title: Depth discrimination from shading under diffuse lighting.
abstract: The human visual system has a remarkable ability to interpret smooth patterns of light on a surface in terms of 3-D surface geometry. Classical studies of shape-from-shading perception have assumed that surface irradiance varies with the angle between the local surface normal and a collimated light source. This model holds, for example, on a sunny day. One common situation in which this model fails to hold, however, is under diffuse lighting such as on a cloudy day. Here we report on the first psychophysical experiments that address shape-from-shading under a uniform diffuse-lighting condition. Our hypothesis was that shape perception can be explained with a perceptual model that "dark means deep". We tested this hypothesis by comparing performance in a depth-discrimination task to performance in a brightness-discrimination task, using identical stimuli. We found a significant correlation between responses in the two tasks, supporting a dark-means-deep model. However, overall performance in the depth-discrimination task was superior to that predicted by a dark-means-deep model. This implies that humans use a more accurate model than dark-means-deep to perceive shape-from-shading under diffuse lighting.
authors.affiliation: Max Planck Institute for Biological Cybernetics, Tübingen, Germany. michael.langer@tuebingen.mpg.de
authors.forename: M S
authors.initials: MS
authors.lastname: Langer
authors.forename: H H
authors.initials: HH
authors.lastname: Bülthoff
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D015350:Contrast Sensitivity / Q000502:physiology*; D003867:Depth Perception / Q000502:physiology*; D005556:Form Perception / Q000502:physiology; D006801:Humans; D008029:Lighting; D008962:Models, Theoretical; D011601:Psychophysics