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.

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.

What is the function of immature vocalizing in early learning environments? Previous work on infants in the US indicates that prelinguistic vocalizations elicit caregiver speech which is simplified in its linguistic structure. However, there is substantial cross-cultural variation in the extent to which children's vocalizations elicit responses from caregivers. In the current study we ask whether children's vocalizations elicit similar changes in their immediate caregivers' speech structure across two cultural sites with differing perspectives on how to interact with infants and young children. Here we compare Tseltal Mayan and US caregivers' verbal responses to their children's vocalizations. Similar to findings from US dyads, we found that children from the Tseltal community regulate the statistical structure of caregivers' speech simply by vocalizing. Following the interaction burst hypothesis, where clusters of child-adult contingent response alternations facilitate learning from limited input, we reveal a stable source of information facilitating language learning within ongoing interaction.

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