Extracting object motion during observer motion: combining constraints from optic flow and binocular disparity

Detection of object motion by moving observers and perception of velocity by stationary or moving observers ordinarily require information about object distance. It might be expected that object motion could be obtained without distance by use of a combination of optic flow and binocular disparity information. We describe how object motion could, in principle, be derived this way. The analysis also permits recovery of target distance. Finally, information about the observer's motion may be obtained in a similar fashion, assuming the existence of two stationary environmental points at an unknown distance. Although studies of human observers have not been completed, it appears that these informational variables are available under conditions in which observers perform well at detecting motion and stability. In particular, the information may help to explain why a visible surface in near space facilitates accurate perception.