Berna Güler¹ (), Sümeyye Karahamza², Yağmur Damla Şentürk³, Oded Bein⁴, David Clewett⁵, Eren Günseli⁶; ¹Sabanci University, ²Sabanci University, ³Sabanci University, ⁴Weill Cornell Medical College, ⁵University of California, UCLA, ⁶Sabanci University

Working memory (WM) plays a critical role in constructing the segmented structure of episodic memories, a process known as event segmentation, where experiences are divided into meaningful units. However, its specific contributions remain unclear. This study evaluated two competing perspectives: (1) the accumulation view, which posits that sequences of items are stored in WM until an event boundary is encountered, and (2) the reactivation view, which suggests that WM stores items temporarily but reactivates them at boundaries. Participants viewed sequences of images and sounds organized into alternating mini-blocks: six items from one category followed by two from another (e.g., 6-2-6-2-6-2), with category switches marking event boundaries. After each block of 36 items, participants completed temporal order and sequential memory tasks to assess event segmentation. The sequential memory accuracy was higher for within-event items compared to across-event items, reflecting event segmentation. The EEG indices of WM storage, which were alpha power negativity and contralateral delay activity (CDA), provided stronger support for the reactivation view: Alpha power was more negative at boundaries signaling the end of main events (6 items) than boundary events (2 items), indicating larger reactivated memory loads following longer events. Evidence for the accumulation view was mixed: there was moderate evidence for a CDA increase and no evidence for an alpha negativity increase across items within events. These results suggest that while WM may accumulate items to some extent during events, reactivation at event boundaries plays a more prominent role. This dynamic interplay between WM and long-term memory processes appears critical for constructing the segmented temporal structure of episodic memories.