The more they hear the more they learn? Using data from bilinguals to test models of early lexical development

Children have an early ability to learn and comprehend words, a skill that develops as they age. A critical question remains regarding what drives this development. Maturation-based theories emphasise cognitive maturity as a driver of comprehension, while accumulator theories emphasise children's accumulation of language experience over time. In this study we used archival looking-while-listening data from 155 children aged 14-48 months with a range of exposure to the target languages (from 10% to 100%) to evaluate the relative contributions of maturation and experience. We compared four statistical models of noun learning: maturation-only, experience-only, additive (maturation plus experience), and accumulator (maturation times experience). The best-fitting model was the additive model in which both maturation (age) and experience were independent contributors to noun comprehension: older children as well as children who had more experience with the target language were more accurate and looked faster to the target in the looking-while-listening task. A 25% change in relative language exposure was equivalent to a 4 month change in age, and age effects were stronger at younger than at older ages. Whereas accumulator models predict that the lexical development of children with less exposure to a language (as is typical in bilinguals) should fall further and further behind children with more exposure to a language (such as monolinguals), our results indicate that bilinguals are buffered against effects of reduced exposure in each language. This study shows that continuous-level measures from individual children's looking-while-listening data, gathered from children with a range of language experience, provide a powerful window into lexical development.