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Garance Merholz, Rufin VanRullen, Laura Dugué; Oscillations modulate attentional search performance periodically. Journal of Vision 2019;19(10):279b. doi: https://doi.org/10.1167/19.10.279b.
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Is attention processing information continuously, or as a discrete sequence of events, like samples from a video camera? If attention is periodically modulating behavioral performance, it should be supported by periodicity in its neural correlates. Previous studies have shown that attentional performance in visual search—looking for a target among similar looking distractors—is periodic at the theta frequency (~6Hz), and that this periodicity is underlined by brain oscillations at the same frequency. We hypothesize that if oscillations are the support of attentional periodicity, the more time one spends exploring the environment, the longer the neural oscillatory process should last. Participants (n = 12) performed a visual search task (looking for the letter T among Ls) in which we varied the number of elements in the set (4 vs. 8) and simultaneously measured electro-encephalography (EEG). The behavioral data show a better sensitivity and faster reaction time in the smaller set size condition, suggesting that attention was successfully manipulated, with no speed-accuracy trade-off. Moreover, we replicated previous results: the phase of pre-stimulus, spontaneous, low-frequency oscillations predicted attentional search performance, i.e. successful and unsuccessful search trials were associated with opposite oscillatory phases. We further observed that search performance was associated with different amounts of post-stimulus oscillatory phase-locking (i.e. phase coherence across trials) in the alpha (8–12Hz) and theta (4–7Hz) frequencies. The alpha effect peaked early, and was localized in the frontal electrodes. The theta effect peaked later and was localized in the occipital electrodes. We speculate that alpha reflects top-down, voluntary attention, while theta reflects attentional exploration. Our study suggests a close relation between attentional sampling and low-frequency brain oscillations.
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