Effects of Transcranial Direct-Current Stimulation on Hand Redirection

In virtual reality (VR), hand redirection (HR) has been proposed to enhance the flexibility of haptic feedback. HR takes advantage of the dominance of visual signals over proprioception signals in hand movements, which is achieved by shifting the posture and position of the virtual hand from its physical posture and position. The user does not notice this manipulation within a certain range, but the discomfort becomes apparent when the manipulation is applied beyond a certain range. Given that attention plays a pivotal role in the sensory integration of vision and proprioception, we hypothesized that interventions targeting the left dorsolateral prefrontal cortex (DLPFC), a region associated with attention, could modulate the effects of HR. This study assessed HR detection thresholds (DTs) during left DLPFC intervention using transcranial direct current stimulation (tDCS). Anodal stimulation was applied to enhance left DLPFC activity, and DTs were measured before and after the stimulation. A sham stimulation condition served as a control. In both stimulation conditions, we systematically varied the magnitude of HR from -20 deg (leftward shift) to 20 deg (rightward shift). Based on a user study, our findings revealed that DTs for leftward shifts significantly increased in the sham condition, likely due to habituation. Interestingly, tDCS effectively mitigated this increase in DTs. These results suggest that tDCS may reset the effects of HR habituation or enhance attention for HR.