Interaction of visual prior constraints.

The visual system relies on two types of information to interpret a visual scene: the cues that can be extracted from the retinal images and prior constraints that are used to disambiguate the scene. Many studies have looked at how multiple visual cues are combined. We examined the interaction of multiple prior constraints. The particular constraints studied here are assumptions the observer makes concerning the location of the light source (for the shading cue to depth) and the orientation of a surface (for depth based on image contours). The reliability of each of the two cues was manipulated by changing the contrast of different parts of the stimuli. We developed a model based on elements of Bayesian decision theory that permitted us to track the weights applied to each of the prior constraints as a function of the cue reliabilities. The results provided evidence that prior constraints behave just like visual cues to depth: cues with more reliable information have higher weight attributed to their corresponding prior constraint.