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DY P Henriques, PW Medendorp, CC A M Gielen, JD Crawford; Eye-hand Coordination During Reaching in 3D Space: Binocular Fixation and Internal Models . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4667.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: (1) To examine whether shifts in eye location, caused by rotation of the head, are compensated for when reaching to targets in peri-personal space. (2) To examine whether deviations in the binocular gaze points (the point in space where the gaze lines meet) help guide the hand during reaching to remembered targets. Methods: We had 9 subjects place a fingertip on the remembered location of a target LED (30, 38 and 50 cm front the eye) with the head held at one of seven horizontal eccentric positions in the dark. They reached both when they were looking at the target site and when they were looking elsewhere. Search coils were used to record 2-D eye positions, while 3-D location of the eyes, the head and the fingertip were recorded using an Optotrak system. Results: Reaching responses were fairly accurate when gaze was on target, varying little with head position. But when subjects also deviated their gaze from the target, they produced systematic localization errors in direction and depth. Reaching also deteriorated when the fixation point was displaced from the target in depth. Finally, naturally-produced variations in binocular gaze points, when subjects aimed their eyes toward the target site during reaching, did not cause the fingertip to be similarly displaced. Conclusion: The findings suggest that the eye-hand coordination system maintains an internal model of body linkage geometry, and while this representation is much better calibrated for foveal input than non-foveal ones, the brain does not appear to use signals coding for the binocular gaze point to guide reaching.
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