Sensory dynamics can be reshaped by environmental interaction, allowing adaptation to altered or unfamiliar conditions that would otherwise provoke challenges for the central nervous system. One such condition occurs in virtual reality, where sensory conflict is thought to induce cybersickness. Although the sensory re-weighting process is likely to underlie adaptation to cybersickness, evidence of a link between sensory re-weighting dynamics and cybersickness is rare. Here, we characterize the relationship between sensory re-weighting in a balance control task and cybersickness. Participants were exposed to visual oscillation while standing in tandem stance. The sway path length of the center of pressure (COP) was measured and averaged for each level of visual oscillation, and a ratio was computed between high and low oscillation magnitudes to reflect the relative contributions of multiple sensory sources of information concerning balance control. Results showed a significant relationship between the magnitude dependency of sway and common sub-scales of cybersickness: disorientation [r (21) = 0.45, p = 0.028] and oculomotor discomfort [r (21) = 0.45, p = 0.033]. We conclude that participants who reported less cybersickness were better-able to down-weight visual information at high magnitude oscillations, thus demonstrating a lower dependency between sway and visual magnitude. The results confirm the utility of balance control as an indicator of cybersickness, and support the role of multisensory re-weighting in determining an individual's tolerance to VR applications.

Large-field optic flow generates the illusory percept of self-motion, termed 'vection'. Smoother visual motion displays generate a more compelling subjective sense of vection and objective postural responses, as well as a greater sense of immersiveness for the user observing the visual display. Research suggests that the function linking frame rate and vection asymptotes at 60 frames per second (FPS), but previous studies have used only moderate frame rates that do not approach the limits of human perception. Here, we measure vection using subjective and objective (mean frequency and path length of postural centre-ofpressure (COP) excursions) responses following the presentation of high-contrast optic flow stimuli at slow and fast speeds and low and ultra-high frame rates. We achieve this using a novel rendering method implemented with a projector capable of sub-millisecond temporal resolution in order to simulate refresh rates ranging from very low (15 FPS) to ultra-high frame rates (480 FPS). The results suggest that subjective vection was experienced most strongly at 60 FPS. Below and above 60 FPS, subjective vection is generally weaker, shorter, and starts later, although this pattern varied slightly according to the speed of stimuli. For objective measures, while the frequency of postural sway was unaffected by frame rate, COP path length was greatest for 480 FPS stimuli. Together, our results support diminishing returns for vection above 60 FPS and provide insight into the use of high frame rate for enhancing the user experience in visual displays.

Introduction: The vergence oculomotor system possesses two robust adaptive mechanisms; a fast "dynamic" and a slow "tonic" system that are both vital for single, clear and comfortable binocular vision. The neural substrates underlying these vergence adaptive mechanisms in humans is unclear. Methods: We investigated the role of the posterior cerebellum in convergence adaptation using inhibitory continuous theta-burst repetitive transcranial magnetic stimulation (cTBS) within a double-blind, sham controlled design while eye movements were recorded at 250hz via infrared oculography. Results: In a preliminary experiment we validated our stimulation protocols by reproducing results from previous work on saccadic adaptation during the classic double-step adaptive shortening paradigm. Following this, across a series of three separate experiments we observed a clear dissociation in the effect of cTBS on convergence adaptation. Dynamic adaptation was substantially reduced while tonic adaptation was unaffected. Baseline dynamic fusional vergence response were also unaffected by stimulation. Conclusions: These results indicate a differential role for the posterior cerebellum in the adaptive control of convergence eye movements and provide initial evidence that repetitive transcranial magnetic stimulation is a viable tool to investigate the neurophysiology of vergence control. The results are discussed in the context of the current models of implicit motor adaptation of vergence and their application to clinical populations and technology design in virtual and augmented head mounted display architectures. Significance statement: The cerebellum plays a critical role in the adaptive control of motor systems. Vergence eye movements shift our gaze in depth allowing us to see in 3D and exhibit two distinct adaptive mechanisms that are engaged under a range of conditions including reading, wearing headmounted displays and using a new spectacle prescription. It is unclear what role the cerebellum plays in these adaptive mechanisms. To answer this, we temporarily disrupted the function of the posterior cerebellum using non-invasive brain stimulation and report impairment of only one adaptive mechanism, providing evidence for neural compartmentalization. The results have implications for vergence control models and applications to comfort and experience studies in head-mounted displays and the rehabilitation of clinical populations exhibiting vergence dysfunctions.

Large-field optic flow generates the illusory percept of self-motion, termed 'vection'. Smoother visual motion displays generate a more compelling subjective sense of vection and objective postural responses, as well as a greater sense of immersiveness for the user observing the visual display. Research suggests that the function linking frame rate and vection asymptotes at 60 frames per second (FPS), but previous studies have used only moderate frame rates that do not approach the limits of human perception. Here, we measure vection using subjective and objective (mean frequency and path length of postural centre-ofpressure (COP) excursions) responses following the presentation of high-contrast optic flow stimuli at slow and fast speeds and low and ultra-high frame rates. We achieve this using a novel rendering method implemented with a projector capable of sub-millisecond temporal resolution in order to simulate refresh rates ranging from very low (15 FPS) to ultra-high frame rates (480 FPS). The results suggest that subjective vection was experienced most strongly at 60 FPS. Below and above 60 FPS, subjective vection is generally weaker, shorter, and starts later, although this pattern varied slightly according to the speed of stimuli. For objective measures, while the frequency of postural sway was unaffected by frame rate, COP path length was greatest for 480 FPS stimuli. Together, our results support diminishing returns for vection above 60 FPS and provide insight into the use of high frame rate for enhancing the user experience in visual displays.

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