Mapping theories of developmental language impairment: Premises, predictions and evidence

This paper presents the case for a mapping theory of developmental language impairment, which branches into a theory that Specific Language Impairment (SLI) arises from impaired phonological processing and the consequent disr uption of the mapping process through which the words and sentence structur e of a language are established. The prelude to the case is that the mappin g process, which is a sine qua non of language acquisition, is the first pl ace to look for possible sources of deficits in language acquisition; that recent research on the mapping process points up the contribution of comple x phonological processing not just in the segmentation and representation o f lexical phonology, but in wider lexical and syntactic development; and th at phonological processing is therefore a plausible source of the deficits observed in SLI. Detailed analysis of the mapping process and the role of p honological processing gives rise to specific predictions which are evaluat ed against wide-ranging research findings on children with SLI. It is argue d that the phonological theory provides a better fit with this empirical ev idence than theories which posit either specific grammatical deficits or lo w-level auditory processing deficits, and offers more far-reaching insights than theories which invoke a general limitation in processing capacity. Th e paper concludes with wider implications, further predictions, and further questions arising from the mapping theory of developmental language impair ment and its particular instantiation in the phonological theory of SLI.