September 2021
Volume 21, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2021
Third-order Motion, Not First-order Motion, Is Used to Control Locomotion When Following a Crowd
Author Affiliations & Notes
  • Zhenyu Zhu
    Brown University
  • William H. Warren
    Brown University
  • Footnotes
    Acknowledgements  Funding: NIH R01EY029745
Journal of Vision September 2021, Vol.21, 2447. doi:https://doi.org/10.1167/jov.21.9.2447
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      Zhenyu Zhu, William H. Warren; Third-order Motion, Not First-order Motion, Is Used to Control Locomotion When Following a Crowd. Journal of Vision 2021;21(9):2447. doi: https://doi.org/10.1167/jov.21.9.2447.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Humans locomote in complex dynamic environments and constantly interact with other pedestrians. We investigate whether the visual-motor system relies on first-order motion (motion energy) or third-order motion (tracking bounded ‘figures’) (Lu & Sperling, 1995) to control walking when following a crowd. One might expect that visual-motor processes are driven by 1st-order motion, as in insect flight control; on the other hand, interacting with other pedestrians could require tracking their boundaries, consistent with 3rd-order motion. To dissociate the two, we presented ‘reverse-phi’ motion (Anstis, 1970) in a virtual-reality display during walking. Participants (N=12) wore a head-mounted display (Samsung Odyssey+, 110º FOV) and were asked to “walk with” a crowd of virtual objects. The simulated ‘crowd’ consisted of 9 vertical rectangles (1.6m x 0.5m) mapped with a grayscale granite texture. The ‘crowd’ initially moved forward at 1.2 m/s, then we briefly perturbed (for 2s) the motion of a subset of the objects (0, 6, 9). With a heading perturbation (±20˚), the subset moved left or right; with a speed perturbation (±0.2 m/s), the subset optically expanded or contracted. During the perturbation, object texture underwent 4-frame reverse-phi motion, such that the 1st-order motion moved in the Same or the Opposite direction as the 3rd-order motion. In the Control condition (subset=0), all objects continued moving forward at a constant speed, with no contrast reversal. The participant’s walking direction and speed were recorded. Responses were as predicted by 3rd-order motion in all conditions. The mean heading response was 7.38° in the Same condition and 7.93° in the Opposite condition, in the 3rd-order direction (p<.001). The mean speed response was 0.069m/s in the Same condition and 0.071m/s in the Opposite condition, also in the 3rd-order direction (p<.001). The results indicate that human locomotor interactions are controlled by 3rd-order motion, consistent with tracking moving and expanding boundaries.

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