Quantifying postural responses to galvanic vestibular stimulation for a four-electrode montage

Standing balance is maintained through the integration of signals from the proprioceptive, visual, and vestibular systems. Galvanic vestibular stimulation (GVS) delivered through head-worn electrodes is increasingly used in clinical vestibular rehabilitation and immersive entertainment interfaces, but it is known to impact on-feet postural stability. Prior studies assessing balance and postural effects have predominantly focused on bilateral mastoid-based uniaxial GVS paradigms. Limited research has characterized balance metrics under multiaxial GVS configurations using four-electrode montages generating multiple directional stimulation paradigms. Standing balance was assessed in healthy participants with eyes closed using a dual force-plate system to record center-of-pressure (COP) dynamics. Participants were exposed to six randomized GVS stimulation conditions across four electrodes placed on the left and right mastoids, center forehead, and nape of the neck, while static, dynamic sway, and velocity-based COP features were extracted to characterize postural responses. GVS significantly altered static, dynamic sway, and velocity-based balance measures compared with the Null condition across six stimulation paradigms. All GVS stimulations increased COP displacement, sway length, sway area, and peak velocities, while reducing sway density metrics across mediolateral (ML) and anteroposterior (AP) axes. These findings provide an early quantitative characterization of postural responses to an unconventional GVS montage and create a foundation for predicting body motion during multiaxial vestibular stimulations. Such insights are important for the safe application of GVS in standing and ambulatory contexts, including clinical vestibular rehabilitation and immersive simulation environments.