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M Nawrot, B Nordenstrom, A Olson, A Stark, A Drayton; Reducing Slow Eye Movement Gain Disrupts the Perception of Depth From Motion Parallax . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2880.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Our current theory of motion parallax uses a comparison of the direction of an object's retinal motion to the direction of the slow eye movement (SEM) for its assignment of depth sign. That is, objects with a retinal image moving the same direction as the SEM are nearer than fixation while those in the opposite direction are farther than fixation. A disruption of the SEM system may have an effect on the perception of depth from motion parallax. It is well known that alcohol intoxication reduces SEM gain leading to easily observable horizontal gaze nystagmus. Does this reduction in SEM gain due to alcohol intoxication have an effect on the perception of depth from motion parallax.? Methods: A repeated measures design was used to assess the effects of SEM gain on the perception of depth from motion parallax. Binocular stereopsis, active (lateral head movement) and passive (translating chair) motion parallax thresholds were assessed with a computerized random-dot stimulus. The staircase procedure used a 2AFC, phase discrimination task. In the second test session observers were administered ethyl alcohol at 0.8 g per kg body weight to achieve a blood alcohol content (BAC) near 0.1% before starting the tests. Eye movements were recorded during active head movements in both light and dark to examine changes in the gain of translational vestibular ocular response (TVOR) and the optokinetic response (OKR) eye movements. Results: Acuity and contrast sensitivity were unchanged. For most observers binocular stereopsis thresholds remained unchanged at 20 sec (the floor). Average SEM gain decreased from near perfect gain between 0.9 and 1.0 to gain values between 0.6 and 0.7. As expected, observers with low gain values also had numerous "catch-up" saccades where the fast eye movement system is recruited to jerk the eyes into to a position to resume pursuit of the target. Both active and passive motion parallax thresholds increased between two and three times the normal threshold value. There was a significant correlation between SEM gain change and the passive motion parallax threshold change. Although the gain of the compensatory eye movements generated in response to lateral head movements decreased, the large variability we find makes it difficult to determine the specific change in the TVOR and the OKR components. Conclusion:The reduction of slow eye movement gain due to alcohol intoxication is well known. This effect on SEM gain appears to have a detrimental effect on the perception of depth from motion parallax. However, the effect of the SEM decrease and the effect of the saccadic intrusions still remain to be separated.
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