Multisensory processing during self-motion

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Think about a time you or a friend felt motion sick. Perhaps you were in the backseat of a car on a twisty road. Maybe, you were on an amusement ride, where you and your friend were on a spaceship zipping around a virtual world. Why is it that only one of you got sick? Now imagine a time you fell down. Perhaps you tripped, fell down the stairs, or slid on some ice. Do you have a good sense of recalling the full sequence of events from the onset of the fall? Perhaps you remember just one moment such as the blueness of the sky or reaching out to a rail on your way down. We know relatively little about how sensory information is processed during self-motion (even less during a fall) and what can predict the incidence of motion sickness across individuals. My past research has shown that the brain dissociates how it processes vestibular signals (information about head movement) for generating reflexive responses and for making perceptual responses, and that individuals vary when judging the perceived relative timing of sensory events. The goal of this proposal is to develop a comprehensive model of how the timing of multisensory events affects perceptual, physiological, and neural responses to self-motion. I will develop three themes: (1) PERCEIVED TIMING OF MULTISENSORY EVENTS DURING SELF-MOTION. My recent work has found that vestibular information must be presented prior to other sensory events in order to be perceived as simultaneous. This suggests, surprisingly, that vestibular perception is slow while vestibular reflexes are fast. I expect to find similar results when people fall. Much needed parametric assessment of perceived vestibular delay paired with physiological and neural responses to self-motion will be used to construct a theoretical model of the neural mechanisms that subserve delayed vestibular perception. (2) SENSORY CUE INTEGRATION DURING SELF-MOTION. Maximum-likelihood estimation can be used to reliably predict how sensory cues are integrated by the brain. To investigate cue combination for self-motion quantitatively, variances associated with visual and vestibular estimation of self-motion are independently measured, combined by a maximum-likelihood integrator, and compared to perceived self-motion with both cues present. I expect that discrepancies in finding optimal integration of visual and vestibular cues in the literature result from change in visual sensitivity during self-motion and perceived temporal delays between sensory cues. (3) MOTION SICKNESS COUNTERMEASURES DURING SELF-MOTION. Sensory conflict occurs in man-made environments, often leading to motion sickness whose severity and incidence varies widely across individuals. Temporal delay in motion simulators is well known to induce motion sickness and engineers do their best to reduce temporal delay between visual and vestibular cues to zero. I expect that motion sickness can be minimized when this temporal delay is calibrated relative to each individual's point of subjective simultaneity. My research program recognizes the role of the vestibular system as fundamental to cognition. Knowing how vestibular information is temporally processed and how it affects perceived self-motion is critical not only to understand how the brain works but also to reduce the incidence of motion sickness, which is holding back wider adoption of cost-saving virtual reality technology in the aviation, space, design, mobile computing, and healthcare industries. Likewise, a deeper understanding of the dissociation between processing vestibular information for reflexive responses versus conscious awareness could help in the development of preventative interventions to help reduce fall-related injury; a $3 billion burden to the Canadian economy (Public Health Agency of Canada).