Coherent motion, magnocellular sensitivity and the causation of dyslexia.

The central tenet of the magnocellular deficit theory of dyslexia is that dyslexia is caused by a magnocellular deficit. A number of investigators have found deficiencies in visual coherent motion perception among dyslexic readers. These deficiencies have been attributed to magnocellular deficits, which means that they directly reflect the cause of dyslexia. However, similar perceptual deficiencies have been found in association with autism, Williams's syndrome, hemiplegia, and schizophrenia. These findings appear to undermine at least one of the following claims: (1) that a magnocellular deficit is the cause of dyslexia, and (2) that coherent motion is a reliable test of magnocellular sensitivity.