PREATTENTIVE PROCESSES GUIDE VISUAL-SEARCH - EVIDENCE FROM PATIENTS WITH UNILATERAL VISUAL NEGLECT

Preattentive processes such as perceptual grouping are thought to be i mportant in the initial guidance of visual attention and may also oper ate in unilateral neglect by contributing to the definition of a task- appropriate reference frame. We explored this question with a visual s earch task in which patients with unilateral visual neglect (5 with ri ght-, 2 with left-hemisphere damage) searched a diamond-shaped matrix for a conjunction target that shared one feature with each of two dist ractor elements. Additional grouping stimuli appeared as flanks either on the left, right, or both sides of the central matrix, and signific antly changed performance in the search task. As expected, when flanks appeared only on the ipsilesional side a decrement in search performa nce was observed, but the further addition of contralesional flanks ac tually reduced the decrement and returned performance to near baseline levels. These data suggest that flanking stimuli on the neglected con tralesional side of visual space can influence the reference frame by grouping with task-relevant stimuli, and that this preattentive influe nce can be preserved in patients with unilateral visual neglect.