Event boundaries impair immediate and delayed story recall in healthy aging and Mild Cognitive Impairment

Changes in a narrative storyline are perceived as event boundaries and are associated with increased attention to the story and better memory for sections of the narrative where the changes occur. However, the effect of event boundaries on overall memory for a story is unclear. Here we employed a new naturalistic task in which we manipulated the number of event boundaries in short stories. We tested story recall at two retention intervals (immediate, one-hour delay), in two participant groups (healthy adults, adults with Mild Cognitive Impairment, MCI). Despite lower overall performance in the MCI group, the findings were consistent across retention intervals and groups; the addition of an event boundary resulted in poorer story recall. Importantly, this effect was driven by "all-or-none" forgetting of the event following a boundary. We suggest that event boundaries induce a contextual shift that disrupts the causal structure of a narrative and weakens the binding of story elements. As a result, recalling one event is less likely to cue the retrieval of the subsequent event, compared with recalling elements that cue the retrieval of successive details from the same event. Thus, overall, stories that comprise fewer longer events will be remembered better than stories that comprise more shorter events.