Oculometric assessment of dynamic visual processing

Eye movements are the most frequent (∼3/s), shortest-latency (∼150-250 ms), and biomechanically simplest (one joint, no inertial complexities) voluntary motor behavior in primates, providing a model system to assess sensorimotor disturbances arising from trauma, fatigue, aging, or disease states. We have developed a 15-min behavioral tracking protocol consisting of randomized Rashbass (1961) step-ramp radial target motion to assess several aspects of the behavioral response to visual motion, including pursuit initiation, steady-state tracking, direction tuning, and speed tuning. We show how oculomotor data can be converted into direction- and speed-tuning oculometric functions, with large increases in efficiency over traditional button-press psychophysics. We also show how the latter two can be converted into standard visual psychometric thresholds. To assess our paradigm, we first tested for the psychometric criterion of repeatability, and report that our metrics are reliable across repeated sessions. Second, we tested for the psychometric criterion of validity, and report that our metrics show the anticipated changes as the motion stimulus degrades due to spatiotemporal undersampling. Third, we documented the distribution of these metrics across a population of 41 normal observers to provide a thorough quantitative picture of normal human ocular tracking performance, with practice and expectation effects minimized. Our method computes 10 metrics that quantify various aspects of the eye-movement response during a simple 15-min clinical test, which could be used as a screening or assessment tool for disorders affecting sensorimotor processing, including degenerative retinal disease; developmental, neurological or psychiatric disorders; strokes; and traumatic brain injury.