Free recall is shaped by inference and scaffolded by event structure.

Though everyday life is continuous, people understand and remember experiences as discrete events separated by boundaries. Event boundaries influence the temporal structure of memory, and have been proposed to enhance encoding of boundary-adjacent information. However, the extent to which event boundaries influence memory for specific items, and their effect on memory in interactive environments are not well understood. Here, we designed a task to test how boundaries between hidden rules and uncertainty about those rules affect free recall of item-level information. Participants (n = 66) responded to a sequence of individual word stimuli, with words grouped by hidden rules forming events, and abrupt shifts between rules causing event boundaries. Afterwards, participants freely recalled words from the task. Recall was clustered based on event structure, such that words from the same discrete event tended to be recalled together. Contrary to predictions of theories of event cognition, recall was worse for words encoded immediately after event boundaries. Finally, we used a reinforcement-learning model to characterize recall performance, allowing us to infer a positive relationship between decision certainty and recall success. These findings indicate that the structure of events and inferences made over that structure play important roles in shaping episodic memories.