Head tilt–induced spatial orientation errors associated with functional vestibular disorders and motion sickness susceptibility during non-driving activities in a moving vehicle

BackgroundPersistent postural-perceptual dizziness (PPPD) and motion sickness (MS) are associated with disturbances in spatial orientation related to altered multisensory integration. Impaired perception of upright orientation during head tilt may therefore occur in these conditions. Subjective visual vertical (SVV) and subjective visual horizontal (SVH) testing under head-tilted conditions provide quantitative measures of such perceptual errors. We hypothesized that headtilt-induced perceptual errors would be associated with PPPD and with susceptibility to clinically significant MS during non-driving tasks.Methods80 participants were enrolled: 27 healthy controls, 36 individuals with high Motion Sickness Susceptibility Questionnaire scores who reported MS during real-world driving, and 17 patients with PPPD diagnosed according to the Bárány Society criteria. SVV and SVH were measured at ±30° and ±60° head-roll tilts in a virtual environment. Perceptual error was defined as the signed deviation from the true vertical or horizontal orientation. Diagnostic accuracy was assessed using receiver operating characteristic analysis.ResultsSVV and SVH errors under head-tilt conditions differed significantly between groups, with healthy controls showing contraversive deviations and both individuals with high-MS and patients with PPPD exhibiting ipsiversive deviations, particularly at ±60° roll tilts, whereas errors in the upright (0°) position were negligible. Several tilt conditions demonstrated excellent diagnostic accuracy (AUC ≥ 0.90). Real-world MS severity correlated with ipsiversive SVV errors but not with questionnaire-based susceptibility scores.ConclusionsBased on the present findings, further methodological refinement may allow head-tilt SVV/SVH testing to serve as a rapid and sensitive tool for detecting perceptual alterations underlying functional dizziness, with translational potential for MS risk screening in future autonomous vehicle environments.