Social regulatory effects of infant nondistress vocalization on maternal behavior.

This study investigated the social regulatory function of infant nondistress vocalization in modulating maternal response. Thirteen infants and their mothers were observed weekly in a face-to-face interaction situation from 4 to 24 weeks. After the occurrences and the speech quality of infant nondistress vocalization were identified, maternal contingent responses to these vocalizations were also coded. Each responsive action was further classified by the change processes involved. Results showed that it was the occurrence of infant nondistress vocalization rather than its speech quality that regulated maternal verbal response concurrently and that infant nondistress vocalization was more likely to be synchronized with maternal facial expression and touch than with head movements. Developmentally, significant individual differences were found in the linear growth patterns of overall maternal response and within the individual modalities when responding to speechlike vocalizations.