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 disruption of the mapping process through which the words and sentence structure of a language are established. The prelude to the case is that the mapping process, which is a sine qua non of language acquisition, is the first place to look for possible sources of deficits in language acquisition; that recent research on the mapping process points up the contribution of complex phonological processing not just in the segmentation and representation of lexical phonology, but in wider lexical and syntactic development; and that phonological processing is therefore a plausible source of the deficits observed in SLI. Detailed analysis of the mapping process and the role of phonological processing gives rise to specific predictions which are evaluated against wide-ranging research findings on children with SLI. It is argued that the phonological theory provides a better fit with this empirical evidence than theories which posit either specific grammatical deficits or low-level auditory processing deficits, and offers more far-reaching insights than theories which invoke a general limitation in processing capacity. The paper concludes with wider implications, further predictions, and further questions arising from the mapping theory of developmental language impairment and its particular instantiation in the phonological theory of SLI.