Neurobehavioural analogies between syndromes of acquired and developmental language impairment: Hypotheses for research

Abstract

From traditional accounts of acquired aphasia this paper generates hypotheses about a developmental language disorder called specific language impairment SLI). We first propose that there are two types of SLI and that they share behavioural characteristics with two types of aphasia. We suggest that adult-onset Broca's aphasia, the typical type of child-onset aphasia, and the phonological—syntactic type of SLI share a common set of non-fluent language behaviours; and that adult-onset and child-onset fluent aphasias and the semantic—pragmatic type of SLI share a common set of fluent language behaviours. Our approach is then to infer, by analogical reasoning, the neuroanatomical basis of the two types of SLI from what is known about the neuroanatomical basis of the two types of aphasia. Previous investigators who reasoned by analogy have explained SLI as a unitary phenomenon by positing bilateral hemispheric dysfunction. We posit instead that the bilateral hemisphere hypothesis is needed only to account for the semantic-pragmatic type of SLI, whereas a unilateral left-hemisphere hypothesis is sufficient to account for the phonological—syntactic type. The conflicting hypotheses are discussed in light of alternative interpretations of severity and persistence data in the study of child language disorders.