Infant non-distress vocalization during mother-infant face-to-face interaction: Factors associated with quantitative and qualitative differences

This study investigated the associations of the quantity and quality of infant nondistress vocalization with maternal and infant social actions (smiling and gazing) during dyadic interaction. Thirteen infants and their mothers were observed weekly in a face-to-face interaction situation from 4 to 24 weeks. Results showed that the quantity (rate per minute) and quality (speech-likeness) of infant nondistress vocalization changed systematically with maternal smiling and gazing as well as with the infants' own smiling and gazing. Infants produced more speech-like syllabic sounds when their mothers were smiling, when they were looking at their mothers' faces, and when the infants themselves were smiling. Follow-up analysis revealed that the amount of infant speech-like syllabic sound was highest during Duchenne smiling (cheek-raise smiling), which is thought to be more emotionally positive than non-Duchenne smiling (smiling without cheek-raise). Sequential analysis further indicated that infants were more likely to produce speech-like syllabic sounds, following the onset of their smiling and gazing at mother and their mothers' smiling as compared to nonspeech-like vocalic sounds. These coordinative associations found within the child and between the dyad suggest that the speech quality of nondistress vocalization may be an index of positivity in dyadic face-to-face interactions during early infancy.