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L. Battelli, P. Cavanagh, J. Barton; High-level motion reveals two different attentional deficits following parietal damage. Journal of Vision 2001;1(3):409. doi: 10.1167/1.3.409.
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We examined the effects of human parietal lesions upon the performance of attention-mediated motion tests. Two attentive-motion tasks were used: 1) a multiple object tracking task, in which one or more moving targets must be tracked among otherwise identical moving distractors, and 2) an apparent motion task, in which dots in apparent motion must be differentiated from flickering dots. Six patients with parietal lesions were tested on both tasks. The lesions involved the parietal cortex unilaterally or bilaterally. Control tasks indicated that these patients were impaired on static tests of divided attention but not on tests of low-level motion perception. Performance in the multiple object tracking task was severely degraded in all contralesional fields but was normal in the ipsilesional field of patients with unilateral lesion. Surprisingly perception of apparent motion was severely impaired in both hemifields, indicating that this relatively automatic percept likely relies on attentional mechanisms. We hypothesized that the bilateral impairment in unilateral patients might reveal a more general timing perception deficit. To test this possibility we devised a further control experiment: a temporal resolution task, in which six squares were flickering at the same temporal frequency and the target to be detected was flickering out of phase. Performance of the one right parietal patient tested to date was degraded in both hemifields. Altogether our data show that the dissociation between preserved low-level motion and loss of attentive tracking and apparent motion suggests different anatomical substrates subserving the two motion systems. Furthermore we suggest that the disruption we found is due to a loss in the temporal resolution of events that normally drives the capture of attention.
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