The relationship between dyslexia and specific language impairment: Multiple phonological processing deficits

The relationship between dyslexia and Specific Language Impairment (SLI) was examined. The severity and nature of phonological deficits in SLI and dyslexia have been unclear in previous studies, due to the moderately high overlap between the two disorders, the limited number of direct comparisons between the two groups, and the broadly defined term, "phonological deficits". The major goal of my dissertation was to examine the nature and extent of phonological deficits across these two groups of children. A series of studies compared phonological awareness, phonological STM, and speech perception in school aged children with dyslexia, SLI, and control children. The relationship between syntactic processing and verbal storage and processing demands was also examined. An ancillary question addressed was the prevalence of reading deficits in children with SLI. Phonological awareness deficits were observed in both groups, though overall they were more severe in children with dyslexia compared to children with SLI. Phonological STM deficits were observed in both groups. There was some evidence that children with dyslexia had a subtle speech perception deficit, though children with SLI showed a stronger and qualitatively different speech perception deficit. Children with SLI also showed evidence for a syntactic deficit, but children with dyslexia only showed syntactic processing problems when verbal storage and processing demands were high. In general, children with SLI showed better reading skills than children with dyslexia. A model of multiple phonological processing deficits (phonological awareness, phonological STM, and speech perception) was proposed to help describe the relationship between developmental reading and language disorders. In conclusion, these studies suggested that multiple phonological deficits reveal important qualitative differences between SLI and dyslexia.