Optimizing Noisy Galvanic Vestibular Stimulation Frequency Range for Enhancing Vestibular Perception and Manual Control Performance

Vestibular perceptual sensitivity was assessed using roll-tilt and interaural translation direction recognition tasks performed on a six-degree-of-freedom motion platform. Direction recognition thresholds were estimated from participant responses using an adaptive three-down, one-up staircase procedure and cumulative Gaussian psychometric curve fitting. Lower threshold values indicate greater vestibular sensitivity and improved perception of self-motion.

Perceptual motion tracking performance was evaluated during continuous pseudorandom roll motion. Participants used a joystick to continuously indicate their perceived direction and magnitude of platform motion. Performance was quantified using the root mean square error (RMSE) between joystick responses and the programmed motion stimulus, with lower RMSE values indicating more accurate perception and tracking of self-motion.

Manual control performance was evaluated during continuous pseudorandom roll motion while participants used a joystick to actively minimize platform motion by generating corrective control inputs. Performance was quantified using the root mean square error (RMSE) between the platform tilt angle and the upright position over time. Lower RMSE values indicate more effective manual control and disturbance rejection.

Vestibular perceptual threshold for roll-tilt motion was measured using a computerized three-down, one-up adaptive staircase procedure during a 1 Hz sinusoidal motion stimulus. Thresholds were estimated by fitting a cumulative Gaussian psychometric function to participants' left/right direction recognition responses. Lower threshold values indicate greater vestibular sensitivity.

Vestibular perceptual threshold for interaural translation motion was measured using a computerized three-down, one-up adaptive staircase procedure during a 1 Hz sinusoidal motion stimulus. Thresholds were estimated by fitting a cumulative Gaussian psychometric function to participants' left/right direction recognition responses. Lower threshold values indicate greater vestibular sensitivity.

Response bias during the vestibular direction recognition task was estimated from the mean of the cumulative Gaussian psychometric function. Bias represents the stimulus magnitude at which participants were equally likely to perceive motion in either direction, providing a measure of systematic perceptual offset.

Variability of perceptual motion tracking performance during continuous pseudorandom roll motion. Tracking variability was quantified using statistical measures including standard deviation and variance of tracking performance, providing an assessment of the consistency and precision of participant responses.

Variability of manual control performance during the nulling task was quantified using standard deviation, variance, and mean absolute deviation of chair tilt relative to the upright position. These measures assessed the consistency and precision of participants' ability to minimize platform motion.