Visual search asymmetry depends on target-distractor feature similarity: Is the asymmetry simply a result of distractor rejection speed?

Previous studies have shown that in visual search, varying the target and distractor familiarity produces a search asymmetry: Detecting a novel target among familiar distractors is more efficient than detecting a familiar target among novel distractors. One explanation is that novel targets have enhanced salience and are detected preattentively. Conversely, familiar distractors may be easier to reject. The current study postulates that target-distractor feature similarity, in addition to target or distractor familiarity, is a key determinant of visual search efficiency. The results of two experiments reveal that visual search is more efficient when distractors are familiar regardless of target familiarity, but only when the target-distractor similarity is high. When similarity is low, the visual search asymmetry disappears and the search times become highly efficient, with search slopes not different from zero regardless of target or distractor familiarity. However, although distractor familiarity plays an important role in inducing the search asymmetry, comparisons of search efficiency in target-present and target-absent trials reveal that search asymmetries cannot be explained solely by the faster speed of rejecting familiar distractors, as proposed by previous studies. Rather, distractor familiarity influences processes outside of stimulus selection, such as search monitoring and termination decisions. Competition among bottom-up item salience effects and top-down shape recognition processes is proposed to account for these findings.