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 to tease apart the transparent from the opaque parts. In this study, we 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.
