Caregiver-infant interactions and child vocabulary: A large-scale, longitudinal study of dyadic and multimodal behaviours

The goal of this dissertation is to predict variation in Dutch children’s vocabulary size using data from the large-scale, longitudinal YOUth cohort study. We take a dyadic approach to study the effects of verbal and multimodal behaviours during caregiver-infant interactions on children’s vocabulary size. This dissertation consists of four empirical articles. Three key findings emerged: First, while there is a large interest in the annotation of infant-directed speech, the accuracy of automatic speech recognition tools has remained largely unexplored. We show researchers can use automated tools to facilitate the labour-intensive manual annotation process. Second, we show that key demographic factors explaining variation in children’s vocabulary, such as maternal education, are age-specific and task-specific. This highlights the importance of including multiple vocabulary outcomes across children’s development. Third, while there is robust evidence that infants’ gestures and vocalisations on the one hand, and caregivers’ contingent responses on the other hand, influence children’s vocabulary outcomes, we show that dyadic and multimodal combinations of these behaviours are better predictors. Infants’ pointing gestures relate to children’s later receptive vocabulary, while infants’ showing and giving gestures relate to children’s later productive vocabulary – but only when they elicited multimodal responses from caregivers during free play. In research on children’s vocabulary development, we aim to describe how infants gather sufficient information from the language input that allows them to learn words. Studying the dyadic and multimodal nature of early caregiver-infant interactions creates a more complete picture of children’s learning environments which brings us closer to solving this puzzle.