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Barton L Anderson, Michael Whitbread; Distortions of illusory shape and motion by unseen motions. Journal of Vision 2010;10(7):1161. doi: 10.1167/10.7.1161.
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© ARVO (1962-2015); The Authors (2016-present)
Most models of illusory contours (ICs) have focused on geometric factors as the primary determinant of IC shape. Here, we report a new class of IC displays in which distortions of both perceived shape and motion are induced by unseen, locally ambiguous motion signals that arise from the ambiguity of aperture problem. When an outline diamond is translated behind a counter-translating camouflaged triangular occluder, the perceived motion and shape of the triangular occluder are distorted: the translating occluder appears to contain a strong illusory rotational component of motion, and the angular subtense of the triangle is substantially reduced. We performed a series of experiments that parametrically varied the velocity of the occluding and occluded figures and the aspect ratio of the occluded diamond and (illusory) occluding triangle. Observers adjusted a triangular figure in which the angles of the triangle, as well as the translational and rotational components of motion of the triangle matched the perceived motion and shape of the IC. Our results show that the distortions in perceived shape and rotational motion was primarily a function of angular subtense of both the occluded and occluding figures; other factors, such as the translational velocity, or the velocity of contour terminators, played a negligible role in these distortions. Our results are consistent with a model in which the motions and shapes of the ICs are distorted by an induced motion imparted by the unseen orthogonal component of motion of the occluded diamond. If correct, these data suggest that the observed distortions in shape and perceived motion arise at a very early stage of cortical motion processing, prior to the resolution of the aperture problem.
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