Hemispatial neglect affected by non-neglected stimuli.

Patients with hemispatial neglect fail to cancel lines distributed on one side of a piece of paper. This defect is thought to be induced by a deficit in the neuronal systems that mediate attention, intention, and exploration toward and in the hemispace contralateral to the lesion. However, an alternate (but not mutually exclusive) interpretation is that the patients are either strongly attracted to or impaired in disengaging from the stimuli occupying the other, non-neglected hemispace. We tested ten patients with neglect on two versions of a cancellation test. In the control test they cancelled lines by drawing over them, and in the experimental test they erased lines. There were significantly more omissions in the drawing-over task than in the erasing task. The improved performance when lines were cancelled by removal instead of by marking them suggests that hemispatial neglect is influenced by the presence of stimuli in the non-neglected hemispace.