This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Visual depth perception is crucial for obstacle avoidance while moving through a cluttered environment. Considering the significance of human mobility, and the tragedy of its failures, much will be gained by understanding the neural mechanisms of dynamic depth perception. Motion parallax, one of the most important cues to depth, is created when the observer translates one direction while maintaining a stable "side" view of the scene through compensatory eye movements in the opposite direction. While we are just starting to understand the neural mechanisms for the perception of depth from motion parallax, we now know it requires an extra-retinal signal that comes only from the pursuit eye movement system (the pursuit theory of motion parallax). We now believe that the visual mechanism relies on a ratio of retinal motion and pursuit eye movement to determine relative depth of objects in the scene (the motion/pursuit law). With this theoretical and quantitative foundation we have several well-defined and testable hypotheses about the role of the pursuit system to test with psychophycial experiments. These hypotheses include an explanation of depth scaling from motion parallax and an explanation of a specific set of perceptual errors that people make. Other experiments will determine more about the nature of the pursuit system signal, and how the visual system uses it in the unambiguous perception of depth from motion parallax. To address some deep controversies in the field, we will look for an electrical signature of pursuit system activity by measuring event related potentials on the scalp. What we learn about motion parallax from these studies will guide our research understanding of the perception of depth from optic flow, another dynamic depth cue critical for driving. Ggreg DeAngelis and Keith Stroyan served as Dr. Nawrot's Individual Project Mentor/Consultants. Drs. DeAngelis and Stroyan visit Dr. Nawrot's laboatory to assist him with the design and interpretation of experiments, and with the preparation and critical review of grant proposals.