StudyUnilateral Right Parietal Damage Leads to Bilateral Deficit for High - Level Motion

mechanisms can signal motion even when a stimulus is Boston, Massachusetts 02215 not attentively tracked and responds to motion at much 3 Department of Neurology higher temporal frequencies. This low-level passive sys-Harvard Medical School and tem is putatively mediated by directionally selective Massachusetts General Hospital cells in the early visual cortices (Hubel and Wiesel, 1968) Boston, Massachusetts 02114 and is velocity based, whereas the high-level system is 4 INSERM position based and depends on attention (Seiffert and Unité 280 Cavanagh, 1998, 1999). Since parietal lesions are asso-Lyon, France ciated with deficits in attention, we hypothesized that parietal lesions ought to impair high-level motion perception. In the present report, we examine two high-Summary level motion tasks, namely multiple object tracking and apparent motion. Similarities and differences in the im-Patients with right parietal damage demonstrate a va-pairments for these two high-level motion tasks should riety of attentional deficits in their left visual field con-reveal similarities and differences in the attention mech-tralateral to their lesion. We now report that patients anisms they may call on. with right lesions also show a severe loss in the per-Selective attention mechanisms were tested with a ception of apparent motion in their " good " right visual task of divided attention in which the subject had to field ipsilateral to their lesion. Three tests of attention report a letter presented among three different letters were conducted, and losses were found only in the for 66 or 300 ms. At the offset of the display, the subject contralesional fields for a selective attention and a was required to identify a letter based on its position in multiple object tracking task. Losses in apparent mo-the letter string. The cued report for brief visual displays tion, however, were bilateral in all cases. The deficit was first developed by Sperling (1960), and we used a in apparent motion in the parietal patients supports modified version of his task. Recent studies have shown previous claims that this relatively effortless percept how patients with parietal lobe lesions can be affected is mediated by attention. However, the bilateral deficit in their ability to perform this type of task (Duncan et suggests that the disruption is due to a bilateral loss in al., 1999). In contrast to the tasks of Duncan et al., we the temporal resolution of attention to transient events asked our subjects to report only one letter among four, that drive the …