Ordinary Interactions Challenge Proposals That Maternal Verbal Responses Shape Infant Vocal Development.

Abstract

This study tested proposals that maternal verbal responses shape infant vocal development, proposals based in part on evidence that infants modified their vocalizations to match mothers' experimentally manipulated vowel or consonant-vowel responses to most (i.e., 70%-80%) infant vocalizations. We tested the proposal in ordinary rather than experimentally manipulated interactions. Response-based proposals were tested in a cross-sectional study of 35 infants, ages 4 to 14 months, engaged in everyday interactions in their homes with their mothers using a standard set of toys and picture books. Mothers responded to 30% of infant vocalizations with vocal behaviors of their own, far fewer than experimentally manipulated response rates. Moreover, mothers produced comparatively few vowel and consonant-vowel models and responded to infants' vowel and consonant-vowel vocalizations in similar numbers. Infants showed little evidence of systematically modifying their vocal forms to match maternal responses in these interactions. Instead, consonant-vowel vocalizations increased significantly with infant age. Results obtained in ordinary interactions, rather than response manipulation, did not provide substantial support for response-based mechanisms of infant vocal development. Consistent with other research, however, consonant-vowel productions increased with infant age.