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Oh-sang Kwon, Duje Tadin, David Knill; Optimal tracking model accounts for perceptual conflict between motion and position in the curveball illusion. Journal of Vision 2014;14(10):470. doi: https://doi.org/10.1167/14.10.470.
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We have previously shown that an optimal object tracking model accounts for the well-known illusory motion-induced position shift (in which the position of a stationary envelope that contains a moving pattern is shifted in the direction of pattern motion). The model works by optimally using noisy sensory signals to estimate both the motion of the object containing a pattern and the motion of the pattern within the object (VSS 2013). The model makes the novel prediction that when the pattern motion within an envelope differs from the motion of the envelope one's percept of object motion should conflict with temporal changes in one's percept of object position. METHODS: To measure both perceived position and perceived motion of an object, we adapted the well-known 'curveball illusion' stimulus. In this illusion, an object moves downward, while the pattern within the object moves horizontally. In peripheral vision (11°), the object appears to move obliquely. We measured subjects' perceived object position and motion direction for different stimulus durations (20-400 ms). In position blocks, subjects reported the final perceived object position. In motion blocks, subjects reported the final object motion direction. RESULTS: Subjects' horizontal object position biases initially increased with stimulus duration, but asymptoted after 200 ms. (suggesting a constant estimate of horizontal position after 200 msec.) In contrast, their perceived object motion trajectory was oblique at all durations, indicating a non-zero percept of the object's horizontal component of motion. While seemingly irrational, this conflict is consistent with the prediction of the optimal tacking model.
Meeting abstract presented at VSS 2014
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