Oral “pacification” and arousal in the human newborn

JOURNAL

OF EXPERIMENTAL

Oral

“Pacification” CAROLYN

CHILD

PSYCHOLOGY

and KENT

3,

1-17 (1966)

Arousal ROVEE

Brown

AND

in the

Human

GERALD

R.

Newborn1

LEVIN?

University

Response to oral nipple stimulation was studied in human infants as a function of their prestimulation arousal levels. The general procedure consisted of a five-minute baseline period followed by 15 seconds of stimulation. Level of arousal was assessed by observational and stabilimetric ratings over corresponding time samples. In the initial study, the direction and magnitude of activity change was found to vary inversely with the pre-stimulus arousal level. Succeeding studies replicated the initial findings and indicated that convergence of activity at an intermediate level during intraoral stimulation could not be explained on the basis of spontaneous activity cycles, the influence of stimulation per se, or procedural artifact. The phenomenon was discussed in terms of the “law of initial values.”

Persons concerned with infant. care have long observed that distressed or crying infants become quiet or less active when allowed to mouth or suck a rubber nipple, or pacifier. Although investigators have made practical use of this observation in studying other phenomena (e.g., Graham, 1956)) they have rarely studied “pacification” directly. Insofar as reliable functional relationships are relatively difficult to find in the newborn, and because the pacification effect occurs with striking consistency, it is surprising that there has been little documentation of the phenomenon. The first systematic attempt to demonstrate the pacification effect experimentally was reported by Kessen and Leutzendorff (1963). They observed marked decreases in general movement of highly aroused infants within 10 seconds of receiving intra-oral stimulation. The quiescent effect was transitory, persisting no longer than 10 seconds after nipple withdrawal. Sharp decreases in activity did not occur in control Ss receiving tactile stimulation of t.he forehead for a comparable period. 1 This report is based on a thesis by the senior author submitted to Brown University in pa&al fulfillment of the requirements for the Sc.M. degree, 1964, under the direction of the second author. The research was support,ed by grant NB-04268 from the National Institute of Mental Health, United States Public Health Service, to L. P. Lipsitt, Brown University. The authors express appreciation to Dr. Lipsitt and Dr. Herbert Kaye for their advice and critical comment. ‘NOW at the Department of Psychology, Swarthmore College, Swarthmore, Pennsylvania.

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While the term pacification and some theoretical orientations (e.g., Kessen and Mandler, 1961) imply that the process is one in which the level of arousal is always reduced, this assumption is questionable. For example, Halverson (1938) found that, sucking behavior was accompanied by signs of increased muscular tension in the limbs. Moreover, amount of non-nutritive sucking has been found to correlate with level of arousal (Levin and Kaye, 1964), and a number of infant studies have evaluated individual differences in autonomic response to stimulation in terms of initial level of functioning (Block and Bridger, 1962; Escalona, 1962; Lacey, Bateman, and Van Lehn, 1953; Lipton, Steinschneider, and Richmond, 1960, 1961a, 1961b; Richmond and Lipton, 1959). Thus, a clarification of the relationship between pacification and arousal would seem fundamental to a better understanding of the problem. The present series of experiments was instigated to determine whether intraoral stimulation would produce only activity reduction in infants, or whether the stimulation might assume properties other than those of an inhibitory nature, depending on the initial level of arousal. A basic methodological problem of interest in the present study was the use of polygraphic stabilimeter records to determine level of arousal. Stabilimeter movements have long provided neonatal researchers with inexpensive and instantaneous records of changes in activity, although Kessen, Hendry, and Leutzendorff (1961) have criticized the use of stabilimeter records for this purpose. In an attempt to refine the measure, Kessen proposed the complex and time-consuming technique whereby motion pictures taken at successive J&second intervals might be evaluated by a set of coordinates indicative of linear limb displacement. The inherent weaknesses in this approach, however, include its restriction to a two-dimensional analysis only, its failure to provide continuous behavioral records over an experimental session, and its precluGon of vocalization and mouthing normally accompanying periods of heightened arousal. Accordingly, one of the goals of the present study was to clarify whether polygraphically recorded stabilimeter data would correlate adequately with a multi-dimensional index of arousal level and whether stabilimeter records would prove sensitive enough to document the pacification phenomenon. The present report describes four experiments. Experiment 1 was the basic study, and the other experiments were designed to replicate and clarify its findings. EXPERIMENT

1

The initial experiment was designed to investigate two problems, one methodological and the other substantive.

“PACIFIC.4TION”

AND

AROUSAL

IX

HT-?dAN

NEWBORN

3

The methodological problem involved the use of ratings of polygraphic records of stabilimeter and breathing activity as indices of level of arousal for between-& comparisons. In the past at the Brown Laboratories, such records have typically been restricted to use in within-& comparisons only (e.g., Engen, Lipsitt, and Kaye, 1963), thus circumventing calibration problems arising from different body weights, crib placemen&, and pneumograph strappings. The present study sought t,o determine whether independent observational ratings of activity were related to stabilimeter and breathing activity obtained from polygraphin tracings over the same time samples. The lat,ter relationship, if valid, would t,hen permit assessment of individual arousal between&. In addition, it was hoped that a relatively short time sample, such as 15 seconds, was sufficient to provide a reliable evaluation of the activity diminution. The main substantive questions were (a) whether the pacification effect was sufficiently reliable that individual predictions might be made, am1 (b) if so, whether measures of change in arousal level (luring intra-oral stimulation were related to prestimulation measures of level of arousal. Of secondary interest was the relationship between non-nutritive sucking frequency and activity diminution. Method Subjects. Thirty full term and apparently healthy infants, 12 males and 18 females, were selected from the clinic population of the Providence Lying-In Hospital on the basis of availability with respect to hospital routine.” Subjects range in age from 10 to 113 hours; the mean age was 60 hours and the standard deviation 24. Apparatus. Sucking responses were recorded continuously as digital deflections of constant amplitude on a Grass S5 Polygraph. The sucking device consisted of a nipple-covered holder attached to a microswitch (Levin and Kaye, 1964). In addition to sucking records, general body movements, foot-withdrawals, and breathing changes were recorded polygraphically. Both the general body movement and foot withdrawal were obtained from the experimental crib designed by Lipsitt and DeLucia (1960)) and breathing was monitored by a pressure transducerlinked Phipps and Bird pneumograph. A manually operated event marker was used to record stimulation and observation periods. Ratings of direct observations of general activity and vocalization provided the means of validating the polygraphic ratings as an index of arousal. Observational rat,ings were based on a scale described by Levin 3The authors wish t,o thank the Brown Dorothy Westlake, and the staff of the assistance and cooperation.

University Providence

Collaborative Project, Lying-In Hospital for

Mrs. thril

4

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and Kaye (1964) and modified for this purpose. The procedure involved lo-second observation periods, signalled by the onset of a dim light and the activation of the marker pen denoting the segment of polygraphic activity corresponding to the observational sample. Eight time samples per S were rated independently by 2 trained observers without reference to the polygraphic recordings. Categories of general activity and vocalization were each assigned ratings of 0, 1, 2, or 3 such that scores of 6 and 0, maximum and minimum arousal, respectively, defined the limits of a composite score. The polygraphic activity for corresponding periods was rated independently at the conclusion of the experiment by the same observers. Ratings of 0, 1, 2, or 3 were assigned on the basis of magnitude and frequency of stabilimeter and foot-withdrawal deflection and breathing regularity, the rating 0 defining regular respiration and no activity deflection, and 3 defining irregular breathing and/or crying and maximum frequency and magnitude of deflection. Procedure. All Ss were tested individually between 11 AM and 12:15 PM, within two hours of the next scheduled feeding, in order to maximize the probability of obtaining awake Sa. The experimental session consisted of alternating sucking (S) and rest (R) periods, preceded by a five-minute baseline rest period. The sucking periods were 15, 60, or 240 seconds in length, each infant being presented with all three in one of the six possible permutations of the order. Between each sucking period and after the last presentation there was a 3-minute rest period. Activity was observed at the end of the first minute and at the beginning of the last minute of each rest period. The procedure for stimulus presentation has been described in detail elsewhere (Levin et aZ., 1964). Throughout, E1 presented the nipple and E, monitored the polygraph and signaled observation and stimulation periods.4 When E, signaled “touch” E, touched the nipple to the infant’s lips and stroked the lips with a light, uniform pressure, signaling when the lips closed about the nipple. At this time, Sl, S2, or S3 was initiated, terminating with removal of the nipple. After R4, the S was returned to the hospital nursery. It should be noted that the 60- and 240-second stimulation durations were included in the present design to provide pilot information for a planned habituation study. This did not interfere with the testing of a 15-second time sample in the present study; data from the first 15 seconds ,of the first nipple presentation only were considered. Irrespective of subsequent stimulation, the treatment of all Xs was identical through this. period, and their data have been pooled. ’ Herbert

Kaye

served

as the second

E in Exp.

1.

cLPACIFICATION”

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IN

HUMAN

NEWBORN

5

Results and Discussion The data analysis revealed a reliable and valid arousal measure, highly consistent. performance of individuals within a given activity range, and an inverse relationship between prestimulation activity and activity during intra-oral stimulation. Of secondary interest, sucking frequency and magnit’ude of activity change were related for highly aroused Ss only, and a I.5-second interval of stimulation was found to provide an adecluate index of activity change. Methodologicnl findings. In order to minimize the possibility that the in&-observer reliability might reflect a bias as a function of increasing familiarity with a S’s activity cycle and range, only scores from the two baseline rating periods were used in the determination of inter-observer reliabilities for both the observational scale and the polygraphic ratings. Spearman correlations of .97 and .92, obtained for the 7-point observational scale and the 4-point polygraphic ratings, respectively, were significant beyond the .OOl level. The agreement between the observational ratings and the ratings of polygraph tracings obtained over the same time samples was determined by comparison of inter-observer sums over the baseline rating periods. The resulting correlation (63; p < .OOl) indicates that the stabilimeter is capable of reproducing an accurate account of ongoing behavior within the gross numerical categories defined by the rating scale irrespective of individual body weight differences. Insofar as t.he stabilimeter ratings were measuring variables similar to those tapped by the observational scale, use of the stabilimeter for providing meaningful records of activity for between-& comparisons was supported. Activities preparatory to nipple presentation interfered with observational ratings which would have been made during the 15-second prestimulation period. Consequently, observational ratings were obtained 60 seconds prior to stimulation. A Spearman correlation of .64 (p < 901) between polygraph activity ratings 60 seconds and 15 seconds prior to stimulation supported generalization of activity ratings from the 60- to the 15-second period. IndiilGhnl performnnce and pre-stimulus nro~~d. Nine of 11 Ss who showed decreased activity during intra-oral stimulation (ST) had prestimulation (PRST) activity ratings of 4 or greater (inter-observer sums) on the polygraphic scale. Of 12 8s shouing no activity change, eight had PRST ratings of 2. All 7 Ss showing heightened activity in ST and PRST ratings of 0. The consistency bet,ween PRST and ST activity suggested a post hoc analysis in terms of high activity (HA), medium activity (MA), and low activity (LA), as defined by PRST sums of 4-6, 2-3. and

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O-l, respectively. Of those Ss affected by stimulation, HA Xs decreased and LA Ss increased in activity. Although 80% of MA Ss showed no change during ST, the remaining decreased in activity; however, the latter instance also reflects an inter-observer disagreement as to whether Ss had decreased (Table 1). TABLE 1 SIGNED

ACTIVITY

CHANGE FROM PRESTIMULATION AND THE COMBINED RATINGS Activity

Subjects (No.) High

activity 1

PRST

ST

Direction magnitude change

2 2 2 6 3a 2 la 4 4 3a 2

-4 -4 -4 0 -3 -2 -3 0 0 -1 -2

35 2 2 2 2 2 2 2 2 2

2 2 2 2 2 la 2 2 2 2

-1 0 0 0 0 -1 0 0 0 0

2 4 6 12 16 22 23

10 0 0 0 0 0 0 0

29

0

1" 0 0 2 4 4 2 2 3a

0 0 +2 +2 +4 +4 +2 +2 +3

Medium

activity

5 13 15 19 20 21 25 26 27 2s

0 Indicates

rating

EXPRESSED

6 6 6 6 6 4 4 4 4 4 4

17 IS 24 30 3 7 8 10 11 14

Low

TO STIMULATION PERIOD OF Two OBSERVERS

activity 9

inter-observer

disagreement

with

respect

to activity

rating.

and of

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AND

AROCSAL

IN

Ht-MAX

SE\VBORX

7

A Kruskal-Wallis analysis revealed a significant change (p < .OOl) in the inter-group relationship between PRST and ST activity, but, no group difference was found at either ST or poststimulation (POST) periods (Fig. 1). This suggests that the groups, nonconvergent during PRST by definition, converged at ST and remained thus for as long as 30 seconds after nipple removal. The HA, MA, and LA curves shown in Fig. 1 are indicative of individual as well as of group performance within the specified activity range. The mean curve for all levels combined is unreliable as a basis for individual prediction and ineffective in revealing activity change over periods.

PRST

15”

RATING

ST

POST

PERIODS

Fro. 1. Mean group activity ratings, bascld on inter-observer sums from polygraph records, showing convergence at the intermediate arousal level during the &second ST period. The 15-second periods before and after ST correspond to PRST and POST, respectively. Note that the convergence persisted for at least 30 seconds after ST.

Activity and sucking frequency. Non-nutritive sucking frequency for the first 1.5secondsof ST and polygraphic activity rated 60 secondsprior to nipple presentation correlated .32 (p < .05). Difference scores for HA Ss with respect to activity diminution from PRST to ST correlated aignificantly with sucking frequency (.77; p < .Ol). The activity levels of all prestimulus activity groups were at approximately the 2 rating during intra-oral stimulation. Yet the number of sucks during the l&second stimulation period ranged from 28 to 0. It would appear that an explanation of the convergence in terms of the movement arising from the sucking activity per se is inadequate. Optimal trial length. An activity change occurred within 15 seconds of ST initiation in 17 of the 22 Ss who showed any change from PRST ratings (p < .Ol). The change occurred in the remaining 5 Ss within 15

8

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seconds of POST initiation. These data, when considered with the finding that a group convergence occurred by the end of the 15-second ST period and continued through the 15-second POST period, support the use of a 15 second stimulation interval as optimal for revealing the greatest portion of activity change and for providing a reliable index of POST arousal. It should be noted that the apparent effect of administering different stimulation durations was to depress slightly t.he POST activity level for combined groups but not to alter the form of the POST function, as obtained from the 15-second ST group. Touch-to-In time. The correlation between the amount of time required to insert the nipple after “touch” and PRST activity was --.59 (p < .ool) . EXPERIMENT

2

The findings of the first study demonstrated consistent changes in individual activity, contingent on initial arousal level, during the first 15 seconds of intra-oral contact with the nipple. The second study examined whether the natural activity cycle of the newborn would produce a concomitant change in activity irrespective of the experimental manipulation, and tested the generality of the original finding by replicating the procedure at a point later in the experimental session. The specific hypothesis was that all Ss regardless of initial arousal level, would exhibit activity equivalent to the intermediate value on the activity scale during ST and that the activity of cycle-control groups during this period would be equally distributed across levels. The high correlation obtained in Exp. 1 between raters and rating instruments prompted the use of one rater and one instrument (polygraph) in the present study. Method

Subjects. A second group of full term, apparently healthy neonates from the same clinic population was used. Thirty Xs, 19 males and 11 females, ranging in age from 31 to 122 hours with a mean of 61, were used in the cycle-control analysis. Records from only 19 of these Ss were complete for use in the replication analysis; however, records of 5 additional Ss, obtained under the same experimental conditions but after cycle-control cells had been filled, were used. The final sample of replication Ss consisted of 14 males and 10 females, from 31 to 122 hours of age with a mean of 64 hours. Procedure. Those procedural details involving experimental room, apparatus, personnel present, and session schedule remained unchanged. In conjunction with earlier findings, duration of ST and POST periods

“PACIFICATION”

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9

was reduced to 15 and 60 seconds, respectively. The first half of the experiment consisted of an observational control period which corrcsponded to a 5-minute baseline, 15-second ST, and 60-second POST period. In the second half, immediately after, the original PRST, ST, and POST conditions prevailed. During the final 15 seconds of the initial baseline period, Ss were designated as HA, NA, or LA cycle-controls on the basis of activity ratings of 2-3, 1, or 0, respectively. The Ss were tested until each cycle-control category contained ten Ss. Shifting arousal levels necessitated reclassification of Ss according to PRST activity in the second half of the experiment for inclusion in the rcpliention analysis.

0kk-+-

POST

15” RATING

FIG. 2. Mean group polygraph activity over sent activity of 17 HA, 5 MA, and 12 LA Ss.

Results

PERIODS

successive

rating

periods.

Curvrs

reprc-

and Discussion

Replication analysis. The results of the replication, in which a single ST duration was used, confirmed the generality of those obtained originally (Fig. 2). A Kruskal-Wallis analysis of the signed activity change for 12 LA, 5 MA, and 7 HA Ss indicated significance beyond the .OOl level. With respect to the specific hypothesis tested, the analysis of group ST levels in terms of deviation units from the intermediate activity level of 1 yielded probabilities of less than .OOl (sign test) and .05 (Kruskal-Wallis) that all groups would be convergent at the predicted level during ST. Inspection of the individual data indicated that 22 of 24 Ss were at the predicted value during ST and that the two remaining Ss had diminished in activity from PRST levels of 3 to ST levels of 2 and were continuing to decline in activity when the nipple was removed for POST. Cycle-control analysis. Figure 3 shows the activity of cycle-control Ss for periods corresponding to PRST, ST, and POST. A Kruskal-Wallis

10

ROWE

15”

AiYD

RATING

LEVIN

PERIODS

FIG. 3. Mean group activity of all “pacification” Ss of Exs. 1 and 2, classified with respect to pre-level, and corresponding groups of cycle-controls, rated over successive l&second PRST, ST, and POST periods. Represented are 18 HA, 16 MA, and 24) LA “pacification” Ss, and three groups of 10 cycle-controls each.

revealed no significant differences between HA, MA, and LA controls with respect, to either absolute or signed activity change from PRST to ST. Inspection of the individual data verified that there was a tendency for some Ss to regress toward the intermediate activity range over the extent of observation, but the effect on the group function was negligible at POST. Thus the cyclical activity normally occurring within neonates was not responsible for t,he behavior of experimental Ss during the intraoral stimulation period. Touch-to-ln time. The correlation obtained between PRST activity and time required to insert the nipple into the mouth after “touch” was -.79 (p < .OOl). The greater variability in T-I times in the second study probably accounted for the slightly higher correlation than obtained in Exp. 1. Figure 4 presents the T-I analysis with respect to PRST activity level for the 54 “pacification” Ss of Exps. 1 and 2. The consistency with the correlation reported by Levin and Kaye (1964) suggests that T-I time per se might provide an index of arousal level sensitive beyond the minimum rating now possible. EXPERIMENT

3

It has been demonstrated that infants of all activity levels will shift rapidly to an intermediate arousal level when stimulated int.ra-orally and that the shift cannot be attributed to normally occurring cycles. Still unspecified, however, is the effect of T-I stimulation on arousal. It is possible that stroking the lips prior to nipple insertion arousesSs in such a way as to contribute to the intermediacy phenomenon observed during ST. On the other hand, although activity might increase during stroking,

“PACIFICATIOiX”

AiVD

AROUSjAL

1X

HCM.0

SIX-BORN

II

0 0.0

05

LOG

10

T-I

TIME

15

LO

(sec.)

FIG. 4. Frequency of T-I 1:ttcncies for 54 5’s with rcspcct to pre-stimulus ratings of polygrsphic activity. Absolute latencies in seconds are presented as log unit transformations. Sate that latenq :md varinhility seem to tlecrexse as a function of higher PRST ratings.

the enduring effect on arousal from thi s source might be negligible. Although Kessen et al. (1963) reported no information regarding the T-I period, Levin and Kaye (19641 found T-I time to be correlated significantly with total number of sucking responses,wakefulness, and hour of test,ing. Insofar as a high negative correlation has similarly been obtained between T-I time and PRST activity in the present study, any effect arising from tactile stimulation would probably be exhibited in LA Ss, who experienced the most lengthy stroking periods. It is also possible that intermediate level during ST might be E-induced movement artifact resulting from the pressure of maintainin g the nipple upright in the infant’s mouth. Any hand tremor of E would be most easily studied in the records of I,.\ Sa. The present investigation sought to determine the relative contribution of T-I and movement artifact to the intermediate ST arousal shift. Method S~Ojects. The IA S’sn-crc drawn from the same clinic population as in preceding studies with the specification that, PRST activity in the last 15 seconds of the initial 5-minute baseline period must be 0. Five males and 5 females ; ranging in age from 28 to 122 hours with a mean age of 71 hours, were used. The mean age and age range of the 4 male and 8 female LA Ss of Exp. 2, with whom the present, Ss were compared, were 62 hours and 31 to 92 hours, respectively. Procedure. All details with respect to handling and apparatus remained the same. The Ss received an initial 5-minute baseline period followed by stroking with uniform pressure across the lips for 15 seconds, the mean

12 stroking duration tional period.

ROVEE

AND

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of LA Ss in Exp. 2, and a 60-second

Results

POST observa--

and Discussion

It was found that the increase in activity level from pretouch for LA Ss receiving only T-I stimulation for 15 seconds was significant (p < .02). However, the same Ss were found to differ significantly (p < .Ol) from replication study LA Ss who had received stroking for a mean duration of 15 seconds followed by 15 seconds of intra-oral stimulation. This suggests that stroking per se, although producing effects enduring for at least 15 seconds after termination, did not contribute systematically to the intermediate arousal level phenomenon observed in preceding studies and that the intra-oral stimulation was necessary to produce the final activation of the initially quiescent Ss. The fact that 50% of the stroking controls remained at an activity level of 0 during stimulation negates the possibility that E-induced movement artifact resulting from the process of stroking was responsible for the intermediate level observed on the polygraph tracings. EXPERIMENT

4

It has been shown previously that extra-oral stimulation with a nipple will arouse some but not all LA Ss. In an effort to determine whether the arousal and pacification effect demonstrated in the newborn is a nondifferentiated response to any stimulus or is specific to intra-oral stimulation, the effects of an acoustic stimulus were studied with respect to activity prelevel, final level, and an intermediate rating of 1 during stimulation. In addition, the generality of the polygraphic rating scale was tested on a new modality. Method Subjects. Thirteen males and 13 females, ranging in age from 32 to 121 hours with a mean age of 64 hours, were selected from the clinic population. Within HA, MA, and LA categories there were 8, 8, and 10 Ss, respectively. Two additional MA Ss who received intra-oral stimulation prior to the tone presentation were discarded. Procedure. The procedure was the same as that of the preceding study except that the tactile stimulus (stroking) was replaced by a 15-second acoustic stimulus generated by an audio oscillator located centrally at the foot of the stabilimeter crib. The stimulus was a 23 cps square-wave buzzer-like tone at approximately 93 db above adult threshold, selected for its high probability of arousal elicitation. Preliminary observations indicated that this tone produced little response decrement over suc-

“PACIFICATION”

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cessive presentations and would reliably evoke a response in infants irrespective of the hour of testing, although in some cases the response was nothing more than a respiratory disruption at stimulus onset. Results

and Discussion

Inter-observer reliability. Arousal state was rated during successive l&second PRST, ST, and POST periods for the first 22 Ss by E and independently at a later time by a second observer unfamiliar with the mode of stimulation and with the characteristic activity level of a given S, By using only the first rating of each X to insure uncontaminated scores, a Spearman correlation of .95 (p < .OOl) was obtained. This was consistent with the inter-observer correlation of .96, obtained for the sum of all three ratings per 8. An additional reliability coefficient was computed over the first rating of each S to determine intra-observer consistency. Ratings made of each polygraph record by E at the time it was obtained and re-ratings of all records simultaneously at a later date correlated .96. This suggested that the immediate bias of familiarity with S’s observed performance was minimal. Tone analysis. A Kruskal-Wallis analysis of the absolute activity change from PRST to ST revealed no differences in the inter-group relationship (p < .05) with respect to initial activity level. Although the tone appeared to suppress slightly the activity of HA Ss and to increase the activity of LA Ss (see Figs. 5 and 6)) the group curves are not representa-

-8

PRST

15” RATING

ST

POST

PERIODS

PRST

-ST-

15” RATING

POST

PERIODS

FIG. 5. Mean activity change in HA, MA, and LA groups over three successive 15-second periods rated prior, during, and after stimulation with a tone. FIG. 6. Microanalysis of the mean activity change in HA, MA, and LA groups during tonal stimulation (see Fig. 5). PRST and POST points represent l&second rating periods and correspond to PRST and POST ratings in Fig. 5; the six intervening points represent the preceding 16second ST period in terms of 2%~seconds ratings.

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tive of the individual functions. Irrespective of initial pre-level, a significant number of Xs retained the same activity level from PRST to ST (p = .95). Of the 8 who changed in activity during acoustic stimulation, only 1 of 3 HA and 2 of 3 LA Ss changed to the intermediate level. The probability of the intermediate level occurring during ST is .ll for LA Ss, .71 for MA Ss, and .07 for HA 8s. These measures indicated that a single tonal stimulation had no systematic effect on arousal in the neonate. GENERAL

DISCUSSION

The present series describes an inverse relationship between the initial level of arousal and the direction and magnitude of arousal change induced by intra-oral stimulation of the newborn. Procedures initiated to determine whether the phenomenon of moderate arousal stimulation could be artifact arising from accessory experimental manipulation, coincident organismic conditions, or the measure employed have yielded negative findings. Specifically, convergence of high-, medium-, and low-activity groups at the intermediate level during stimulation cannot be attributed to (1) the cyclical activity normally occurring within the neonate irrespective of t.he stimulating conditions, (aj artifact produced by the pressure of nipple contact or maintenance, or (3) movement produced by sucking activity per se. In addition, the phenomenon is neither procedurebound, having been replicated at a temporally disparate point in Exp. 2, nondifferentiated with respect to stimulus or modality employed, nor systematically reIated to stimulation by stroking during T-I. This information is summarized in Table 2, which presents the frequencies before and during stimulation of all experimental Ss in terms of deviation units (e) from an intermediate activity level. For purposes of comparison, frequencies of Ss in “pacification” Exps. 1 and 2 have been presented also in combined form as a hypothetical group revealing no activity change TABLE

2

GROUP FREQUENCY WITH RESPECT TO NUMBER OF RATING UNITS (e) DEVIANT FROM ACTIVITY RATING OF 1 (Oe) BEFORE AND AFTER STIMULATION Group Hypothetical (no change) Pacification I Pacification II Cycle controls II Stroking controls III Tone IV

Pre-stimulus +2e +le

frequency Oe -1e

10 5 5 4

8 6 2 6

16 11 5 10

20 8 12 10

5

3

8

10

Stimulus +2e +le 10 1 0 4

8 6 2 6

4

6

10

frequency Oe -1e 16 22 22 8 5 9

20 1 0 12 5 7

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IS

HI-MAN

NEW-BORS

1 .i

from the PRST period. Absolute ratings of 3 and 2 (HA), 1 (MA), and 0 (LA) correspond to deviations of 2e, le, Oe, and --le, respectively. Because a ls-second interval was chosen for the stroking control study and many of the original Ss received much longer durations, the differential effects of st,roking and intra-oral stimulation could note be specified conclusively, and the possibility remains that, T-I stroking primes or arouses 8s to some common level at which they will accept the nipple. It is also possible that. differential behavioral effects produced in LA Xs by stroking merely reflect an inadequacy of the present rating system, which does not permit assessment of depth of sleep within the minimal activit,? category of 0. The additional stimulation of stroking required by several Ss prior to nipple insertion might have bcacn a condition &llcient for producing intermediate arousal (Nauta. 19,561, and the 1.5 seconds of stimulation received by all Ss in Exp. 3 might not have been sufficient to awaken Se at greater depths of sleep. This woultl support the generality of tllc l~t~enonienon, howcvcr, in that intra-oral stimulation rc~duccd to an intcrlnctlintc~ lcrcl cvcn those Ss in the original cspcGlcnts who vverc artificially :irou~ed. The activity diminution exhibited by HA groups during intra-or:il stimulation is consistent with the data reported by Lessen and Leutzendorff ( 1963’), although the inhibitory effect. of the present. study lasts longer. Insofar as Eiessen’s hypothesized effect of a short-term reduction in infant arousal following non-nutritive int.ra-oral stimulation was not rcstrictcd as such to highly aroused S e, one might infer that the activity of bI.4 Ss as well as of HA S’s would be reduced during nipple contact, and t.hat the activity level of LA Xs would remain unchanged. Experimcnts I and 2 of the present, series, however, indicate that MA Ss retain the prc>.\timulus arousal level and that HA and LA Ps converge at the It is suggested, t,hen, that, the intermcdintc level during stimulation. Lessen and Leutzendorff experimental population was high-activity restricted, Kesecn et aZ. (1961) have shown that general movement increases over tlie first .!I days of life, so that the greater probabilit)y of lower total functioning levels within the younger Ss of the Kessen and Leutzendorff study, as well as individual variability in cyclical activity within an hour after feeding. would otherwise have projected some S’sof moderate or low act.ivity into their population sample. =Imount, of sucking can be predicted from the arousal level of Xs prior to T-I, but only t,he activity change from HA to MA is correlated significantly with sucking frequency. The great variability in sucking frequency during intra-oral stimulation at the intermediate arousal level indicated in Exp. 1 suggests t.hat the presence of t.he nipple per se and not the act.irity of sucking is responsible for t.he arousal shift.. It is sug-

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LEVIN

gested that the nipple serves to channel the activity of HA Ss into coordinated sucking responses while “energizing” the behavior of LA Ss. The relationship observed between initial arousal and responsivity to intra-oral stimulation appears to conform to the “law of initial values” (Block et al., 1962; Lacey et al., 1953), which states that a negative correlation exists between the initial functioninng level of an organ and the size of the response of that organ to a given stimulus. Heretofore the “law of initial values” has only been applied to autonomic or homeostatic functioning. Insofar as intra-oral stimulation does not, on the surface, resemble autonomic functions, it is interesting that, within the limits of the measuring system, similar results have been obtained. In both the present report and studies of the concomitant behavioral activity induced by autonomic nervous system changes, responses are interpreted as a function of the state of the organism prior to stimulation. Whereas the latter studies have reported differences in characteristic heart rate across individuals, the present investigation has determined differences in arousal across groups of Ss representing a continuum of arousal Richmond and Lipton (1959) have demonstrated that tactile stimulation produces heart rate changes in neonates and have also obtained a high correlation between change in motor activity and heart rate. Insofar as the variable under consideration in the present investigation was arousal, as manipulated by intra-oral stimulation and as measured in terms of motor activity, it is indeed possible that the resulting phenomenon is a behavioral reflection of underlying autonomic activity change induced by nipple stimulation. If so, it is not surprising that the “law of initial values” describes the resulting function. In addition, from the finding that seemingly identical stimuli applied to different body sites produce different degrees of heart rate response (Richmond et al., 1959), it would then follow that the effect of extra-oral stimulation in Exp. 3 was only slightly arousing relative to the effect of intra-oral stimulation. Insofar as intra-oral stimulation acts as an independent variable with respect to level of arousal, and since sucking frequency is relevant to the arousal change for highly active Xs only, it is suggested that in future studies employing sucking behavior as a dependent variable, activity prelevel should be a factor in the selection of 8s. REFERENCES BLOCK, J. D., AND BRIDGER, W. H. The “law of initial value” A reformulation in terms of experimental and theoretical N. Y. Acad. Sci., 1962, pre-publication copy. ENGEN, T., LIPSI~, L. P., AND KAYE, H. Olfactory responses human neonate. J. camp. physiol. Psychol., 1963,56,73-77.

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