Productivity with word order and morphology: a comparative look at children with SLI and children with normal language abilities.

The study investigated the development of grammatical categories (verb and noun) in young language learners. Specifically, children's ability to mark correctly the semantic roles of agent and patient was investigated. Second, children's productive use of the present tense progressive -ing, past tense -ed, third person singular -s and plural -s inflection was investigated. Twenty-eight children with specific language impairment (SLI) with a mean language age of 35 months and 28 children with normal language (NL) with a mean language age of 34 months were exposed to four novel verbs and four novel nouns during ten experimental child-directed play sessions. The lexical items were modelled with four experimentally controlled argument structures. Furthermore, both groups of children were administered structured tests of grammatical morphology (involving both verbs and nouns). First, children in both groups did not correctly mark semantic roles for agent and patient, unless specific semantic roles had already been modelled in the linguistic input by the experimenter. Second, children's productive use of grammatical morphology in their spontaneous utterances was better for nouns than verbs. Importantly, however, children with NL were significantly better at marking verbs for past tense than in children with SLI, although both groups performed poorly overall. These findings are discussed in relation to current theories of normal and impaired language development, in particular the usefulness of tense marking as a clinical marker of preschool children with SLI.