Visual magnocellular impairment in adult developmental dyslexics

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Abstract
Previous research,has suggested,that visual magnocellular,impairment,may,be characteristic,of up to 75% of developmentaldyslexics. In this study,we compared,18 adult dyslexics,and 18 controls on two tasks of putative visual magnocellular,function. We examined,whether,these tasks could discriminate,dyslexics,from controls and also the relationship between these measures and nonword reading, a sensitive measure of phonological,awareness.,Our results showed,that dyslexics were,significantly less sensitive than,controls for detection,of coherent motion,in random,dot kinematograms (RDK) and,also the highest,frequency,at which temporal,modulation,at full contrast,was detectable, the critical flicker fusion frequency (CFF). Across the two groups and within each group examined separately, motion and flicker sensitivity correlated strongly with nonword reading ability. Together, the temporal perception measures were able to discriminate 72.2% of the dyslexics from controls, so this type of visual deficit may be an important,feature of dyslexia. Our results support,the hypothesis,that dyslexics’ reading problems,are not entirely caused,by a specific deficit in language,processing. These visual deficits are also found,in younger,subjects; hence,visual temporal,perception measures,may,be used to identify children,at risk for dyslexia,prior to actual reading failure. Key words: dyslexia, magnocellular, flicker fusion, motion Visual deficits in developmentaldyslexia 3

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