Rebecca Weinberg¹, Yosun Yoon^1,2, Sang Wook Hong^1,2; ¹Florida Atlantic University, ²Stiles-Nicholson Brain Institute

Visual adaption is a critical tool for probing neural mechanisms of visual information processing. The current study investigates how enhanced neural excitability due to transcranial direct current stimulation (tDCS) affects motion perception using motion aftereffect (MAE). Participants completed 10 trials of MAE duration measurements in four conditions: (1) low contrast, (2) high contrast, (3) attention directed to the adapting stimulus, and (4) low contrast paired with either anodal or sham tDCS (randomized across participants) to the right visual cortex. Each trial began with participants viewing an adapting stimulus (rotating radial pattern) for 10 seconds. Following the adaptation phase, the same but static radial pattern was presented on the screen and participants were instructed to press and hold down the "z" key on the keyboard for as long as they continued to experience the MAE. The duration of the MAE was recorded as the time elapsed between the initial keypress and its release. We found that anodal tDCS significantly increased MAE duration compared to sham in the low-contrast condition, indicating enhanced neural adaptation under weak stimulus conditions. This lengthened MAE duration for the low-contrast with anodal tDCS was comparable to the MAE duration for the high-contrast adapting stimulus. Our results demonstrate that enhanced neural excitability by tDCS strengthens visual adaptation, suggesting that tDCS may elevate effective contrast of the adapting stimulus. Future research will investigate the role of tDCS across low to high contrast to reveal whether the modulational effect of tDCS on MAE is mediated by contrast gain or response gain.