Double trouble: Co-occurring visual and phonological impairments in childhood dyslexia

Abstract

Extensive research has characterised developmental dyslexia as a disorder associated with phonological impairment, but increasing evidence suggests that visual processing difficulties may also contribute. Whether visual deficits are evident early in development remains unclear, since most evidence derives from adult samples or language-related tasks and accuracy-based measurements. The present study investigated visual processing in children with dyslexia using a validated, non-linguistic test battery previously employed in adults. Phonological functioning was indexed using a measure of phonological working memory to examine whether any visual performance differences occurred alongside deficits in a core phonological domain. Children with dyslexia performed significantly worse than neurotypical readers on visual tasks and on the phonological measure. Discriminant function analysis revealed that measures from both domains distinguished between the two groups. Deficits were most pronounced for visually complex and similar stimuli and were associated with severity of reading impairment. By examining visual processing using non-linguistic tasks that eliminate orthographic confounds, this study addresses an important developmental gap and suggests that visual processing deficits may be evident alongside phonological weakness in childhood dyslexia. These findings are consistent with multidimensional accounts of dyslexia and highlight the value of domain-inclusive approaches to assessment and intervention.