Neglect and hemianopia superimposed.

In patients with posterior-parietal brain damage it is often difficult to decide whether left-sided omissions in perimetry are due to primary visual loss or due to visual neglect. We investigated 11 patients with combined neglect/hemianopia and 11 patients with pure hemianopia using a visual search task with single or double stimulation conditions. The second stimulus was either the fixation point itself (like in perimetry) or a distractor appearing in the hemifield opposite to the target. The fixation point did not worsen left-sided perception, but its disappearance led to a bias of exploration towards the right side in neglect patients but not in pure hemianopics. A distractor in the intact hemifield worsened the performance to left-sided stimuli, that is, neglect patients behaved as if they were completely hemianopic, even in intact parts of the visual field (VF). Three of the neglect patients showed unconscious processing of the distractor in the left VF, suggesting that the visual field defect was produced by neglect mechanisms rather than primary visual loss. This visual search paradigm appears to be helpful in understanding of the nature of hemianopia versus neglect deficits in individual patients.