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.     

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.     

Does category-training facilitate 11-month-olds’ acquisition of unfamiliar category-property associations?

The ability to form category-property links allows infants to extend a property from one category member to another. In two experiments, we examined whether orienting infants to the demands of the task, through categorization training, would facilitate 11-month-old infants’ category-property extensions when familiarized with a single exemplar of an unfamiliar animal category. In Experiment 1, 11-month-olds (N = 35) were trained with two familiar animal-sound pairings (i.e., dog-bark, cat-meow), familiarized with two unfamiliar animal-sound pairings and then tested on their learning and generalization of the unfamiliar animal-sound associations. Across two conditions, Experiment 2 familiarized 11-month-olds (N = 69) to one familiar (i.e., dog-bark) and one novel animal-sound pairing. Conditions differed in their presentation of familiarization trials (i.e., random or blocked). Infants were then tested on their learning and extension of the animal-sound associations. In both experiments, infants did not demonstrate learning of the original animal sound pairing, nor generalization of the sound property to new members of the animal categories. These results indicate that the two category training paradigms implemented in the current studies did not facilitate 11-month-olds’ ability to learn or generalize an unfamiliar animal-sound association, when familiarized with a single exemplar.     

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.     

Acquisition of social referencing via discrimination training in infants

This experiment investigated social referencing as a form of discriminative learning in which maternal facial expressions signaled the consequences of the infant's behavior in an ambiguous context. Eleven 4- and 5-month-old infants and their mothers participated in a discrimination-training procedure using an ABAB design. Different consequences followed infants' reaching toward an unfamiliar object depending on the particular maternal facial expression. During the training phases, a joyful facial expression signaled positive reinforcement for the infant reaching for an ambiguous object, whereas a fearful expression signaled aversive stimulation for the same response. Baseline and extinction conditions were implemented as controls. Mothers' expressions acquired control over infants' approach behavior for all participants. All participants ceased to show discriminated responding during the extinction phase. The results suggest that 4- and 5-month-old infants can learn social referencing via discrimination training.     

The still-face response in newborn, 1.5-, and 3-month-old infants

The present study investigated the still-face response to a female stranger in newborn, 1.5-, and 3-month-old infants. The results revealed that 1.5- and 3-month-olds, but not newborns, reliably decreased their visual attention and positive affect when the interaction partner became unresponsive during the still-face period.     

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.     

Sharing attention and pointing to objects at 12 months: is the intentional stance implied?

The goal of the present research was to assess whether communicative gestures, such as gazing and declarative pointing of 12-month-old infants indicate that infants perceive people as intentional agents, or whether infant communicative behaviors are merely triggered by specific perceptual cues in joint visual attention situations. Two experiments were conducted. In Experiment 1, thirty-two 12-month-olds were conditioned to follow the gaze of a contingently interacting person or object. They were then submitted to a paradigm designed to incite them to initiate communicative gestures to the person or object. The temporal coordination between pointing, gazing, and vocalizations occurred at a significantly higher rate in the Person than in the Object condition. In Experiment 2, the effect of the attentional focus of others on the gaze, points and vocalizations of thirty 12-month-olds was investigated. Infants were assessed in conditions where the experimenter vocalized while looking at the same (In-focus), or a different (Out-of-focus) toy than the infants. Infants who pointed produced more co-occurrences of gaze, vocalizations and points in the Out-of-focus condition than in the In-focus condition. Thus, by 12 months, infants are aware of the attentional state of the person. Discussion centers on the implications of these findings for theories of social and cognitive knowing.     

The effect of positive emotion on infants' gaze shift

Infants often voluntarily glance at their social partner during their toy play, disengaging their gaze from a toy and selecting a caregiver as their new looking target. This study posed two research questions: Do positive emotions disengage infants' gaze from their point of fixation, and do positive emotions facilitate the selection of the caregiver as their next looking target? The rate of gaze shifts was calculated for neutral and positive emotional states during their toy play. Across all ages, infants exhibited more disengagement from their point of fixation in the positive state than in the neutral one. However, 6- and 9-month-old infants revealed no difference in selecting a caregiver or a physical object as their next looking target in the positive state, but 12-month-olds increased gazing at caregivers in the positive state. These results were discussed with regard to the role of positive emotions on the development of infants' initiating joint attention.     

Vocal imitation between mothers and infants

The aim of the present mixed cross-sectional and longitudinal study was to observe and describe some aspects of vocal imitation in natural mother-infant interaction. Specifically, maternal imitation of infant utterances was observed in relation to the imitative modeling, mirrored equivalence, and social guided learning models of infant speech development. Nine mother-infant dyads were audio-video recorded. Infants were recruited at different ages between 6 and 11 months and followed for 3 months, providing a quasi-longitudinal series of data from 6 through 14 months of age. It was observed that maternal imitation was more frequent than infant imitation even though vocal imitation was a rare maternal response. Importantly, mothers used a range of contingent and noncontingent vocal responses in interaction with their infants. Mothers responded to three-quarters of their infant's vocalizations, including speech-like and less mature vocalization types. The infants’ phonetic repertoire expanded with age. Overall, the findings are most consistent with the social guided learning approach. Infants rarely imitated their mothers, suggests a creative self-motivated learning mechanism that requires further investigation.     

Facial experience during the first year

Parents of 2-, 5-, 8-, and 11-month-olds used two scales we developed to provide information about their infants' facial experience with familiar and unfamiliar individuals during one week. Results showed large discrepancies in the race, sex, and age of faces that infants experience during their first year with the majority of their facial experience being with their primary caregiver, females, and other individuals of the same-race and age as their primary caregiver. The infant's age and an unfamiliar individual's sex were predictive of their time spent interacting with one another. Moreover, an unfamiliar individual's sex was predictive of the attention infants allocated during social interactions. Differences in frequency and length of interactions with certain types of faces, as well as in infant attention toward certain individuals, all likely contribute to the development of expertise in processing commonly experienced face types and deficiencies in processing less commonly experienced face types.     

Individual differences in non-clinical maternal depression impact infant affect and behavior during the still-face paradigm across the first year

Maternal depression can significantly impact mothers’ sensitivity to their infants’ needs as well as infants’ social and emotional development. The still-face paradigm (SFP) is widely used to assess infants’ understanding of the contingency between their own behavior and that of their caregivers, as well as infants’ ability to self-regulate arousal levels during sudden changes in maternal responsiveness. Infants of clinically depressed mothers display blunted levels of negative affect compared to infants of non-depressed mothers during the still-face (SF) phase. However, little is known about whether individual differences in elevated, non-clinical levels of maternal depression similarly affect mother-infant interactions. The current study examines the longitudinal effects of non-clinical maternal depression on infant and maternal behaviors during the SFP. Infants (N = 63) were assessed at 5 and 9 months and maternal depression was assessed at 5 months using the Beck Depression Inventory (BDI). Infants of mothers with elevated levels of depression displayed less negative engagement during the SF phase compared to infants of mothers with lower levels of depression. This effect was present at 5 months, but not at 9 months. Findings demonstrate that non-clinical levels of maternal depressive symptomatology can have a significant impact on infants’ affective regulation during the first half of the first year of life, but this does not necessarily have a long-lasting influence later in infancy. Interventions may want to target mothers with non-clinical depression to promote healthy infant social and emotional development.     

Fourteen-month-olds’ imitation is influenced more strongly by a model’s competence than by a model’s certainty

Research has shown that infants are more likely to learn from certain and competent models than from uncertain and incompetent models. However, it is unknown which of these cues to a model’s reliability infants consider more important. In Experiment 1, we investigated whether 14-month-old infants (n = 35) imitate and adopt tool choices selectively from an uncertain but competent compared to a certain but incompetent model. Infants watched videos in which an adult expressed either uncertainty but acted competently or expressed certainty but acted incompetently with familiar objects. In tool-choice tasks, the adult then chose one of two objects to operate an apparatus, and in imitation tasks, the adult then demonstrated a novel action. Infants did not adopt the model’s choice in the tool-choice tasks but they imitated the uncertain but competent model more often than the certain but incompetent model in the imitation tasks. In Experiment 2, 14-month-olds (n = 33) watched videos in which an adult expressed only either certainty or uncertainty in order to test whether infants at this age are sensitive to a model’s certainty. Infants imitated and adopted the tool choice from a certain model more than from an uncertain model. These results suggest that 14-month-olds acknowledge both a model’s competence and certainty when learning novel actions. However, they rely more on a model’s competence than on his certainty when both cues are in conflict. The ability to detect reliable models when learning how to handle cultural artifacts helps infants to become well-integrated members of their culture.     

Infants' vagal regulation in the still-face paradigm is related to dyadic coordination of mother-infant interaction

The authors investigated relations between mother-infant dyadic coordination and infants' physiological responses. Mothers (N=73) and 3-month-old male and female infants were observed in the still-face paradigm, and mothers' and infants' affective states were coded at 1-s intervals. Synchrony and levels of matching between mother-infant affective states were computed, and infants' heart rate and vagal tone were measured. Infants showed increased negative affect and heart rate and decreased vagal tone during mothers' still-face, indicating physiological regulation of distress. Infants who did not suppress vagal tone during the still-face (nonsuppressors) showed less positive affect, higher reactivity and vagal suppression in normal play and reunion episodes, and lower synchrony in normal play with mothers. The results indicate that infants' physiological regulation in social interaction differs in relation to dyadic coordination of affective behaviors.     

Intentions make a difference: infant responses to still-face and modified still-face conditions

In two studies, 3-, 6- and 9-month-old infants interacted with their mothers during natural, still-face, and modified still-face (i.e., mothers wearing a mask, or drinking from bottle) conditions. Infants were also presented with matching doll conditions to control for the possibility that their responses might be due to changes in superficial perceptual features. Regardless of age, infants displayed negative affect to the still-face, but, in contrast to recent reports, not to the modified still-face conditions. However, whereas infants' positive affect also depended on their mothers' communicative intentions, these responses changed with cognitive maturation. As expected, infant responses to their mothers were significantly different from those to the doll. The implications of these findings for theories of communication are discussed.     

Consistent responses of human mothers to prelinguistic infants: the effect of prelinguistic repertoire size

The salience of infants' vocal and visual cues was examined to evaluate the efficacy of prelinguistic vocalizations to guide adult behavior. A videotape, constructed of brief behavioral episodes from 3 infants with different-sized vocal repertoires, was played to 40 mothers of prelinguistic infants. Playback mothers' responses to the episodes were consistent, demonstrating that preverbal behavior elicits comparable reactions across unfamiliar receivers. The audio and video components of the infants' episodes were then recombined. As the vocal repertoire of the stimulus infants increased, changes in the audio component more often led playback mothers to change responses. Thus, playback mothers used vocalizations as cues as the infants' vocal repertoires became larger.     

Infant behavioural effects of smartphone interrupted parent-infant interaction

Infants are vulnerable to changes in the dyadic synchrony with their caregivers, as demonstrated in numerous experiments employing the still-face paradigm. The sudden lack of attunement causes infant stress reactions and the still-face literature have suggested potential long-term costs of this in terms of development of social, emotional and cognitive skills. Acknowledging the rapid technological development accompanied by altered practices in the parent-infant interaction, the current study investigates infant behavioural reactions in a similar experimental paradigm, manipulating parental responsiveness and sensitivity in a slightly different manner. In the current study, the parent interrupts the ongoing interaction, simulating occupation with a smartphone, rather than making a ‘still-face’. In a cross-sectional design, infants of six, nine and twelve months display increased levels of protest behaviour in response to the interrupted interaction with their parent, together with lowered levels of positive engagement and social monitoring, suggesting similar behavioural responses as the still-face effect. Implications for infant social and emotional development, as well as for mindful tech habits are 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.     

Social elicitation of infant vocal behavior.

The time course and the nature of social elicitation of vocalizations in 3-month-old infants were analyzed. Adult stimulation produced an immediate and significant increase in both the rate and the percent of bursts of vocal sounds of eight infants (Experiment 1). Both response-independent and response-dependent social stimulation were effective in producing increased rates of vocalizations, but only when each of four infants could see the eyes of the adult who delivered the social stimulus (Experiment 2).     

Infants’ vocalizations at 6 months predict their productive vocabulary at one year

Long before their first words, children communicate by using speech-like vocalizations. These protophones might be indicative of infants’ later language development. We here examined infants’ (n = 56) early vocalizations at 6 months (vocal reactivity scale of the IBQ-R) as a predictor of their expressive and receptive language at 12 months (German version of the CDI). Regression analyses revealed vocalizations to significantly predict expressive, but not receptive language. Our findings in German-learning 6-month-olds extend previous predictive evidence of early vocalizations reported for older infants. Together these findings are informative in light of early assessments monitoring typical and atypical language development.