Influences of lesions of parietal cortex on visual spatial attention in humans

Several brain areas have been identified with attention, because damage to these regions leads to neglect and extinction. We have tested elements of visual attentional processing in patients with parietal, frontal, or temporal lesions and compared their responses to control subjects. Normal humans respond faster in a reaction time task when the spatial location of a target is correctly predicted by an antecedent stimulus (valid cue) than when the location is incorrectly predicted (invalid cue). The cue is hypothesized to shift attention towards its location and thereby facilitate or impede response latencies. The reaction times of individuals with damage to the parietal lobe are somewhat slowed for targets ipsilateral or contralateral to the side of the lesion if the targets are preceded by valid cues. These same patients are extremely slow in responding to targets in the visual field contralateral to the lesion when the cue has just appeared in the unaffected (ipsilateral) visual field. In addition, these individuals are especially slow in responding to targets in either visual field when the lights are preceded by weak, diffuse illumination of the entire visual field. Patients with lesions of the frontal lobe have very slow reaction times in general and, as is the case for patients with lesions of the temporal lobe, are slow in all conditions for targets in the field contralateral to the lesion. These patterns are probably not associated with attentional defects. For patients with parietal lesions, these studies demonstrate a further deficit in a cued reaction-time task suggesting abnormal visual attention. Since different sites of brain damage yield different patterns of responses, tests such as these could be of analytic and diagnostic value.