The Impact of Noisy Vestibular Stimulation on Self-motion Phenomena
Low immersion and sickness experienced in virtual reality (VR) are two important barriers that inhibit the widespread adoption of VR technology. Both are thought to relate to visual-vestibular mismatch. Recoupling multisensory cues can generate more convincing illusory self-motion (vection) and reduce sickness, but current methods rely on expensive or invasive techniques to simulate expected cues. According to a Bayesian framework of sensory integration, adding sensory noise may also reduce mismatch by changing sensory weights. This thesis explores this idea and proposes that ‘noisy’ vestibular stimulation presents an attractive solution to the above problems. I investigated the potential for improving VR experiences using two techniques that generate noise in the vestibular system. Rather than recoupling the senses, I aimed to encourage discounting of vestibular cues that are inconsistent with vision. In Chapter 2 I assessed the potential for improving immersion by measuring the effect of noisy vestibular stimulation (either bone-conducted vibration, BCV; or galvanic vestibular stimulation, GVS) on vection onset latency. I found a large reduction in vection latency when transient BCV or GVS were used at visual motion onset. The evidence suggests that a more compelling sensation of self-motion is achieved when sensory mismatch is reduced. In a second study I examined the extent to which sickness is reduced when BCV is applied during path navigation in a high-end VR display (Chapter 3). Results revealed lower sickness when transient noisy stimulation was applied. In a replication of this experiment I found that BCV reduced sickness to a similar extent when observers used a commercial head-mounted display. The results of Chapter 2 and 3 offer evidence that BCV reduces multisensory mismatch by down-weighting vestibular information according to Bayesian cue combination models. Given this context I also expected BCV to reduce self-motion sensitivity in a real-world movement discrimination task (Chapter 4). The results of a third study did not support my predictions, suggesting that the effects of noisy stimulation on self-motion may be more complex than previously considered. Together the findings give rise to a variety of opportunities for further testing of the technique, which are discussed in Chapter 5.