What’s Normal? Specific Language Impairment in an Individual Differences Perspective

Abstract
In this paper, the issue of language impairment is set in a broader perspective of individual differences. Two aspects of language development are identified in which the discrepancies between domains of language and/or cognitive development often observed in specific language impairment (SLI) children occur naturally as a consequence of individual variation in rate of development together with relative independence of specific domains. In the first case, concerning bound morphemes versus syntactic development, research with precocious children complements data from language-impaired children in demonstrating that morphology is the component of language most tied to general language learning ability. In the second case, the definition of specific language impairment as a distinct etiology on the basis of discrepancy between language and nonverbal cognitive development (the "Cognitive Hypothesis") is shown to lead to an invalid prediction. Children with SLI do not show a distinctive response to language intervention, relative to children with even profiles of language and nonverbal cognitive abilities.