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Z. Tai, R. W. Hertle, E. S. Hald, D. Yang; Vergence and Three-Dimensional Perception Induced by Ground-Plane Motion. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2890.
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A moving observer experiences optic flow stimulus during fore/aft movements. It is known that optic flow induced vergence eye movements to stabilize gaze (Yang et al 1999). However, disparity stimuli are also available to the moving observer in the real world and their effect on optic flow vergence is not clear. To study the effect of disparity on vergence induced by optic flow motion in the gound plane, we tested subjects with a modified grating pattern used to induce optic flow vegence (Yang et al 2007 and Zhu et al 2008).
By interpolating sinusoidal grating stripes with reversed polarity on a sinusoidal grating pattern, a checkboard-like pattern was generated. The motion of the checkboard pattern or a sinusoidal grating pattern was displayed on a computer monitor in the ground plane and binocular movements were recorded with a video-based eye tracking system (EyeLink 1000 desktop). Three normal subjects looked at the center of the pattern for 8 seconds in each trial and they were instructed to press a gamepad button when they perceived a 3 dimensional (3D)layer in the pattern. All experimental conditions including various velocities, two patterns, and two directions were randomized. Vergence amplitudes, velocities, and latencies were quantitively analyzed.
Horizontal vergence in a form of optokintic nystagmus was induced by each pattern. In addition, a clear 3D layer was perceived by all 3 subjects when the checkboard pattern was used. The 3D perception occured 1.5-5 seconds after the initiation of the motion and it was usually associated with an brief increase in vergence. The latency and velocity of the initial open-loop responses were the same for the two different stimulus patterns. The velocity of closed-loop vergence was significantly increased by 20-30% when checkboard pattern was used. There was no increase in vergence with monocular viewing of checkboard pattern.
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