Lexical word formation in children with grammatical SLI: a grammar-specific versus an input-processing deficit?

An ongoing controversy is whether an input-processing deficit or a grammar-specific deficit causes specific language impairment (SLI) in children. Previous studies have focussed on SLI childrens' omission of inflectional morphemes or impaired performance on language tasks, but such data can be accounted for by either theory. To distinguish between these theories we study compound formation in a subgroup of SLI children with 'grammatical (G)-SLI'. An input-processing account (e.g. Leonard, L. (1998). Children with specific language impairment. Cambridge, MA: MIT Press), in which perception and production of inflections requires extra processing resources, would predict that G-SLI children will omit the regular plural -s in compounds (e.g. rat-eater). A grammar-specific deficit account (e.g. Ullman, M. & Gopnik, M. (1994) The production of inflectional morphology in hereditary specific language impairment. The McGill Working Papers in Linguistics, 10, 81-118; van der Lely, H. K. J. & Ullman, M. (1996). The computation and representation of past-tense morphology in normally developing and specifically language impaired children. In A. Stringfellow, D. Cahana-Amitay, E. Hughes & A. Zukowski, Proceedings of the 20th Annual Boston University Conference on Language Development (pp. 816-827). Somerville, MA: Cascadilla Press), in which G-SLI children are impaired in regular inflectional morphology, would predict that G-SLI children will produce regular plural -s forms inside compounds (e.g. *rats-eater). We compared the responses of 16 G-SLI subjects (aged 10 years 4 months to 18 years) with those of 36 normally developing control children (24 matched on language ability and 12 matched on age and cognitive ability). All the groups produced irregular plural nouns in compounds (mice-eater). The normally developing children and teenagers rarely, if ever. produced regular plural nouns inside compounds (*rats-eater), whereas the G-SLI subjects did so often. This pattern of results conflicts with the predictions ofthe input-processing deficit account. The findings support the grammar-specific deficit hypothesis. The data rovide further evidence that specialized grammatical abilities may be differentially impaired within the language system.