Event boundaries are steppingstones for memory retrieval
Personal experience extends over time. When we recall memories from our lives, we often scan extended episodes to remember, for instance, where we placed our car keys. Here we investigate the hypothesis that high level structure, marked by boundaries between events, guides us through this retrieval process. We present a model of memory search in which humans can replay past experience on a fine-grained temporal scale, but also skip ahead to the beginning of a new event in order to speed up the retrieval process. In a naturalistic interview paradigm, we provide evidence in human response times for such a skipping mechanism: When participants scanned extended segments from a movie in their memory, their reaction times were better explained by a model incorporating the number of event boundaries in the segment and the distance of the target to the previous event boundary (with both predictors explaining significant variance), compared to a model incorporating the actual duration of a segment. This supports the idea that, in scanning their memory, humans can skip to the beginning of a new event if they decide that the target is not present in that event; this has the effect of decoupling their memory scanning reaction times from the actual duration of the segment. This conclusion is further supported by the results of a second study where participants were asked to do detailed mental simulation instead of memory scanning. Participants took substantially longer to perform such mental simulation compared to participants that scanned their memory. Those mental simulation times were still explained better by a model where participants skip, but -- compared to memory scanning -- the threshold for skipping was much higher.