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Aleksandra Pastuszak, Kimron Shapiro, Simon Hanslmayr; The role of pre-stimulus alpha oscillation in distractor filtering during a Visual Search task. Journal of Vision 2018;18(10):979. doi: 10.1167/18.10.979.
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It is widely accepted that high occipital alpha power is detrimental to performance on visual perception tasks(Ergenoglu, et al.,2004). However, given the evidence of occipital alpha oscillations playing a role in inhibition of distracting stimuli(Worden, 2000; Foxe, et al., 1998), we hypothesize that pre-stimulus alpha power acts as a filter for interfering stimuli, which can be optimised based on the expected amount of distracting information. We investigated this relationship between pre-stimulus alpha power and attention using a conjunction Visual Search(VS) task(Triesman, et al. 1980). Based on previous research and pilot data we anticipated a negative correlation between pre-stimulus alpha power and reaction times(RTs), with high alpha power being related to improved performance, reflecting the inhibition of distractors. We also expected that anticipation of the difficulty of oncoming trials, would result in modulation of pre-stimulus alpha power, with high set size conditions showing higher alpha power as compared to low set size conditions. Thus, we conducted two VS studies using electroencephalography. In Experiment 1 set size conditions were randomly intermixed throughout the experiment, and thus the oncoming trial difficulty was not predictable. In Experiment 2 we employed a blocked design, preceding each block with information of the set size so that trial difficulty could be anticipated. In both experiments we find a significant negative correlation between pre-stimulus occipital alpha power and RTs, in the high set size condition, with high alpha power being related to faster RTs and vice versa. We show, that when it is possible to anticipate task difficulty, pre-stimulus alpha power is modulated in preparation, with high set size conditions showing significantly higher pre-stimulus alpha power as compared to low set size conditions. These results indicate that occipital alpha is indeed a filtering mechanism which can be optimised depending on the amount of anticipated distracting information.
Meeting abstract presented at VSS 2018
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