First words in the second year: Continuity, stability, and models of concurrent and predictive correspondence in vocabulary and verbal responsiveness across age and context

This prospective longitudinal study assessed children's and mothers' productive vocabulary and mothers' verbal responses to children's exploratory and vocal behavior in spontaneous speech, and evaluated multiple relations in those measures in two contexts (play and mealtimes) at two child ages (13 and 20 months). Continuity, stability, and several models of concurrent and lagged child-mother correspondences were evaluated. Child and mother vocabulary increased across the second year, but did so differently in the two contexts; vocabulary of both showed significant stability of individual variation across context and age. Developmental change in maternal verbal responses predicted child vocabulary (maternal vocabulary did not), and developmental change in child vocabulary predicted maternal responses. The results support a model of specificity in mother-child language exchange and child vocabulary growth.