Ignoring distractors takes its (memory) toll

Effective attentional selection requires filtering task-irrelevant stimuli. We examined the cognitive cost of such filtering using an object-based attention paradigm across four experiments (N = 320). Participants discriminated the orientation of a Gabor patch presented either alone or overlapped with an irrelevant object or scrambled stimulus. The filtering cost was measured as an increase in response times on distractor-absent trials embedded in 'mixed' blocks (with interleaved distractor-present trials) compared to 'pure' distractor-absent blocks. The filtering cost was robust and scaled with distractor probability and with the presence of one, two or four possible distractors occurring within the session. The cost disappeared when eight distractors were interleaved randomly, but re-emerged when the same eight distractors were presented orderly, one in each sequential mini-block, indicating a strategy shift once working-memory capacity is exceeded. The cost correlated negatively with interference on distractor-present trials and was unaffected by distractor semantic content, consistent with the active maintenance in working memory of distractor templates.