The social functions of babbling: acoustic and contextual characteristics that facilitate maternal responsiveness

What is the social function of babbling? An important function of prelinguistic vocalizing may be to elicit parental behavior in ways that facilitate the infant's own learning about speech and language. Infants use parental feedback to their babbling to learn new vocal forms, but the microstructure of parental responses to babbling has not been studied. To enable precise manipulation of the proximal infant cues that may influence maternal behavior, we used a playback paradigm to assess mothers’ responsiveness to prerecorded audiovisual clips of unfamiliar infants’ noncry prelinguistic vocalizations and actions. Acoustic characteristics and directedness of vocalizations were manipulated to test their efficacy in structuring social interactions. We also compared maternal responsiveness in the playback paradigm and in free play with their own infants. Maternal patterns of reactions to babbling were stable across both tasks. In the playback task, we found specific vocal cues, such as the degree of resonance and the transition timing of consonant‐vowel syllables, predicted contingent maternal responding. Vocalizations directed at objects also facilitated increased responsiveness. The responses mothers exhibited, such as sensitive speech and vocal imitation, are known to facilitate vocal learning and development. Infants, by influencing the behavior of their caregivers with their babbling, create social interactions that facilitate their own communicative development.     

Social feedback to infants' babbling facilitates rapid phonological learning

Infants' prelinguistic vocalizations are rarely considered relevant for communicative development. As a result, there are few studies of mechanisms underlying developmental changes in prelinguistic vocal production. Here we report the first evidence that caregivers' speech to babbling infants provides crucial, real-time guidance to the development of prelinguistic vocalizations. Mothers of 9.5-month-old infants were instructed to provide models of vocal production timed to be either contingent or noncontingent on their infants' babbling. Infants given contingent feedback rapidly restructured their babbling, incorporating phonological patterns from caregivers' speech, but infants given noncontingent feedback did not. The new vocalizations of the infants in the contingent condition shared phonological form but not phonetic content with their mothers' speech. Thus, prelinguistic infants learned new vocal forms by discovering phonological patterns in their mothers' contingent speech and then generalizing from these patterns.     

Maternal speech style with prelinguistic twin infants

The mother–infant communicative speech of a group of mothers of 4‐month‐old first‐born twin infants was compared to the speech of a group of mothers of first‐born singleton infants. Maternal groups were matched on age, education level, mother–infant attachment status and infant gender, and maternal depression was assessed as a control variable. Maternal speech was coded for focus, content, complexity and syntax of mothers' utterances. The findings of earlier studies with toddler age twins, that maternal speech style was more directive and less infant‐focused, were replicated in this prelinguistic period of infancy. Compared to mothers of singletons, mothers of twins used less infant‐focused speech, were less responsive to their infants' cues, and attributed less agency to their infants. Mothers of twins also used fewer questions and requests but did not differ from mothers of singletons in their use of negatives and imperatives. These early differences in the language learning environments of twin and singleton infants may be due to the reduced opportunities that mothers of twins have to establish dyadic communicative routines with their infants and to familiarize themselves with their infants as interactive partners, and may have implications for the early language development of twins. Copyright © 2002 John Wiley & Sons, Ltd.     

Socially guided attention influences infants’ communicative behavior

For effective prelinguistic communication, infants must be able to direct their attention, vocalizations, and nonverbal gestures in social interactions. The purpose of our study was to examine how different styles of caregiver responses influenced infant attentional and communicative behavior in social interactions, based on prior studies that have shown influences of responsiveness on attention, language and cognitive outcomes. Infants were exposed to redirective and sensitive behavior systematically using an ABA design to examine real-time changes in infants’ behavior as a function of caregiver responses. During the two baseline “A” periods, caregivers were instructed to play as they would at home. During the social response “B” period, caregivers were instructed to respond sensitively to infants’ behavior on one visit and redirectively on the other visit. Results demonstrated that when caregivers behaved redirectively, infants shifted their attention more frequently and decreased the duration of their visual attention. Caregiver responses also resulted in changes in vocal and gesture production. Infants decreased their production of caregiver-directed vocalizations, gestures, and gesture-vocal combinations during in the redirective condition. Results suggest that caregiver sensitive responding to infants’ attentional focus may be one influence on infants’ attentional and prelinguistic communicative behavior.     

A prelinguistic gestural universal of human communication

Several cognitive accounts of human communication argue for a language-independent, prelinguistic basis of human communication and language. The current study provides evidence for the universality of a prelinguistic gestural basis for human communication. We used a standardized, semi-natural elicitation procedure in seven very different cultures around the world to test for the existence of preverbal pointing in infants and their caregivers. Results were that by 10-14 months of age, infants and their caregivers pointed in all cultures in the same basic situation with similar frequencies and the same proto-typical morphology of the extended index finger. Infants' pointing was best predicted by age and caregiver pointing, but not by cultural group. Further analyses revealed a strong relation between the temporal unfolding of caregivers' and infants' pointing events, uncovering a structure of early prelinguistic gestural conversation. Findings support the existence of a gestural, language-independent universal of human communication that forms a culturally shared, prelinguistic basis for diversified linguistic communication.     

Vocal congruence in mother-infant play

Turn-taking is the fundamental temporal structure of adult dialogue. This structure defines two types of joint silence: intrapersonal pause (silence bounded by the vocalizations of a single speaker) and switching pause (silence bounded by the vocalizations of different speakers). Switching pauses mark the boundaries of the turn exchange. In adult conversation the mean durations of both types of pause are characteristically matched between partners. This matching, termed vocal congruence, occurs developmentally earlier in the case of switching pauses. We hypothesized and confirmed that mothers and infants match switching pauses but not intrapersonal pauses at 4 months, even though the infants' vocalizations are prelinguistic. Second, since there are known affective correlates of vocal congruence in adult conversation, we hypothesized a similar affective correlate for mother-infant vocal congruence. We found, for the intrapersonal pause only, that the degree of matching within a dyad correlated with infant affective engagement. We conclude, from switching pause congruence, that a turntaking dialogic structure is being regulated in the mother-infant pair at 4 months in the same way as seen in adult conversation. Thus, both the temporal structure of adult dialogue and its affective correlate are prelinguistic.Supported in part by NIMH grant No. 41675.     

Is visual reference necessary? Contributions of facial versus vocal cues in 12‐month‐olds’ social referencing behavior

To examine the influences of facial versus vocal cues on infants' behavior in a potentially threatening situation, 12-month-olds on a visual cliff received positive facial-only, vocal-only, or both facial and vocal cues from mothers. Infants' crossing times and looks to mother were assessed. Infants crossed the cliff faster with multimodal and vocal than with facial cues, and looked more to mother in the Face Plus Voice compared to the Voice Only condition. The findings suggest that vocal cues, even without a visual reference, are more potent than facial cues in guiding infants' behavior. The discussion focuses on the meaning of infants' looks and the role of voice in development of social cognition.     

Learning how to learn from social feedback: The origins of early vocal development

Infants’ prelinguistic vocalizations reliably organize vocal turn-taking with social partners, creating opportunities for learning to produce the sound patterns of the ambient language. This social feedback loop supporting early vocal learning is well-documented, but its developmental origins have yet to be addressed. When do infants learn that their non-cry vocalizations influence others? To test developmental changes in infant vocal learning, we assessed the vocalizations of 2- and 5-month-old infants in a still-face interaction with an unfamiliar adult. During the still-face, infants who have learned the social efficacy of vocalizing increase their babbling rate. In addition, to assess the expectations for social responsiveness that infants build from their everyday experience, we recorded caregiver responsiveness to their infants’ vocalizations during unstructured play. During the still-face, only 5-month-old infants showed an increase in vocalizing (a vocal extinction burst) indicating that they had learned to expect adult responses to their vocalizations. Caregiver responsiveness predicted the magnitude of the vocal extinction burst for 5-month-olds. Because 5-month-olds show a vocal extinction burst with unfamiliar adults, they must have generalized the social efficacy of their vocalizations beyond their familiar caregiver. Caregiver responsiveness to infant vocalizations during unstructured play was similar for 2- and 5-month-olds. Infants thus learn the social efficacy of their vocalizations between 2 and 5 months of age. During this time, infants build associations between their own non-cry sounds and the reactions of adults, which allows learning of the instrumental value of vocalizing.     

Temporal Relationships Between Gaze and Vocal Behavior in Prelinguistic and Linguistic Communication

This work reports longitudinal evaluation of the temporal relationships between gaze and vocal behavior addressed to interactive partners (mother or experimenter) in a free-play situation. Thirteen children were observed at the ages of 1;0 and 1;8 during laboratory sessions, and video recordings of free-play interactions with mother and a female experimenter were coded separately for children's vocal behavior (vocalizations and words) and gaze toward their interactive partners. The difference between the observed and expected cooccurrence of these two communicative behaviors was evaluated by transformation into z-scores. The most important findings are related to differences in the temporal relationship observed at age 1;0 between gaze and vocalizations and at age 1;8 between gaze and words. At the earlier age, the infants who exhibited greater coordination between gaze and vocal behavior than was expected by chance (z-score > +1.96) preferred to look at the interlocutor at the beginning of the vocal turn. Instead, when they were older and began to produce words, they frequently looked at the interlocutor at the end of the vocal turn. These results are interpreted as referring to characteristics of conversational competence in the prelinguistic and linguistic periods. Moreover, looking at the interlocutor at the beginning of the vocal turn at age 1;0 was found to be related to language production at age 1:8, highlighting a significant relationship between conversational competence during the prelinguistic period and language acquisition.     

Some Personality Characteristics of the Culturally Disadvantaged

The relationship between sensitive maternal behavior and mother-infant vocalization during feedings was examined in an effort to determine this situational meaning of Ainsworth's concept of sensitivity. Ss were 28 white, middle-class mothers and their infants. Excerpts of home feedings videotaped at 6 and 9 months were coded for frequency of contingent vocal interaction and quality of vocal affect. Sensitive mothers were distinguished from insensitive mothers at each age period by differing vocal patterns. At 6 months, infants of sensitive mothers vocalized significantly less than did infants of insensitive mothers. Mothers in both groups responded to their infants' vocalizations equally as often. At 9 months, infants in both groups vocalized the same amount, while sensitive mothers vocalized more often in response to their infants than did insensitive mothers. The only significant difference in vocal affect was found in the greater positive affect among sensitive mothers at 9 months.     

Maternal soothing and infant stress responses: soothing, crying and adrenocortical activity during inoculation

The relation between maternal soothing and infant stress response during inoculation was examined in a sample of 37 mothers and their 3-month-old infants. The mothers' soothing and the infants' cry vocalizations and the mothers' and the infants' salivary cortisol level pre- and post-injection were analysed. There was a positive relation between infants' cry vocalization post-injection and maternal soothing pre- and post-injection. The sample was divided in two sub-groups depending on whether the mothers evidenced most soothing of the infants in the period before (Preparatory group; n=20) or after (Contingent group; n=17) the syringe injection. In the Preparatory group, the duration of infant cry vocalizations was related to amount of maternal soothing before and after the injection, while cry vocalizations in the Contingent group was related to amount of maternal soothing after the injection. The Contingent infants responded to the injection with a significant increase in cortisol, while there was no increase in the Preparatory infants. The Preparatory infants evidenced significantly longer duration of looking at the target stimuli in a visual marking task, suggesting greater difficulties in disengaging attention. These findings indicate that 3-month-olds' stress responses and their mothers' situational behaviour are mutually regulated.     

Prelinguistic evolution in early hominins: whence motherese?

In order to formulate hypotheses about the evolutionary underpinnings that preceded the first glimmerings of language, mother-infant gestural and vocal interactions are compared in chimpanzees and humans and used to model those of early hominins. These data, along with paleoanthropological evidence, suggest that prelinguistic vocal substrates for protolanguage that had prosodic features similar to contemporary motherese evolved as the trend for enlarging brains in late australopithecines/early Homo progressively increased the difficulty of parturition, thus causing a selective shift toward females that gave birth to relatively undeveloped neonates. It is hypothesized that hominin mothers adopted new foraging strategies that entailed maternal silencing, reassuring, and controlling of the behaviors of physically removed infants (i.e., that shared human babies' inability to cling to their mothers' bodies). As mothers increasingly used prosodic and gestural markings to encourage juveniles to behave and to follow, the meanings of certain utterances (words) became conventionalized. This hypothesis is based on the premises that hominin mothers that attended vigilantly to infants were strongly selected for, and that such mothers had genetically based potentials for consciously modifying vocalizations and gestures to control infants, both of which receive support from the literature.     

Mother-infant responsiveness: timing, mutual regulation, and interactional context

Mutual regulation during the naturalistic interaction of 150 mothers and their 4-month-old infants was investigated from a dynamic systems perspective. Microanalyses of a wide range of behaviors and analysis of contingencies indicated that a 3-s time period best captured contingencies. Both mothers and infants communicated primarily through vocal signals and responses, although maternal touches and infant looks also elicited responses. Although more expressive mothers did not have infants who behaved similarly, levels of contingent responsiveness between partners were significantly associated and occurred within distinct behavioral channels, suggesting coregulated interactional processes in which contingently responsive mothers shape their infants' communications toward mutual similarity. Mothers were more influential than infants over object play, whereas infants were more influential than mothers over expressive behavior. Interactional context consistently influenced contingent responsiveness; there was less mutual responsiveness when the infant was exploring, being held, or looking.     

The Cross-Modal Coordination of Interpersonal Timing: Six-Week-Olds Infants' Gaze with Adults' Vocal Behavior

The purpose of this study was to examine the hypothesis that 6-week-old infants are capable of coordinated interpersonal timing within social interactions. Coordinated interpersonal timing refers to changes in the timing of one individual's behavior as a function of the timing of another individual's behavior. Each of 45, first-born 6-week-old infants interacted with his or her mother and a stranger for a total of 14 minutes. The interactions were videotaped and coded for the gaze behavior of the infants and the vocal behavior of the mothers and strangers. Time-series regression analyses were used to assess the extent to which the timing of each of the infants' gazes was coordinated with the timing of the adults' vocal behavior. The results revealed that (a) coordinated timing occurs between infants and their mothers and between infants and strangers as early as when infants are 6 weeks old, and (b) strangers coordinated the timing of their pauses with the infants to a greater extent than did mothers. The findings are discussed in terms of the role of temporal sensitivity in social interaction.     

Co‐occurences of preverbal vocal behavior and motor action in early infancy

This study reports on co‐occurrence of vocal behaviors and motor actions in infants in the prelinguistic stage. Four Japanese infants were studied longitudinally from the age of 6 months to 11 months. For all the infants, a 40 min sample was coded for each monthly period. The vocalizations produced by the infants co‐occurred with their rhythmic actions with high frequency, particularly in the period preceding the onset of canonical babbling. Acoustical analysis was conducted on the vocalizations recorded before and after the period when co‐occurrence took place most frequently. Among the vocalizations recorded in the period when co‐occurrence appeared most frequently, those that co‐occurred with rhythmic action had significantly shorter syllable duration and shorter formant‐frequency transition duration compared with those that did not co‐occur with rhythmic action. The rapid transitions and short syllables were similar to patterns of duration found in mature speech. The acoustic features remained even after co‐occurrence disappeared. These findings suggest that co‐occurrence of rhythmic action and vocal behavior may contribute to the infant’s acquisition of the ability to perform the rapid glottal and articulatory movements that are indispensable for spoken language acquisition.     

The beginning of conversation: Early patterns of mother-infant vocal responsiveness

Microanalytic techniques were used to characterize the structure of the prespeech communication of 4-month-old infants and their mothers. Two observers continuously recorded the interactive behavior of mothers and their infants during hour-long observations in the homes of 25 families. Loglinear models were used to examine the extent to which the vocal behavior of one person was conditional upon the vocal behavior of the partner. Within the limits of this microanalytic approach, analyses indicated that patterns of mother-infant vocal exchange were structurally similar to patterns of adult conversation. Initial vocal responses were followed by suppression of vocalization, allowing the partner to join the conversation. The comparative effectiveness of vocal behavior as an elicitor of vocalization and as a response to vocalization was shown for mothers and infants relative to the other behaviors observed. Vocalization served as a modulator of visual attentiveness: When the partner was not visually attentive, vocalization elicited visual attention.     

Alteration of adults' subjective feeling of familiarity toward infants' sounds

Many adults may have lower subjective feelings of familiarity toward infants' vocalizations since infants' sounds are different from those of adults. However, mothers frequently exposed to infants' vocalizations may be more familiar and less averse. To test this hypothesis, 21 mothers (M age = 31.1 yr., SD = 4.3) of infants (M age = 8.2 mo., SD = 3.5), 18 mothers (M age = 34.4 yr., SD = 4.8) of children between two and five years of age (M age = 2.8 yr., SD = 1.0), and 17 women (M age = 29.2 yr., SD = ll.1) with no children were exposed to 20 types of sounds. Of these sounds, 14 were produced by infants. Although the mothers of infants did not recognize sounds as those of an infant's vocalization, they showed higher subjective feelings of familiarity toward the timbres of the vowel-like stimuli than did the other groups. By contrast, the subjective feelings of familiarity for nonspeech sounds did not differ among groups. Maternal experiences may change women's recognition of perceived sounds.     

Eye contact and vocal responsiveness in squirrel monkey infants and their caregivers

Seventeen newborn squirrel monkeys, housed socially with their mothers and other adult females, were observed during their first 10 days of life. As early as day 1, infants began responding, vocally as well as by eye contact, to vocalizations and gaze directed to them by mothers and allomothers (aunts). Visual contact appeared always to be initiated by the adults. Infants spent less than 4% of awake time in eye contact with adults, but most infant-directed vocalizing occurred during these episodes, when both mothers and allomothers greatly increased their rate of calling. Infants were more likely to respond to vocalizations directed to them while in eye contact; 72% of infants' responsive vocalizing occurred then. These data are compared to those for human mothers and infants, where eye contact has also been shown to stimulate vocal exchange. A functional explanation of the involvement of allomothers, based on the infant's clinging position, is discussed.     

Reinforcement of vocalizations through contingent vocal imitation

Maternal vocal imitation of infant vocalizations is highly prevalent during face-to-face interactions of infants and their caregivers. Although maternal vocal imitation has been associated with later verbal development, its potentially reinforcing effect on infant vocalizations has not been explored experimentally. This study examined the reinforcing effect of maternal vocal imitation of infant vocalizations using a reversal probe BAB design. Eleven 3- to 8-month-old infants at high risk for developmental delays experienced contingent maternal vocal imitation during reinforcement conditions. Differential reinforcement of other behavior served as the control condition. The behavior of 10 infants showed evidence of a reinforcement effect. Results indicated that vocal imitations can serve to reinforce early infant vocalizations.     

Imitation and repetition of prosodic contour in vocal interaction at 3 months

This study investigates vocal imitation of prosodic contour in ongoing spontaneous interaction with 10- to 13-week-old infants. Audio recordings from naturalistic interactions between 20 mothers and infants were analyzed using a vocalization coding system that extracted the pitch and duration of individual vocalizations. Using these data, the authors categorized a sample of 1,359 vocalizations on the basis of 7 predetermined contours. Pairs of identical successive vocalizations were considered to be imitations if they involved both partners or repetitions if they were produced by the same partner. Results show that not only do mothers and infants imitate and repeat prosodic contour types in the course of vocal interaction but they do so selectively. Indeed, different contours are imitated and repeated by each partner. These findings suggest that imitation and repetition of prosodic contours have specific functions for communication and vocal development in the 3rd month of life.