Clinical neurophysiology of visual and auditory processing in dyslexia: a review

Neurophysiological studies on children and adults with dyslexia provide a deeper understanding of how visual and auditory processing in dyslexia might relate to reading deficits. The goal of this review is to provide an overview of research findings in the last two decades on motion related and contrast sensitivity visual evoked potentials and on auditory event related potentials to basic tone and speech sound processing in dyslexia. These results are particularly relevant for three important theories about causality in dyslexia: the magnocellular deficit hypothesis, the temporal processing deficit hypothesis and the phonological deficit hypothesis. Support for magnocellular deficits in dyslexia are primarily provided from evidence for altered visual evoked potentials to rapidly moving stimuli presented at low contrasts. Consistently ERP findings revealed altered neurophysiological processes in individuals with dyslexia to speech stimuli, but evidence for deficits processing certain general acoustic information relevant for speech perception, such as frequency changes and temporal patterns, are also apparent.