Individual Differences in First Language Acquisition

Humans vary in almost every dimension imaginable, and language is no exception. In this article, we review the past research that has focused on individual differences (IDs) in first language acquisition. We first consider how different theoretical traditions in language acquisition treat IDs, and we argue that a focus on IDs is important given its potential to reveal the developmental dynamics and architectural constraints of the linguistic system. We then review IDs research that has examined variation in children's linguistic input, early speech perception, and vocabulary and grammatical development. In each case, we observe systematic and meaningful variation, such that variation in one domain (e.g., early auditory and speech processing) has meaningful developmental consequences for development in higher-order domains (e.g., vocabulary). The research suggests a high degree of integration across the linguistic system, in which development across multiple linguistic domains is tightly coupled.