Characterizing memory space: The neural representational structure of episodic and semantic memory
Cutler, Rebecca Anne
0000-0003-4938-1898
:
2022-09-16
Abstract
Memories are not preserved in the past, they help us navigate the present and predict the future. Our representation of the world is constantly evolving as we experience time unfolding continuously, yet our past is made up of distinct episodes. In a series of three studies, I will look at how temporal and semantic information guide memory search in free recall.
In chapter one I will investigate how a continual inter-item distraction affects memory for a list of items from familiar categories. Retrieved-context theory states that context gradually drifts over time, making nearby items more similar than distant items. In lists of categorized stimuli, items can also be associated to one another by pre-experimental semantic representations. We created 'episodes' by presenting stimuli in triplets of same-category items, so that adjacent items tended to be semantically related. Our neuroimaging analyses show that semantic information is represented across the brain. This category-selective activation was attenuated by distraction in brain regions within core memory networks. Continual distraction decreased overall performance and semantic clustering at recall. Taken together, this suggests that successful encoding depends on the integration of category information within an event, and this process is disrupted by distraction. Chapter two implements a computational model to capture the organizational differences in recall for categorized lists. The best fit models point to an effect of distraction that disrupts neural information integration by altering the rate of contextual drift.
Finally, chapter three uses naturalistic stimuli to explore how meaning is derived from the interaction of temporal and semantic information. Studying memory for narratives allows us to exploit naturally occurring organizational structure. Recall is enhanced when an event is embedded within a structure of similar events that act as a retrieval cue for one another. Over time, and with consolidation into existing memories, the temporal structure of a narrative fades away. Memory for events gradually transforms as specific temporal order information is replaced by conceptual knowledge that can be generalized across episodes. These studies support a theory of human memory whereby meaningful experiences are created by adding a semantic interpretation to temporal event.