Postural stability during illusory self-motion-interactions of vision and touch

The role of vision in stabilizing balance has long been recognized, and previous studies have shown that non-supportive fingertip touch can enhance postural stability. However, the interaction between haptic feedback and the illusion of self-motion remains underexplored. We investigated how different phases of visual motion (no motion, visual motion, self-rotation and displacement illusion), motion order (stationary first vs. motion first), and fingertip cutaneous feedback jointly influence balance and the dynamics of haptic contact. Using a head-mounted display, we presented a virtual room that rotated around the standing participants' vertical axis. Participants viewing the rotating scene soon experience illusory self-motion and displacement. We examined how the moving visual scene destabilized posture and how it interacted with tactile cues that typically stabilize balance. Our findings revealed differential effects in classical and stochasticity-sensitive analyses. Postural regulation was distinctly influenced by motion phase, order, and tactile feedback. Changes in motion perception-no motion, visual motion, and apparent self-rotation-were linked to both classical and stochastic aspects of postural sway. In contrast, motion order specifically influenced balance metrics encoding stochasticity, with no effect on those filtering out stochastic variability. Notably, the influence of past visual motion perception persisted, affecting postural sway even after motion ceased. The stabilizing effects of touch were reaffirmed, and motion perception significantly influenced the applied touch forces. Both stochastic and non-stochastic attributes of balance and touch force are responsive to visual motion perturbations and illusions, though motion order exclusively affects stochastic dynamics. These findings provide insights into multisensory interactions.