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AZ Khan, JD Crawford; Gaze Angle Dependency Of Ocular Dominance In A Pointing Task . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4663.
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Purpose: We previously showed the ocular dominance reverses as a function of gaze angle in a reaching and grasping task (Khan & Crawford, Vision Research, 2001). During this task, 10 subjects reached out and grasped rings located at arm's reach at equal intervals across the binocular visual field. We found that on average, subjects brought the ring toward the left eye for leftward target and the right eye for rightward targets switching between the two approximately 15° off center. This seems to be affected to a minor degree by the hand used. We repeated this experiment with a pointing task in order to confirm the validity of our results across various motor tasks. Methods: Previous studies have shown that when pointing, subjects intersect their finger to a projected line of gaze from their eye to the target. We defined the dominant eye as the one that falls on the finger-target line. 10 subjects binocularly foveated and pointed toward randomly presented LED targets (200cm distance) located at 10° intervals across the binocular field (50° left to 50° right) with their head fixed in the dark. Pointing angles of the eye and arm were measured using 3-D search coils. For comparison, control eye-finger-target lines were established by trials in which either the left or right eye was patched, forcing alignment of all targets with the other eye. Results: In experimental trials, we found that subjects aligned their fingers to both their left and right eyes depending on gaze angle i.e. they tended to choose the left eye for leftward targets and the right eye for rightward targets, but varied in the angle at which they reversed dominance (average: 3° right, range: 20° left to 34° right). The transition between aligning with their left eye to aligning with their right eye occurred abruptly (within 20°). Data show that during the transition there was a gradual shifting of a roughly unimodal distribution where subjects aligned with entirely their left eye for leftward targets, then aligned the target somewhere between both eyes in the middle of the transition and finally aligned entirely to the right eye for rightward targets. Conclusion: Results from the two experiments suggest a mechanism in the brain that optimizes for field of view in eye-hand coordination, i.e. the brain seems to prefer the eye with the better field of view for each gaze direction. This mechanism may involve gating of information entering from the two eyes, or a motor process that aligns the hand with the eye with the better field of view or a mixture of both processes.
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