The role of event number and duration in time-compressed memory replay

Remembering the unfolding of past experiences usually takes less time than their actual duration. In this study, we examined the extent to which this temporal compression in memory depends on the number and duration of events that need to be maintained in a sequence. Participants were asked to watch and then mentally replay short videos depicting one, two, or three continuous events (i.e., people performing continuous actions in an uninterrupted way), each lasting 3, 6, 9, or 12 s. Across two experiments, we computed indices of remembering duration and temporal compression for each event. Results showed that event remembering duration was close to the actual event duration for short events, but smaller for longer ones (i.e., temporal compression was not systematic but occurred selectively depending on event duration). Furthermore, events were mentally replayed more quickly when they were part of a sequence of several events than when they were presented alone, and this decrease in the duration of event recall with the number of events was more pronounced for longer events. Exploratory analyses revealed that individual differences in memory compression were predicted by visual imagery capacity. These results suggest that working memory capacity in representing naturalistic events is limited by both the number and duration of events to be retained, which may in part explain why the unfolding of events is temporally compressed in episodic memory.