Phantom Vibrotactile Sensations on the Plantar Surface: A Wearable Insole Pilot Study

Vibrotactile feedback at the foot sole is investigated for rehabilitation, pedestrian navigation, and virtual ground rendering. The spatial resolution of such displays is bounded by the number of physical actuators. Phantom sensations increase the perceived resolution by rendering virtual stimuli between neighboring actuators, yet their use on the plantar surface is largely unexplored. We present a wearable vibrotactile insole with eight linear resonant actuators and report preliminary results from the first 8 participants of an ongoing localization study comparing real and phantom stimuli under static (standing) and dynamic (walking) conditions. Reported errors are medians with their interquartile range (IQR). In the static condition, phantom stimuli show descriptively larger median errors than real actuators (34.7 mm, IQR 26.8 to 40.2 vs 20.3 mm, IQR 19.8 to 26.2). During walking the gap closes, with phantom errors remaining stable (33.4 mm, IQR 26.1 to 38.9) while real errors increase to 32.8 mm (IQR 24.3 to 40.9). Phantom errors remain comparable to real-actuator errors across both conditions, suggesting that phantom sensations transfer to the plantar surface and can increase the resolution of wearable foot-sole displays.