Holistic processing of words and faces in dyslexia

Research on the perceptual correlates of developmental dyslexia has traditionally focused on phonological processing. Where visual processing has been considered, the emphasis has been on visuotemporal processing along the magnocellular pathway, e.g.,(Stein, 2001). More recently, and guided by brain imaging studies showing hypoactivation in left fusiform gyrus in dyslexia, there is a growing interest in visuospatial processing. In particular, this research questions whether atypical visual processing in dyslexia is restricted to words as is suggested by the disorder’s definition as a ‘specific reading disability’. The current study is unique in comparing the performance of dyslexic (n = 30) and typical readers (n = 29) on both word and face processing tests that are specifically designed to measure ‘holistic processing’, a form of visuospatial processing associated with perceptual expertise. In agreement with recent research on face processing in dyslexia, we report longer response latency on the Vanderbilt Holistic Face Processing Test in dyslexic readers, a difference that cannot be attributed to anomalous holistic processing. In contrast, dyslexic readers show considerable impairment on the word processing task, including marked differences in holistic processing. These findings are discussed with reference to the ‘neuronal recycling hypothesis’ which emphasis the commonalities in how self-similar stimuli such as words and faces are processed by the human brain and to the heterogeneity underlying the dyslexia classification.