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Poster A11, Wednesday, November 8, 10:30 – 11:45 am, Harborview and Loch Raven Ballrooms

Transcranial 10-Hz stimulation but also eye closure modulate auditory attention

Malte Wöstmann1, Lea-Maria Schmitt1, Johannes Vosskuhl2, Christoph S. Herrmann2, Jonas Obleser1;1Department of Psychology, University of Lübeck, Germany, 2Department of Psychology, Oldenburg University, Germany

When humans focus attention to auditory events, neural alpha oscillations (~10 Hz) in the Magneto-/Electroencephalogram (M/EEG) increase in power. Here we test whether experimentally induced increases in alpha power modulate auditory attention. In two studies, healthy human participants attended to spoken target digits against distractors. Alpha power was increased exogenously through transcranial alternating current stimulation (tACS), or endogenously through eye closure. In study I (n = 20), participants were cued to attend to a stream of four spoken digits presented to one ear, while ignoring a distracting (same-talker) stream of digits presented to the other ear. Previous M/EEG studies have shown that such dichotic tasks increase alpha power in auditory and parietal cortex ipsilateral to the focus of attention. To manipulate this alpha lateralization, we applied continuous 10-Hz tACS to temporal and parietal scalp regions in the left hemisphere (1 milliamp; stimulation sites FC5 and TP7). To control for the effect of stimulation frequency, each participant also received sham and gamma-tACS (47.1 Hz). Compared to sham, left-hemisphere alpha-tACS enhanced the recall of target digits in ‘attend-left’ versus ‘attend-right’ trials, while the opposite was found for gamma-tACS. This suggests that an exogenous increase in lateralized alpha power relatively suppresses auditory spatial attention to the side opposite to stimulation. In study II (n = 22), we sought to invoke an endogenous increase of alpha power instead while presenting participants with two alternating (different-talker) streams of five spoken digits. On each trial, participants were instructed to attend to one stream and to ignore the other. In blocks where they closed their eyes (in a dark room; compared to keeping their eyes open), participants induced a baseline increase in parieto-occipital EEG alpha power. During a trial, baseline-corrected alpha power fluctuated rhythmically, with alpha peaks preceding onsets of attended digits by ~100 ms. This attentional modulation of alpha power strongly increased with closed compared to open eyes, demonstrating that eye closure boosts the neural difference in auditory attending versus ignoring. However, eye closure did not enhance participants’ ability to afterwards tell attended from ignored digits, which contradicts the widely held belief that eye closure per se enhances the behavioral outcome of attentive listening. In sum, the observed impact of eye closure and alpha-tACS on neural alpha dynamics and behavioral corollaries suggest that alpha power is more than a mere epiphenomenon but neurally and behaviorally relevant to auditory attention.

Topic Area: Control, Selection, and Executive Processes

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