Motherese, affect, and vocabulary development: dyadic communicative interactions in infants and toddlers.

Responsive parental communication during an infant's first year has been positively associated with later language outcomes. This study explores responsivity in mother-infant communication by modeling how change in guiding language between 7 and 11 months influences toddler vocabulary development. In a group of 32 mother-child dyads, change in early maternal guiding language positively predicted child language outcomes measured at 18 and 24 months. In contrast, a number of other linguistic variables - including total utterances and non-guiding language - did not correlate with toddler vocabulary development, suggesting a critical role of responsive change in infant-directed communication. We further assessed whether maternal affect during early communication influenced toddler vocabulary outcomes, finding that dominant affect during early mother-infant communications correlated to lower child language outcomes. These findings provide evidence that responsive parenting should not only be assessed longitudinally, but unique contributions of language and affect should also be concurrently considered in future study.