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Silvio Savarese, Andrey Del Pozo, Derek Baker, Daniel J. Simons; When are reflections useful in perceiving the shape of shiny surfaces?. Journal of Vision 2008;8(6):446. doi: https://doi.org/10.1167/8.6.446.
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3D shape can be perceived from a single image using contours, shading, and other cues. For shiny objects, an additional cue is available: the surrounding scene is reflected, and the deformation of this reflection varies as a function of the shape of the object's surface. Do human perceivers use this cue? Previous research has produced conflicting results (Savarese et al., VSS03; Fleming et al, VSS03), although the discrepancy might result from differences in the reflected environments. If the reflected scene is composed of objects in close proximity to the mirror surface, then the resulting reflections tend to be uncorrelated to surface shape's principal curvatures. In contrast, when the same scene objects are located further from the mirror objects, the resulting reflections tend to flow along the directions of minimal surface curvature and occluding contours, potentially providing additional cues about the mirrored object's shape. Does this geometric difference correspond to a difference in the ability to use deformation cues to perceive object shape? We tried to answer this question using 35 distinct, computer generated shapes reflecting 28 environments. The environments consisted of a range of objects randomly located in space at increasing distance from the mirror surface. As a control, we used a subset of shapes with no reflective properties but with surface texture. We found that mirror reflections were a weak cue for surface shape for human observers, regardless of the environment and the distance. Further analysis is needed to determine whether other aspects of the objects or environment can contribute to the use of specular reflections in shape perception.
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