The Magnocellular-Dorsal (M-D) Deficit and Associated Theories

There are several visual pathways that convey different types of information to the brain. We review evidence that in dyslexic individuals there is a deficit in one of these pathways, the magnocellular-dorsal (transient; M-D) pathway. A large body of research supports an M-D deficit as a correlate of dyslexia, but the evidence that the deficit plays a causal role in reading difficulty is less compelling. The M-D hypothesis has been linked to impaired visuospatial attention in reading difficulty, and to difficulties in processing crowded contours. Preliminary evidence concerning the treatment of these deficits with action video games is discussed.