Laboratoire Psychologie de la Perception Institut Neurosciences Cognition Université Paris Descartes Centre National de Recherche Scientifique
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Surface representations for visual perception and action

We investigate how human adults interact with physical surfaces from three standpoints: theoretical, perceptual, and motor. From a theoretical standpoint, we describe different representations to characterize the geometry of surfaces. Our analysis emphasizes the first and second order structures of smooth surfaces, that is the surface orientation, curvature, and shape. A careful progression from viewer-centered to object-centered frames of reference leads us to introduce a few new surface descriptors. From a perceptual standpoint, we present two psychophysical studies on the visual perception of shaded smooth surfaces. The first study concentrates on the local surface orientation, while the second study deals with the local solid shape. In both studies, we examine the importance of the occluding contour as a source of information for the object's shape. Both studies suggest that the visual system has a preference for egg-shaped regions of the surface (as opposed to saddle-shaped). From a motor standpoint, we present two separate studies on grasping and active perception of surfaces. In the first study, we investigate eye-hand coordination during the grasping of an object at one of different possible orientations. We find that the object orientation is properly integrated into both the "where" and "what" visuo-motor channels, which transport the hand in the vicinity of the object and control the opening of the hand, respectively. The second study explores the perceived surface curvature through motion of the occluding contour. We find that observers are more accurate when allowed to freely move about the object than when looking passively at a rotating object. (PsycINFO Database Record (c) 2005 APA, all rights reserved)



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