Visual and visuomotor performance in dyslexic children

The present study was designed to compare the performance of nine dyslexic boys and nine age- and IQ-matched controls on tasks which presumably tap visual functions dependent on the subcortical magnocellular (M) pathway (flicker sensitivity) and the cortical dorsal stream (stereoacuity, structure-from-motion, visuomotor control). Increasing evidence suggests that dyslexics experience impairments in M-system functioning. In keeping with previous work supporting this conclusion, dyslexic subjects in the present study were found to have reduced sensitivity to flicker relative to controls. Given that the M system provides the predominant input to the dorsal stream, it was expected that reduced functioning of the M system in dyslexics would result in disruptions of functions related to this cortical visual pathway. Indeed, dyslexic subjects in the present study were found to be less efficient at recognizing structure-from-motion and less accurate at grasping objects precisely. They also showed a mild impairment in stereoacuity. These results, then, lend some support to the hypothesis that dyslexic individuals should show deficiencies on tasks dependent on dorsal stream processing of visual information.