Individual differences in vocabulary acquisition in children with Down syndrome.

Children with Down syndrome offer an opportunity for investigators interested in cognition and language problems to study asynchronous development of vocabulary, and syntax in language production relative to comprehension and cognitive status. Our work to date has documented consistent differences in the rate of vocabulary learning in children with DS relative to their mental age matched peers. These deficits increase with advancing age indicating that the learning rate of the DS group is significantly slower than that of the TD group. While the rate of vocabulary acquisition is significantly slower for the children with DS, not all of the children we studied exhibited similar rates of learning. Thirty-five percent of our children had rates of vocabulary growth consistent with mental age expectations. These data suggest that neither the syndrome alone nor the cognitive deficit associated with Down syndrome can explain the differences observed in vocabulary growth. Our next series of studies will evaluate a variety of causal constructs to explain the significant asynchronies in language learning compared with other cognitive abilities.