Developing a Neurocognitive Model of Temporal and Semantic Organization of Memory Search
Morton, Neal W
Decades of research have established that prior semantic knowledge exerts a strong influence on how new experiences are remembered, causing strengthening, reorganization, or even distortion of episodic memories. However, many questions remain about the cognitive mechanisms and neural substrates involved in these interactions between episodic and semantic memory. Retrieved-context theory proposes that a critical component of episodic memory for an event is the temporal context in which that event occurred. This temporal context is assumed to accumulate information about the content of recently experienced events. Consistent with this prediction, recent scalp electroencephalography (EEG) findings suggest that oscillatory brain activity contains information about the recent history of presented stimuli. We developed a computational model of temporal context evolution that successfully accounts for individual differences in this oscillatory activity during study, as well as individual differences in the degree to which recall is organized by stimulus category. Based on prior work, we predicted that distracting activity between studied items would disrupt the accumulation of semantic information over multiple items, and that this decrease in contextual integration would result in decreased semantic organization. Consistent with these predictions, we found that category-specific oscillatory activity increased as multiple items from the same category were presented; this integrative signal was attenuated by inter-item distraction. Furthermore, category clustering was decreased in the distraction condition, while temporal organization, the tendency to successively recall items studied nearby in time, was unaffected. Finally, we developed a model of temporal and semantic organization that can make predictions about memory search on a recall-by-recall basis. We demonstrated that this modeling framework can be used to test hypotheses about how concepts are associated in semantic memory and how these associations affect memory search.