Baiwei Liu¹, Freek van Ede¹; ¹Vrije Universiteit Amsterdam

Delay-period EEG signals, such as the Contralateral Delay Activity (CDA) or the lateralisation of 8-12 Hz posterior alpha activity, are widely viewed and used as direct markers of selective working-memory maintenance. However, these EEG markers are conventionally studied in pre-cue paradigms where relevant memory content must first be selected at sensory encoding. This potentially conflates the selective maintenance of relevant information with the active translation of this information from sensation into memory. To disentangle selective sensory-to-memory transition from selective memory maintenance, we leveraged a novel task where we could compare situations that were otherwise identical, but where in one case relevant memory content had to first be selected from perception, while in the other case this content could be selected from working-memory directly. In both cases, the selected visual content and the ensuing working-memory task were identical, but only the former engaged a sensory-to-memory transition. Strikingly, our results show that sustained delay activity was contingent on the availability of sensory input: both the CDA and prolonged alpha lateralisation were robust in the ‘select at encoding’ condition but absent in the ‘select from working memory’ condition. Crucially, this was not due to a lack of spatial organisation in the latter ‘select from working-memory’ condition, as we observed robust and comparable N2pc and initial alpha lateralization in both conditions. This result was further supported with multi-variate pattern analysis. Together, our results show how prolonged “delay activity” EEG signatures in posterior electrodes are surprisingly contingent on sensory input, and suggest that such signatures may track the transition from sensory inputs to working memory traces, rather than the pure maintenance of relevant information per se.