The deployment of visual attention in the intact field of hemineglect patients.

Patients with left hemispatial neglect after right hemisphere lesions and control patients with right hemisphere lesions were presented in the ipsilesional (i.e., intact) visual field with stimuli that could occupy left-right relative positions. The patients were required to discriminate between target stimuli and distractors by emitting go/no-go responses. Reaction times (RTs) and measures of sensitivity (d') and response bias (beta) were obtained. The within-subjects comparisons showed that neglect patients were faster in the right than the left relative position, whereas control patients were faster in the left than the right relative position. The between-subjects comparisons showed that neglect patients were faster than control patients in the right relative position but slower in the left relative position. These effects were due to changes in processing efficiency, as attested by the fact that the differences in response speed were accompanied by congruent differences in sensitivity, whereas no differences in response bias were found. The results were interpreted by assuming that neglect patients focus attention on the right relative position and, therefore, have a small attentional focus concentrated on that position. By contrast, control patients, like normal subjects, would distribute attention between the two possible stimulus positions and, therefore, allocate attention to a larger portion of the visual field.