Understanding reversal errors in dyslexia: The role of the magnocellular/dorsal visual stream

Objectives. Although leter reversals errors (e.g., “b” vs. “d”) have been considered a hallmark of dyslexia for decades, there is litle evidence supporng this claim. Moreover, the nature and the origin of these putave errors remains elusive, leading to a current debate on whether these errors are phonological or visual. Recent neuropsychological studies suggest that the magnocellular channel of the visual system play an important role in our ability to discriminate mirror images. In accordance, the present study aims at determining if reversals errors could be explained by a magnocellular deficit in some dyslexic children. Method. Using a lexical decision task, we test the ability of normo-typical and dyslexic children enrolled in the 6th grade to detect mirror (e.g., “d” for “b”) and phonological (e.g., “g” for “b”) errors. In addion, a flicker fusion threshold task, which is well known to assess the magnocellular channel, was proposed to the parcipants. Results and discussion. Results suggest that dyslexic children showing a magnocellular deficit on the flicker fusion threshold task consistently have a significant difficulty to detect mirror errors, suggesting that at least some dyslexics are prone to mirror errors which are of visual origin and nature