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Jonathan Matthis, Karl Muller, Kathryn Bonnen, Mary Hayhoe; Optic flow and self-motion information during real-world locomotion. Journal of Vision 2017;17(10):211. doi: 10.1167/17.10.211.
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A large body of research has examined the way that patterns of motion on the retina contribute to perception of movement through the world, but the actual visual self-motion stimulus experienced during real-world locomotion has never been measured. We used computer vision techniques to estimate optic flow from a head-mounted video camera recorded when subjects walked over various types of real-world terrain. Eye movements and full body kinematics were also recorded. We found that the optic flow experienced during locomotion reveals a pulsing pattern of visual motion that is coupled to the phasic acceleration patterns of the gait cycle. This pulsing optic flow pattern is not present in the constant-velocity flow fields that are generally used to simulate self-motion. This difference between real-world and simulated visual self-motion has important consequences on the behavior of the focus of expansion (FOE) during locomotion, which has been extensively studied as an key locus of information about heading direction but has not been recorded during natural behavior. Results show that the acceleration patterns of the head cause the FOE to follow a complex path in the visual field, in contrast to simulated constant-velocity self-motion stimuli wherein the FOE lies in a stable location in observer's environment. To examine how task-relevant locomotor variables could be derived from real-world stimuli, we processed the head-mounted videos using biologically plausible models of motion sensitive areas in visual cortex. The resulting patterns of simulated neural activity are complex, but display a clear coupling to the bipedal gait cycle. By comparing the resulting patterns of simulated neural activity across different time scales to subjects' kinematics, we found features that correlate with locomotion-relevant variables such as heading direction. We also found features of the visual motion stimulus that may play an important role in postural stability during locomotion over rough terrain.
Meeting abstract presented at VSS 2017
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