Models of visual interpolation emphasize contour relationships. Although the role of surface-level processes has been demonstrated (Yin, Kellman & Shipley, 1998; Fantoni, Bertamini & Gerbino, 2004; for a recent review see Kellman, 2003), specific surface properties and geometric constraints that govern surface interpolation are not well understood. In this study we hypothesize that, even in the absence of contour information, visual interpolation can occur as a product of surface-based processes grounded on orientation information derived from image cues such as scale and shear disparities.

To investigate 3D surface interpolation we asked observers to classify pairs of planar surfaces specified by random dot disparities, visible through circular apertures on a fronto-parallel occluder. Surface slant was manipulated by varying scale and shear disparities. On each trial, slanted textures belonged to either parallel or intersecting planar surfaces with the same absolute slant. Observers made a speeded parallel/intersecting classification of texture pairs of different slants. Surfaces were presented in 20 conditions resulting from the combination of three factors: 3D relatability of the surface pair (relatable vs. non-relatable); tilt of the aperture pair (aligned vs. tilted), absolute surface orientation (20, 35, 46, 54, 60 deg). As in contour interpolation (Kellman et al., in press) observers performed better on the parallel/intersecting classification task when surfaces were 3D-relatable. The orientation of the aperture pair did not play a clear role. The effect of absolute slant was stronger on non-relatable than relatable surfaces.

Results support the notion that visual interpolation includes surface-based processes, independent of contour information and specified by the 3D orientation of visible patches. Scale and shear disparities of isolated textures provide sufficient information for surface interpolation.