September 2021
Volume 21, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2021
Neural coding for the illusion of direction repulsion of transparently moving stimuli
Author Affiliations & Notes
  • Steven Wiesner
    University of Wisconsin-Madison
    Physiology Graduate Training Program
  • Jianbo Xiao
    University of Wisconsin-Madison
    Physiology Graduate Training Program
  • Xin Huang
    University of Wisconsin-Madison
    Physiology Graduate Training Program
    McPherson Eye Research Institute
  • Footnotes
    Acknowledgements  NIH grant R01EY022443, Dissertation Completion Fellowship. Support for this fellowship is provided by the Graduate School, Part of the Office of Vice Chancellor for Research and Graduate Education at the University of Wisconsin-Madison, with funding from the Wisconsin Alumni Research Foundation and the UW-Madison.
Journal of Vision September 2021, Vol.21, 2759. doi:
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      Steven Wiesner, Jianbo Xiao, Xin Huang; Neural coding for the illusion of direction repulsion of transparently moving stimuli. Journal of Vision 2021;21(9):2759.

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

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Humans perceive the angle separation (AS) between two overlapping random-dot stimuli that move transparently in different directions to be wider than it actually is when the veridical AS is less than 90°. The neural basis for this illusion of direction repulsion remains unclear. We recorded from neurons in middle-temporal (MT) cortex of two fixating macaques. Visual stimuli were overlapping random-dot patches (diameter 7.5°) moving in two different directions. The AS was 30°, 45°, 60°, 90°, or 135°. We varied the vector-averaged direction of the bi-directional stimuli to characterize a neuron’s response tuning curve, and also measured each neuron’s direction tuning to a single patch. Visual stimuli had eccentricities from 1.5° to 29° (median=6.3°). We fitted tuning curves to bi-directional stimuli as a weighted sum of the responses to the two component directions, plus a multiplicative term between component responses. In the model fit, we allowed the “component directions” to deviate from the veridical component directions, with either a wider or narrower AS. The best-fit component directions averaged across neurons (n≥96) had mean AS of 54°, 69°, 94°, and 133° for veridical AS of 45°, 60°, 90°, and 135°, respectively. Consistent with human perception, we found a significant effect of direction repulsion at AS of 45° and 60° (p<0.0001), but not at 90° and 135°. Furthermore, the ratio between the overestimated AS and AS (i.e. ∆AS/AS) decreased from 0.2 to -0.015 as the AS increased from 45° to 135°. However, in a smaller neuron sample (N=38), we did not find direction repulsion at AS of 30°, which may be due to stimulus eccentricities and the small AS. In conclusion, we found that within a range of AS, MT neurons encode transparently moving stimuli as if they have a wider AS, which would allow a decoder to read out repelled motion directions.


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