Abstract

In two psychophysical experiments we tested how stereoscopically viewed highlights or specularities can serve as cues for material properties and 3-D local surface geometry. In the first experimental subjects can change interactively both horizontal and vertical disparities of a highlight relative to a textured surface. When the relative disparities of the highlight are veridical the whole surface appears glossy. However, when horizontal relative disparity is non veridical, the surface ceases to look glossy. In a second experiment we asked if the visual system can accommodate to variations in specular disparities by changing its hypothesis about surface curvature, rather than its hypothesis of glossiness. Naive observers, asked where a specularity appears to be in relation to the surface that generated it, usually reply that it appears to lie on the surface. We have shown that their early visual system knows better, choosing for convex/concave ambiguous surfaces (e.g., crater illusion) a configuration which is consistent with the physics of specular reflection. Human visual analysis appears to employ a physical model of the interaction of light with curved surfaces—a model firmly based on ray optics and differential geometry.

© 1989 Optical Society of America