The effect of optical illusions on the vestibular system in individuals with motion sickness: An analysis of sensory reweighting

Exposure to optical illusions during postural control activates the sensory reweighting system. However, the impact of optical illusions on the vestibular system in individuals with motion sickness (MS) remains unclear. This study aims to investigate the effects of optical illusions on the vestibular system in individuals with MS. The study included 33 individuals with MS (MS group) and 34 individuals without MS (control group). The severity of MS was assessed using the Motion Sickness Susceptibility Questionnaire. All participants underwent cervical vestibular evoked myogenic potentials (cVEMP) test, video head impulse test (vHIT), and static posturography, both with and without optical illusions. There were no significant differences between the groups in vHIT and cVEMP responses under both optical illusion-free and optical illusion-present conditions (p > 0.05). However, the postural stability of the MS group with eyes closed was worse compared to the control group (p < 0.05). Optical illusions were found to decrease bilateral lateral semicircular canal (SSC) VOR gains and postural stability in both the MS and control groups (p < 0.05). Additionally, optical illusions significantly reduced the left anterior SSC VOR gains in the MS group (p = 0.042). Our findings indicate that the sensory reweighting system is activated during vection, leading to a reduction in vestibular inputs and an increased reliance on the visual system. The observed decrease in left anterior SSC VOR gains in the MS group compared to the control group during vection may suggest that these individuals rely more heavily on the visual system or exhibit increased visual dependence.