One of the fundamental issues in the study of 3D surface perception is to identify the specific aspects of an object's structure that form the primitive components of an observer's perceptual knowledge. After all, in order to understand shape perception, it is first necessary to define what a??shapea?? is. In this presentation, I will assess several types of data structures that have been proposed for representing 3D surfaces. One of the most common data structures employed for this purpose involves a map of the geometric properties in each local neighborhood, such as depth, orientation or curvature. Numerous experiments have been performed in which observers have been required to make judgments of local surface properties, but the results reveal that these judgments are most often systematically distorted relative to the ground truth and surprisingly imprecise, thus suggesting that local property maps may not be the foundation of our perceptual knowledge about 3D shape. An alternative type of data structure for representing 3D shape involves a graph of the configural relationships among qualitatively distinct surface features, such as edges and vertices. The psychological validity of this type of representation has been supported by numerous psychophysical experiments, and by electrophysiological studies of macaque IT. A third type of data structure will also be considered in which surfaces are represented as a tiling of qualitatively distinct regions based on their patterns of curvature, and there is some neurophysiological evidence to suggest that this type of representation occurs in several areas of the primate cortex.
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