Context Change Shapes the Organization of Memory Recall

Abstract

Our memories of past experiences are strongly linked to rich contextual details—that is, memory for where or when an event took place. This contextual information not only supports memory retrieval but also shapes how memories are organized. Free recall tasks provide a unique window into these organizational processes, revealing that memory organization is often guided by the similarity of contextual features during learning. Contexts can be similar along a number of dimensions, including temporal, source, and motivational context. However, the context in which we form memories is constantly changing, and while context is known to support memory, it remains unclear how such changes influence what is remembered and how memories are organized.Across three studies, this dissertation explores how features of context change influence the organization of free recall memory, using both behavioral measures and brain activity measured with functional magnetic resonance imaging (fMRI). Chapter II presents two behavioral studies using a context switching paradigm to examine how the frequency and relative novelty of context changes interact to influence free recall. I found that recall performance is worse only when rapidly switching to novel contexts. This suggests not only a benefit for switching to a familiar context, but that impairments of switching to novel environments only emerged in the context of rapid versus slower switches. This difference may have been due, in part, to differences in memory organization. Chapter III is an fMRI study in which the rate of external context change was manipulated during encoding. I tested whether this affected memory organization, measured using temporal clustering—the tendency to recall items in the order they were studied. I also examined whether these behavioral patterns were mirrored in the brain by looking at gradually changing activity in the hippocampus. A higher rate of context change was associated with both less temporal clustering and lower hippocampal autocorrelation, a measure of the stability of hippocampal activity patterns over time. Moreover, participants who exhibited greater hippocampal autocorrelation during encoding also exhibited stronger temporal clustering during recall, establishing a link between hippocampal autocorrelation and temporal organization of memory. Chapter IV used a between-subjects free recall paradigm to test whether agency—having control over one’s choices—can act as a context to organize memories. I found that participants with agency showed reduced temporal clustering compared to yoked participants who had no choice. Instead, participants with agency organized their memories more around the meaningful connections they constructed through their choices. Collectively, these findings provide novel insight into how contextual factors shape the organization of memory.