Apparent Opacity Affects Perception of Structure from Motion and Stereo

Abstract : It is well known that the human visual system can reconstruct depth from simple random-dot displays given motion information. This fact has lent support to the notion that structure from stereo and motion systems rely on low-level primitives or tokens, such as edges, derived from image intensities. In contrast, the judgment of surface attributes such as transparency or opacity is often considered to be a higher level visual process that would make use of low-level stereo or motion information, and perhaps attention or later recognition to tease apart the transparent from the opaque parts. This is exemplified by the lack of computational studies dealing with transparency, compared with the at least limited success of a number of algorithms to solve structure from motion or stereo. In this study, the authors describe a new illusion and some results that question the above view by showing that depth from transparency and opacity can override the rigidity bias in perceiving depth from motion. This provides support for the idea that the brain's computation of the surface material attribute of transparency may have to be done either before, or in parallel with, the computation of structure from motion.