title: Three-dimensional object shape from shading and contour disparities.
abstract: Both non-Lambertian shading, specularities in particular, and occluding contours have ill-matched binocular disparities. For example, the disparities of specularities depend not only on a surface's position but also on its curvature. Shading and contour disparities do in general not specify a point on the surface. I investigated how shading and contours contribute to perceived shape in stereoscopic viewing. Observers adjusted surface attitude probes on a globular object. In Experiment 1, the object was either Lambertian or Lambertian with added specularities. In the next experiment, I removed the Lambertian part of the shading. In Experiment 3, I reduced the disparity of the contour to zero, and in Experiment 4, I removed both cues. There was little effect of shading condition in Experiment 1. Removing the Lambertian shading in Experiment 2 rendered the sign of the surface ambiguous (convex/concave) although all surfaces were perceived as curved. Results in Experiment 3 were similar to those in Experiment 1. Removing both cues in Experiment 4 made all surfaces appear flat for three observers and convex for one observer. I conclude that in the absence of Lambertian shading, observers have categorically different perceptions of the surface depending on whether disparate specular highlights and disparate contours are present or not.
authors.affiliation: The School of Psychology, University of St Andrews, St Andrews, UK. harold.nefs@st-andrews.ac.uk
authors.forename: Harold T
authors.initials: HT
authors.lastname: Nefs
mesh_terms: D000293:Adolescent; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D003463:Cues; D003867:Depth Perception / Q000502:physiology*; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D015357:Vision Disparity / Q000502:physiology; D055815:Young Adult