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David F. Nichols, Howard S. Hock; Reverse-Phi Motion Without Reversing Luminance Polarity: Evidence for Edge Detection in the Perception of Object Motion. Journal of Vision 2004;4(8):551. doi: 10.1167/4.8.551.
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© ARVO (1962-2015); The Authors (2016-present)
The mechanism responsible for the perception of apparent motion is studied through a new phenomenon: Reverse phi motion for a displaced object without the object's displacement being accompanied by the reversal of its luminance polarity (the latter as in Anstis & Rogers, 1975). We have found that motion is perceived in the direction opposite to an object's displacement when the object (with greater-than-background luminance) is flanked by contiguous, static bars that are higher in luminance than the object. The reverse phi motion increases as the difference in luminance between the object and flankers is decreased. Reverse phi is lost, however, when a small gap is introduced between the flankers and the object. These results cannot be accounted for by the motion energy of the stimulus, which specifies motion in the direction the object is shifted, irrespective of the presence or absence of static flankers or gaps. It is proposed instead that the perception of apparent motion is based on the counter-changing activation of edge detectors lying along the boundaries of the displaced object. The sensitivity of reverse phi to the presence of small gaps implies that the edge detection occurs in area V1. It is also noteworthy that when reverse phi motion is perceived, it is the space over which the object is shifted that is perceived as moving rather than the object itself. We thus find evidence for structure from motion at the level of figure/ground segregation.
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