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Jie Huang, Robert Sekuler; α-oscillations and the fidelity of visual memory. Journal of Vision 2010;10(7):715. doi: 10.1167/10.7.715.
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Low amplitude of α-oscillations in EEG is associated with selective attention, and has been taken as a sign of enhanced neuronal processing in task-relevant cortical areas (W. Klimesch). As ﬁdelity of encoding is a prerequisite for visual memory, we hypothesized that α-amplitude would be inversely related to the ﬁdelity with which a visual stimulus is encoded and later recalled. We tested this hypothesis by recording scalp EEG while subjects attended to lateralized Gabors whose spatial frequency they would have to reproduce from memory. On each trial, two Gabors were presented simultaneously for 300 msec, one to the left of ﬁxation, the other an equal distance to the right. Either before stimulus presentation or after, subjects were cued which Gabor's frequency they would have to reproduce from memory; subjects were to ignore the non-cued stimulus. Each trial's reproduced spatial frequency showed a strong inﬂuence from information that is not relevant to the task, that is, reproductions were attracted toward the average spatial frequency of Gabors seen on preceding trials. This effect was greatly reduced when the cue preceded the stimulus pair rather than followed it. This improved suppression of task-irrelevant information was accompanied by a consistent change in the contralateral α amplitude. At various, widely-distributed electrode sites, we saw a lateralized, attention-driven reduction in α amplitude, implying enhanced processing of the cued Gabor. However, occipito-parietal electrode sites showed lateralized α amplitude only during early visual encoding (0-200 msec after stimulus onset). Moreover, this reduced α amplitude at contralateral occipito-parietal locations to the cued Gabor was associated with a reduction in the influence of task-irrelevant information from preceding trials. These results suggest that neural enhancement of relevant information is a determinant of optimal memory performance, and that it protects remembered stimulus from intrusion of irrelevant information.
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