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キーワード:
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要旨:
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.
