Attention for action?

The classic definition of 'pure' optic ataxia suggests that these patients' visuomotor impairments are independent of perceptual or attentional deficits. More recent work suggests that some patients with optic ataxia also have difficulty attending to targets in their ataxic field. Thus, an important question is whether these attentional deficits might be related to the well-known problems in visuomotor control evident in these patients. To investigate this question we had controls (N = 5) and CF, a patient with optic ataxia in his left visual field, perform tasks that required them to detect or reach towards targets presented in either central vision, or at different target eccentricities in the periphery. As expected, CF was less accurate than controls when reaching to targets in his ataxic (left) visual field, and was much slower than controls to detect the presence of targets in his ataxic field. The reaction times to lift the hand in the pointing and the detecting conditions were correlated in the ataxic field of patient CF, suggesting a common attentional deficit in both tasks. Importantly, although CF was slower to detect targets in the ataxic field, and less accurate to reach towards those same targets, the two deficits did not follow the same pattern. Specifically, only reaching errors in the ataxic field were strongly modulated by target eccentricity. These results suggest that dorsal posterior parietal lesions result in attention and visuomotor control problems in optic ataxia that arise from damage to independent mechanisms.