Inter- and intrahemispheric processing of letter stimuli by dyslexic children and normal readers.

Manual reaction-times and errors to single letter stimuli presented ipsilaterally (intrahemispherically) or contralaterally (interhemispherically) to the responding hand were compared for dyslexic children and normal readers aged 8 to 13 years. Dyslexic children were significantly slower than normal readers across four field-hand conditions, but for the dyslexic group, reaction times were not discrepantly longer nor were errors more frequent in the contralateral condition, contrary to the hypothesis of impaired interhemispheric processing in that group. Unlike normals, dyslexic children made more errors in the right visual field-right hand condition. These results suggest that cortical and/or subcortical information processing is slower in dyslexics, but that neither the rate nor the accuracy of information transfer between the hemispheres is specifically abnormal. In addition, some defect within the left hemisphere of dyslexics for processing linguistic stimuli is indicated.