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F. A. Miles, G. S. Masson, D.-Y. Yang; Velocity tuning of short-latency version and vergence eye movements in humans: dynamical limits set by retinal image speed. Journal of Vision 2002;2(7):180. doi: 10.1167/2.7.180.
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Purpose: Short-latency version and vergence eye movements can be elicited by conjugate and disconjugate velocity steps, respectively, applied to large random-dot patterns. We investigated the velocity tuning of both types of eye movements to binocularly symmetric and asymmetric stimuli. Methods: Binocular eye movements were recorded in 3 subjects with the scleral search coil technique. Subjects faced a large tangent screen (80×50°) onto which two identical random-dot patterns (dot diameters, 2°; 50% coverage) were back-projected. Each pattern was restricted to one eye only using crossed-polarizers and its position was controlled by X/Y mirror galvanometers. Viewing was always binocular and horizontal velocity steps (range, 10 to 120°/s) were applied shortly (∼50ms) after a centering saccade to one (asymmetric stimulus) or both (symmetric stimulus) patterns. When applied to both, the motion could be in the same (conjugate) or opposite (disconjugate) direction. Results: Conjugate and disconjugate ramps (symmetric and asymmetric) elicited vigorous version and vergence responses, respectively, at similar short latencies (∼80ms). Velocity tuning curves (based on the changes in version and vergence over the time period, 80–160 ms) were all S-shaped and peaked when monocular (i.e., retinal) image speeds were ∼40°/s, regardless of whether the stimuli were conjugate/disconjugate or symmetric/asymmetric. Plots of version (vergence) responses to symmetric stimuli against version (vergence) responses to asymmetric stimuli were linear (r20.9) when expressed in terms of the monocular (i.e., retinal) image speeds but highly curved when expressed in terms of the binocular (i.e., average or difference) image speeds. Conclusions: Short-latency version and vergence eye movements share very similar dynamical tuning functions when expressed in terms of retinal image speed, consistent with the idea that the dynamical limits are imposed early in the monocular pathways.
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