Is there a visual deficit in dyslexia resulting from a lesion of the right posterior parietal lobe?


Dr Bruce J. W. Evans.


Dyslexia has conventionally been attributed to a left hemisphere deficit affecting language skills. However, it has recently been suggested that two-thirds of dyslexic people have a lesion of the right posterior parietal lobe (RPPL) resulting in poor oculo-motor control. It has been reported that neurological patients with RPPL lesions commonly manifest a neglect of the left side of space and this has also been described in clinical observations of ‘visual dyslexics’. We investigated this hypothesis with a sample of 53 dyslexic children and 53 controls using a line-bisection task. In the horizontal test condition both groups tended to transect slightly to the left of the midpoint (mean displacement 0.14 mm for controls; 0.4 mm for dyslexics). The result suggests a small right side neglect which, contrary to one report in the literature, is found here in developmental dyslexics as well as controls, and leads to the conclusion that RPPL lesion is unlikely to be a common feature of dyslexia.