Standing balance responses and habituation to sinusoidal optic flow virtual reality perturbations.

This study investigated the effects of prolonged virtual reality (VR) optic flow exposure on standing balance, focusing on how optic flow parameters influence balance responses and the potential for habituation. While short-term responses to optic flow are well-documented, the impact of extended VR immersion (up to 60 min) on balance remains poorly understood. Twenty healthy young adults were exposed to sinusoidal optic flow stimuli in a novel VR environment, with different velocities (0.1, 1, 10 m/s) and frequencies (0.125, 0.25, 0.5 Hz). Balance responses were assessed using a force plate to measure anteroposterior centre of pressure (CoP) velocity (AP-Vel) and mean power frequency (MPF). VR optic flow elicited significantly greater AP-Vel (P < 0.0001) and MPF (P < 0.0001) compared to non-VR eyes open conditions, with higher optic flow velocities and frequencies inducing greater balance responses (AP-Vel: P = 0.0322; MPF: P = 0.0027). Despite prolonged VR exposure, no evidence of habituation was observed within 90-second trials (P > 0.2110) or over the 40-60-minute experiment (P > 0.6724). Participants reported increased physical (P = 0.0010) and mental fatigue (P = 0.0005) by the end of the experiment, though this did not affect balance. These findings highlight the sensitivity of standing balance to VR optic flow parameters and the stability of balance responses over prolonged VR exposure, even with perceived fatigue. This research advances our understanding of sensory integration in postural control and informs the use of VR for research, rehabilitation, and entertainment.