Anisotropies in the Perception of Three-Dimensional Surfaces

rcent sterile aqueous vehicle (by volume); the 10. Pregnancy was terntinated in one of two mon-aqueous vehicle contained (per milliliter): 10 mg keys treated with a single injection of 3.75 mg of of carboxymethylcel}ulose, 4 mg of polysorbate PGF-analog plus 0.5 mg of PGE-analog and in 80, and 0.42 mg propylparaben. one of two monkeys treated with a single injec-6. 11. Mild anorexia lasting only one day was observed 7. Pregnancy maintenance was confirmied by con-in one of the monkeys given the highest doses of tinued normal secretion patterns of mCG, detec-the PGF-analog plus PGE-analog. tion of uterine enlargement by bimanual palpa-12. I thank A. tion, and failure of the monkeys to show cycles VanEyk for technical assistance. of menstrual bleeding. Abstract. The appearance of certain three-dimensional surfaces was found to depend on the orientation of the depth contours forming the surface. This was true both when the depth was specified by motion parallax and when it was specified by binocular disparities. Slowly chatiging depth surfaces that generated a pattern of relative motions or disparities characterized by a one-dimensional expansion-compression were perceived differently from those that produced a shear transformation. The small dilfferences between the two retinal images (binocular disparities) and the relative motion in each image when the observer moves (motion parallax) have both been shown to accurately specify the structure of three-dimensional surfaces (1, 2). We report here that the perception of depth surfaces can be ori-entationally anisotropic, that is, the appearance of a surface can vary with the retinal orientation of the surface contours (3). Anisotropic effects were initially observed for surfaces in which the three-dimensional structure was specified stereoscopically, but we have since found similar effects for surfaces in which the structure was specified by motion parallax. The most striking demonstration of these effects was found with the depth surfaces depicted in Fig. 1, a and b. The profile of the surface (Fig. lc) consists of a sharp step or discontinuity in depth, flanked on either side by more gradual depth changes to areas that are equidis-tant from the observer. When this profile defines luminance (rather than depth) changes across a surface, observers typically report that the left-hand side appears lighter than the right. This effect is known as the Craik-O'Brien-Cornsweet illusion (4). In the luminance domain, the effect-is usually attributed to the visual system's poor sensitivity to slow or low spatial frequency changes (which characterize …