| Summary: | <p>This project studied the effects of 10-Hz (alpha)-tACS, delivered over occipitoparietal cortex, on sustained attention. Poor performance on all visual tasks used in this project had previously been associated with increased EEG alpha power. I therefore assumed that alpha-tACS would reliably impair visual task performance. However, my results did not support this prediction. In my first two experiments (Chapters 4 & 5), alpha-tACS was found to reduce the slope of deteriorations in task performance that otherwise occurred during control-tACS (i.e. sham- and 50-Hz-tACS). In my third experiment, an auditory control task indicated that such effects are specific to the visual domain (Chapter 6). Furthermore, in a fourth experiment, in which tACS was delivered during a visual task where performance naturally improved over time, alpha-tACS was conversely found to limit the slope of such improvements (Chapter 7). Therefore, regardless of whether task performance improved or deteriorated naturally over time, alpha-tACS seemed to exert a consistently stabilising effect on visual attention. I tested this hypothesis in my fifth experiment, in which alpha-tACS was delivered during an audiovisual switching task. I assumed that, if alpha-tACS stabilises visual attention, this stimulation should impair switching between visual tasks, but leave switching from visual to auditory tasks unaffected. In contrast to this prediction, alpha-tACS was not found to influence visuovisual vs. audiovisual switching. However, alpha-tACS was found to exert a trend-level, impairing effect on visuoauditory switching accuracy, suggesting that this stimulation may help to focus visual attention by preventing transitions of attention away from the visual domain (Chapter 8). A final experiment indicated that 4-Hz-tACS exerts weak, but descriptively similarly effects on visual task performance to those observed during alpha-tACS in my first two experiments (Chapter 9). Throughout these studies, tACS was found to have highly variable and inconsistent effects on EEG power. Overall, these results provide intriguing evidence to suggest that low-frequency tACS can be used to stabilise performance on a range of visual attention tasks. However, the usefulness of tACS for purposes of cognitive enhancement in real-world settings may be limited by the small magnitudes of its influence on both brain activity and behaviour.</p>
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