Plural acquisition in children with specific language impairment.

A plural elicitation task and a nominal compounding task were administered to a group of children with SLI and two groups of normally developing children, an age-equivalent group (CA) and a language-equivalent group (MLU). Across tasks, differences between the CA and SLI groups were significant, but differences between the MLU and SLI groups were not. These findings suggest that by 5 years of age, children with SLI demonstrate a productive and differentiated plural system. However, unlike the normally developing children, the pluralization skills of the children with SLI were affected by input frequency, with nouns that are frequently pluralized in everyday conversation more readily inflected than ones that are infrequently pluralized. Three explanations within a model of linguistic normalcy are proposed to account for the frequency effect. These include (a) delayed independence of rule use, (b) linguistic vulnerability, and (c) a faulty lexicon.