Size constancy in structure from motion

The relative motions of points in a structure-from-motion display involving parallel projection provide depth information in an object-centered framework: differences in velocity do not reflect differences in distance from an eyepoint. In contrast, size constancy is generally regarded to be a perspective effect, based on the relationship between projected size and distance from an eyepoint. Five subjects judged the relative sizes of objects in structure-from-motion scenes. Although the scenes were displayed without perspective, judged size was related to the simulated separation in depth of the objects. These results suggest that relative depths recovered from object-centered information are incorporated into a viewer-centered framework.