Morphological deficits of children with SLI: evaluation of number marking and agreement.

Three accounts of the grammatical deficits of children with specific language impairment (SLI), that is, Missing Feature, Surface Account, and Missing Agreement, were evaluated by examining children with SLI and language-matched non-SLI children's acquisition of number marking and number agreement. The data consisted of spontaneous language transcripts from 108 preschool children. Number marking was evaluated using five indices of plural development: percent of use in obligatory contexts, lexical productivity, selectivity, contrastivity, and morphological productivity. Two levels of number agreement were examined: the traditional agreement between the verb and its subject, and a new measure of agreement within the noun phrase. The results indicated that children with SLI control number marking, counter to the predictions of the Missing Feature hypothesis and the Surface Account. On the other hand, as predicted, number agreement across clausal boundaries was more difficult for the children with SLI as compared to the children in the control group. A close analysis of number marking within the noun phrase revealed two distinctive contexts, determiner+noun versus quantifier+noun. Children with SLI had more difficulty with the latter than the former, whereas the two contexts were not differentiated for the control children. Syntactic and semantic explanations are discussed as interpretive options.