Bilateral deficits of transient visual attention in right parietal patients.

Vision tells us not only what and where objects are but also when they appear and disappear. We have found that patients with right parietal damage have an unusual loss in the ability to differentiate object onset from offset. Specifically, when a single target flickers at the same frequency as five distractors, but out of phase (it is light when they are dark and vice versa), right parietal patients require much slower rates than normals or left parietal patients to detect the target. When we shifted the phase of the flicker in the target relative to the distractors so that the onsets and offsets were not simultaneous, the performance of the patients improved dramatically. Remarkably, the patients showed this loss equally in both visual fields. Since flicker detection was normal for the patients, we suggest that the deficit lies at a level where stimulus transients are interpreted as the appearance or disappearance of objects.