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H. E. Bedell, J. Tong; Asymmetric Attenuation of Perceived Motion Smear During the Slow Phases of Infantile Nystagmus. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1103.
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Normal observers perceive less motion smear for a target that moves opposite the direction of a smooth eye movement than for a target that moves with the same retinal image speed in the direction of the eye movement. This study investigated whether a similar asymmetrical attenuation of perceived motion smear occurs in observers with infantile nystagmus (IN).
Observers (N=2) viewed a 6 arc-min laser spot that was triggered to flash for 100 or 125 ms during the slow phase of jerk IN. The laser spot was 2 log units above its detection threshold and the rest of the visual field was dark. On each presentation the laser spot moved right or left at a speed between 5 and 60 deg/s. Subsequently, the observer adjusted the length of a bright line to match the extent of perceived motion smear. To compare the results for different computed velocities of retinal image motion (target velocity - eye velocity), the matched extent of smear was converted from spatial to temporal units.
For relative motion of the laser spot in the opposite direction vs. the same direction as IN slow phases, the mean durations of perceived smear were 44 and 116 ms, respectively. In one observer with PAN, the direction of spot motion that produced less perceived smear reversed with an alternation in the direction of the IN slow phase.
Extra-retinal signals that accompany IN attenuate perceived motion smear specifically when the relative motion of a target is opposite the direction of the slow-phase eye movement. As during normal eye movements, attenuation of perceived smear for this direction of motion should foster perceived clarity of the stationary visual world. The attenuation of perceived motion smear is more pronounced during IN slow phases than during normal eye movements, suggesting that nystagmus promotes adaptive visual changes when it occurs during early development.
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