Perceptual deficits in optic ataxia?

Abstract

Lesions of the dorsal posterior parietal cortex (PPC) typically result in optic ataxia (OA)—a disorder in which patients have difficulty reaching toward and grasping objects presented in peripheral vision, in the absence of primary sensory or motor deficits. It is therefore considered as a human model of the PPC involvement in visuo-manual control. In the early twentieth century, OA was described as part of the Balint–Holmes syndrome. The main aim of most analyses of OA in the second part of the twentieth century was then to isolate a pure visuo-motor symptomatology from the complex Balint’s syndrome (e.g. Garcin et al., 1967; Rondot et al., 1977). In addition, OA has been used over the last 15 years to argue in favor of dissociable functions within the dorsal (‘How’) and ventral (‘What’) streams of visual information processing and visuo-manual guidance (Jeannerod and Rossetti, 1993; Milner and Goodale, 1995; Rossetti and Pisella, 2002). In these contexts, research on OA has focused primarily on visuo-motor functions (‘How’) and has largely ignored visuo-spatial functions (‘Where’). In this chapter, we will review recent accounts on the nature of the well-established visuo-motor deficits in OA and present original data revealing visuo-perceptual deficits in patients with OA. The possibility of a functional relationship between the visuo-motor deficits of OA patients and their perceptual deficits will be put forward and discussed.