The development of morphosyntactic ability in atypical populations: The acquisition of tag questions in children with early focal lesions and children with specific-language impairment.

We examined the development of some features of morphosyntactic ability, specifically the acquisition of auxiliaries and use of agreement marking, along with sentence processing capacity. We used a conceptually simple task called the Tags Question Task, which is a method for evaluating a number of language processes in the production of a commonly used, familiar linguistic device. We compared the performance of children with early focal lesions (N=21), children with specific-language impairment (N=24), and typically developing children (N=24) matched in age and nonverbal ability; additional analyses involved comparisons of children matched on performance level. The data converge to support a "delayed" development of language behavior in our clinical groups, as overall patterns of performance and age-related changes on individual tag features and tag questions were strikingly similar in all three groups across a number of methods of comparison. Implications for theories of the development of brain-language relationships as they pertain to early focal brain damage, specific-language impairment, and the language acquisition process in typically developing children are discussed.