EEG and behavior were recorded in a dimly lit, electrically shielded, sound attenuated chamber to avoid line noise interference and reduce the possibility of subject-experimenter interaction during testing. HD-tACS Ag/AgCl electrodes and actiCap slim active EEG electrodes were mounted in a BrainCap elastic cap for 128 electrodes prepared with super-visc high-viscosity electrolyte gel (Brain Products GmbH, Germany). EEG was collected from 96 electrodes arrayed according to the international 10–20 system using an ActiChamp active channel amplifier sampling at 1000 Hz. The right mastoid electrode served as the online reference. Horizontal eye position was monitored by recording the electrooculogram from bipolar electrodes placed at the outer canthi of each eye, and vertical eye position and blinks were monitored with bipolar electrodes placed above and below the left orbit. All EEG processing and analysis were conducted using Matlab scripts calling on the Fieldtrip toolbox 57.
