. E., 93, 106, 115

R Rabinowitz, F. M., 241, 253 Ranken, H. B., 191, 196, 210 Ransom, S. W.,6 , 5 5 Rappaport, J., 137, 175 Raskin, D. C.,63, 116 Rausch, M., 145,177 Raymond, A., 33,52 RechtschafTen, A., 228, 251 Reese, H. W.,182,210 Reiser, M., 76, 80,81,89,93, 112 Reynolds, S. R. M., 8,34,55

Rheingold, H. L., 154, 161, 178 Rhines, R., 36, 55 Ricciuti, H. N., 155,178 Richman, A., 240,252 Richmond, J. B., 70,73, 80, 88,89, 91, 109, 110,114, 115, 116, 117 Rieber, M., 218,223,238,242,243,251, 253 Riesen, A. H., 95,116 Robinson, R., 134, 178 Rohwer, W. D., Jr., 198, 203, 210 Rosenbaum, M. E., 197,210 Rosenhan, D. L., 216, 240, 251, 253 Rosenthal, M. K., 153, 178 Rosenzweig, M. R., 33,55 Ross, B. N., 248,249,250,253 Routtenberg, A,, 61, 109, 116 Royer, F. L., 63, I16 Ruch, T. C., 36,56 Rudolph, A. J., 81, 117 Rueping, R. R., 146,177 Rump, E. E., 135.178 Rush,J. B., 81, 117 Ryan, S . M., 199,211

S Saayman, G., 143, 178 Sackett, G. P., 134, 179 Salapatek, P., 134, 179 Salapatek, P. H., 126, 140, 173 Sameroff, A., 97, 107,116 Schachter, J., 73, 78,80, 81, 87, 88,95, 98, 116,117 Schachter, J. S., 80,87, 88, 116 Schaf€er,H. R., 147, 148, 155,179 Scharpenberg, L. G., 47,56 Scheibel, A. B., 85, 96, 116 Scheibel, M. E., 85,96, 116 Scherrer, J., 33,56 Schiff, W.,148. 179 Schneirla, T. C., 61, 116 Schulman, C. A.. 106,116 Schultz, D. P., 214, 253 Schustennan, R. J., 223,233, 243,250, 253 Sheldon, A. B., 152, 156, I79 Sheldon, M. H., 156,179 Sherrington, C. S., 40, 56 Shillitoe, E. E., 142, 179

26 1

Author Index

Shulejkina, K. V., 4, 7, 22, 52 Siebert, W. M., 97,114 Siegel, A. E., 2 15, 248, 249, 254 Siegel, S., 238, 253 Silverman, I. W., 198, 211 Skinner, B. F., 247, 253 Smelkinson, N., 227, 252 Smith, D. B. D., 64, 117 Smith, K., 88, 117 Smith, K. U., 9,56 Smith, R. K.,196, 211 Smock, C. D., 123, 140,179 Soforenko, A. Z., 161,175 Sokolov, E. N., 61,62,63,96, 98.99.117, 140,179 Solley, G. M., 218, 222, 252 Solomon, D., 222, 232, 249, 251 Sontag, L. W., 107,117 Spaulding, S. J., 91, 114 Spencer, W. A., 163,179 Spiker, C. C., 217,253 Spinner, N., 156, 173 Spitz, H. H., 123, 137, 176 Spitz, R. A., 155, 178, 179 Sroges, R. W., 142, 175 Stanley, W. C., 161, 178 Starr, R. H., 237,251 Steffek, A. J., 34,56 Steinschneider, A., 70,73,78,80, 88.89, 90,91,109, 110,114,115,116,117 Stenson, H. H., 134,179 Stevenson, H.W., 217,219,220,221,222, 230, 231, 234, 238, 239, 240, 241, 242, 243,252,253 Strassman, P., 3,49,56 Strawbridge, P. J., 64,117 Streeter, G. L., 12, 56 Stretch, R., 157,179 Sutterer, J. A., 8 9 , l I5 Swenson, E. A., 6 , 5 6 Symmes, D., 161,179 Sztkely, G., 3 1, 56 SzentQothai, J., 31, 56

T Taylor, D. C., 170,179 Tennes, K. H., 155,179 Terwilliger, R. F., 134,179

Thomas,H., 122,131,179 Thompson, R. F., 163,179 Thompson, W. R., 156,179 Thorpe, W. H., 159,180 Thurston, D., 67,113 Tobin, M.. 73, 78, 87, 95, 98, 116, 117 Tolman, E. C., 246,253 Tomnce, E. P., 170,180 Towe, A. L., 36,56 Tracy, H. C., 43,56 Tuge, H., 9,45,56 Tune, G. S., 214,253,254

U Underwood, B. J., 195,211

V Vainstein, I. I., 4,7,22,52 Valannt, E., 39,56 Vallbona,C.,81,113,117 Vereczkey, L.,63,113 Vitz, P. C., 133, 134,180 Vogel, W., 170,174 Vuorenkoski, V., 39,56 Vygotsky, L. S., 184, 196,211

W Wachs, T. D., 156,176 Walberg, F., 36,56 Walker, B. E., 139,180 Walker, E. L., 139,180,247,254 Wall, A.M., 222,239,240,252 Wallach, M. A., 170,180 Wasz-Hijckert, O., 39,56 Watts,J.,81,113 Waugh, M., 35,53 Webb, R.A,, 89,115 Weir,M. W., 130,178,215,216,217,220, 221,222,223,224,225,226,227,228, 229,230,23 1,234,235,236,237,238, 239,240,243,244,246,250,252,253, 254 Weiss, P., 7,30,3 1,56 Weiss, T. F., 97,114 Welker, W. I., 121,139, 146,159,180 Wenger, E., 7,9,43,44,45,53

262

Author lndex

Westcott, M. R., 76, 11 7 Wolff, P. H., 88,99,117 White, 8. L., 134, 176 Wolin, L. R., 157,180 Wickelgren, L. W.,134,180 Woodbury, J. S., 36.56 Wiederhold, M. L., 97,114 Wynns, F. C.,182,209 Wiesel, T. N., 97, 114 Wilder, J., 74,117 Y Williams,J.D.,81,II6 Williams, T. A., 73,78,80,8 1,87,88,95, Yanase, J., 3.49.57 98,116,117 Yost, P. A., 21 5,248,249,254 Windle,W.F.,3,4,5,6,7,9,10,ll,l2,13, Youngstrom, K. A., 45,57 16,33,34,41,42,43,45,47,52,55,56, 57 Wingfield, R. C., 246,254 Z Winters, J. J., Jr., 214,223,246, 251 Wohlwill, J. F., 203,209 Zigler, E. F., 2 17, 2 I9,220,22 I , 234,253

Subject Index A

development of, see under Fetal activity postnatal, relation to fetal activity, see Fetal activity Behavioral state, heart rate response and, 87-91,98-105 Bodily movement, heart rate response and, 87-91 Boredom, specific and diversive activities and, 159-161

Activity, fetal, see Fetal activity Adult, arousal systems and, 62-67 Age-changes, probability learning and, 234-237 Alternation behavior, 246-248 Anesthetics, behavioral development and, 10-12 Anoxia, behavioral development and, 10-12 Approach-avoidance conflict, see under Exploration Arousal systems, 59-1 17 evoked heart rate response and, 78-108 factors affecting developmental shift and, 93-108 in newborn, 79-91 in older infants, 9 1-93 experimental procedure and, 67-78 heart rate response measurement and, 69-78 laboratory arrangements and, 68-69 subjects and, 67-68 OR-DR differentiation in adult subjects and, 62-67 Asphyxia, behavioral development and, 10-12 Attention, complexity as determinant of, 121-138 comparison of variables of complexity and, 135-138 multidimensional complexity and, 122-126 unidimensional complexity and, 127- 135

Drugs, behavioral development and, 10- 12

B

E

Behavior, choice. see Choice behavior

C Choice behavior, 2 13-254 alternation and, 246-248 development of probability concept and, 248-249 guessing and, 242-246 hide-and-seek and, 24 1-242 probability learning and, 214-240 definitions and, 214-216 descriptive developmental changes in, 222-226 historical aspects and, 218-222 methods and, 2 16-2 18 variables influencing, 226-240 Clustering, mediated memory and, 186- 189 Complexity, see under Exploration Conflict, approach-avoidance, see under Exploration Curiosity, specific and diversive activities and, 159-161

D

Environment, novelty as determinant of exploration and, 15 1 - 155

263

Subject Index

264

Experience, postnatal, heart rate response and, 105-108 Exploration, 119- 180 complexity as determinant of, 12 1- 138 comparison of variables of complexity and, 135-138 multidimensional complexity and, 122-126

unidimensional complexity and,

period of widespread reactions and, 12-16

postnatal repetition of fetal reflex activity sequences and, 41 -42 suppression of activity and, 36-40 theories on development of behavior and, 4-7

local reflex concept and, 6 total pattern concept and, 5-6

127-135

G

novelty as determinant of, 138-158 approach-avoidance conflict and, 157-158

Guessing behavior, 242-246

definitions of novelty and, 140-141 fear of novelty and, 155-157 habituation to visual novelty and, 144-145

novelty in a biological context and, 141-143

separation of novelty and complexity variables and, 139-140 sources of novelty and, 145-155 two-dimensional novelty and, 143- 144 specific and diversive activities and,

H Habituation, novelty as determinant of exploration and, 144- 145 Heart rate, see under Arousal systems Hide-and-seek behavior, 24 1-242

I Incentive, probability learning and, 237-240

159- 17 1

characteristics of, 167- 171 curiosity and boredom theories and, 159- 161

investigation and play and, 16 1 - 167

Infant, arousal systems and, see Arousal systems Inhibition, fetal activity and, 36-40 Instructions, probability learning and, 229-230

F Fear, novelty and, 155-157 Fetal activity, 1-57 historical background and, 3-4 integration and the development of behavior and, 46-49 methods of investigating behavioral development and, 7- 12 effects of anoxia, asphyxia, anesthetics, narcotics and other drugs and, 10-12

recording methods and, 8-9 types of stimuli and, 9- 10 spontaneous, 43-46 stimulation other than tactile and, 41 -43 tactile stimulation and, 12-41 function of fetal reflexes and, 30-35 localized reflex activity and, 16-30

Investigation, specific and diversive activities and, 161-167

Learning, probability, see under Choice behavior

M Mediated memory, 18 1-2 1 1 clustering as mediating activity and, 186- 189

nature of mnemonic mediation and, 193-197

nonverbal mediators and, 189- 191 production and mediational deficiencies and, 198-207 verbal production deficiency and, 182-184

265

Subject Index

verbal rehearsal and, 184- 186 verbal versus nonverbal mediating activity and, 19 1 - 193 Memory, mediated, see Mediated memory Mnemonic mediation, see under Mediated memory

N Narcotics, behavioral development and, 10-12 Newborn, evoked heart rate response in, 79-91 Novelty, see under Exploration

P Penalty, probability learning and, 239 Play, specific and diversive activities and, 161- 167 Postnatal experience, see Experience, postnatal Probability learning, see under Choice behavior Problem solving, see Choice behavior

R Reaction, widespread, tactile stimulation of fetuses and, 12- I6 Reflex, defense, arousal systems and, 62-67 function of in fetus, 30-35 local, 6, 16-30 orienting, arousal systems and, 62-67

Reflex sequences, fetal, postnatal repetition of, 4 1-42 Rehearsal, see under Mediated memory Reinforcement, partial, probability learning and, 226-227 social, probability learning and, 239-240 Response, heart rate, see under Arousal systems Response patterns, communality of, probability learning and, 240 Reward, tangible, probability learning and, 237-239

S Social reinforcement, probability learning and, 239-240 Stimulation, characteristics of, heart rate response and, 93-98 methods of investigating behavioral development and, 9-10 tactile, see under Fetal activity

T Transfer of training, probability learning and, 23 1-234

V Verbal mediation, see under Mediated memory Visual novelty, see under Exploration

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ERRATA ADVANCES IN CHILD DEVELOPMENT AND BEHAVIOR VOLUME 5

Edited by Hayne W. Reese and Lewis P. Lipsitt page 136, Fig. 2: The labels “Complex” and “Simple” should be reversed page 143,2nd paragraph, 3rd line: “newborn” should read “young”

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