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Noriaki Washio, Yasuo Suzuki, Masahiro Sawa, Kenji Ohtsuka; Gain of Human Torsional Optokinetic Nystagmus Depends on Horizontal Disparity. Invest. Ophthalmol. Vis. Sci. 2005;46(1):133-136. doi: 10.1167/iovs.04-0276.
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purpose. To investigate the effects of horizontal disparity on torsional optokinetic nystagmus (tOKN) in humans.
methods. Ten healthy human subjects were selected for this experiment. Monocular eye movements were recorded three-dimensionally using dual-search coil methods. Torsional OKN was induced by a rotating random-dot pattern (22° in diameter, constant angular velocity: ±54 deg/s) projected on the virtual screen of the optical see-through, head-mounted display (HMD). The optical distance of the HMD’s virtual screen was 2 m. A red LED that could be fixated through the virtual screen of the HMD was located near the center of the rotating random-dot pattern. Horizontal disparity was induced by changing the distance between the fixated target and the subject systematically (1, 1.5, 2, or 3 m; five subjects) or by the prism (+1.5, +0.5, 0, or −0.5 prism-diopter [PD] in each eye; five subjects) in front of the HMD.
results. The average gain with zero horizontal disparity (0.022 ± 0.008/0.025 ± 0.014, fixated target at 2 m/fixated target with the plain glass) was significantly higher than the gain with crossed disparity (0.017 ± 0.003/0.019 ± 0.008, target at 3 m/with the prism of −0.5 PD) and uncrossed disparity (0.017 ± 0.002, target at 1 m/with the prism of +1.5 PD; one-way ANOVA, P < 0.05).
conclusions. The horizontal disparity of optokinetic stimulus affects tOKN. Nonzero horizontal disparity decreases the gain of tOKN.
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