Changes in the nonnutritive sucking response to stimulation during infancy

JOURNAL

OF

EXPERIMENTAI,

Changes

CHILD

in the

I’GYCIIOLOtiY

10,

112-119

Nonnutritive

to Stimulation ARNOLD University

Sucking

During J.

(1970)

Response

Infancy’

SAMEROFF of Rochester

Nonnutritive sucking response change to auditory stimulation was studied in l-, 2, and 3-month-old infants. Each of 22 Ss was stimulated with five stimuli, presented four times during three sessions at 24-hour intervals. The l- and a-month-old 8s were tested again 1 month later for another three sessions. The response of younger infants was ambiguous. The response of older infants showed reliable shortening of sucking burst and lengthening of sucking interval. Neither differential effects of the stimuli nor habituation of response were found.

The study of sucking-response change t#o stimulation in the human newborn has been mainly confined in recent years to the newborn period (Haith, 1966; Kaye, 1966’; Kron et al., 1967; Semb & Lipsitt, 1968; and Sameroff, 1967). However, the work of Bronshtein et al. (1958), which stimulated much of the above-mentioned research, was done with a wide age range during the first year of life. In view of the difficulty many investigators have had replicating with newborns the Bronshtein et al. (1958) findings that auditory stimulation inhibited sucking (Kaye & Levin, 1963; Keen, 1964; Sameroff, 1967), it seemed worthwhile to extend the age range studied to the first few months of life. The current study attempted to compare in older infants the effects of auditory stimulation when stimulus change occurred during a period of sucking (sucking burst) with the effect when change occurred during an interval between sucking periods (sucking interval). Subjects The Ss were 22 normal, healthy infants, at the Institute for the Care of Mother

10 male and 12 female, seen and Child, Prague, Czecho-

“This investigation was supported by USPHS Grants USPHS Postdoctoral Research Fellowship MH!HD-16028. to the stti of the Institute for the Care of Mother Franzlova, and to P. Kelly, R. Mont, and A. Konow Author’s address: Department of Psychology. University New York 14627. 112

HD-03454, HD-O@390 and Special thanks is given and Child, especially Jana for t,heir computing skills. of Rochester, Rochester,

SUCKING

RESPONSE

STIMULATION

DURING

113

INFANCY

Slovakia. l-, 2-, and S-month-old infants (Groups A, B, and C, respectively; see Table 1) were used to test for age changes in the sucking response. An attempt was made to use 4-month-old infants but they consistently rejected the nipple within the first 5 minutes of each session. Groups A and B were seen once (Pre) and then a second time when they were a month older (Post) to test for longitudinal, within-subject changes in response for comparison with the cross-sectional data. Six groups of four Ss were used: one group at each age in a condition where stimulation occurred during sucking bursts, and one group at each age in a condition where stimulation occurred during sucking intervals. Each group of four contained two females and two maies, except for the stimulation-during-interval Group C. The research project ended before the last group was completed. The age range at which the infants were first seen was 25-34 days for the l-month-old, 51-67 days for the 2-month-old, and 84-97 days for the 3-month-old infants. For those infants that were seen a month later, from 24 to 36 days had elapsed before the second group of sessions. Apparatus Sucking was recorded through a Statham pressure transducer connected to a Galileo polygraphic recorder. A blind (holeless) Evenflo nipple was connected to the transducer by a length of polyethylene tubing. Auditory stimulation was provided by an Ameco code oscillator placed in a midline position, 20 cm beyond the infant’s head. A 60-rpm motor rotated two cams which operated a lever switch in series with the speaker to produce the appropriate time intervals for the interSUBJECT

GROUPS

Burst stimulation condition (BS)

Interval stimulation condition (IS)

AND AVERAGE

Group

N

A

4

B

4

c

4

A

4

B

4

C

2

TABLE 1 BURST AND INTERVAL SUCKING UNIT

Age Pre Post Pre Post

1 2 2 3 3

month months months months months

Pre 1 month Post 2 months Pre 2 months Post 3 months 3 months

LENC:TH

Burst length (seconds)

FOR FIRST

Int,erval (seconds‘,

4.12 3.73 5.36 5.23 5.09

5.*50 5.86 5.38 5.99 4.10

4.21 4.14 5.26 6.51 C5.23

3.99 4.33 5.05 5 .23 6.83

114

ARKOLD

J. SAMEROFF

mittent stimulation. Ih~kgrou~d hound l(~\cl wa:: measured a General Radio Sound Level IMeter re 0.0002 dynrs,‘cm’.

at 55 db by

Procedure At t,he appropriate ages each S was seen on three consecutive days ior a session which lasted about 20 minutes. At the start of each session the infant was carried from the nursery to the laboratory by a nurse and placed in a crib wit,11 his head held in the midline position by a cushioned headrest. The infant was given the nipple to suck and 60 seconds after the start of sucking the stimulations were begun. Each session consisted of 20 stimulus presentations. A 500-Hz tone was used and each condition was presented four consecutive times. The first stimulus was always a 65-db, continuous tone in order to establish a baseline response to stimulation for comparison with the following stimuli. The next three stimuli were a 75-db continuous tone; a 65-db, 500msec, on-off tone; and a 65-db, 250-msec, on-off tone. These three stimuli were randomized so that they were in a different order for each session of each subject. The final stimulus was the 65-clb, continuous tone again. The beginning of each stimulus trial was a function of the sucking state of the infant, isee Fig. I). Each trial lasted for five consecutive sucking units, each consistin, CTof a burst and an interval. For the Burst Stimulation (BS) Xs, stimulus onset occurred after two sucks in the second burst and offs& after two sucks in the fourth burst. For Interval Stimulation (IS) Ss, stimulus onset occurred after 1 second of no sucking in the second interval and offset after 1 second of no sucking in the fourth interval. The first, third, and fifth sucking units served as controls for the onset and offset effects of the stimulation. A sucking burst was defined as two or more sucks having a frequency greater than one per scconcl and an amplitude greater than 10 mm Kg. A sucking interval was defined a s an intcrburst lime greater than 1 second (Sameroff, 1967 1. STIMULATION z:,

BURST

---II

CONDITION I SUCKING

I

2

I

3

I

4

5

I

1

UNIT I

I

INTERVAL

I

CONDITION

I

I

2

I

3

I

4

I

5

STIMULATION Ii:, FE.

1. Paradigm

I---lp

and units of analysis for each stimulus

trial.

SuCIcING

RESPONSE

STIMULATION

DURING

115

INFANCY

RESULTS

Repeated-measures analyses of variance were used in all comparisons between conditions and ages. For the longitudinal data the analyses were sixway : sucking unit (either burst or interval length) X trial X stimulus X session x Pre-Post X age group. For the cross-sectional analyses each age was analyzed separately in a four-way analysis: sucking unit X trial x session X age group. (For t’he l-month-old infants there was no group variable.) Figures 2, 3, and 4 equate the groups on sucking unit 1 to better depict differing effects of stimulation. For the actual values of these points for each group at each age see Tab’le 1. Sti,mulus

Change

When the data were collapsed over trials and stimuli, the effect of stimulus onset on burst length was essentially the same for both conditions, BS and IS (see Figs. 2 and 3). Although at 1 and 2 months of age there is a slight shortening of burst length it was statistically reliable in neither the cross-sectional nor the longitudinal data. For the 3-monthold infants t’here was an inhibition of sucking effect in the cross-sectional data (F = 5.58, df = 4,24; p < .Ol, for the BS group and F = 4.92; df = 4,24, p < .Ol for the IS group). In the longitudinal data the prepost interaction with sucking burst was significant (F = 7.85; df = 4,24; p < .Ol for BS group and F = 5.21, df = 4,24, p < .Ol for IS group). There was no comparable offset effect to stimulation on burst length.

1.0

0.5 I

\

I 3

-1.0

-

ON I

2

OFF 3 BURST

FIG. 2. Average sucking burst Post ages in the Burst Stimulation for Groups A and B combined.

4

and

5

interval (BS) and

I

response Interval

2

3 INTERVAL

to stimulation Stimulation

4

5

for (IS)

Pre and conditions

116

ARNOLD

J. SAMEROFF

0 0 0

ON I

2

BURST

FIG.

ON

OFF 3 BURST

4

I

!I

OFF 2

INTERVAL

STIMULATION

3. Average sucking burst response to stimulation

I MONTH 2 MONTH 3 MONTH

3 BURST

I 5

4

STIMULATION

for Ss at each age level.

In other words, when stimulus onset occurred during a burst as in the BS condition the burst was shortened. When stimulus onset occurred during an interval as in the IS condition the next’ burst was shortened. The interval data presented a somewhat different picture from the burst data (see Figs. 2 and 4). In the BS condition the data were straightforward in showing that stimulus onset during a burst, caused the next interval to be lengthened. The greatest effect was in the 3-month-old group (F = 5.94, df = 4,24, p < .Ol). There was no reliable interaction in the longitudinal data with both groups showing the effect both Pre and Post (F = 7.71, df = 4,24, p < .Ol). The IS condition, however, showed different effects. Stimulus onset caused either no effect or a nonsignificant shortening of interval length for l- and 2-month-old infants both in the cross-sectional and longitudinal data. An analysis comparing the interval response to stimulus onset of subjects in the two conditions (BS and IS) showed a significant interaction effect for l-month-old infants (F = 6.74, df = 1,14, p < .05). The interaction effect for 2-month-old infants was not reliable. For 3-month-old infants in the IS condition the stimulus onset effect was a clear increase in interval length (F = 5.07, df = 4,20, p < .Ol) ; the same effect as in the BS condition. Ej’ect of Stimulation TO assess the effect of stimulation

pendent

d stimulus

on burst

and interval

length

in&-

change, onset, or offset, an analysis was made

SUCKING

RESPONSE

STIMULATION

DURING

117

INFANCY

0 0 0

2.0

I MONTH 2 MONT” 3 HONTN

I.4 :: 2 : w

1.0

0.5

0 ON I BURST FlG.

4.

Average

OFF 2

sucking

3 INTERVAL

4

ON

I 5

I

STIMULATION interval

response

2

INTERVAL to

stimulation

OFF 3 INTERVAL

4

3

STIMULATION

for ss at each age level.

comparing sucking unit 3, when the stimulation was on, with sucking units 1 and 5, before and after the stimulation period. The burst data in both conditions showed no effect of stimulation alone, that is, there were no reliable differences between bursts 1, 3, and 5 for any age group in any condition. There was an effect of stimulation on interval length in bot’h BS and IS conditions. The interval during stimulation was longer than the intervals preceding and following stimulation for l- and 2-month-old infants in both conditions and S-month-old infants in the IS condition. The differences for S-month-old infants in the BS condition were in the same direction but not reliable. There was no difference in effect on sucking related to the different stimuli used in the study. Habituation There were no reliable habituation effects related to comparisons of responsesacross the four trials, between the three sessions,nor between groups of subjects of the same age of which one group was Pre and one group Post. An analysis comparing response to the initial four trials of the 65-db continuous tone with the final four trials of the same stimulus also showed no reliable changes in response from the beginning of a session

118

ARKOLD

to t’he end, although significance.

J.

SAMEROF‘F

the tlcc~rement, in interval

rrsponre

approached

DISCUSSION

This study attemptetl to csplorc~ t’llc> chttngu with age of the nonStimulation effects nutritive sucking response to auditory stimulation. were found at all ages in the increased sucking interval length while t’he tones were on. The inhibition effect reported by Bronshtein et nZ. (1958), i.e., the shortening of the sucking burst in which t’he stimulus onset occurred, was found in the 3-month-old infants, but not reliably in t’he l- and 2-month-old infants. However, t’he Bronshtein group’s report of habituation effects was not replicated at any age. The effect of stimulus onset on the sucking interval noted at 3 months of age could be explained as a decrease in response latency with age. In the I- and 2-month-old groups, the increase in interval length only occurred later in the stimulation period. For the IS group it occurred during the second interval, while for the BS group it occurred in the first interval after the burst in which stimulus change occurred. By 3 months of age it was occurring in the sa.me interval in which the stimulus change occurred. In summary, the data for the younger age groups are not sufficiently clear to define t’he nonnutritive sucking response t’o stimulation. The present data show a clear increase in size of response with age and a possible shortening in response latency. REFERENCES T. G., KAMENETSKAYA, 8. G., Luppov.4, N. N.. & SYTOVA, V. A. On the early development of the functions of analyzers in infants and some animals at the early stage of ontogenesis. In Problems of evolution of physiological functions (translated in Office of Technical Services, Report no. 6081066. 1960. pp. 106-116). Moscow: Academy of Sciences, 1958. HAITH, M. M. The response of the human newborn to visual movement. Journal of Experimental Child Psychology, 1966, 3, 23&243. KAYE. H. The effects of feeding and tonal stimulation on non-nutritive sucking in the human newborn. Journcrl of Experimental Child Psychology, 1966, 3, B-145. KAYE, H., & LEVIN, G. R. Two attempts to demonstrate tonal stimulation of nonnutritive sucking in neonates. Perceptual Motor Skills, 1963, 17, 521-522. KEEN, R. Effects of auditory stimulation on sucking behavior in the human neonate. Journal of Experimental Child Psychology, 1966, 3, 131-145. KFLON. R. E., STEIN, M., GODDARD, K. E.. & PHOENIX, M. D. Effect of nutrient upon the sucking behavior of newborn infants. Psychosomatic Medicine, 1967, 29, 24-32. SAMEROFF, A. Nonnutritive sucking in newborns under visual and auditory stimulation. Child Development, 1967, 38, 443452. BRONSHTEIN,

il.

I.,

ANTONOVA,

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119

A. J. Respiration and surkin g as components of the orienting reaction in newborns. Psychophysiology, in press. SEMB, G., & LIPSITT, L. P. The effects of acoustic stimulation on cessation and initiation of non-nutritive sucking in neonates. Journal of Experimental Child Psychology, 1968, 6, 585-597. SAMEROFF,