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

Although reversal errors (e.g., “b” vs. “d”) are often considered a hallmark of dyslexia, the origin of these errors remains elusive. Neuropsychological studies suggest that the magnocellular/dorsal visual stream may play an important role in our ability to discriminate mirror images. Other studies suggest that some dyslexics have a deficient magnocellular/dorsal stream. Accordingly, we tested the hypothesis that reversal errors in dyslexia are caused by a magnocellular/dorsal deficit. We measured the ability of normo-typical and dyslexic children enrolled in 6th grade to detect mirror (e.g., “d” for “b”) and phonological (e.g., “g” for “b”) errors in a lexical decision task. We also measured the efficiency of their visual magnocellular/dorsal stream using a flicker fusion threshold task. The obtained results are in line with our hypothesis, as dyslexic children showing a magnocellular/dorsal deficit also have significant difficulties to detect mirror errors in the lexical decision task