Optic ataxia: A gateway to the human visual action system

Abstract

Stroke patients with optic ataxia have an outstanding inability to perform spatially accurate movements to visual targets located in their peripheral visual field. Neuropsychological investigations of such patients contributed essentially to the two visual stream hypothesis, which presumes dissociated action- and perception-related processing of visual information in the human brain. Here we review the anatomical foundations of optic ataxia that have been elucidated in detail quite recently and allow for the identification of brain areas that are necessary for the control of hand in space. We further evaluate the behavioral findings from crucial experimental paradigms in patients with optic ataxia, in comparison to results from patients with visual form agnosia, a disorder characterized by severely impaired visual perception without deficits of action control. On this background, the actual validity of the two visual streams model is discussed facing the (I) perceptual functions of the dorsal posterior parietal cortex, (II) sustained activation of these areas supporting the retention of spatial information, and (III) the anatomical dissociation between a foveal and an extrafoveal action system.