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Doug Crawford, Gunnar Blohm; Calculation of accurate 3-D reach commands from initial retinal and extra-retinal conditions. Journal of Vision 2011;11(11):27. doi: 10.1167/11.11.27.
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Reach movements can be guided in ‘closed loop’ fashion, using visual feedback, but in biological systems such feedback is relatively slow. Thus rapid movements require ‘open loop’ transformations based on initial retinal and extra-retinal conditions. This is complicated, because the retina is attached to the interior surface of a sphere (the eye) that rotates three-dimensionally with respect to the world, the other eye, and effectors such as the reach system. Further, head movement causes the eyes to translate with respect to both the visual world and the shoulder. Optimism continues to abound that linear approximations will capture the main properties of this system (i.e., most visuomotor studies implicitly treat the retina as a flat, shifting plane), but unfortunately this ignores several fundamentals that the real brain must deal with. Amongst these is the need for eye and head orientation signals to solve the spatial relationships between patterns of stimulation on the two retinas (for depth vision) and between the external world and motor effectors. Here we will describe recent efforts to 1) understand the geometric problems that the brain encounters in planning reach, 2) determine if the brain actually solves these problems, and 3) model how the brain might solve these problems.
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