Abstract
tACS is a noninvasive method to modulate brain oscillation and functions. Although there is rapidly growing interest in using tACS to modulate visual perception (e.g., motion perception) in humans, previous findings are inconsistent and some of them have been shown to be unreliable. Here, we recruited 11 subjects and tested the tACS effect on their motion direction identification. One electrode was place at PO7-PO3 in the 10-20 EEG system (left hemisphere) and the other electrode was placed on the vertex (Cz). We used a sinusoid current (1 mA peak to peak) at a frequency of 10 Hz, which was delivered during visual stimulus presentation. Visual stimuli were random dot kinematograms (RDKs) consisting of 700 dots. The dots moved at a velocity of 3°/s within a virtual circular area subtending 10° in diameter. The center of the aperture was positioned 7° horizontally to the left or right of the central fixation point. The coherence level of the RDKs could be 0%, 2%, 4%, 8%, or 16% and those coherent dots moved either upward or downward. Each of the nine stimuli (i.e., a combination of coherence level and motion direction) were presented 50 times and each presentation lasted 4 sec. Subjects needed to make a two-alternative forced-choice (2-AFC) judgment to identify the global motion direction (either upward or downward). Eye movement was recorded to ensure that subjects' eye positions were within a 2° window around fixation. We found that, relative to the no-tACS condition, subjects' motion identification accuracy could be significantly improved by 10Hz tACS. The improvement occurred when the stimulus were presented in either the left or the right visual field. Our finding demonstrated that visual motion perception could be enhanced by tACS and suggest that the mechanisms underlying the enhancement might not be restricted to retinotopic visual areas.
Meeting abstract presented at VSS 2018