The Effects of Electrical Stimulation of Ankle Tendons on Redirected Walking with the Gradient Gain

As a redirected walking technique, a method has been proposed to enable users to walk in an undulating virtual space even in a flat physical environment by setting the slope of the floor in the virtual environment to be different from that in the physical environment without causing discomfort. However, the slope range in which discrepancies between visual and proprioceptive sensations are not perceived is limited, restricting the slopes that can be presented. In this study, we proposed redirected walking using electrical stimulation of the Achilles and tibialis anterior muscle tendons, extending the applicable slope range of redirected walking without compromising the natural gait sensation. Electrical stimulation of the ankle tendons affects the proprioceptive sensation and gives the illusion of tilting in the standing posture, expanding the applicable slope range. Two experiments showed that the proposed method improved the experience of uphill and downhill walking in terms of the range of the virtual slope where a high naturalness of gait and a high congruency of visual and proprioceptive sensations are maintained. Notably, electrical stimulation of the Achilles tendons significantly improved the naturalness of the walking experience during virtual downhill walking, which has been considered more challenging in previous studies.