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J. Tong, H. E. Bedell, S. B. Stevenson; Modulation of Perceived Motion Smear During Passive Eye Movements. Invest. Ophthalmol. Vis. Sci. 2007;48(13):906.
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Previous studies indicated that the extent of perceived motion smear is attenuated asymmetrically during voluntary and involuntary eye movements. In this study, we investigated whether a directionally specific reduction of perceived smear occurs also when the eyes are moved passively by a finger press.
Observers (N=4) pressed the temporal side of the left eye to generate passive eye movements in darkness. The horizontal and vertical positions of both eyes were recorded using a SRI dual-Purkinje tracker. To verify that tracking was accurate, the perceived separation between two sequentially flashed spots was shown to equal the measured eye displacement during eye press. In the experiment, a laser spot was presented to the left eye for 150 ms during each passive eye movement. On each trial, the spot moved randomly to the right or left, producing retinal image speeds up to 40 deg/s in the same or the opposite direction of the passive eye movement. After each presentation, the observer adjusted the length of a bright bar to match the extent of perceived motion smear. For comparison, matches were obtained also when the observers fixated in darkness, without generating passive eye movements.
When the spot moved in the direction of passive eye movement, the extent of perceived motion smear was similar to that during fixation. In contrast, the extent of perceived motion smear was approximately 40 ms less when the spot moved opposite the direction of passive eye movement. Recordings indicated virtually no movement of the non-pressed eye.
Because the motion of the retinal image was similar during eye press and fixation, the observed difference in the extent of perceived smear suggests that extra-retinal signals from eye-muscle proprioception contribute to perceived visual clarity during passive as well as normal eye movements.
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