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Context and Episodic Memory
Dr. Michael Kahana
Tuesday, December 01, 2009, 01:00pm - 02:00pm
University of Pennsylvannia, Department of Psychology
The fundamental problem of episodic memory concerns linking items with their temporal context (during study) and retrieving the context associated with items (during recall). The reinstatement of mental context is distinguished from the idea that remembering solely involves a reactivation of content information that is specific to that event. I will first present behavioral evidence for the idea associations in episodic memory arise from this contextual encoding/retrieval process, and that forgetting largely reflects the loss of effective contextual cues at retrieval. I will then show how the Context Maintenance and Retrieval model (CMR, Polyn et al., 2009)---a computational model of episodic memory---can account for these data, along with data on the role of semantic and source information in memory retrieval. Finally, I will present direct neurophysiological evidence for context reinstatement based on an analysis of intracranial recordings taken as 63 neurosurgical patients studied and recalled lists of words. We first identified a global pattern of neural activity that exhibits a fundamental property of temporal context: namely, that it changes gradually over time. Upon recalling a studied item, we found that this pattern of activity was not only similar to the pattern observed when the item was studied, but was also similar to neighboring list items with similarity decreasing reliably as a function of distance. This finding provides direct neural evidence in support of the context reinstatement hypothesis.