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.

The ecology of prelinguistic vocal learning: parents simplify the structure of their speech in response to babbling.

What is the function of babbling in language learning? We examined the structure of parental speech as a function of contingency on infants' non-cry prelinguistic vocalizations. We analyzed several acoustic and linguistic measures of caregivers' speech. Contingent speech was less lexically diverse and shorter in utterance length than non-contingent speech. We also found that the lexical diversity of contingent parental speech only predicted infant vocal maturity. These findings illustrate a new form of influence infants have over their ambient language in everyday learning environments. By vocalizing, infants catalyze the production of simplified, more easily learnable language from caregivers.

Comparing statistical learning across perceptual modalities in infancy: An investigation of underlying learning mechanism(s).

Statistical learning (SL), sensitivity to probabilistic regularities in sensory input, has been widely implicated in cognitive and perceptual development. Little is known, however, about the underlying mechanisms of SL and whether they undergo developmental change. One way to approach these questions is to compare SL across perceptual modalities. While a decade of research has compared auditory and visual SL in adults, we present the first direct comparison of visual and auditory SL in infants (8-10 months). Learning was evidenced in both perceptual modalities but with opposite directions of preference: Infants in the auditory condition displayed a novelty preference, while infants in the visual condition showed a familiarity preference. Interpreting these results within the Hunter and Ames model (1988), where familiarity preferences reflect a weaker stage of encoding than novelty preferences, we conclude that there is weaker learning in the visual modality than the auditory modality for this age. In addition, we found evidence of different developmental trajectories across modalities: Auditory SL increased while visual SL did not change for this age range. The results suggest that SL is not an abstract, amodal ability; for the types of stimuli and statistics tested, we find that auditory SL precedes the development of visual SL and is consistent with recent work comparing SL across modalities in older children.

The role of multisensory development in early language learning.

In typical development, communicative skills such as language emerge from infants' ability to combine multisensory information into cohesive percepts. For example, the act of associating the visual or tactile experience of an object with its spoken name is commonly used as a measure of early word learning, and social attention and speech perception frequently involve integrating both visual and auditory attributes. Early perspectives once regarded perceptual integration as one of infants' primary challenges, whereas recent work suggests that caregivers' social responses contain structured patterns that may facilitate infants' perception of multisensory social cues. In the current review, we discuss the regularities within caregiver feedback that may allow infants to more easily discriminate and learn from social signals. We focus on the statistical regularities that emerge in the moment-by-moment behaviors observed in studies of naturalistic caregiver-infant play. We propose that the spatial form and contingencies of caregivers' responses to infants' looks and prelinguistic vocalizations facilitate communicative and cognitive development. We also explore how individual differences in infants' sensory and motor abilities may reciprocally influence caregivers' response patterns, in turn regulating and constraining the types of social learning opportunities that infants experience across early development. We end by discussing implications for neurodevelopmental conditions affecting both multisensory integration and communication (i.e., autism) and suggest avenues for further research and intervention.

The Role of Dyadic Coordination in Organizing Visual Attention in 5-Month-Old Infants.

In human infants, the ability to share attention with others is facilitated by increases in attentional selectivity and focus. Differences in early attention have been associated with socio-cognitive outcomes including language, yet the social mechanisms of attention organization in early infancy have only recently been considered. Here, we examined how social coordination between 5-month-old infants and caregivers relate to differences in infant attention, including looking preferences, span, and reactivity to caregivers' social cues. Using a naturalistic play paradigm, we found that 5-month-olds who received a high ratio of sensitive (jointly focused) contingent responses showed strong preferences for objects with which their caregivers were manually engaged. In contrast, infants whose caregivers exhibited high ratios of redirection (attempts to shift focus) showed no preferences for caregivers' held objects. Such differences have implications for recent models of cognitive development, which rely on early looking preferences for adults' manually engaged objects as a pathway toward joint attention and word learning. Further, sensitivity and redirectiveness predicted infant attention even in reaction to caregiver responses that were non-referential (neither sensitive nor redirective). In response to non-referentials, infants of highly sensitive caregivers oriented less frequently than infants of highly redirective caregivers, who showed increased distractibility. Our results suggest that specific dyadic exchanges predict infant attention differences toward broader social cues, which may have consequences for social-cognitive outcomes.

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.

General cognitive principles for learning structure in time and space.

How are hierarchically structured sequences of objects, events or actions learned from experience and represented in the brain? When several streams of regularities present themselves, which will be learned and which ignored? Can statistical regularities take effect on their own, or are additional factors such as behavioral outcomes expected to influence statistical learning? Answers to these questions are starting to emerge through a convergence of findings from naturalistic observations, behavioral experiments, neurobiological studies, and computational analyses and simulations. We propose that a small set of principles are at work in every situation that involves learning of structure from patterns of experience and outline a general framework that accounts for such learning.

The value of vocalizing: five-month-old infants associate their own noncry vocalizations with responses from caregivers.

The early noncry vocalizations of infants are salient social signals. Caregivers spontaneously respond to 30%-50% of these sounds, and their responsiveness to infants' prelinguistic noncry vocalizations facilitates the development of phonology and speech. Have infants learned that their vocalizations influence the behavior of social partners? If they have, infants should show an extinction burst in vocalizing when adults temporarily stop responding to infant vocalizations. Thirty-eight 5-month-olds were tested in the still-face paradigm with an unfamiliar adult. When the adult assumed a still face, infants showed an extinction burst. Thus, 5-month-olds have learned the social efficacy of their vocalizations on caregivers' behavior. Furthermore, the magnitude of 5-month infants' extinction bursts predicted their language comprehension at 13 months.

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.