Physics embedded in visual perception of three-dimensional shape from motion.

Visual perception, and by implication underlying neural events, can become unstable when optical information specifying objects is ambiguous. Here we report that one striking form of instability-perceived three-dimensional structure-from-motion (SFM)-can be stabilized when an otherwise ambiguous object appears within a context implying frictional interactions with another rotating object; violations of physical conditions specifying friction disrupt stabilization. Evidently, information about frictional interaction is embedded within neural mechanisms specifying SFM.