An intrahemispheric integration deficit in dyslexia

In order to investigate the hypothesis that dyslexia may result from a failure of intrahemispheric integration between auditory-verbal and visual-verbal processing, a dichotic listening task and a parallel divided visual field task were administered to a group of dyslexic boys between the ages of 8 and 11 years, and a group of normal control subjects individually matched for age and WISC intelligence. The dyslexics were on average over two years retarded in reading and spelling. Dyslexics exhibited a normal right ear advantage on dichotic listening for digits although lesser right ear advantage was related to reading retardation. In the divided visual field task, the normal controls showed a left visual field advantage for digits which it is argued resulted from a failure in fixation linked to reading habits. Within the dyslexic group greater reading deficiency was associated with relative bilateralization for visual verbal processing. The results therefore support the hypothesis.