Stephanie Dietz¹ (), Anupama Nair², Jared Medina³; ¹Emory University, ²University of Delaware

Information from different senses is weighted based on their relative precision. For instance, in the mirror box illusion, the greater spatial precision of vision compared to proprioception causes observers to feel their hand in its seen location rather than its actual location. How does the brain resolve conflicting visual and tactile information? To address this question, we ran three experiments using a novel mirror box illusion. Both hands (one hand in front of the mirror, one hand behind the mirror) were stroked simultaneously across the entire hand dorsum in congruent or incongruent directions (stroke disparity ranging from 45-180°) for 30 seconds with the mirror viewed or covered. Participants then reported the perceived stroke direction on their hidden hand. We found evidence for a visuotactile illusion, such that participants frequently perceived touch in the seen direction rather than the actual direction. Interestingly, when the angular disparity was 180° (e.g., viewed stroke towards the fingers, felt stroke towards the wrist), we observed an all-or-nothing effect, such that participants reported either the actual touch or complete visual capture. To investigate whether the effect of vision is modulated by hand realism, we examined performance with a real or rubber hand. Although we predicted greater illusion for the real than rubber hand, we found no difference between the two conditions, suggesting that body ownership may not modulate the illusion. Lastly, to determine whether vision influences the perception of tactile stroke direction in a hand-centered or external reference frame, we varied the posture of the viewed hand relative to the hidden hand (0-90°). When the viewed hand was rotated and stroke direction was somatotopically congruent, participants reported a shift in perceived stroke direction towards the visual stroke direction in external space. Our results suggest that visuotactile temporal congruence can override spatial incongruence, leading to illusory percepts.