Inflectional morphology in a family with inherited specific language impairment

The production of regular and irregular past tense forms was investigated a mong the members of an English-speaking family with a hereditary disorder o f language. Unlike the control subjects, the family members affected by the disorder failed to generate overregularizations (e.g., digged) or novel re gular forms (plammed, crived), whereas they did produce novel irregularizat ions (crive-crove). They showed word frequency effects for regular past ten se forms (looked) and had trouble producing regulars and irregulars (looked , dug). This pattern cannot be easily explained by deficits of articulation or of perceptual processing, by previous simulations of impairments to a s ingle-mechanism system, or by the extended optional infinitive hypothesis. We argue that the pattern is consistent with a three-level explanation. Fir st, we posit a grammatical deficit of rules or morphological paradigms. Thi s may be caused by a dysfunction of a frontal/basal-ganglia "procedural mem ory" system previously implicated in the implicit learning and use of motor and cognitive skills. Second, in contexts requiring inflection in the norm al adult grammar, the affected subjects appear to retrieve word forms as a function of their accessibility and conceptual appropriateness ("conceptual selection"). Their acquisition and use of these word forms may rely on a " declarative memory" system previously implicated in the explicit learning a nd use of facts and events. Third, a compensatory strategy may be at work. Some family members may have explicitly learned a strategy of adding suffix -like endings to forms retrieved by conceptual selection. The morphological errors of young normal children appear to be similar to those of the affec ted family members, who may have been left stranded with conceptual selecti on by a specific developmental arrest. The same underlying deficit may also explain the impaired subjects' difficulties with derivational morphology.