Investigated the stability of line drawing perception from psychophysical and computational standpoints. For a given family of simple line drawings, human Os could perceive the drawings as depicting either an elliptic (egg-shaped) or hyperbolic (saddle-shaped) smooth surface patch. Rotation of the image along the line of sight and change in aspect ratio of the line drawing could bias Os toward either interpretation. The results were modeled by a simple Bayesian observer that computes the probability to choose either interpretation given the information in the image and prior preferences. The model's decision rule is noncommitting: for a given input image its responses are still probabilistic, reflecting variability in the modeled Os' judgments. A good fit to the data was obtained when 3 observer assumptions were introduced: preferences for convex surfaces, surface contours aligned with the principal lines of curvature, and a surface orientation consistent with an object viewed from above. (PsycINFO Database Record (c) 2005 APA, all rights reserved)

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