Figure 1.

Experimental design. (A) tACS and EEG electrode positioning. EEG electrodes were positioned at PO7, PO8, P3, P4, Fz, and Fpz. tACS electrodes were positioned at Oz and Cz. (B) Illustration of a single, audio-visual switch trial. (i) During the cue presentation period, which lasted for 250 ms, a word was presented in the central box telling participants which task to perform (“MOTION,” “COLOUR,” or “SOUND”). (ii) This was followed by the stimulation presentation period, during which the outer box filled with either red or blue, the inner box filled with black dots that moved in either an upward or downwards direction, and the letter “E” or “O” was played through earphones. This period lasted for 300 ms. (iii) Participants could respond until the end of the post-stimulus period, which lasted for 1,250 ms. (C) Task and stimulation timing. Participants performed five task blocks in a single task session, with each block lasting 4 min and 50 s. A fixed-duration break of 100 s was allowed between blocks. EEG was recorded before and after the delivery of stimulation. During alpha and gamma tACS, stimulation was applied for 19 min and 30 s from the start of the second block to the start of the fifth block. During sham tACS, stimulation was applied at 10 Hz during only the first 50 s of this period (including ramp-up and down times). Participants each performed two task sessions (i.e., 8 blocks in total), separated by a break of 25 min.