Changes in imitative behavior during early infancy

INFANT BEHAVIOR AND DEVELOPMENT 9, 415421 (1986)

Changes in Imitative Behavior during Early Infancy

TIFFANY FIELD, SHERI GOLDSTEIN, NITZA VEGA-LAHR, AND KATHLEEN PORTER

Mailman Center for Child Development University of Miami Medical School

Changes in imitotive behavior and attentiveness were observed in 40 infants when they were 2 to 6 months of age. The facial expressions happy, sad, and surprised were modeled in o trials-to-criterion procedure, and the infants’ looking time and mouth movements were recorded by an observer who was unaware of the face being modeled. In addition, the observer recorded her guess OS to the expression being modeled by the corresponding expression on the infant’s face and rated the infant’s expressivity. The results suggested that looking time, correspondence between the mouth expression of the infant and the mouth expression modeled, accuracy of the observer’s guess, and expressivity ratings decreased from 2 to 3 and 4 to 6 months. Although matching of mouth movements with the modeled mouth movements and accuracy of guesses were greater than chance over the 2 to 6 month-period, the decreases in these measures suggest that imitative behavior declined across early infancy. The decrease in looking time suggests that imitative behavior and attentiveness may be related and highlights the limitation of this paradigm for assessing the development of imitation during early infancy.

imitation behavior imitation facial expressions

Newborns can discriminate and imitate facial expressions shortly after birth (Field, Woodson, Cohen, Greenberg, Garcia, & Collins, 1983; Field, Wood- son, Greenberg, & Cohen, 1982; Meltzoff & Moore, 1983a) and during the first month of life (Heimann & Schaller, 1985; Meltzoff & Moore, 1977). However, very little is known about the subsequent development of these abilities in the months that follow. In at least one theoretical interpretation of imitation-that imitation is an intentional reproduction of a visually perceived model (Meltzoff & Moore, 1977)-that skill might be expected to improve with development. Although Meltzoff and Moore (1983b) point out other developmental factors that may intervene, this is not a necessary prediction from their model. At least two investigators have reported a decrease in imitative behavior during early infancy (Abravanel & Sigafoos, 1984; Fontaine, 1984a). Instead of the expected increase in imitation over the early months, Abravanel and Sigafoos

This research was supported by NIMH Research Scientist development Award #MHOO331 to the first author. We wish to thank the mothers and infants who participated in this study and Bene Alpert for her assistance with data collection.

Correspondence and requests for reprints should be addressed to Tiffany Field, Mailman Center for Child Development, University of Miami Medical School, P.O. Box 016820, Miami, FL 33101.

415

416 FIELD, GOLDSTEIN, VEGA-LAHR, AND PORTER

reported an actual decrease in the percentage of infants showing imitation at older ages for a number of actions. Similarly; Fontaine (1984a) noted an increase in imitative behavior during the second month of life, followed by a decrease until the sixth month for the facial models of tongue protrusion and mouth opening.

Because these were cross-sectional studies, sampling different infants at different ages, it is possible that individual differences contributed to the negative findings. As has been noted in neonatal imitation studies, many infants are not good imitators (Field, 1985; Heimann & Schaller, 1985). Thus, by chance, the infants sampled at older ages by Abravanel and Sigafoos (1984) and by Fontaine (1984a) could have been less imitative individuals. An alternative possibility is that infants, in general, may become less interested in static facial displays as they experience animated expressions during their early interactions. Less visual attentiveness to models of behavior could contribute to less imitative behavior, suggesting a major limitation of this paradigm for eliciting imitative behavior in older infants. Congruent with this suggestion are the data from Fon- taine (1984a) showing that 2-month-old infants, as compared to older infants, were not only more imitative but also more attentive to the model, suggesting the need to specify the relationship between the infant’s state or attentiveness and its responses (Fontaine, 1984b).

The purpose of the present study was to assess the development of attentiveness and imitative behavior in a longitudinal sample seen every month from the age of 2 months to 6 months. The same facial expressions (happy, sad, surprised) and the same paradigm as those used in the Field et al. (1982, 1983) studies were used in this longitudinal investigation.

METHOD

Sample The sample contained 40 normal infants (16 males, 24 females) of middle socioeconomic status parents who were medical faculty or staff and who en- rolled their infants in a medical school infant nursery at 2 months of age. Each infant ranged in age between 2 and 6 months over the course of the study (M= 8.0 weeks, r=7-9 weeks; M= 12.6, r= 11-14; M= 17.4, r= 16-18; M=21.4, r=20-22; M=25.0, r=24-27).

Procedure For each imitation session, the infants were accompanied by their mothers to a videotaping laboratory located in the same facility as the infant nursery. Be- cause the infants were attending this all-day nursery on the medical campus where their mothers were employed, the imitation sessions could be scheduled during the infants’ most alert time of day for approximately ‘/ hour. If the infant was not in an alert state, the session was rescheduled. Initial state of alert- ness was more characteristically a problem for the younger infants.

IMITATIVE BEHAVIOR 417

For the imitation procedure, the infant was positioned in a semi-upright infant seat placed on ‘a table in a face-to-face position approximately 30.48 cm from the model’s face. Video cameras were positioned approximately 182.88 cm away with one camera focused on the model’s face and the other on the infant’s face, yielding a split-screen image of the infant and model. The infant’s visual fixation on the model’s face and the infant’s mouth movement Patterns were also recorded by an observer who stood behind the model in order to see the infant’s face yet remain unaware of the expression being modeled. Split- screen videotaping was used to provide checks on the reliability of coding by the observer and face presentation and lack of differential reinforcement by the model.

A series of trials of three facial expressions (happy, sad, surprised) was then modeled by one of two female models. To elicit the infant’s visual fixation on the model’s face, the model provided auditory stimulation (two tongue clicks) prior to each trial. The model then fixed one of these expressions on her face: a happy, sad, or surprised expression. Three series of trials (one series for each face) were presented in a counterbalanced Greco-Latin square order to control for state change of the infants. Face one was sustained in a fixed expression until the infant looked away from the model’s face (one trial), at which time the model again elicited the infant’s visual fixation with auditory stimulation. Face one was repeated for a series of these trials until the infant reached criterion, a visual fixation on the model’s face of less than 2 s. Face two and face three were then presented in a series of trials using the same trials-to-criterion habituation procedure.

The observer held a stopwatch and clipboard in one hand and with the other coded a checklist on: (1) total fixation time per trial; (2) the presence of specific mouth movements of the infant, including widening of the lips (as in a happy face), protruded lower lip (pouting or sad face), and wide opening of the mouth (as in a surprise face); (3) the observer’s guess as to which expression was being modeled; and (4) a subjective rating of the expressivity of the infant on a 5-point Likert-type scale (with 5 being extremely expressive and 1 being non- expressive). This was basically a measure of the observer’s judgment as to the frequency with which the infant was emitting facial-expression changes. Inter- observer reliability, based on the live observer’s coding and on an independent observer’s coding of one-third of the videotapes, was calculated by Kappa, a chance-corrected statistic (Bartko & Carpenter, 1976). Reliability coefficients were .93 for fixation time per trial, .83 for mouth movement, .77 for “guess” on facial expression being modeled, and .82 on expressivity rating.

Following a break of approximately 5 min, this procedure was repeated with the infant’s mother modeling the facial expressions. However, several of the mother-infant imitation sessions could not be completed due to the mother’s difficulty in maintaining the fixed expressions or infant fussiness or both. It could not be determined whether infant fussiness was related to the procedural time that had elapsed, for example, habituation or boredom with the procedure,

418 FIELD, GOLDSTEIN, VEGA-LAHR, AND PORTER

or to the violation of expectancy experienced by the infant presented with a fixed facial expression rather than the naturally animated face of the mother. For those infants who completed the procedure with both the experimenter and the mother, the data appeared to be very. similar. However, because of unequal observations, comparisons between the experimenter and mother as models will not be presented here.

RESULTS

Repeated-measures analyses of variance were conducted on the four dependent measures: total looking time, mouth movements, the observer’s guess, and the expressivity rating. For these analyses, sex was entered as a between-groups measure, and month of observation and facial expression being modeled were entered as repeated measures. Post hoc comparisons were made by testing each age mean against every other age mean by Bonferroni &-tests.

As can be seen in Table 1, a repeated-measures effect suggested that mean looking times for the series of face trials were significantly lower at 4 to 6

TABLE 1 Means, F Values and p Levels for Measures’

Observation Period (in months)

Percentage of trials’

Looking time (s) Happy face Sad face Surprised face

Mouth expression’

2 3 4 5 6 F

5.7 6.0 5.9 6.1 6.1 ns.

57.2.l 65.4.' 33.1 b 28.i’b 24&b 14.13”’ 42.0. 34.3. 23.3b 25.3b 20.9b B.58** 46.00 41.4. 32.0,, 33.8b 24.2b 5.21 l

Happy model/widened lips 3. 33. .25b .23b .22,, 4.71. Sad model/pouting lips .37. 35, .23,, .21b .2ob 5.34'

Surprised model/wide-open lips .32. 30. .16b .21b .23b 4.19*

Expressivity rating 3.4. 3.0.b 2.!& 2.5b 2.5b 4.23'

Accuracy of guess

Happy .B%l .B7s .62b .63b .67b 5.17* Sad .78. 34, .67b .Mb .67b 4.42' Surprised 300 .77. .66b .ub .69b 4.85’

Different Letter Subscripts indicate Significant Differences in Post Hoc Comparisons by Bonferrani t-tests, p levels (‘p< .OS, l *p< .Ol, l **p< .OOl)

’ These comparisons were made by testing each age mean against every other age mean. f Mean number trials were collapsed across expressions inasmuch as number of trials did

not vary across expressions. 1 Significantly longer looking time for happy face than sad or surprised face at 2 months,

Fs=5.81, 4.97, p< .05. 4 Significantly longer looking time for happy face than sad or surprised face at 3 months,

Fs=7.76, 7.59, p<.Ol. 5 Figures for this measure are percentage of trials mouth expression emitted by infant cor-

responded to mouth expression modeled. For example, in the 2-month-old happy-model cell, .38 is the mean proportion of trials in which there was a correct response.


months than at &and 3 months for each of the faces modeled (happy, sad, and surprised) even though the number of trials-to-criterion per expression re- mained the same across months. In addition, a month-by-facial-expression in- teraction effect suggested that at 2 and 3 months the infants looked at the happy face for longer periods of time than they did at the sad and surprised faces.

A repeated-measures observation-month effect for the mouth expression measure suggested that the percentage of trials that the mouth expression emitted by the infant corresponded to the mouth expression being modeled was greater at 2 and 3 months than at 4 to 6 months. This finding suggests that imitative expressions in the mouth region decreased from 2 to 3 to 4 to 6 months (as seen in Table 1). This was true for all three expressions-the happy model eliciting widened lips in the infant, the sad model-pouting lips, and the surprised expression, a wide-open mouth. Despite this decrease, the data averaged across the 2 to 6 month period suggest that more appropriate (imitative) responses were elicited by the matching expression of the model than by the non- matching expression, suggesting significant imitation (see Figure 1). Repeated measures analysis of variance suggested (as seen in Figure 1) that widened lips of the infant occurred significantly more often during the happy than the sad and surprised model trials, F= 3.23, p < .05; pouting lips occurred more often

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- WIDENED LIPS POUTING LIPS WIDE OPEN MOUTH

Figure 1. Mean proportion of trials over 2 to 6-month observation periods that different infant mouth movements occurred as a function of facial expression modeled (HA=happy, SAcsad, and SU=surprised). Infant mouth movements include widened lips (as in a happy expression),

pouting lips (sad) and wide-open mouth (surprised).

420 FIELD, GOLDSTEIN, VEGA-LAHR. AND PORTER

during the sad model trials than the happy or surprised face trials, F=4.91, p< .Ol; and wide-open mouth occurred more frequently during the surprised face model trials than the happy or sad face trials, F= 3.41, pc .05.

Similarly, the global expressivity ratings decreased from 2 to 3 to 4 to 6 months (see Table 1). Although the accuracy of guessing the facial expressions being modeled was significantly greater than chance (> 33%) at each month’s observation, the accuracy of guessing significantly decreased over the 4-month period.

To address the question of individual differences in imitative behavior, the data on accuracy of guesses were examined for each subject. For each session, the observer had recorded a guess at the end of each series of expression trials as to which expression was being modeled by simply observing the infant’s face. The number of correct guesses was summed across sessions and converted to a proportion. Forty percent of the infants emitted expressions from which the observer could accurately guess the expressions being modeled 100% of the time. In contrast, the remaining 60% of the infants emitted expressions that were accurately guessed an average of 63% (range=33-67%) of the time.

DISCUSSION

These data suggest that the looking times, the correspondence between mouth expression of the infant and mouth expression modeled, the accuracy of the observer’s guesses as to which expression was being modeled, and the expressivity ratings decreased from 2 to 3 to 4 to 6 months. Although the infants’ matching of mouth movements with the modeled mouth movements and the accuracy of the observer’s guessing were greater than chance at each observation period, the less frequent mimicry, less accurate guessing and ‘less expressivity at the older ages suggests that imitative behavior declined across early infancy.

The fact that interest in the modeled expressions also waned, as manifested by decreased looking times, suggests that imitative behavior and interest/ attentiveness may be related. An alternative possibility may be that blends of these facial expressions are developing in the infants (Malatesta dc Haviland, 1982; Oster, 1978), such that they are less frequently emitting the exaggerated mouth movements of happy, sad, and surprised expressions. Thus, they were rated as less expressive, and mimicry of the mouth movements occurred less often. Coding of additional components of the expressions, for example, movements in the brow and eye regions may be necessary, or a more finely tuned coding system, for example, the Facial Action Coding System (FACS) system for coding specific muscle movements, may be critical for detecting more subtle developmental changes.

Nonetheless, these data are consistent with those of Abravanel and Sigafoos (1984) and Fontaine (1984a), suggesting that imitative behavior may decline over the early months of infancy. Because both Field (1985) and Heimann and


Schaller (1985) had reported individual differences in imitative behavior, the possibility was raised that declines in imitation in cross-sectional samples such as those of Abravanel and Sigafoos and Fontaine could relate to chance sampling of less imitative individuals at older ages. But a developmental decline in imitative behavior was also noted in this study in which as many as 40% of the infants were good imitators or consistently emitted expressions that could be accurately guessed as imitations of the model across the 6-month period.

Unfortunately, it is also not clear from this study whether the decline in imitative behavior was related to lesser interest in the static face (because faces are typically animated instead of static), the development of facial expression blends, or to a simple developmental shift from reflexive-like behavior to more natural interactive responses to the model’s behavior (e.g., a puzzled expression in response to a fixed, surprised expression). Future studies are needed to determine whether these apparent decreases in imitative behavior are real or simply an artifact of a limited paradigm.

REFERENCES

Abravanel, E., & Sigafoos, A.D. (1984). Exploring the presence of imitation during early infancy. Child Development, 55, 381-392.

Bartko, J.J., & Carpenter, W.T., (1976). On the methods of reliability. The Journal of Nervous and Mental Disease, 163, 307-317.

Field, T. (1985). Neonatal perception of people: Maturational and individual differences. In T. Field & N. Fox (Eds.), Social perception in infunts. Norwood, NJ: Ablex.

Field, T., Woodson, R., Cohen, D., Greenberg, R., Garcia, R., & Collins, K. (1983). Discrimina- tion and imitation of facial expressions by term and preterm neonates. Infunt Behavior and Development, 6, 485-490.

Field, T., Woodson, R., Greenberg, R.. & Cohen. D. (1982). Discrimination and imitation of facial expressions by neonates. Science, 218, 179-181.

Fontaine, R. (1984a). Imitative skills between birth and six months. Infunt Behavior and Develop- ment, 7, 323-333.

Fontaine, R. (1984b). Les imitations pr&oces: Problkmes m&hodologiques et thbriques. Cuhiers Psychologie Cognitive, 4, 5 17-536.

Heimann, M., & Schaller, J. (1985). Imitative reactions among 14-21day-old infants. Znfunt Mental Health Journal, 6, 31-39.

Malatesta, C.Z., & Haviland, J.M. (1982). Learning display rules: The socialization of emotion expression in infancy. Child Development, 53, 991-1003.

Meltzoff, A.N., & Moore. M.K. (1977). Imitation of facial and manual gestures by human neonates. Science, 198. 75-78.

Meltzoff, A.N., & Moore, M.K. (1983a). Newborn infants imitate adult facial gestures. Child Development, 54, 702-709.

Meltzoff, A.N., & Moore, M.K. (1983b). The origins of imitation in infancy: Paradigm, phe- nomena, and theories. In L.P. Lipsitt (Ed.), Advunces in infuncy research (Vol. 2). Nor- wood, NJ: Ablex.

Oster, H. (1978). Facial expressions and affect development. In M. Lewis & L.A. Rosenblum (Eds.). The development of 4ffect. New York: Plenum.

2 February 1986; Revised22May 1986 W

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Changes in imitative behavior during early infancy