Reaching into cluttered visual environments: spatial and temporal influences of distracting objects.

Subjects reached for visual target lights in the presence of distractor lights. Previous studies (e.g., Tipper, Lortie, & Baylis, 1992) have shown that distractors at locations between the starting position of the hand and the target location caused greater interference (as indexed by response time) than distractors beyond the target. This finding has been attributed to the former distractors being in the path of the response to the target, but we provide evidence that they interfere more because of their proximity to the starting position of the hand (a "proximity-to-hand effect"). Also, distractors located in the hemispace ipsilateral to the responding hand caused more interference than contralateral distractors (an "ipsilateral effect"). The proximity-to-hand and ipsilateral effects were found in both reaction and movement time, suggesting that the resolution of the selection problem caused by a distractor could occur before or after movement initiation. Further evidence for this suggestion was provided by individual differences in movement initiation strategies which were predictive of the temporal locus of distractor influence. Errors of touching the distractor location also showed proximity-to-hand and ipsilateral effects. We discuss applications of these findings to real-world situations in which people reach for the wrong object in multiple-object visual displays.