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David W. Bressler, David Whitney; Second-order motion shifts apparent position. Journal of Vision 2005;5(8):652. doi: 10.1167/5.8.652.
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Many studies have documented that first-order motion influences perceived position. Here we show that second-order (contrast-defined) motion influences the perceived positions of stationary objects. We used a Gabor pattern as our second-order stimulus, which consisted of a drifting sinusoidal contrast modulation of a dynamic random dot background; this carrier was enveloped by a static gaussian contrast modulation. Two vertically aligned Gabors had carrier motion in opposite directions. Subjects judged the relative positions of the Gabors' static envelopes. The positions of the Gabors appeared shifted in the direction of carrier motion as a function of the second-order carrier's temporal and spatial frequency. The results show that second-order motion detection mechanisms contribute to perceived position. Further, the differential spatial and temporal tuning of the illusion supports the idea that position is determined independently for first and second-order motion.
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