Visual and language processing deficits are concurrent in dyslexia.

Research has demonstrated that dyslexic subjects have language processing problems. More recent evidence indicates that dyslexic subjects also suffer a low-level visual information processing deficit. Little evidence is available to indicate the extent to which dyslexic subjects simultaneously show a visual and language processing dysfunction. In this study, 35 normal and 35 dyslexic subjects aged from 7.9 to 14 years of age were compared on three reading process variables, a visual processing score, a test of phonological coding and a test of language comprehension, each of which were shown to be related to reading performance. The visual processing score was the slope of the regression line predicting the duration of visible persistence as a function of spatial frequency. The language processing measures were a test of phonological coding of orthographically legal Non-Words and a test of language comprehension, the Token Test. The results showed that the visual processing score was significantly predictive of group membership with 91% of the dyslexic group and only 20% of the normal readers having low scores on this measure. The Non-Word test was found to be a perfect discriminator for dyslexia by indicating that every subject in this group had a major phonological coding deficit. An unexpected finding of the present results was that the Token Test did not discriminate between the groups. The results are interpreted as providing evidence for the concurrence of visual and language deficits in dyslexia.