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Thomas Papathomas, Jordan Ash, James Hughes, Brian Keane, Qasim Zaidi; Face priors overcome shape-from-motion signals in the rotating hollow face illusion. Journal of Vision 2011;11(11):51. doi: https://doi.org/10.1167/11.11.51.
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© ARVO (1962-2015); The Authors (2016-present)
OBJECTIVE: In the rotating hollow face illusion (HFI), viewers perceive a hollow face as a convex face rotating in the opposite direction. Our objective: compare the strength of data-driven motion-perspective signals (faster-is-closer) to schema-driven influences (faces-are-convex) in the HFI. BACKGROUND: Meng and Zaidi (VSS 2008) obtained evidence for strong motion-perspective depth effects: two half-cycles of a sinusoidal corrugation (one concave, one convex) rotating about the zero crossing both appear convex; while rotating about their apex, both appear concave. HFI studies generally use masks rotating about an axis through the center of gravity. This generates retinal velocities that are larger for the nose than the cheeks and eyes. These relative velocities signal that the nose is closer, enhancing the illusion. We varied the relative velocities by placing the rotation axis at various distances from the nose. METHODS: We used: (1) physical masks painted realistically on both sides (convex and concave) rotating on a turntable; (2) computer-generated painted virtual masks (using FaceGen), rotating as in (1), allowing a greater range of axis-to-nose distances. We varied the relative velocities of the features, including conditions where the nose had a smaller velocity than the cheeks and eyes. We estimated the illusion's predominance as the time spent in the illusory percept divided by the total time that the mask had its concave side facing the observer. RESULTS: In both experiments, the concave face was seen as convex for significant intervals, even when the nose had lower velocity than the cheeks and eyes, which should reinforce the concave percept based on motion perspective. There was relatively little variation of the illusion predominance as the axis position was varied.
CONCLUSIONS: The results provide evidence that, in the HFI, the top-down prior of convex faces dominates the velocity-driven 3D shape-from-motion signals resulting from object rotation.
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