Working Memory Facilitates Event Segmentation via Boundary-Triggered Reactivation and Partial Accumulation During Events

Event segmentation is the cognitive process of dividing continuous experiences into meaningful units. Although working memory (WM) is believed to play an instrumental role in event segmentation, its specific contribution remains under debate. Here, we used two electroencephalography (EEG) indices of WM load, alpha-band suppression and contralateral delay activity (CDA) amplitude, to test whether WM supports event segmentation by gradually accumulating information during unfolding events or by reactivating information at the transitions between events (i.e., event boundaries). Participants viewed object images paired with sounds that both remained in the same category for 6 consecutive items to form a stable event, followed by 2 items from another category, creating an event boundary. Temporal order and sequential memory were used to assess event segmentation. We found increased alpha-band suppression following event transitions, supporting the reactivation account. Evidence for the accumulation was mixed, with no evidence for increased alpha-band suppression and moderate evidence for increased CDA during events. These results indicate that WM contributes to event segmentation primarily through boundary-triggered reactivation, with only limited evidence for within-event accumulation.