Neural Evidence for the Contribution of Active Suppression During Working Memory Filtering

In order to efficiently process incoming visual information, selective attention acts as a filter that enhances relevant and suppresses irrelevant information. In this study, we used an event-related potential (ERP) approach with systematic lateralization to investigate enhancement and suppression during encoding of information into visual working memory (WM) separately. We used a change detection task in which observers had to memorize some items while ignoring other items. We found that the to-be-ignored items elicited a PD component in the ERP, suggesting that irrelevant information is actively suppressed from WM. The PD amplitude increased with distractor load and decreased with the ability to group distractors according to Gestalt principles. This suggests that the PD can be used as an indicator of how efficiently items can be suppressed from entering WM. Furthermore, while lateral memory-targets elicited a traditional CDA (starting similar to 300 ms), lateral memory-distractors elicited a sustained positivity contralateral to memory-distractors (CDAp, starting similar to 400 ms). In sum the results suggest that inhibition of irrelevant information is an important factor for efficient WM and is reflected in spontaneous (PD) and sustained suppression (CDAp).