Horizontal visual motion modulates focal attention in left unilateral spatial neglect.

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Abstract
Patients with unilateral spatial neglect are impaired in directing focal attention toward the contralesional side of space. Provision of static spatial cues on the neglected side has previously been shown to help overcome this deficit. Common movement of visual stimuli may also guide the allocation of spatial attention, although such effects have not been examined in patients with unilateral spatial neglect. Eleven patients with right hemisphere damage and clinical evidence of left unilateral spatial neglect, and 11 matched, healthy controls were tested on a task of horizontal line bisection. Lines were presented on a computer display, with a neutral, static, or slowly drifting, random dot background. Under conditions of motion, background stimuli drifted either leftward or rightward, across the full width of the display, at speeds that did not elicit optokinetic nystagmus or perceptual aftereffects. Controls were accurate in all conditions, and showed minimal effects of background conditions. By contrast, patients with left unilateral spatial neglect were sensitive to leftward background motion, showing a significant leftward shift in bisection error, relative to neutral, static, and rightward moving backgrounds. There was no significant effect of rightward motion in comparison with the neutral and static conditions. The extent to which patients were susceptible to the effects of background motion was not related to severity of unilateral spatial neglect, as measured by clinical tests. The benefits of leftward motion may reflect activity of preserved motion processing mechanisms, which provide input to an otherwise dysfunctional attentional network. The use of visual motion to assist in contralesionally guiding focal attention may be useful in the rehabilitation of unilateral spatial neglect.