Perception of surface contours and surface shape: from computation to psychophysics.

Contours projected from surface markings provide information for the perception of surface shape. The nature of this information depends on how the shapes of surface marking are constrained relative to the shapes of the surfaces upon which they lie. A natural constraint is that of figural regularity relative to the shape of an underlying surface. Such a constraint would be expressed in terms of the geodesic curvature of a marking, with markings having zero geodesic curvature (geodesics of a surface) being the prototypic regular figures. I propose a number of forms for a geodesic constraint and present psychophysical evidence from a contour-labeling experiment that the human visual system implicitly incorporates a geodesic constraint in the processing of reflectance contours.