Use of interreflection and shadow for surface contact.
The interaction of light with surfaces results in a number of lighting effects that may serve as valuable visual cues. Previous research on shadows has shown them to be effective in determining the three-dimensional (3-D) layout of a scene, but interreflections have been ignored as cues for spatial layout. Interreflections as well as shadows may help to disambiguate the 3-D layout of objects by providing information about an object's contact with a surface. We generated computer images of a box on an extended textured ground plane that was either in contact with the ground or was slightly above the ground. Images were rendered for four conditions: (1) no shadow + no interreflection, (2) shadow only, (3) interreflection only, and (4) shadow + interreflection. A photometrically incorrect condition was also included. The participants rated the degree of contact for each image on a scale, which was used to generate receiver operating characteristic (ROC) curves and a measure of sensitivity. In the images with no shadows or interreflections, the participants performed at chance levels. Interreflections, shadows, and a combination of interreflections and shadows all resulted in high sensitivity for judging object contact. More important, information from shadows and interreflections can be combined, resulting in near-perfect judgment of surface contact. Interreflections and shadows can be effective cues for object contact.
University of Minnesota, 75 East River Rd., Minneapolis, MN 55455, USA. cindee@cyclops.psych.umn.edu
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Madison
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Thompson
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Kersten
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Shirley
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Smits
D001288:Attention; D003196:Computer Graphics; D015350:Contrast Sensitivity; D003463:Cues; D003867:Depth Perception; D004193:Discrimination Learning; D006801:Humans; D008029:Lighting; D009903:Optical Illusions; D009949:Orientation; D011601:Psychophysics