VISUAL-EVOKED POTENTIAL EVIDENCE FOR MAGNOCELLULAR SYSTEM DEFICIT IN DYSLEXIA

Some recent studies on dyslexia have suggested a selective abnormality in the magnocellular visual pathway. To verify this hypothesis, we in vestigated motion-onset visual evoked potentials (VEPs) (predominantly testing the magnocellular system) as well as pattern-reversal VEPs (p resumably testing the parvocellular system) in 20 dyslexics and 16 con trols (both groups with a mean age of 10.0 years). Although the latenc ies and amplitudes of the main positive peak of pattern-reversal VEPs did not differ between the dyslexic and control group, the motion spec ific negative peak of motion-onset VEPs was significantly delayed (p<0 .001) in dyslexics. Our results confirm a selective magnocellular path way disorder in dyslexics and indicate that the motion-onset VEPs migh t serve as an objective method for early diagnosis of dyslexia.