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Ayelet Landau, Helene Schreyer, Stan Van Pelt, Pascal Fries; Evidence for Attentional Sampling in the MEG Gamma Band Response. Journal of Vision 2013;13(9):225. doi: https://doi.org/10.1167/13.9.225.
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Overt exploration or sampling behaviors, such as whisking, sniffing, and saccadic eye movements are often characterized by a theta/alpha rhythm (4-10Hz; Otero-Millan, Troncoso, Macknik, Serrano-Pedraza and Martinex-Conde, 2008; Buzsaki, 2006). In addition, the electrophysiologically recorded theta or alpha phase predicts global detection performance (Busch, Dubois and VanRullen, 2009; Methewson, Gratton, Fabioani, Beck and Ro, 2009). These two observations raise the intriguing possibility that covert selective attention samples from multiple stimuli rhythmically. To investigate this possibility, we measured change detection performance on two simultaneously presented stimuli. Previously we have found that following a reset event to one location, detection performance fluctuated rhythmically. Additionally, different locations were associated with different (opposing) phases of the rhythmic sampling supporting a sequential model of sampling. This suggests that selective attention entails exploration rhythms similar to other exploration behaviors. Spatial attention has been mechanistically linked to gamma band activity in visual brain regions. Gamma band synchronization is a proposed mechanism supporting inter-areal communication of behaviorally relevant stimuli (Bosman et al., 2012). In the present study, we used MEG to identify bilateral sources of gamma-band activity induced by two corresponding contralateral stimuli. In contrast to the behavioral evidence, the assessment of stimulus-specific gamma responses allowed the investigation of fluctuations preceding lateralized target events without requiring a flash event. We find that band-limited power in the gamma band fluctuates at a theta/alpha rhythm, and the phase of gamma-band power fluctuations predicts behavioral outcome. Importantly, different behavioral outcomes (hits vs. misses) are preceded by opposing phases of the theta/alpha fluctuations. These findings provide further support for the idea that attention to multiple locations is supported by sequential sampling and suggest a functional role for cross frequency coupling between sustained gamma band response and lower frequencies in the theta/alpha range.
Meeting abstract presented at VSS 2013
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