Quality of early parent input predicts child vocabulary 3 years later

TLDR

Children’s vocabulary at school varies widely, partly due to differences in parental speech quantity, but also because the clarity of word meaning in the surrounding context—referential transparency—differs among parents. The study aimed to assess how the clarity of word meaning in parents’ speech—reflected in the ease of identifying words from visual context—affects child vocabulary. To do so, 218 adults were asked to identify 50 parent‑spoken words from muted videos of parent‑child interactions with 14‑ to 18‑month‑old children. The study found that parents whose words were easier to identify from visual context provided higher‑quality input, and this quality predicted children’s vocabulary three years later even after accounting for input quantity, while input quantity varied with socioeconomic status but input quality did not.

Abstract

Children vary greatly in the number of words they know when they enter school, a major factor influencing subsequent school and workplace success. This variability is partially explained by the differential quantity of parental speech to preschoolers. However, the contexts in which young learners hear new words are also likely to vary in referential transparency; that is, in how clearly word meaning can be inferred from the immediate extralinguistic context, an aspect of input quality. To examine this aspect, we asked 218 adult participants to guess 50 parents’ words from (muted) videos of their interactions with their 14- to 18-mo-old children. We found systematic differences in how easily individual parents’ words could be identified purely from this socio-visual context. Differences in this kind of input quality correlated with the size of the children’s vocabulary 3 y later, even after controlling for differences in input quantity. Although input quantity differed as a function of socioeconomic status, input quality (as here measured) did not, suggesting that the quality of nonverbal cues to word meaning that parents offer to their children is an individual matter, widely distributed across the population of parents.