Developmental dyslexia: Passive visual stimulation provides no evidence for a magnocellular processing defect

Livingstone et al. presented evidence for a defect of the magnocellular visual processing stream in developmental dyslexia. They reported diminished visual evoked potentials (VEP) to low-contrast, rapid checkerboard reversal patterns in the dyslexics. We attempted to replicate this effect using transient and steady-state VEPs to checkerboard reversal stimuli in a group of adult developmental dyslexics. Several different reversal rates and contrast levels were utilized. No differences were found between the dyslexic and control groups for the low-contrast, rapidly reversing patterns, nor for any combination of stimulus rate or contrast that was tested. Thus, these findings do not support a magnocellular processing deficit in developmental dyslexia.