Multiprocess lateralisation in dyslexia.

Previous studies of behavioural asymmetries in dyslexia have emphasised verbal measures, and have not generally supported differences in functional asymmetry between dyslexic and normal readers. Here a multiprocess approach is taken, employing a sample of adult dyslexic readers. An unusual pattern of lateralisation is found for bargraph recognition, a visual spatial quantitative task. Unlike the right hemisphere pattern found in normal readers, dyslexic readers appear to perform spatial quantitative processing in the left hemisphere. These results are consistent with parietal lobe dysfunction in reading disability, and more specifically with an angular gyrus dysfunction as suggested by recent MRI and PET results. Possible causes are discussed for this right-to-left shift in function, in the face of a left-to-right shift in brain tissue reported in the literature.