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Zheng Ma, Steve Heinen; Altered smooth pursuit of global motion caused by illusory positon shifts in local elements. Journal of Vision 2017;17(10):276. doi: https://doi.org/10.1167/17.10.276.
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Previously we showed that the pursuit system can integrate local motion information to veridically pursue the global motion of a large object. Here, we demonstrate that illusory position shifts in local elements alter pursuit gain for global motion, and similarly affect global motion perception. The target consisted of four Gabor patches arranged in a diamond configuration, each drifting within a circular aperture. It is well known that Gabors drifting within static apertures produce an illusory displacement of the Gabor in the drift direction. In the current experiment, the apertures containing the Gabor patches translated together to the left or right in each trial at a constant velocity of 10°/s. Drift direction conditions relative to the global translation direction were Same, Opposite, or Orthogonal. Observers were instructed to pursue the global motion. Pursuit gain was higher in the Same than the Opposite condition, evidence that the local drifting motion patches disrupted the pursuit system's ability to integrate global motion. To test if the effect originated in the motion perception system, we assessed observers' perceived speed of the translating stimuli using a staircase method. Consistent with the pursuit result, we found higher global speed perception in the Same than in the Opposite condition. We further asked if integration could be restored when a non-illusory local motion cue was provided by adding circular frames to each Gabor patch. This manipulation reduced the difference between the Same and Opposite conditions for both smooth pursuit and perception. The results suggest that local moving elements that produce an illusory position shift can interfere with the pursuit and perception of global motion. However, when additional local translation cues are provided, motion information is successfully integrated to accurately guide pursuit and perception.
Meeting abstract presented at VSS 2017
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