Vestibular time constant and individual susceptibility to motion sickness in real-world driving.

Motion sickness is an important challenge for the acceptance of autonomous vehicles. Although the Motion Sickness Susceptibility Questionnaire (MSSQ) is widely used, it relies on retrospective self-report and does not directly capture vestibular characteristics. This study examined the association between the vestibular time constant (VTC), which reflects the velocity storage mechanism, and motion sickness severity during on-road driving. VTC was measured in 24 female adults; 21 completed four 30-min acceleration sessions, and all 24 completed nine 30-min deceleration sessions involving regenerative braking. Motion sickness severity was repeatedly assessed using the Misery Scale (MISC). MSSQ scores showed weak, non-significant associations with MISC-derived outcomes, whereas longer VTCs were associated with greater symptom severity, particularly under deceleration and among participants who developed symptoms. Participant-level receiver operating characteristic analyses showed that the VTC discriminated participants who reached the nausea threshold (MISC ≥ 6) better than the MSSQ. Under deceleration, this difference was significant (area under the curve, 0.89 versus 0.60; DeLong p = 0.048). VTC associations were descriptively stronger under deceleration, possibly reflecting condition-specific characteristics of braking-related vestibular stimulation. These findings indicate that the VTC provides objective physiological information that may complement questionnaire-based susceptibility assessment in automotive environments.