The real-time effects of parent speech on infants' multimodal attention and dyadic coordination.

Parental responsiveness to infant behaviors is a strong predictor of infants' language and cognitive outcomes. The mechanisms underlying this effect, however, are relatively unknown. We examined the effects of parent speech on infants' visual attention, manual actions, hand-eye coordination, and dyadic joint attention during parent-infant free play. We report on two studies that used head-mounted eye trackers in increasingly naturalistic laboratory environments. In Study 1, 12-to-24-month-old infants and their parents played on the floor of a seminaturalistic environment with 24 toys. In Study 2, a different sample of dyads played in a home-like laboratory with 10 toys and no restrictions on their movement. In both studies, we present evidence that responsive parent speech extends the duration of infants' multimodal attention. This social "boost" of parent speech impacts multiple behaviors that have been linked to later outcomes-visual attention, manual actions, hand-eye coordination, and joint attention. Further, the amount that parents talked during the interaction was negatively related to the effects of parent speech on infant attention. Together, these results provide evidence of a trade-off between quantity of speech and its effects, suggesting multiple pathways through which parents impact infants' multimodal attention to shape the moment-by-moment dynamics of an interaction.