Mark Nawrot - US grants

The perception of depth from motion is perhaps the important aspect of visual processing. Monocular cues to depth are all easily deceived, and binocular stereopsis is not available to monocular observers or animals with laterally places eyes. However, depth from motion may produce either ambiguous depth assignments (e.g., kinetic depth effect-KDE) or unambiguous depth percepts in the case of motion parallax even though the retinal information may be the same in the two cases. What is it that makes depth from motion parallax unambiguous? While information about the direction of observer head movement appears necessary, current research shows that the visual system actually uses a slow eye movement signal for this purpose. This project will study the mechanism by which the visual system accomplishes this task. Psychophysical experiments will use a computer system capable of integrating information from a linear head-tracking system and an infra-red eye-tracking system so that both head and eye position can be monitored. This system can also present stereoscopic versions of the motion parallax displays (using ferroelectric shutter system) so that binocular stereopsis can be used as a control to which depth from motion parallax is compared. Experiments will determine the utility of OKR or pursuit eye movements in the perception of depth from motion, including previously ambiguous conditions such as KDE. Additionally, as eye movement magnitude depends on viewing distance, the role of viewing distance in motion parallax displays will be explored. Finally, if depth from motion parallax relies on slow eye movements, then patients with eye movement dysfunction due to cortical or cerebellar lesions should show problems in the perception of depth from motion parallax. The theoretical goal is to develop a single neural network model that can account for the perception of depth from motion parallax, motion perspective, kinetic depth, stereopsis and the various neural interactions between these different depth cues. The previous neural network model (Nawrot and Blake, 1991) was confined to kinetic depth, stereopsis, and their interaction. The addition of an eye movement signal would expand the scope of the model to include motion parallax and its various interactions with binocular stereopsis.

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.