Manipulating the focus of attention in working memory: Evidence for a protection of multiple items against perceptual interference.

Visual working memory representations can be shielded from interference by selective attentional focusing using retroactive cues (retro-cues). However, it is not clear how many representations can be effectively cued and which neural mechanisms provide the protection from distractors. To address these questions, we manipulated the number of attended items by means of a retro-cue (one, two, or three items) and presented a distractor display during the retention of information in working memory. Analyses of the raw error and a mixture model revealed that a general performance benefit was only present when one item was retro-cued. Nevertheless, a protection of the item representations against subsequent interference occurred also after a two-item cue. ERPs revealed a modulation of the posterior negative slow wave following the retro-cues, reflecting the applied working memory resources dependent on the number of attended representations. Further, the distractor information was encoded into working memory only when the number of attended items was not changed by the retro-cues (neutral and three-item conditions), reflected by a P3b following the distractor display. These results suggest that more than one item can be effectively protected from perceptual interference. We propose that the protective effect of selective attention within working memory is based on both a reduction of the number of focused representations and the attentional refreshing of item context and features.