Deficits in finite verb morphology: some assumptions in recent accounts of specific language impairment

The grammatical morphology deficits common in children with specific language impairment (SLI) are characterized in some models as linguistic deficits. Such models must assume some mechanism for correct productions of finite verb forms. Three such assumptions were tested by analyzing speech samples from 18 children with SLI (aged 3 years 6 months to 6 years 9 months). Assumption 1, that nonfinite forms are used consistently until replaced by memorized finite forms, was tested by examining the distribution of verb types in present third-person singular and noun types in present third-person singular contractible copula contexts. Significantly more word types than expected were inflected inconsistently. Both Assumption 2, that finite and nonfinite verb forms are memorized but used indiscriminately, and Assumption 3, that affixation rules are applied indiscriminately, predict random use of finite forms. This prediction was not supported.