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Dorion Liston, Leland Stone; Oculometric assessment of visual motion processing. Journal of Vision 2014;14(10):640. doi: 10.1167/14.10.640.
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© ARVO (1962-2015); The Authors (2016-present)
Eye movements are the most frequent (~3 per second), shortest-latency (~150-250 ms), and biomechanically simplest (1 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 developed a 15-minute behavioral tracking protocol consisting of randomized 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. Whereas our initiation and steady-state tracking metrics quantify the motor response, our direction and speed-tuning metrics can be converted into standard psychophysical thresholds. Methods. Observers were asked to pursue a small spot that made an initial step from fixation, then moved back through fixation in a Rashbass (1961) step-ramp design. De-saccaded eye-velocity responses were used to measure: pursuit latency and acceleration during initiation; gain, catch-up saccade amplitude, and proportion of smooth movements during steady-state tracking; direction-tuning anisotropy, asymmetry, and direction noise; and speed-tuning slope and noise. Variations on the step-ramp task were run to evaluate the test-retest repeatability and validity of our task, and to collect a baseline dataset from a population of 41 observers. Results. Our test-retest repeatability evaluation showed that initiation and steady-state tracking metrics were stable enough to allow individual differences to be measured (p<0.0001, Kruskal-Wallis). Our validity evaluation showed that initiation metrics show large decrements as the motion stimulus degrades with sampling (p<0.0001, ANOVA) and two of three steady-state tracking metrics show more subdued impairments (p<0.05, ANOVA). Conclusion. Our method delivers ten metrics that quantify pursuit and saccadic eye movements following a simple 15-minute clinical test, which may be useful as a screening tool for disorders affecting sensorimotor processing.
Meeting abstract presented at VSS 2014
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