Stimulus-specific postural responses to optokinetic stimulation using a semi-immersive virtual reality system

Background Virtual reality (VR)-based balance assessment tools are increasingly integrated into vestibular rehabilitation, yet preliminary reference data for semi-immersive optokinetic stimulation (OKS) remain limited. The Computer-Assisted Rehabilitation Environment (CAREN), a semi-immersive projection-based system, may reduce the risk of cybersickness compared to head-mounted displays, but its utility for characterizing stimulus-specific postural responses in healthy adults has not been established. Methods One hundred healthy participants underwent 12 trials, including pre- and post-test eyes-open and eyes-closed baselines and eight directional OKS conditions (yaw, pitch, roll, tunnel flow). Postural sway was quantified via center-of-pressure (COP) metrics: mean COP position, mean distance, root mean square (RMS) distance, mean velocity, and 95% confidence ellipse area. Results OKS increased postural sway relative to the eyes-open baseline, but the effect was stimulus- and metric-specific. Roll-plane OKS (clockwise and counter-clockwise) produced the largest disruption, with ellipse area more than three times the baseline value ( p < 0.001). Tunnel flow caused less postural disruption than roll. Sway increases were mainly anterior-posterior; ellipse area and medial-lateral RMS increased only during roll. Mean COP position showed a significant unidirectional lean only during roll (rightward with clockwise rotation, leftward with counter-clockwise rotation). Exploratory analyses found no association with age or sex. Conclusion Semi-immersive OKS elicits reproducible, stimulus-specific postural responses in healthy adults, with roll-plane stimuli producing maximal instability and tunnel flow engaging distinct adaptive mechanisms. These preliminary reference data provide benchmarks for characterizing healthy postural responses to semi-immersive OKS and support the design of future studies to validate stimulus-specific OKS paradigms in clinical populations.