The temporal dynamics and preparatory nature of oscillatory EEG correlates of retrieval orientation
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Retrieval of episodic memories is classically considered to be a function of cue-trace overlap, in which incidental internal or external cues reactivate similar patterns of brain activity as were first activated during encoding. However, retrieval is also supported by strategic, goal-directed processes that increase an individual's chance of successfully completing a memory search. One such method is through the adoption of a "retrieval orientation," in which the same retrieval cue may be processed differently (and used to retrieve different kinds of information) depending on current retrieval goals. Prior studies investigating retrieval orientation have shown that event-related potentials (ERPs) reliably differ according to different aspects (item form, modality, and associated tasks) of targeted memories that were previously established during encoding. In two experiments, we expanded existing evidence for retrieval orientation to the domain of oscillatory EEG activity by: 1) investigating differences due to item form and varying levels of required specificity, and 2) assessing characteristics of an optimal orienting state by relating activity to behavioral indices of performance. We found increased beta and gamma activity over right frontal areas related to a general orienting state (compared to simple recognition), as well as increased theta over right central sites associated with a general orienting state compared to an orienting state requiring a higher degree of specificity. In contrast to prior ERP experiments, we failed to observe statistically reliable effects related to orienting to item form in either of our two experiments. These findings highlight the need for additional research on oscillatory activity pertaining to episodic memory retrieval, as well as the further development of other methods that might be more sensitive to detecting individual differences in retrieval strategies.
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