What Makes Joint Visual Search Efficient? A Distractor Suppression Account

Visual search is thought to operate via a priority map that weights targets against distractors. Any process that modulates the weight assigned to distractors can influence search efficiency. Prior work on joint visual search has examined how distractors matching a partner's target receive enhanced weighting and impair individual performance. The present study asks instead whether the items the partner must reject are processed more efficiently in a joint context, thereby improving individual search efficiency. One possible account is enhanced distractor suppression, on which such items are down-weighted more effectively when another person is rejecting them concurrently. Participants searched shared multi-item displays for color-defined targets, and search slopes (response time per item) were analyzed with linear mixed-effects models. Experiment 1 (N = 114) compared joint, individual, and passive observer conditions. Experiment 2 (N = 76) compared in-group and out-group pairs formed via a minimal-group paradigm. In Experiment 1 the joint slope was shallower than both the individual and passive observer slopes. In Experiment 2 the slope was shallower for out-group than for in-group pairs, revealing a group-based modulation of joint search efficiency. On log-transformed response times, this difference appeared instead as a constant proportional advantage. Although search slopes index overall efficiency rather than directly measuring suppression, and alternative processes could also contribute to shallower slopes, these findings are consistent with a distractor suppression account of what makes joint visual search efficient.