We measured saccadic eye movements of macaques while they performed visual search monocularly across the central 30 deg of the visual field. Monkeys made eye movements to choose the target that matched a prior sample stimulus among 0 to 7 distractors. Positional jitter was used to make target and distractor locations unpredictable from trial to trial. Target and distractors were gray discs presented on a white background and targets could be either lighter or darker than the distractors.

When distractors were present, the decreased target identification accuracy that was observed was accompanied by very little increase in search times. When there was only a single distractor, its location relative to the target altered search performance, with optimal detection when there was an intermediate distance between target and distractors. Search latency and landing accuracy showed little variation with eccentricity, but percent correct target identification decreased with eccentricity. For both monkeys, performance was slightly better in the nasal inferior visual field. Asymmetric performance was observed (greater percent correct identification but not different search times) when targets were of higher contrast than distractors, and search times for error trials were longer than for correct trials.

Our results show how search performance changes with both stimulus conditions and location in the visual field.