Visual and vestibular reweighting after cyber- and space-sickness

ABSTRACT Sensory conflicts are widely recognized as the primary drivers of motion sickness (MS), though the underlying integrative processes remain poorly understood. This study investigated sensory reweighting that follows exposure to different sensory conflict paradigms. First, visual and vestibular reflexes were assessed before and after a visuo-vestibular conflict induced by purely visual stimulation in virtual reality. Second, visual and vestibular integration were evaluated before and after an otolith-canal conflict induced by gravitational changes in parabolic flight. Semi-circular canal integration was measured via the vestibuloocular reflex (VOR) suppression task, while visual weighting was assessed through optokinetic nystagmus (OKN). Our findings revealed that different sensory conflict paradigms elicit distinct sensory reweighting processes. Visuo-vestibular conflict resulted in a decreased VOR response, whereas vestibulo-vestibular conflict mainly led to a reduction in OKN following parabolic flight. Sensory down-weighting occured in the modality that did not detected displacement, likely perceived as the less reliable input, regardless of its accuracy. Additionally, visual sensitivity emerged as a potential predictor of cybersickness, while vestibular sensitivity seemed to influence MS severity in parabolic flight. Our data suggest that the sensitivity of the most stimulated sensory modality during a given conflict may determine an individual’s susceptibility to MS. KEY POINTS Sensory reweighting occur through brief and specific exposure to motion sickness. Adaptive reweighting is modulated by the nature of the motion sickness exposure, with distinct effects observed between space-sickness and Earth-like motion sickness cues. Motionless cues are consistently downweighted, regardless of their accuracy. Motion sickness intensity depends on individual’s sensitivity to the stimulated sensory sources, which varies across provocative sensory environments.