A classic way to study different aspects of perception is to consider how information from different cues is combined to generate a percept. Artists and others use luminance gradients (shading) to provide a sense of depth and shape in images. Here we report on studies examining factors that influence the combination of depth cues defined by monocular shading and the well studied depth cue of binocular disparity. Ray-traced images (RADIANCE) were created either featuring a smooth surface illuminated from above (shading-channel), or a surface defined by small spheres (disparity-channel). The shading- and disparity-defined pairs were combined by placing dots in the stimulus image, superimposed upon the shaded surface, at the locations of the spheres, resulting in veridical shading and binocular disparity. By independently varying the depth delivered by these channels, we created stimuli with conflicting depth-defined and shading-defined information. We find that when disparity and shape information are combined for depth perception, disparity information does not dominate perception. Under some circumstances, PSEs for depth judgments reflect values that lie between the two conflicting cues. The combination of depth cues is influenced by the extent of the overall discrepancy, larger conflicts appear to force the identification of dual-layers rather than a combined surface
