UC San Diego

Vocabulary knowledge and speed of lexical access are early components of linguistic skill that co-develop rapidly in the first two years of life. Evidence suggests that these components are foundational for downstream linguistic and cognitive skills and that early individual differences set the stage for a developmental cascade throughout the lifespan. The three studies in this dissertation seek to clarify how early, decontextualized vocabulary predicts later development, whether it has utility in individual prediction, and how vocabulary and speed of lexical access support language development together and separately.

Chapter 1 reviews the current literature on vocabulary development and speed of lexical access, exploring how these skills are interrelated and their relation to other domain-general learning mechanisms, closing with extant evidence on predictive utility. Chapter 2 follows from recent findings that early vocabulary predicts later literacy but that it accounts for a modest amount of variance in outcomes. Chapter 2 uses an assessment of decontextualized vocabulary and shows that early, decontextualized vocabulary predicts later vocabulary and kindergarten readiness at age four, explaining additional variance above and beyond a parent report assessment of early vocabulary. In a similar vein, results from Chapter 3 reveal decontextualized vocabulary to be a robust predictor of language abilities at age three and present preliminary evidence for its utility as a screening measure. Finally, Chapter 4 presents preliminary evidence for the hypothesis that although vocabulary knowledge and lexical access are related, they are somewhat distinct in the extent to which they depend on long-term learning vs. processing efficiency. Results tentatively support this conclusion by revealing dissociation in prediction between these two components of early language. All three chapters examine these effects across groups differing linguistically and geographically and explore whether patterns across samples suggest generalization of effects across languages or reveal linguistic differences. Practically, the goal of this research is to elucidate the processes of early language development, improve identification of children at risk for language delay and inform intervention strategies