Less is More: Step-Synchronized Mastoid Vibration for Comfort-Preserving Redirected Walking

Redirected Walking (RDW) enables users to explore large virtual environments within limited physical spaces by exploiting tolerances in self-motion perception. Previous research has shown that adding vestibular noise through electrical or continuous vibratory stimulation can increase redirection detection thresholds (DTs). However, electrical stimulation may compromise gait stability, while continuous vibration can induce discomfort. Therefore, alternative approaches that better balance effectiveness and user comfort are needed. To address this issue, this study investigates whether temporally synchronizing vestibular vibration with gait events can enhance redirection tolerance while preserving comfort and locomotor stability. Thirty-six participants performed a curvature-based RDW task under three conditions: no vibration, continuous vibration, and stepsynchronized vibration. DTs were estimated using a two-alternative forced-choice paradigm combined with psychometric modeling. Subjective discomfort, simulator sickness, and presence were also assessed, alongside objective gait stability measures obtained through markerless motion analysis. Results showed that both vibration conditions significantly increased curvature DTs compared with the no-vibration baseline. Notably, step-synchronized vibration produced curvature DTs comparable to continuous vibration while significantly reducing discomfort. Furthermore, simulator sickness, presence, and markerless gait analysis showed no significant differences across conditions. These findings suggest that gait-synchronized vestibular vibration enhances redirection tolerance while preserving comfort and gait stability.