Phonological Processing Deficits as the Basis of Developmental Dyslexia: Implications for Remediation

Stanovich (1988a; 1988b) has proposed that deficits in phonological processing are at the basis of developmental dyslexia. According to this theoretical approach, phonological processing constitutes a modular function that operates automatically and independently of general cognitive ability. In this chapter, I will provide evidence for the nature and extent of the phonological processing deficits in dyslexia and I will discuss these phonological processing skills in the context of dual route theories of reading. Evidence is offered that dyslexic children have deficits in a variety of phonological skills, including the reading and spelling of pseudowords, recognising the visual form of a pseudoword and a phonological-lexical task that involved recognising whether a pseudoword could be pronounced like an English word. In particular, their reading of pseudowords was significantly poorer than normal readers of the same chronological age and even reading age controls. In addition, evidence is presented to show that phonological processing skills is independent of general cognitive ability as measured by intelligence test scores. Although phonological processing skills are relevant to reading by grapheme-phoneme conversion (GPC) rules, orthographic skills may be considered a measure of reading by the lexical, or visual, route. The performance of dyslexics and normal readers on two orthographic tasks will also be described. The orthographic tasks included detecting the spelling of a word when required to choose between the correct spelling and a pseudohomophone and recognising whether a pseudoword contained an orthographically illegal bigram. Whereas the dyslexic children matched on 380reading grade with the normal reader, they lagged behind the normal readers on all the phonological tasks, the dyslexics were, in some cases, significantly more advanced than reading level matched controls in orthographic skills. These results are interpreted to indicate that dyslexics have a significant impairment in the use of the phonological route but are less impaired in the direct lexical access, or visual route, and, in some cases, may be more sensitive to the orthographic features of words than normal readers. These results suggest that extreme difficulties with phonics are characteristics of dyslexics and have some implications for the remediation of reading problems. Drill with phonics would seem to be relatively unproductive in the teaching of reading to dyslexics, although there obviously needs to be some exposure to grapheme-phoneme conversion rules. However, remediation capitalising on the strengths of the dyslexics in the visual route might prove to be more successful. In a test of this hypothesis, dyslexics were taught a sight word vocabulary using the Bridge Reading System, which uses icons as picture cues for words. After eight months of reading instruction with this method, the children who had been exposed to this program achieved significantly higher scores on tests of word reading and were able to read letters, individual words, and connected text more quickly than a control group of children who did not receive the special program. Severe phonological processing deficits appear to be the fundamental problems of developmental dyslexia although orthographic processing is relatively intact. Early reading instruction for dyslexics which capitalises on the strength of the direct lexical access or visual route appears to be useful for the remediation of reading skills in dyslexic children.