Abstract
Background: The ability to strategically retrieve task-relevant information from episodic memory is thought to rely on goal-directed executive processes, and there is evidence that neural correlates of strategic retrieval are sensitive to reserves of cognitive control. The present study extended this work, exploring the role of cognitive control in the flexible orienting of strategic retrieval processes across alternating retrieval goals. Method: Pre-stimulus cues directed participants to endorse memory targets from one of two encoding contexts, with the target encoding context alternating every two trials. Items from the nontarget encoding context were rejected alongside new items. One group of participants completed a Stroop task prior to the memory test in order to deplete their reserves of cognitive control, while a second group performed a control task. Event-related potentials (ERPs) were recorded throughout the memory task, and time-locked to both pre-stimulus cues and memory probes. Results: Control participants' pre-stimulus ERPs showed sustained divergences at frontal electrode sites according to retrieval goal. This effect was evident on the first trial of each memory task, and linked with the initiation of goal-specific retrieval orientations. Control participants also showed enhanced ERP correlates of recollection (the 'left parietal effect') for correctly classified targets relative to nontargets on the second trial of each memory task, indexing strategic retrieval of task-relevant information. Both the pre-stimulus index of retrieval orientation and the target/nontarget left parietal effect were significantly attenuated in participants that completed the Stroop task. Conclusions: The reduction of pre-stimulus and stimulus-locked ERP effects following the Stroop task indicates that available reserves of cognitive control play an important role in both proactive and recollection-related aspects of strategic retrieval.
Highlights
The retrieval of episodic information in accordance with current goals is enabled by an ensemble of memory control processes which occur prior to, during and after the reactivation of the episodic trace
Switching between different memory tasks requires a greater degree of cognitive control, and it was predicted that event-related potentials (ERPs) measures of strategic retrieval would be more vulnerable to the Stroop manipulation
It was predicted that ERP measures of strategic retrieval in a task-switching design would be attenuated in participants who first completed the Stroop task
Summary
The retrieval of episodic information in accordance with current goals is enabled by an ensemble of memory control processes which occur prior to, during and after the reactivation of the episodic trace. Task-switching memory studies have revealed that pre-stimulus cues signalling the onset of different source memory tasks elicit sustained slow-wave ERPs that diverge at frontal electrode sites according to retrieval goals. Task-switching memory studies have revealed that pre-stimulus cues signalling the onset of different source memory tasks elicit sustained slow-wave ERPs that diverge at frontal electrode sites according to retrieval goals2 This effect occurs only when a new memory task begins, linking it with processes involved in the initiation of orientations (e.g. task-set configuration) rather than their maintenance throughout tasks. A large body of ERP and fMRI research supports this view, and an individual differences analysis demonstrated that this index is positively correlated with memory accuracy25 This is an indirect measure of retrieval orientation, reflecting task-specific processes operating downstream from those directly involved in sustaining the orientation. There were two principal experimental hypotheses: i) participants completing the Stroop task would show attenuated pre-stimulus ERP measures of retrieval orientation initiation on the first trial of each memory task when compared with controls, and ii) item-locked ERP measures of strategic retrieval (i.e. greater positivity for targets than for nontargets between 500–800ms) would be evident in the control group but reduced in the Stroop group
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