Development of the Sensory Analyzers During Infancy1

D E V E L O P M E N T OF T H E S E N S O R Y A N A L Y Z E R S DURING INFANCY'

Yvonne Brackbil12 cind H i r a m E. Fitzgeruld UNIVERSITY OF D E N V ER A N D M I C H I G A N STATE UNIVERSITY

I INTRODUCTION 11. U N C O N D I T I O N E D R F S P O N S F S -1 0 S ~ f I M U 1 . . 4 T I O N . . . . . . . . . . . . A. LEVEL OF A R O U S A I . . . . . . . . . . . . . . . . . . . . . . . . . . . B. R E S P O N S E TO t J N ( - l - l , 4 N ( i l N C i S I - I b I U L PACIFICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C . R E S P O N S E T'O ( ' H A N ( r k IN S I IRIULATION: T H E O R I E N T I N G RFl-l.FX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. S T A T E A N D R E S P O N S I \ ' I - N I 1-0 S T l h l U L A T l O N . . . . . . . .

173

171 171 177 181 1x1

I l l . C O N D I T I O N E D RESPONSl'S r 0 \ I l h l U L A ' f I O N . . . . . . . . . . . . . . . I X X A . T E M P O R A L . C'ONDI'I I O N I N ( ; ........................... I90 B. A U D I T O R Y CS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I96 C O M P O U N D C S : . r i h i E IIUS S O U N D . . . . . . . . . . . . . . . . . . . . . . 200 D. T A C T I L E CS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 E. S U M M A R Y A N D C O N C I I I S I O N S . . . . . . . . . . . . . . . . . . . . . . . . . . 202

c.

REFERENCES

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

205

'Preparation of this paper wii\ suppot tcd i n pal I b y the following grant\. ( i B-47x4 from the National Science Foundation: l - K 3 - h l H - T 9 2 5 . 14094. and 14100 from the National Institute of Mental Health. 'Present addres\: Department o f Ohstctt-ic\ ,tnd Gynecology. Georgetown UniLci-sity School of hledicine. WashingIon. 11 C 173

174

1. Introduction Work is described in the present paper that is currently underway or has been recently completed in the Behavior Development Laboratory of the University of Denver. The first part covers studies of orienting and arousal in infants, and the second, studies of conditioning t o various types of stimuli. As superficially discrepant as studies of arousal. orienting, and conditioning may seem, they have the common aim of seeking to understand the human being’s developing ability to cope with sensory stimulation. (The conditioning studies, of course, yield infomation on this and other problems as well.) Much of the research strategy represented here, including the aspect of diversification just mentioned. stems from that used by Pavlov, who felt that the two principal ways of studying the fiinctional development of sensory analyzers - which may be translated as “sensory modalities” without violating Pavlov’s meaning-are. first, via the study of the orienting reflex, a basic response to stimulation common to all sensory analyrcrs, and, second, by studying the ways in which sensory function reveals itself during the process ofconditioning.

11. Unconditioned Responses to Stiniulativn

The terms l e i ~ c of’aroirsrrl ~l or sratr refer to the organism’s overall level of functioning at any given period of time on ;I continuum ranging from deep sleep to awake, alert, and active. (Another meaning of trroirscrl. lcss frequently encountered in developmental research, refers t o waking up from a state of sleep. T o avoid confusion, we will use “arousability” to refer to a stimulus-elicited change in state, including the tran\ition from a sleep state to a waking state.) A typical scale for rating state is that shown in Table I . I t has been in use at the University of Denver for several years and is essentially the same as an earlier scale developed by Wolff ( 1 959). Like most other infant scales of state, its major components consist of motor movements, appearance of the eyes. speed and regularity of respiration, and vocalizations. T o describe the points of t h e scale briefly, there are, first o f all, two sleep states: “quiet sleep,” the undifferentiated forerunner of adult sleep states 2, 3, and 4 (according to the denotative system introduced by Dement & Kleitman. 1957) and “active sleep,” which is equivalent to adult rapid eye movement (REM) sleep. Although some infant state scales have

TABLE I A

st:rte

n IImbe II

State 112in1e

SCAI F I-OR

RATlNC, STATE'' Desc rip t i o n

Quiet sleep

T h e infant's whole body gives the appearance of general n i ~ ~ s c u l arelaxation. iT h i s is inter-rupted periodically, hobever. by bi-ief startles o f a n apparently spontaneous nature. T h e infant's eyes ai-e ~ i s ~ i a l l y closed. Respiration is regular and is somewhat slowei- than in active sleep.

Active sleep

Characteristic of this stage w e diffuse mocements of relatively frequent occui-rence. 1-hese movements m a y involve the u h o l e body but are most typically seen in the cxtr-emities a n d in the muscles of the face i n the form of tuitches. gr-imaces. smiling..sticking. and the like. I n x i d i t i o n . one can sometimes see conjugate movements o f the eyeballs. ( A s i n state I. the eyelids ;ire usually closcd.) Respiration is considerahl) more ii-i-eylai-:inti i\ \ o n i e u hat faster than i n quiet sleep.

,

Durnne this \tape the inf:int'\ i n r o t o r hehacior IS often much like that of \leep! people i-iding w b ~ ' t \ train>- hc i-eLi\e\ nioi-e m d nioihe ?i-aduall> liilli :i\lecp. then \uJdenl\ lerhs 'ibahe. H I \ r.be!id\ . upheii visible. h a c e a gl ippeai-ance. Respiration I\ m o r e apt t o he marked b> reytilarity than i r r e g u l x i t )

4

There I\ little gross motor' acti\it>. i.e.. niovements involving the whole hod). although there ma) he some movements of the extremities a n d face. T h e baby's eyes are open and in WolfYs terms (1966)are characterized by :I bright. shiny appearance. T h e m:ijor difference between this state and the other t h o waking states is that this i s ii prtrc,qfirl state. .Accordingly. the vocalizations that occur during this state are not o f an "unhappy" variety. Respiration is relatively regular. though l e s s regular than i n quiet sleep.

i

,Active awake

T h i s state i s marked b y ;I considerable xniount of gross motor activity. For example. iis an infant become< unhappy he ma) begin to wi-ithe. Ke4piration i\ often quite irregular. W i t h i n the qpectrum of vocaliziitions occurring during this per-iod are those of the c r a n k y . fussy car-iety.

6

(.vying awake

T h e criteria for this state are the same ;IS t h o w for the preceding state except that i n addition the infant I S ci-ying. ( H e may 01- m a y not be producing tears: most very young infants do not.) T h e lower limit of crying is defined iis pi.otesting of a definite, sustained nature.

"Used b y Hrackhill a n d associates at the University o f D e n v e r Behavior Development l-aboratorq

5

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Y w n n e Bruchhill und Hirum E . Fitzgrrald

been developed with three sleep states, e.g., Wolff s ( 1 966), or even more -there are six in the scale used by Metcalf et ul. (personal communication)-it has not yet been demonstrated that these or other more elaborate categorizations can be made reliably or that such a refinement is useful. Two points might be noted about the category “drowsiness.” First, since it is a transition state (the others are not) it occurs less frequently than the other states. Second, as Wolff has pointed out ( 1 966), a state of drowsiness occurs more frequently in the transition from awake to asleep than from asleep to awake. From data on changes in state that we have collected in connection with various studies of infancy, we estimate that the probability of an infant’s passing through a drowsy period en route to sleep is about .8, while the probability of his being judged as drowsy as he passes from sleep to awake is about half that. The number of categories for ~ w k i r z gstates in this scale may be reduced from three to two if there is some reason for recording crying as a separate variable, for crying is indeed the only point of distinction between states 5 and 6. The chief advantage of including it as the end point on a scale of state is that it dispenses with the need for another event marker when recording is carried out by mechanical aids. Roffwarg, Muzio, and Dement ( 1 966) have stated that in falling asleep all neonates move directly into active sleep rather than quiet sleep. Our data show that the picture is not so clear for infants beyond the neonatal period. Some of our data on I-month-old infants, for example, show that in only 68% of the instances in which infants fell asleep did they go directly into active sleep from a waking state. I n fact, the transition in the opposite direction was more striking for these infants: 83% of them awoke from active sleep, while only 1 7 5 awoke from quiet sleep. The scale shown in Table I is. generally speaking, both easy and reliable to use. In fact, it is simple enough for reliable use by people who have never heard of “state” nor even encountered a baby at close range. By way of illustration, the first author recently escorted three groups of undergraduate volunteers from a lower division child psychology course to a residential nursery where, after reading through the scale definitions, they proceeded to observe and rate every available infant between the ages of 4 days and 6 months. The median correlation between their judgments and the author’s was .98. In terms of absolute number of agreements with the standard observer, 168 of 186 observations (or 90.32%) agreed perfectly, 15 or 8.06% disagreed by one point. 1 or .54% disagreed by two points, and 2 or 1.08% disagreed by three points. Two final notes may be made on the measurement of state. The first is that, generally speaking, spot checking or time sampling yields greater

agreement among judges than does the continuous recording of state. This is chiefly because continuous recording involves making decisions apropos transitions from one level to another, and these are not always easy to make, especially when the infant is moving toward lower levels of activity. T h e second point is that the assessment of state in infants depends, far more than during any subsequent stage of development, on the observation of real, live behavior and on-the-spot judging. With adult S s , it is entirely possible to determine state “blindly” from a polygraphic record taken when no observer was present during the recording; even relatively inexperienced judges can distinguish with considerable accuracy whether an adult S had been awake or asleep, and, moreover, which of the five sleep states his record exhibited at any given time (though the distinction between states 3 and 4 cannot be made as accurately as the others. On the other hand, for infants (at least for young infants) this is not possible. Polygraph records, unaccompanied by an observer’s records, cannot be reliably interpreted since in young infants neither behavioral nor physiological functions have as yet developed the unique characteristics that impose distinctiveness and clarity on the various states identified so easily in adults. Fur one example, the range of speed of electroencephalographic (EEG) activity in adults is about twice that for infants. For another, adult polygraph records show peculiar forms of EEG activity, e.g., K complexes and sleep spindles, which almost invariably indicate a particular state o f sleep. but such distinctive patterns are absent from infant records. Again. in adults, the hallmark of REM sleep is, as t h e name implies, rapid movements of the eyes; these occur on the order of 5 to 10 times a minute. I n infants, however, truly conjugate eye movements during active sleep are both rarer and less distinct. B. RESPONSE TO U N C H A N ( , I N CS,I I M ~ J AI I I O N : PACIFICATION

Most adults require an environment of low-intensity stimulation in order to fall asleep. Light is excluded: noise is blocked out: and the temperature is regulated. This is not the way we responded as infants to such stimulation. For most young infants, continued sensory input of a monotonoiis character has the effect of lowering rather than raising level of arousal. Thus infants are less aroused in ii noisy environment than in a quiet one, less aroused under high illumination than in darkness, less aroused when swaddled or clothed than when naked. and less aroused when being jiggled than when lying quietly in their cribs. And by “less aroused” is meant a quite specific pattern of behavioral and physiological effects: I t means that infants move about less, that they cry less and sleep more, and that their heart and respiration rates are lower and more stable. A more conno-

tatively appealing term for this pattern is “pacification” or “quieting.” [Lipton. Steinschneider, and Richmond (1960) have referred to it as “removal from a state of stress.”J Empirical evidence relating to pacification under continued stimulation has a long history but one that is composed mostly of bits and pieces. [Some of it is reviewed by Brackbill, Adams, Ct-owell, and Gray (1966).] I t has never previously been the focus of programmatic research so that many of the larger and more important questions have yet to be answered. For example. one of the first that comes to mind is how long such an effect lasts. I n work currently underway at the University of Denver, we are trying to find out whether pacification increases as one increases the number of sensory modalities continuously stimulated. The design of this study requires each infant S to serve as his own control under five difierent conditions: no extra stimulation (the control condition) and continuous stimulation of one, two, three, and four sensory modalities. The particular stimulus conditions being used are as follows: Auditory stinzulritiori. The sound stimulus used is a tape-recorded heartbeat found in previous research to be an effective quieting agent although no better or worse than any other auditory stimulus used in that study (Brackbill ct al., 1966). This particular sound is truly a continuous one, although periodic variation in intensity lends it ;in intermittent character. It is played at 85 db. Ambient noise level during the control condition is 671 db., and all frequencies above 500 H z are attenuated to less than 30 db. Visual stiniulation. l’he visual stimulus comes from two 40-watt fluorescent lamps, approximately 4 feet above S. Illumination during the control session comes from a 50-watt incandescent bulb in a translucent bowl. giving the minimum level that allows u s to monitor state over c I o sed-c i rc u i t t e I e v i si o n . Proprioceptive-tactil~stimulation. Under this condition, the infant is swaddled tightly from neck to toes in long, narrow strips of flannel in the old-fashioned style still used today in some parts of the world.:’This mode of swaddling and the almost immediate effect it has on most young infants, is illustrated in Fig. 1. (A glance at Fig. 1 will also reveal why it seemed necessary to eliminate state 5 [active awake] from the rating scale, since the accurate discrimination of state 5 depends upon the observer’s ability Lipton (’I ~ z l (. 1960) interpreted swaddling :I\ ;i drc.rc,cisc, of \timulation. an interpretation that certainly accords with logical considerations. O n empirical grounds. however. swaddling compels definition as irlrre.u.srd stimulation. since its use produces patterns of behavioral and physiological change that are identical to those found untlei- continuous stimulation of other modalities. ,J

I79

to perceive movement of the body a s a whole.) The swaddling strips weigh 3 ounces; during the control condition the infant is clothed with an extra 3 ounces of shirting or blanketing which d o not, of course, restrict his movements. Temperature stimulafion. During the high-temperature condition, the temperature averages 88"F, and during the control condition, 78°F. To date, 15 one-month-old infants have been tested under all five conditions. Figure 2 shows the principal results tabulated concerning state amount of sleep (states 1 and 2) and amount of crying (state 6) -as a function of the number of sensory modalities stimulated. T h e data are plotted

I80

Yvonne Brackhill and Hiram E . Fitzgerald

State I (Ouiet sleep) State 2 (&five skep)

\

State 6 (Crying) I

I

2

3

.

.

4

Number of modalities stimulated in experimental condition

Fig. 2. Preliminary results showing amount of sleep (state5 I and 2 ) and amount of crying (state 6 ) a s a function of the number of senson modalities stimulated.

in terms of the difference between each S’s performance under the control condition and his performance under one continuously administered stimulus, two continuously administered stimuli, and so on. These results show a very definite additive effect for stimulus conditions: The infant who is continuously stimulated by light and sound and temperature and swaddling sleeps more and cries less than when he is bombarded by only three of these stimuli; in turn, three stimuli are more effective than two, and two are more effective than one. One is not more effective than no extra stimulation -a result not in keeping with previous findings (Brackbill et al., 1966). A final word is in order about the significance of pacification research for practical application. One would not, of course, want to keep a normal baby in a constant state of high-intensity stimulation. For one thing, longterm changes do take place, as Dennis and Dennis noted of Hopi babies who preferred being swaddled (1940).N o adult should be so out of step with his culture that he is unable to sleep except in a brightly lit, hot, noisy room. However, even normal babies have spells of sickness and crankiness when it is advisable to arrange, for the sakes of all concerned, that they cry less and sleep more. Moreover, there are some types of abnormal babies, chiefly prematures, for whom the most important and immediate goal of life is simply to sustain life. For these babies restricting energy output is literally synonymous with survival, and this means not only

maximizing sleep and minimizing crying but also controlling the spontaneous motor discharges that occur with such great frequency in the very premature and that constitute in themselves a real threat to viability. It is probably no exaggeration to say that whether or not one can keep a 1000gm infant from writhing continuously may swing the balance between life and death. Here is a situation in which the long-term application of continuously administered stimulation is more a necessity than an advantage. C. RESPONSETO

C H A N G E I N S l ~ I M I l L . 4 T I O N :THEO R I E N T I N G

REFLEX

The entire foregoing discussion of arousal or state has dealt with the effects of continuously applied, unchanging stimulation. What of the infant's response to the onset of such stimulation or to discrete stimuli of brief duration'? An organism's first response upon sensing a new stimulus or some change in an old one is to attend to it. Pavlov, who was the first to study this most basic, primitive aspect of response to stimulation, called it the orienting reflex. Orienting can be thought of as the preliminary step in processing sensory information (Pavlov also called it the \z~hat-i.s-it'? reflex). The orienting reflex has several identifiable components that have differential probabilities of occurrence, depending upon such factors as the intensity of the stimulus, its signal value. and the age and state of the organism. T h e orienting reflex includes both behavioral and physiological components. They include attempts to localize the source of stimulation; increased muscular tonus and muscular contractions such as eyeblinks or movements of the extremities; diminution of any motor activity that had been going on just prior to stimulation (external inhibition); momentary decreases in absolute sensory thresholds; pupillary dilation; increased galvanic skin response (GSK); a change in E E G toward low amplitude, fast waves, and evidence of a n evoked response; vasodilation in the forehead and vasoconstriction in the extremities; respiratory pause; and change in heart rate (most often seen ;is deceleration). I t has taken about half a century for Eastern interests in the orienting reflex to infect Western research so that until recently practically all studies of orienting in young organisms were of Russian origin." The classic study of orienting in infants was carried out by Bronshtein and Petrova "he Soviet Union has also been the wurce of many theoretical and expenmental refinements in the study of orienting, e.g., the di\tinction between generalized and localized orienting reflexes o r among the adaptive. orienting. and defensive reflexes. Such refinements have as yet undetermined relevance to infant research so they will not be considered in thi\ chapter. The interested reader should c ~ n ~ uI.ynn l t ( 1966) oi- Sokolov ( 1 963).

I82

Yvonne Bmckhill und Hiram E . Fii,-gt>rald

(1952), who used external inhibition (cessation of sucking) as their measure of orienting. [Keen ( 1 964) and Sameroff ( 1967) recently tried, with some success, to repeat this study.] Other Soviet investigations have been concerned with differences in orienting as a function of structural and functional maturity at birth (Polikanina & Probatova, 1955a) and with conditionability of the orienting reflex (Kasatkin, Mirzoiants, & Khokhitva, 1953; Mirzoiants, 1954; Polikanina & Probatova, 1955b). In most of these investigations, a major focus of concern has been to use the orienting reflex, or more specifically, the rate at which it extinguishes (“habituates” in American terminology), as an index of the organism’s ability to inhibit a response. For this reason, premature infants are especially interesting as Ss: Their prematurity presumes structural incompleteness of cortical development, and this, in turn, presumes incomplete development of the functional ability to inhibit responding. In their study of the orienting reflex in premature infants, Polikanina and Probatova remarked of Ss in their most extreme group, who were premature by 3 months: I t is important to note. however. that even at this period in very premature children during momentary repetitions of the sound. the orienting reflex does not extinguish. T h e latter occurs later and very slowly; it is not fully apparent even by the age of 3 months. For example. in one of these infants extinction could not be obtained through repeated application of the sound stimulus even at the age of 3 months and 17 days [Polikanina& Probatova, 1955a. p. 2301.

However, from work being carried out in the Behavior Development Laboratory, it does not appear that the premature’s inability to inhibit orienting to a sound stimulus is quite so clear-cut. In cooperation with Marion Downs of the University of Colorado Medical Center, we are currently studying the behavioral or motor-response components of the orienting reflex, as enumerated on p. 18 1, to auditory stimuli in premature infants. (The sound on each trial is a 2-second burst of 90 db white noise; trials are separated by 10 seconds.) T o date we have tested 38 prematures whose gestational ages range from 26 to 37 weeks (M = 32 weeks) and whose chronological ages range from 1 to 63 days (M = 19.9 days). None of these infants has failed to reach an extinction criterion of five consecutive failures to respond. On the other hand, it is true that the orienting reflex, as enumerated on p. I8 I , to auditory stimuli in premanormal infants matched for chronological age (CA) and for state at the time of testing. For 32 matched cases, the mean number of trials to extinction taken by prematures is 26.00, while the same figure for full-term infants is 18.81. Although this is a substantial difference in relative terms, it should be pointed out that the gestational-age difference between the two groups is also substantial, a mean of 7 weeks for the sample tested to date.

In any event, these data, as well as data from other American studies, are not in full accord with the conclusions drawn by Soviet investigators. Why? Among the several possibilities are t h e following three. The first has to do with a general failure to pay sufficient attention to the parameters of stimulation and stimulus presentation. Studies of orienting in Ss other than infants suggest that the orienting reflex is very sensitive to such stimulus characteristics as duration, interstimulus interval, and others, but parametric studies of stimulus variables have yet to be done on infants. In fact, stimulus characteristics vary so widely from study to study and are reported with such casualness, if at all, that one often gets the impression t h e y were selected for reasons of expedience rather than rep1icabilit y . A second reason for the discrepant findings on orienting may be that there are real differences in responsiveness. Many studies of the orienting response, especially the American ones, have been carried out on neonates since hospitalized Ss are captive and convenient to use. But it is precisely during this period that one expects all CNS-mediated functions to be maximally depressed from the anesthetics and analgesics administered to the mother during delivery. Although there have been relatively few studies of these effects, we do know that responsiveness to visual stimuli is impaired in those neonates whose mothers have been given medication during childbirth (Stechler, I964), and it is difficult to imagine that responsiveness to auditory stimuli w ~ t i l dnot be impaired as well. Some form of anesthesia is the rule in the United States, but it is the exception in the Soviet Union, where a system o f natural childbirth has been in use on a nation-wide scale for over a quarter o f a century. It is quite likely that many real differences in neonatal behavior do exist between the two countries' populations of newborns. A third possibility underlying the discrepancies in results stems from investigators' failure to take into account the infant's state at the time of stimulation. There is no doubt that t h e orienting reflex does differ both in qualitative and quantitative aspects depending on whether the infant is asleep or awake at t h e time of stimulation. (More will be said about this point later .) Orieritirig to Sociully Sign$crrrir StirTiirli In the United States, pupillary reactivity has for the most part been conceptualized not as a component of the orienting reflex but rather as an index of affective responsiveness, piipillary dilation being regarded as an indicator of pleasant experience and constriction as a measure of unpleasant experience (Hess, 1060. Notice that in the case of pleasant

184

Yvonne Bruckhill und Hirurn E . Ficzgerald

experience the same outcome, pupillary dilation following stimulus presentation, is predicted from both the orienting and affectivity frames of reference regarding pupillary activity. However, when an unpleasant stimulus is presented, the two different perspectives suggest different outcomes: From an orienting point of view, the response should still be dilation; whereas from an affectivity point of view, it should be con~ t r i c t i o n Thus, .~ from either point of view, presentation to a baby of a picture of his own mother should be followed by dilation. On the other hand, according to the orienting point of view, presentation of a stranger’s face should still be followed by dilation, but, according to the affectivity point of view, it should be followed by constriction, or at least should not be followed by dilation. (This assumes, of course, that S s are old enough to discriminate between mothers and nonmothers.) Fitzgerald’s recently completed study ( 1968) was designed along these lines of investigation. H e confronted babies with pictures of their mothers and of a female stranger and compared pupil diameters before and during stimulus presentations. Fitzgerald found that nine of his ten 4-month-old Ss, most probably the only group old enough to have made any significant progress toward a mother-stranger discrimination in real, three-dimensional life, showed pupillary dilation upon viewing a stranger (Fig. 3, 10% by Hess’s method of measuring change). These same S s , however, showed no consistent response to pictures of their mothers. In general, the results suggest that orienting to novel stimuli is the more influential determinant at this age of pupil change under constant illumination. D. STATEA N D RESPONSIVENESS TO STIMULATION

Two important questions yet to be explored systematically in developmental psychology concern the interaction of the orienting reflex and arousal level. In what way does responsiveness to stimulus onset depend upon preexisting state, i.e.. the infant’s state at the time of stimulation? I n what way does arousability depend upon preexisting state‘? At present the only possible answer to either question is “in some way,” since currently available evidence is scanty and some of it contradictory. Moreover,judging by the number of contradictions and qualifications apropos the same questions that have emerged from research with adult human beings and subhuman species, it will take some time and a ‘These two point\ of view are not neceswr-ily conrradictory. hlomentai-y initial dilation can precede constriction but remain undetected when the measure used involves averaging pupil diameters over several seconds rather than a trial-by-trial examination of pupil size. Another consideration here is that pupillary constriction is by far the stronger and faster of the two unconditioned pupillary reflexes.

185

Fig. 3. Photograph of a n injhnt ,gtrzing (it the televised picture o f his mother a s u n e.rperimc~nterphotographshis pupillury w c i c t i o t i t o this srirnulits (Fitzgernld, 1968).

great many research studies before definitive answers are forthcoming. When the question of infant responsiveness during sleep is considered in terms of specific monosynaptic or polysynaptic reflexes, contradictions are more prevalent than agreements in the literature. Thus, for example, Prechtl, Akiyama, Zinkin, and Grant ( 1968) find t a t one component of the lip-tap reflex, the lip-jerk, is greater, both in terms of probability of occurrence and amplitude, during quiet sleep than active sleep but that just the opposite is true for the other component, lip-protrusion. In his article on the palmomental reflex in premature infants, Parmelee remarked that “Though the palmomental reflex was somewhat more easily obtained in babies awake than asleep. it was nevertheless obtained with great frequency during sleep and in three out of four infants considered to be in coma. Thus the response does not seem to be very dependent on state” (1963, p.384). It looks at present as if more congruence will result from considering responsiveness in terms of the specific modality stimulated rather than in terms of a specific reflex or response. By way of illustration, Table I1 con-

T A B L E II SI EEPING

K E S P O N S I V E N E S S .TO S T I M U I . A T I O N IN

I N F A N T S AS A

JOIN-I FUNCTION

OF S L E E P S T A T F A N D S T I M U I . U S M O D A L I T Y

Sleep state

Percent change in motor movement of twelve neonates“ Painful Tactile Vestibular Auditory stimulation stimulation stimulation stimulation (jarri ng)

Quiet sleep Active sleep “

”

94.1

96.3

57.1 61.8

47.5 13.3

19.1 44.x

Percent increased motor movement in eighteen I month-old infants” Auditory stimulation 5.6 22.2

From Wolff ( 1966). From Brackbill f t r r l . (unpublished obsei-vations)

tains data from two studies of responsiveness as a function of state and sensory modality. The first of these studies, by Wolff ( 1966), used as criteria of responsiveness both increased motor movements (if the preexisting state had been quiet) and decreased motor movements (if the preexisting state had been active). The second set of data comes from an unpublished study carried out by Brackbill, Fitzgerald, and David Metcalf, of the University of Colorado Medical Center, on responsiveness of 1 -month-old babies to discrete auditory stimuli as a function of ( a ) the nature of the measure of responsiveness (EEG and evoked response as opposed to behavioral measures), ( h )background auditory condition (quiet vs. noisy), and (c) state of the organism at the time of stimulation. The criterion of a motor response to the auditory stimulus was agreement by two judges that a definite startle-like pattern had appeared on stabilimeter and arm movement recordings within 2 seconds of stimulus onset. From the data shown in Table 11, it appears that vestibular stimulation is more effective in producing a response during quiet sleep than during active sleep, that tactile and painful stimuli are equally effective in both states, and that auditory stimulation is more effective during active than during quiet sleep. The agreement between Wolff s data and ours on responsiveness to auditory stimuli is reasonably good if one considers the difference in Ss’ ages and in the criterion of “responsiveness.” [Wolff has found ( I 966), as we have, that the probability of a spontaneous startle, i.e., a startle to no apparent external stimulation, is greater in quiet sleep than in active sleep.] Another variable that we have found to affect responsiveness during sleep is the type of measure one uses a s the index of responsiveness. Up to this point we have spoken only of motor movements, changes ef-

fected by the skeletal niuscitl;ititt-e. A rather different picture emerges when we consider the evoked I-ehponhe. Under the usual quiet laboratory conditions, evoked response aniplitude is higher when the subject is in quiet sleep rather than active slecp. This is apparently true both for adults (Goff, Allison, Shapiro, & Knsner, 1966) and for infants (Pi-echtl et al., 1968). In our laboratory we have found the two amplitudes to be on the order of 17.2 and 12.0 p V . respectively. This greater responsiveness to auditory stimuli during quiet \leep than during active sleep is, as the reader will recall. just the opposite from the active-quiet response differential found when motor movement is uvxl as the index of responsiven e s s .'; Stritr rind Arousrihility

from Slcop

Almost no developmental data ;tre available regarding the interaction of state and arousability. I t would be, of course, outside the scope of this paper to review in detail the results from studies of adults that are pertinent to this question. However. it i 4 worthwhile mentioning, if only to suggest some of the directions that future developmental research might take, some of the major findings regarding arousability in adults. It appears that adult Ss are more easily awakened from the KEM state or from state 2 than from delta sleep (states 3 and 4) (Kechtschaffen, Hauri, & Zeitlin, 1966; Stoyva, personal communication) although the clarity of this difference in arousability disappears after the first 3 hours of a night's sleep o r when the stimulus to i i aken ~ is a painful shock (Pisano, Rosadini, Rossi. & Zattoni, 1966). ( I n genet-al. this agrees with a study of young infants recently completed i n o ~ i rlaboratory in which we observed 64 instances of spontaneous awakening and found that in 83% of these instances the sleep state existing just prior to the infant's awakening had been active rather than quiet sleep.) Among the other variables that have been found to affect arousability in iiclults, often in interaction with each other, are the following: ( n ) stiniuliis parameters such as intensity and meaningfulness or signal value to S (e.g.. Buendia, Sierra, Goode, & Segundo, 1963; Wilson & Zung, 1966): ( h )degree of fatigue (e.g., Williams, Hammack, Daly, Dement. & I .ubin. 1964); ( c )time of night, or more precisely, cumulative sleep time since the beginning of the session (e.g.. a pel-sonal communication. 1)i- I homa\ Williams of the National In.;titute o l Mental Health reports that he and D r . Joscph Schacter of Columbia University are now analyzing heart rate data that so far reveal no cle:d\ discer-nible differences in responsiveneb\ during R E M a s compared with NKEM sleep. I he slimuli used were repetitive. I-millisecond. 100db clicks. and the auditory backgrounti condition was a constant random noise lebel of 7 5 db. T h e S s , neonates. were inimobili,ed i i i air rplints during testing sessions.

188

Yvonne Bruckbill and Hiruni E . Fitzgeruld

Rechtschaffen et al., 1966; Williams et al., 1964); and ( d ) sex of S (e.g., Wilson & Zung, 1966). As a final discomforting note, we should mention that results have already appeared in the sleep literature indicating definite species differences when adult human beings are compared with adults of subhuman species. For example, one of the distinguishing features of REM periods for subhuman species is a sharp decrease in muscle tonus throughout the body, while in human beings this decrease is restricted to the muscles of the head and neck.

111. Conditioned Responses to Stimulation During the past few years we have been engaged in a program of experiments with the intent of exploring in a systematic way parameters of perceptual development and learning in infancy. The primary orientation of these studies has been toward testing two principles advanced by Soviet physiologists. T h e first principle holds that there is an immutable developmental order in which conditional stimuli become effective in establishing a conditioned response. According to this view, vestibular stimulation is the earliest effective conditional stimulus (CS), followed in order by auditory, tactile, olfactory, gustatory, visual, and thermal stimuli (Brackbill & Koltsova, 1967). [It has been suggested (Brackbill & Koltsova, 1967) that time as a C S should probably be at the very earliest end of the developmental scale, but among true Pavlovians time discrimination is regarded a s a capacity intrinsic to all sensory analyzers rather than as the work of a separate sensory analyzer.] The second principle that derives from Soviet physiology and that has guided the direction of our research is that the nature of the unconditioned stimulus (UCS), and consequently the natures of the unconditioned response (UCR) and the conditioned response (CR), are not important factors in classical conditioning. If a particular C S is effective at all in conditioning, then any response that an organism is capable of making can be conditioned to that CS. In spite of the uniformity with which these beliefs are held, there are no comprehensive or systematic studies in the Russian literature that will confirm or deny these propositions. Instead, the beliefs are referable only to a vast amount of unpublished research experience and to widely scattered, typically single-variable studies. The American and Czech literatures similarly lack information on a possible rank ordering by C S modality during early infancy. One reason for this is that the Americans, at least, have never previously considered

the question. A second reason is t h a t American and Czech investigators have generally used the same type of C S , auditory, from one study to the next. This is largely because auditory CSs are in many ways the easiest to use, from the viewpoint of methodology, at early age levels. (For example, the infant cannot escape the action of an auditory stimulus to the extent he can that of a visual stimulus.) I t should be pointed out that challenging the proposed rank order means, in effect, posing a null hypothesis: posing. for example, that a visual stimulus cannot successfully be used in establishing a C R at a s early an age as an auditory CS. The available experimental evidence is too thin to give much support to such ;I null hypothesis. With additional experiments, using C Ss in different modalities and using Ss of different ages, evidence for o r against the hypothesis should begin to emerge -although like any other null hypothesis this can never really be "proved." The second principle, that the CS i s important and the UCS is unimportant in classical conditioning, is also insufficiently supported by experimental evidence. In fact, the evidence that is currently available suggests that the nature of the U C S is an important factor in infant conditioning. It might be pointed out in this respect that if the UCS does determine the outcome of conditioning, then the validity of the principle of rank-ordering stimulus modalities in terms of their effectiveness as C S s is even more seriously in doubt. The UCS-UCR combinations of airpuff and eyeblink, bright light and eyeblink, food and sucking, shock and limb withdrawal, and shock and GS R account for a majority of the conditioning studies with infant Ss. (The orienting response and cardiac and vascular changes have also served as U C R s in a few studies.) Not one of these UCS-UCR combinations has been paired with CSs trorn all modalities with infant Ss; in fact, relatively few of the many possible ('S-UCS pairings have been investigated at all. Our experimental program is attempting, as one of its aims, to introduce systematization into this area. It is worth adding that if there is indeed a developmental sequence of effectiveness of CS modalities i n classical conditioning, this presumably must depend in turn on a sequence of development of cortical (or at least central nervous system) interconnections. Certainly the simple visual stimuli used for conditioning are clearly sensed well before the age of 40 days, yet this is supposedly the earliest age at which a C R can be established to a visual CS (Brackbill Kr Koltsova, 1967, p. 2 18). Ineffectiveness of a visual CS cannot be attributed t o a failure to sense on t h e part of the infant. Neither can it be attributed simply to immaturity of neural or motor mechanisms necessary to conditioning in general since a C R to a vestibular o r an auditory CS can be established before this age. Logically, it

seems the failure must be due to some as-yet-undeveloped interconnections between the visual centers and the motor centers. Assuming that this is true, then it seems profitable to speculate a little further and to suggest that there is no compelling reason to assume that interconnections from a particular sensory area will develop to all effector areas simultaneously. If this is true. then there should be a C S by UCS interaction, developmentally, and it would become necessary to pair each C S modality with each response in order to trace out the interactions. This is not a prospect that invokes lightheartedness and joyous anticipation, but then, neither psychology nor neurophysiology has a reputation for simplicity. I t remains possible, however. that a simpler categorization of interactions might represent the true state of affairs, i.e.. that C R s can perhaps be grouped as autonomic vs. somatic or that UCSs can be grouped as appetitive 1’s.noxious. The studies to be described have something to say to this point, but much more evidence is necessary before any conclusions may be drawn with confidence. In the Behavior Development Laboratory. the infant conditioning studies recently completed or currently underway have dealt with an autonomic response (the pupillary response) and a somatic response (the eyeblink). The CSs have been either auditory, tactile, or temporal (elapsed time). T o be more specific, the CSs that have been used thus far in our laboratory and the responses with which they have been paired, are: temporal CSs with eyeblinking and pupillary responses: an auditory CS with eyeblinking and pupillary responses; a compound C S consisting of time plus sound with pupillary response nd a tactile CS paired with pupillary constriction. Three of these studies have also been done with adults for a developmental comparison of the conditioning involved. All of our classical conditioning experiments have been planned with as many common components 21s possible in order to maximize their- comparability. Almost all Ss for these studies come from the same population and are of like age. In addition, a partial reinforcement design has been used consistently. with the ratio of reinforced to test trials averaging 3.5: 1. Finally, the experimental room and general surroundings are the same from one study to the next. Brief descriptions of these studies follow. A . TEMPORAL ~ONDIIIONING

For the most part, temporal conditioning studies have been carried out by Soviet investigators and usually with infrahuman Ss. Three investigations (Bystroletova, 1954; Krachkovskaia, 1959; Marquis. 194 1 ) have studied “natural” temporal conditioning in human infants in connection

with feeding schedules. although only one of these studies, Bystroletov a’s , was actual 1y c o nc e i ve d iis t e iii por i i I conditioning by the e x pe r i in e n ter. None of the three investigiitions is Iree of methodological flaws; however, their combined results suggest that time is indeed an effective CS within the first 1 0 days of life. More recently, Lipsitt and Anibrose ( 1 967) reported successful temporal conditioning with a 30-second CS in fifteen Ss ranging in age from 3 to 5 days. These investigators used auditory, 01factory, and vestibular stimuli ;is lJCSs and heart rate, respiration. and body movement as CKs. The paradigm for temporal cc)nditioning is simply that the interval from one U C S onset to the next is constant throughout conditioning sessions. This period of elapsed time is the CS. and a test trial consists of withholding the UCS and noting whether. at this time, a response appears despite the absence of the UCS. 1 . Trmporul C S in Piipill~iryCcrtrtlitiotritig The experimental setting for pupilhry conditioning i n this experiment (Fitzgei-ald. I-intz. Br-ackhill. R Atlam\. 1967)and in subsequent pupillar-y conditioning experiments, was ; I I i-;tngrti iis shown i n Fig. 4. The CS was a 20-second period of elapsed tinie. and the UCS was ;t change in illumination level. For conditioning dilation, ii 100-uatt blue bulb. 15 inches in front of the subject, was tut-tied oft‘ t o i - 4 seconds: for conditioning constriction. the same bulb, norrii;illv olf. was turned on for the it-second UCS duration. Hunter timers controllecl (’S kind UCS duration. The pupillar-y response was recorcletl on iiifr;ired tilm by a Bolex 16-mm motion picture c;inier;i driven at one li-;ime per second by an external synchronous motor. A 4-inch telephoto Icn\ with extension tubes permitted photographing a I .S-inch square :ii-e:i of’ s ’ s face from a distance of approximately 3 feet. A small red pilot hulh taped above S ’ s left eye arid shielded from his view provided a record of c\etits on the film. A mirt-or reflected an image of S’s left eye thi-ough ;I tuhc to the camera outside the booth. Light for photography came froin t h o 25-watt red twlbs, 12 inches in front of S . which were turned on A I :ill times during experimental sessions. A red filter on the camera len\ elYecti\ely blocked the predominantly blue illumination from the UCS lami> s o that exposure of the film was practically independent of t h e state ot’ the II(‘S lamp. One experimenter inside the booth held S ’ s head in position and. when necessary. also held S ’ s lcft eyelid open. After processing, the films wcic pt-oJectetlon a Kekordak viewer. ‘The scorer adjusted ii caliper t o iiiiitch the piujected pupil diameter and pressed a ’’record but t o n . A 11 t o i 1i;i t i c i i na I og- t o -d i g i t al conversion ecl u i 1)nient. compensated for the enlaigerriciit and reduction steps between S ”

I92

Yi,onne Brnckhill und Hirum E . Fitzgern/d

F i g . 4 . A scaled rrpresentntion of the inside o j ’ r / i e experinientul boorh. The picture s h o ~ , s pupillary photogrcrpliy.

t/7e crppnrcitus necessary f o r

and the projected image. printed actual pupil diameters to the nearest hundredth millimeter. Interscorer reliability checks with this apparatus yielded correlations ranging from .90 to .96 (median = .94). The 20-second elapsed time CS was not chosen arbitrarily. In pilot temporal conditioning work with infants, a 1 0-second intertrial interval (ITI)was tried but proved too short: 10 seconds after one UC S presentation, the pupil was still in the process of recovery. Consequently, we collected data on recovery time from both constriction and dilation with both infant and adult Ss. On the average, recovery from the 4-second duration of the 100-watt UCS used in these experiments was essentially complete after 14 seconds. Therefore, a 20-second interval from U C S offset to UCS onset was adopted as the temporal C S . Sixteen infants with a median age of 54 days served as Ss. There were two experimental groups (dilation U C R and constriction UCR) and two

Developmeni

of'

thv Sensory Analyzers

193

pseudoconditioning control groups (dilation and constriction) with four Ss per group. I n a single session, 32 paired presentations of C S and UCS were given to each experimental S . Nine test trials, on which the U C S was omitted, were randomly interspersed among t h e conditioning trials. Without interruption, 35 extinction trials followed. For half the Ss:the U C S was offset of the 100-watt lamp, and for the other half the UCS was onset of the lamp. The control groups also received 32 paired presentations of CS and UCS, and nine intermixed test trials, but the IT1 was varied randomly between 10 and 30 seconds (and averaged to 20 seconds) rather than the constant 20-second interval used for the experimental groups. The data on pupil size for all comparisons were from all photographic frames collected during the 4 seconds immediately preceding each test trial and the 4 seconds of the test trial itself. For conditioned dilation. difference scores were obtained by comparing the single largest diameter during a 4-second test trial with the single largest diameter during the corresponding 4-second pretest period. For conditioned constriction, the difference score was the single smallest test diameter compared with the single smallest pretest diameter. Difference scores were obtained in the same manner for all extinction trials. The data were analyzed using f tests for the difference between the correlated pretest and posttest nienns. The mean pupillary change for the experimental dilation group was +. I 1 m m ,and the mean change for the experimental constriction group was - - . 3 1 mm. Both differences were significant (in both cases, P<'.OOI ) , indicating that conditioning was established in the constriction and i n the dilation groups. Individual t tests showed that conditioning was successfully established in every experimental S. The extinction data, analy7,ed in the same manner as the conditioning data, showed that extinction was complete in the first block of nine trials. There was no evidence of conditioning for any S in the control groups: Mean pupillary change for the dilation control group was -.02 mm, and for the constriction group +.O 1 mm. Neither difference approached significance. The results of this experiment indicated that a temporal CIS was effective in conditioning t h e pupillary response in infants. Because of the conflicting evidence from earlier studies of adult pupillary conditioning (see Brackbill, Fitzgerald, & L h t z . 1967. for a review of this literature) and because our results with infant .Ss wet-e so uniformly successful. the same methodology and design ( a s far :IS possible) were used in an attempt to condition adults. There was no evidence that any of the adult Ss formed a conditioned dilation response. l ' w o Ss showed evidence of a conditioned

constriction response, but the nature of this response did not change over the course of extinction. Apparently. the same procedures that produced pupillary conditioning in infant S s were not effective with adults.

2. T emposal Prr t tesn CS it I S tc rco type Pit pillory Con(litioning Stereotype conditioning is ;I typical Pavlovian procedure for studying sequential responding. Using this procedure, two (11-more C S s are presented in the same sequence from trial to trial, each being followed by reinforcement. Our predictions were two for conditioning a pupillary stereotype: first, that acquisition of a stereotype would be a slower process than simple conditioning, arid second, that individual differences in conditionability would be more pronounced. The Ss were eight normal infants with ;I mean age of 52 days. Dilation was the CK for four and constriction for the other four. The procedure was as follows. One trial lasted 58 seconds and contained two CSs, CS,, a 20-second period of elapsed time, and C S ? , a 30-second period of elapsed time. The UCS for each was ii 4-second change in illumination (light offset for half the Ss and light onset for- the other half). In analyzing the data, the last 4-second interval of the 20-second CS, period preceding a test trial was adopted ;IS the “pretest” interval, and the single largest pupil diameter (for dilation) or smallest pupil diameter (lot- constriction) that occurred during this period was compared with the single largest (or smallest) diameter from the 4-second test intervals following C‘S, and CS,. Although 80-minute sessions had been scheduled (64 conditioning trials with 18 intermixed test trials), none of the eight Ss was able to complete Isession of this length. The number of test trials actually completed ranged from 12 to 17. with ii median of 13.5. I n the CK-dilation group, three of the f w r Ss conditioned to C S , . and two of these three also showed a C‘K to (‘S?. I n the CK-constriction group, no sut?.iect conditioned to both components of the temporal pattern. although one apparently conditioned to the second or 30-second component. As predicted, temporal conditioning of ii stereotype was more difficult arid less consiste n t t h ;in was si in p I e tempo r a I condition i rig. As ;I further check oin the validity of our- hypotheses, three Ss who had served in the CK-constriction stereotype group were rescheduled a s soon ;is possible for ii session of simple teinpoi-al conditioning with ;i constant 20-second I‘PI. (The fourth S had been ntlopted before a session could be scheduled for hei-.)Simple conditioning of pupi1lai.y constriction was successfully carried out in all three cases. 3 . Trmposril C S in E1.chlitiL C‘onrlitionrng Having found a tempor,il ( ’ S to he effective in conditioning t h e pupillary

response, we were interested in pairing a temporal CS with another response. The eyeblink response to an airpuff UCS was chosen for several reasons. First, although the eyeblink has been the CR in many experiments in the United States, the S s i n these experiments have usually been animals or adult human beings. The results with infant S s have been inconsistent. Morgan and Morgan ( 1944) and Rendle-Short ( 196 1 ) reported failures to condition infants younger than 45 days and 6 months, respectively. I n addition to the methodological deficiencies (pointed out by Lipsitt, 1963), these studies have used a visual CS, the next-to-last modality to become effective in the developmental sequence of conditionability according to t h e Soviet view. We were also interested in the eyeblink as a response for methodological reasons. T h e blink can be readily elicited by an airpuff, can be observed easily, and an instrumented record of latency can be obtained. The airpufY-eyeblink combination represents it very mild sort of defensive conditioning (two infants have been run in our laboratory through 25 and 37 daily sessions, respectively. for t o t a l s of 369 and 570 airpuffs, without developing any apparent antipathy t o the experimental situation). Eight infants were used in the experiment; each served as his own control in two sessions-an initial control session and a subsequent conditioning session. The apparatus is shown in Fig. 5 . The UCS was an airpuff of 0.3 second duration delivered at 2 psi pressure from a tube 2.5 inches from S’s right eye. Two records of the response were recorded on a polygraph chart: an observer’s judgments of blinks, defined as complete closure of the eyelid followed by opening sufficient to expose t h e upper half of the iris completely. and an instrumented record (Lintz & Fitzgerald, 1966). The observer’s record was the final authority in determining blink occurrence, and the instrumented record then established the time of occurrence of the blink. (The observer‘s judgments of occurrence are slightly more conservative than judgments made from the detector record.) I n each S’s first session, the IJC‘S was presented 32 times, at intervals varying randomly between 10 and 30 seconds. Eight test trials, a 20-second IT1 followed by a UCS, were interspersed randomly among the UCS trials. The conditioning session was on the following day, with a 0.3-second airpuff delivered every 2 0 seconds and test trials randomly interspersed among reinforced trials. The total number of reinforced trials that we were able to administer ranged from 59 to 96 per S. with a median of 8 I .5 trials. The results are shown in ‘l’able 111. i f temporal conditioning had occurred. there should have been a concentration of blinks in the central column of the table. clustering around the interval 20 seconds after the

196

Yvonne Brackbill and Hiram E . Fitzgerald

Fig. 5 . Apparatus for eyeblink conditioning. The magnet is taped t o the upper eyelid, and the detector iJ mounted under the plustic bridge.

preceding UCS. In fact, the distribution of blinks in the table is fairly uniform, and there is no indication that temporal conditioning of the eyeblink did take place.

4. Summury o f Temporul Conditioning These experiments demonstrate that a simple 20-second temporal CS is effective in conditioning both pupillary constriction and dilation. Simple conditioning of the pupillary reflex to time occurs rapidly and uniformly, and extinction of the C R is also rapid. When the procedure is more complex (stereotype conditioning), conditioning may still occur but more slowly and irregularly. T h e same 20-second temporal CS proved completely ineffective for conditioning the eyeblink response with an airpuff

ucs.

B. AUDITORY CS

The most frequently used type of CS in infant conditioning is auditory stimulation. The physical parameters of an auditory stimulus are easily

TABLE I l l OCCURRENCE AND TEMPORAL POSITION OF TEST-TRIAL EYEBLINKS"

Session

Test trial blocks

Control

1-8

Conditioning

1-8 9-16 17-24 25-29

Number of Ss per test trial

Number of seconds following offset of preceding UCS 12.6-14.5

14.6-16.5

16.6-18.5

18.6-21.4

21.5-23.4

23.5-25.4

25.5-27.4

Blinks per test trial per

8

3

1

2

3

2

2

2

.234

8 8 5-8 2-5

7 7 4

7 5 2 0

3 6 2 2

8 5 2 1

6 7 2 2

5 3 0 2

7 6 2 2

.672 .609 .286 .562

0

"Blinks are tabulated according to the number of seconds they followed administration of the UCS preceding each test trial. Temporal conditioning would be shown by a preponderance of eyeblinks 20 seconds following the last UCS, i.e., during the central interval of any test trial (18.6-21.4 sec.). The central interval encompasses 3 seconds; the intervals preceding and following it, 2 seconds.

e

2

e

>iF 2

:

a

$ 3

198

Yvonne Brackhill and Hiram E . Fitzgerald

controlled, and the stimulus cannot be easily overlooked or escaped (unlike a visual stimulus). The impetus for the auditory conditioning studies to be described was our wish to pair an auditory CS with the UCSs used in temporal conditioning under conditions comparable to those used in the temporal conditioning studies. 1 . Auditorv C S in Pupillary Conditioning

The S s in this experiment (Brackbill et ul., 1967) were 32 infants with a median age of 53 days. Four Ss were assigned to each of six experimental groups and two control groups. T h e experimental groups differed in terms of the C R (constriction vs. dilation) and interstimulus interval (1.5 seconds, 6 seconds, or 9 seconds). For the pseudoconditioning control groups, constriction and dilation U C R s were combined with the limiting case of backward conditioning, i.e.. a 0-second interstimulus interval (ISI). T o avoid conditioning to time, the intertrial intervals were randomized for all groups; they ranged between 10 and 30 seconds, with a mean of 20 seconds. As in tcrnporal conditioning, each S received 39 conditioning trials intermixed with nine test trials in a single session. The CS was a 65-db complex sound, with experimental groups receiving CS onset either I .S,6. o r 9 seconds prior to the onset of t h e 4-second UCS. For the control groups, onset of the CS was simultaneous with the onset of the UCS, i.e., a 0-second IS1 was used as described previously. I n all groups, C S and UCS ended simultaneously. The apparatus for controlling intervals. recording the response, and scoring the records was the same a s described earlier. DiFerence scores were derived by comparing pupil diameters during the 4-second test trial intervals with the 4-second intervals preceding CS onset on test trials. As in the temporal conditioning experiment, f tests for the differences between correlated means were used in analyzing the results. There was no evidence of conditioning in any group. Although the pupillai-y response could be conditioned to time as a CS, it apparently could not be conditioned to an auditory CS. However, it irernained possible that with more conditioning trials a CR might be established. Therefore, one infant (S weeks old) was run through six conditioning sessions, on successive days, with a maximum of 68 reinforced trials and 20 intermixed test trials per session, for a total of 392 paired presentations of CS and UCS. Even at the end of this extended period, this S showed no evidence of conditioning. It seems likely that pupillary conditioning to an auditory C S is impossible at this age. Using the same design, and as far as possible the same procedures, the study of auditory conditioning of pupillary dilation and constriction was repeated with 32 adults. Again there were eight groups of four Ss: con-

striction and dilation experimental groups with CS onset 1 . S , 6, or 9 seconds before U C S onset, and control groups with simultaneous onset of C S and UCS. One of the four Ss showed conditioned dilation and three of four conditioned constriction when the IS1 was 1 .S seconds. N o subject conditioned in the 6- and 9-second IS1 groups. Apparently the pupillary response can be conditioned to an auditory C S in at least some adults and under some conditions.

2. Auditory C S in Eyeblink Conditioning Twenty infants were used in this experiment (Lintz, Fitzgerald, & Brdckbill, 1967). Their ages ranged, at the beginning of the experiment, between 3 3 and 133 days, with a median age of 69.5 days. Eight Ss were used in the experimental group and four S s in each of three control groups. All details of UCS presentation and of recording the response were the same as described for temporal conditioning of the eyeblink. The CS was a tape-recorded sound, 0.20 second in duration, played at a 65-db level. Intertrial intervals were random between 30 and 60 seconds (mean = 39.2 seconds), and the interstimulus interval was 1 .OO second. Each daily session consisted of a maximum of I9 conditioning trials with six intermixed test trials. A session was ended if the infant could no longer be maintained in a state of quiet alertness. A relatively stringent criterion of conditioning, nine C R s in ten successive test trials, was adopted. All eight experimental Ss reached this criterion. T h e number of paired CS-U(’S presentations up to, but not including, criterion ranged from SO to 774. In Control Group I , Ss received the same total number of C S and U C S presentations as the four slowest conditioners in the experimental group, but C S and U C S were never paired for this control group. Control Group 1 I received random-interval presentations of CS only. Control Group 111 received no CS o r UCS presentations and furnished a measure of spontaneous blinking. The test-trial results for the experimental group and for the major control condition, Control 1, are shown in Fig. 6. For Control I I , the probability of a blink to the C S was .OX. For Control I I I , the probability of a blink during any of the 1.3-second intervals that corresponded in time with CS presentations administered to Ss in Control I I was .06. Clearly. the eyeblink was conditioned to an auditory CS. 3. S u m m a s y of Auditosy Conditioning These experiments demonstrate that an auditory C S is effective in conditioning a n eyeblink response with infant Ss. An auditory CS is not effective in conditioning a pupillary response with infant Ss, but is effective in some cases with adult Ss.

200

o-----O

c'.

Experimental gnwp

COMPOUND

c's: ? r I M F

P l U S SOUND

Because time had been an effective CS in conditioning pupillary responses in infants and because sound had been totally ineffective, we were interested in presenting a compound CS combining the temporal CS used in infant pupillary conditioning with the auditory CS used in the same procedure. Eight Ss, 32 to 67 days old (median = S 3 ) , were run in the same procedure as in temporal conditioning of the pupillary reflex, except that t h e 65-db complex sound used in auditory conditioning accompanied the UCS presentations. O n test trials, the sound was presented at the standard 20-second interval after the preceding UCS had terminated, but the UCS was omitted. Data were scored and analyzed exactly as for temporal pupillary conditioning. Both conditioned constriction and conditioned dilation were successfully established in every S. N o pseudoconditioning control groups were run specifically for this procedure. The control groups for temporal conditioning already indicated that UCS presentations at random intervals which averaged 20 seconds did not result in a pupillar-y response that could be mistaken for a CR. Similarly, the control groups for auditory conditioning already indicated that unpaired presentations of C S and UCS did not result in sensitization, i.e., that the sound component of the compound stimulus did not evoke a pupillary response in the absence of conditioning. I n addition, of course, our failure to find conditioning in the auditory CS groups also establishes

that the sound component alone should not contribute to any observed response. Response magnitudes of the (‘Ksin temporal and in compound conditioning were compared, and significant difyerences ( P < .01) were found for both dilation and constriction. l’he compound CS produced a larger dilation CK than did time alone, but time alone produced a larger constriction C R . The direction of this diffcrence is, in both groups, consistent with the fact that sound on its initial presentations evokes pupillary dilation. However, the results from the control groups who received random-interval unpaired presentations of ( - S and LJCS indicated that the sound CS did not. at least after the first few presentations, evoke a pupillary response. The reason for this diffet-ence cannot be satisfactorily explained by the available data. Because we had found that adults did not condition to a temporal CS and that some adults did condition to an auditory CS, the compound CS of time plus sound was also used in an attempt to condition pupillary dilation and constriction in adult Ss. Only one of four Ss in the dilation group and one of four in the constriction gtoup showed evidence of conditioning. I).

I4c111 t

(‘s

Brackbill and Koltsova (1967. p. 2 7 6 ) pointed out that very little systematic work exists on tactile stimulation in conditioning. I n fact, Spears and Hohle (1967) devote only two paragraphs to summarizing what is known of pressure and touch sensitivity i n infants. However, a tactile stimulus can easily be used in classical conditioning, without elaborate apparatus, and the very lack o f knowledge about a tactile CS makes it an interesting modality for classical conditioning studies. The experiments described in this section are ;is yet incomplete, and the results in some cases must be regarded as preliminary rather than final.

Tactile CS in Pupillurv Conditiotiitig This experiment uses much the same procedure and apparatus as was used in the pupillary conditioning experiments already described. However, the services of a second experimenter, inside the booth, are required to time lTIs with a stopwatch, to initiate one cycle of the timers by pressing a silent pushbutton, and to deliver the tactile CS at the appropriate times by stroking the sole of S’s foot with a large camel‘s hair brush. The ITls range between 10 and 30 seconds: CS onset is 1.5 seconds before UCS onset; and the CS overlaps with the 4-second UCS but terminates before it ends. The UCS is not presented on test trials, which are randomly intermixed with conditioning trials in :I I : 3 ratio. Subjects in the pseudocondi-

tioning control group receive presentations of the CS and UCS in intermixed but unpaired order. Light onset is the UCS, and constriction the CK. Ten Ss, with a median age of SO days. have been run to date in the conditioning procedure, with total numbers of conditioning trials ranging from 33 to 100 (mean = 56). Only one of the 10 Ss showed evidence of conditioned constriction. Two Ss of the experimental group were seen in repeated sessions, on successive days, to check on the possibility that conditioning might occur following a greater number of reinforcements. These Ss received 343 and 240 conditioning trials. respectively. but neither showed any evidence of conditioning. For the Ss in the control group, alternate CS-only trials were scored, taking a s prestimulus diameter on each trial the single smallest diameter during the 4-second period preceding CS onset and as test diameter the smallest during the 4-second period beginning 1 .S seconds after CS onset. Two Ss showed no significant response to the CS, and one showed a significant response ( P < .()I). Figure 7 shows. in blocks of C S presentations, t h e average data for the 3 Ss run so far under the control procedure. There is a tendency, at least during later trials, for the tactile CS to elicit a constriction response; the explanation of this is not clear. All in all, however, it seems that the failure to condition in the experimental Ss cannot be attributed to any effects of the CS itself; in fact, CS effects should have favored finding a significant constriction response in the experimental Ss. The parsimonious conclusion, based on currently available data, seems to be that pupillary conditioning t o a tactile C S is not possible under the experimental conditions we have used, and that the one experimental S who did show a conditioned constriction response was probably showing nothing more than a response elicited by the C'S. i.e., that this was pseudoconditioning rather than true conditioning. E.

S U M M A R Y 4 N D C O N C l USIONS

We have used CSs from three modalities, time, auditory, and tactile, in our studies of infant classical conditioning. In addition, we have used a CS compounded of time plus sound. All four of these have been used in attempts to condition both pupillary dilation and pupillary constriction. The time and auditory CSs have, in addition, been used in experiments attempting to condition the eyeblink reflex to an airpuff. 1. The Soviet Developmental Sequence of Conditionability One of our research interests is to find whether or not there is an invariant sequence, developmentally, in which CS modalities become effective in

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classical conditioning. An additional interest, closely related to the sequence of conditionability, is to determine something of the importance (or, in the Soviet view, the unimportance) of t h e nature of the response to be conditioned. The conclusion4 to be drawn from our studies that bear on these points seem plain: l'here is not an immutable developmental sequence of CS modalities, nor is the outcome of conditioning predictable without taking into account the response that is being conditioned. I t appears that any adequate developmental theory of conditioning must deal not only with CS modality but, also. on some basis with the response. When two CSs in difTei.enr moclalities can both be perceived by S. but one is effective in conditioning a response and the other is not efTective in conditioning the same I-esponsc, then it seems that there must be differential rates of maturation of' the cei-ebral structures that serve as the central portions of conditioned rellex arcs. When S is perfectly capable of making two responses, and one of those responses can be conditioned to a particular CS but the other response cannot be conditioned to the same CS, again it seems that difl'ei-ential maturation of cerebral structures must be responsible. With infant Ss, the autonomic response did condition to time as ;I CS and did not condition to auditory or Lactile C S s : the eyeblink response conditioned to an auditory CS bul not to time. Tentatively, it seems possi-

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ble that a contrast between autonomic and somatic responses may be useful in predicting the outcome of conditioning studies in that the pupillary reflex is an autonomically controlled response whereas the eyeblink reflex is somatically controlled. Such a conclusion must remain tentative, of course, until the conditioning outcomes for other autonomic and somatic responses have been determined. As an interesting, and purely speculative, basis for explaining the CS by UCS interaction in classical conditioning of infants, adaptive significance for homeostasis is a possibility. Of all the sensory modalities, it seems logical that time and temperature are the two which, very early in life, should require an autonomic response from the organism in order to maintain homeostasis. For these two modalities, then, the early establishment of interconnections between sensory structures and autonomic effector structures would be of greater adaptive significance than, say, an interconnection between the visual sensory system and the autonomic effector system. This hypothesis would suggest that in classically conditioning an autonomic response, time and temperature should be the CS modalities that are effective earliest in life. Unfortunately, there seems to be no study that has paired a thermal CS with an autonomic response and that has used very young Ss, either human or animal. Usoltsev and Terekhova’s (1958) study used a somatic response (the eyeblink reflex to an airpuff). 2. Sensory Analyzer Function in Infants With regard to sensory analyzer function in infants, our results with the temporal CS are of particular interest. The literature on time perception (summarized by Brackbill et al., 1967) is extensive, but there has been little research with infant S s . The most pertinent references are those of Hellbriigge (1960) and Lobban (1965) on developmental phases in the acquisition of diurnal rhythms. Hellbriigge’s results indicated that cyclic rhythms for skin resistance, temperature, and heart rate appear at 1, 4, and 6 weeks of age, respectively. Lobban’s review of the literature led her to conclude that there is “. . . good evidence for the existence of true endogenous physiological diurnal rhythms in man” (p. 381). She also points out that all the diurnal rhythms of older children and adults appear to develop from polyphasic rhythms which, in her opinion, appear “independently of external stimuli” (p. 380). Our results for temporal conditioning of the pupillary response indicate that infants at least as young as 26 days can accurately perceive and respond to the passage of a short standard interval of time (20 seconds). The results for conditioning stereotype pupillary responses suggest that 2-month-old infants can also perceive temporal patterns, although with considerably less accuracy than is found for a single interval.

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An interesting issue is raised by the contrast between the pupillary conditioning results with infant S s and with adult Ss. All infant Ss did condition to the temporal CS, but no adult S showed clear evidence of conditioning. In addition, although n o infant S showed a conditioned pupillary response to an auditory CS, whether the IS1 was 1.5, 6, or 9 seconds, four of eight adult Ss did show pupillary conditioning to an auditory CS with a I .5-second ISI. Given, then, that it is possible to condition a pupillary response in adults, and given that a temporal C S was uniformly successful for such conditioning in infant Ss, it is sui-prising that the temporal C S was completely unsuccessful with adult Ss. There is nothing in the Soviet or American literature on conditioning that would suggest an inverse relationship between age and the effectiveness of a C S modality for conditioning; yet that is apparently the state of affairs for a temporal CS. Certainly the literature establishes that children do a great deal of learning with regard to time and time concepts. (‘ertainly, too, it is possible that time perception begins in infancy as a function of the first signal system (in Soviet terminology), but that with progressive acquisition of facility in language, time perception becomes more and more a function of the second signal system. At any rate, we believe that further studies of time perceptiop in the human infant are necessary and are of potentially great value in contributing to our knowledge of sensory development.

3 . D evelopni en tal Di’erences in Contiit ion ing The contrast between adult Ss and i n f m t Ss in pupillary conditioning, described in the preceding section, points to developmental changes in sensory analyzer function, or in conditionability, or both. I n any case, whether the change in conditioning outcome is caused by learning new ways of processing time information that supplant an earlier and perhaps more primitive (but nevertheless surprisingly accurate) way, or whether caused by maturational changes in neural structures, the course of conditioning the pupillary response to time is markedly different, and less effective, in adults than in infants. Obviously. infant conditionability is not the same as adult conditionability, nor is the first simply a less well-developed or less efficient version of the second. Generalizations from adult data can be in error, and the need for additional developmental studies is apparent.

Brackbill, Y . , Adams, G . , Crowell, D. H . , Xr Gray., M . L. Arousal level in neonates and preschool children under continuous auditory stimulation. Journal of Experinienral Child Psychology. 1966.4, 178- 188.

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