Orientation Discrimination in a Visual Form Agnosic: Evidence from the McCollough Effect

Abstract

The McCollough effect is a color aftereffect contingent on pattern orientation. The effect was induced in a woman who has a profound impairment in orientation perception due to brain damage. The fact that she experiences the McCollough effect indicates that her visual system is still representing orientation at some level. Further, the finding that her occipital lobe damage is confined mainly to the prestriate regions suggests that the McCollough effect may be mediated by mechanisms at a low level in the visual system, perhaps in area 17.