Correlated Deficits of Perception and Action in Optic Ataxia

Optic ataxia, following dorsal stream lesions, is characterised by impaired visuomotor guidance. Recent studies have found concurrent perceptual deficits, but it is unclear whether these are functionally related to the visuomotor symptoms. We studied the ability of a well-documented patient (IG) with bilateral optic ataxia to react to sudden target jumps by correcting ongoing reaches or by explicitly reporting the jump direction. IG showed deficient reach corrections, especially for target jumps to the visual periphery, and was similarly slow to discriminate the same jumps perceptually. Across six test conditions, in which the retinal locations of target jumps were varied, her perceptual slowing mirrored her reaching deficit precisely. These findings confirm perceptual impairments after dorsal stream lesions, and imply a shared functional basis with the classical visuomotor symptoms of optic ataxia. Additionally, we show that the online correction deficit is determined dually by the retinal location to which the reach must be diverted, and the location to which it is initially directed. We suggest that this deficit, and its perceptual counterpart, can be traced to a slowed contralesional orienting of attention in optic ataxia.