Vestibulomotor Coupling and Gain Associated with Cybersickness in Virtual Reality

Cybersickness is a major barrier to the adoption of virtual reality (VR), yet its underlying neurophysiological mechanisms remain poorly understood. This study investigated whether vestibulomotor responses, quantified using coherence and gain between electrical vestibular stimulation (EVS) and mediolateral centre-of-pressure (ML-CoP) responses, are associated with susceptibility to cybersickness. Thirty-eight healthy young adults (21 females, 17 males) completed a standing VR rollercoaster task while receiving continuous stochastic EVS (0-25 Hz; ±4.5 mA), with ML-CoP responses measured using a force plate. Cybersickness was assessed using the Fast Motion Sickness Scale (FMS), and participants were classified as non-sick (FMS < 5), medium-sick (FMS ≥ 5), or high-sick (terminated the VR exposure early due to intolerance). Baseline EVS-ML-CoP coherence and gain were significantly greater in high-sick than in non-sick participants, with gain increasing by 61%, indicating stronger vestibulomotor responses before symptom onset. During VR exposure, coherence declined over time in symptomatic participants but remained stable in non-sick participants. Despite this reduction in vestibulomotor coupling, postural sway variation increased in the high-sick group relative to the medium- and non-sick groups (+29% vs. -7% and -30% ML-CoP RMS, respectively), whereas vestibular-evoked response amplitude decreased. These findings indicate that greater baseline vestibulomotor responses were associated with increased susceptibility to cybersickness, whereas reductions during VR exposure were insufficient to prevent increases in sway variation and symptom progression. Together, the results suggest that baseline vestibulomotor responses are more strongly associated with cybersickness susceptibility than changes occurring during VR exposure.