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Martin Rolfs, Tomas Knapen, Patrick Cavanagh; Shrinking the oculomotor world using global saccadic adaptation. Journal of Vision 2009;9(8):417. doi: 10.1167/9.8.417.
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© ARVO (1962-2015); The Authors (2016-present)
Visual perception depends on saccadic eye movements to bring objects of interest onto the fovea. To achieve this with continuing efficiency, the oculomotor system needs to calibrate saccades so that they reliably land on their targets. Saccades can be made to systematically miss their target by shifting its position during the saccade, when the observer is oblivious to such a change. As a result, saccadic magnitude will progressively adapt until the saccades finally land close to the artificially displaced target. This saccadic adaptation is thought to be spatially selective, dropping off with distance from the adapted target saccade vector. Although this is a robust finding, it is hard to envision an error in the oculomotor system that would make such spatially specific calibration in saccade landing sites necessary. Global adaptation mechanisms for overall gain in all directions, or in directions of specific ocular muscle groups would seem more ecologically valid. To test for global adaptation, we implemented an adaptation paradigm in which saccades had random directions and amplitudes, following a quasi random walk within the display. During each saccade the target was displaced 25% closer to the current fixation position. We found that adaptation was indeed spatially generalized and, moreover, developed very fast. In fact, saccades adapted faster than during traditional adaptation, where typically only one saccade vector is adapted. Our findings suggest that the generality and speed of saccadic adaptation depend on the distribution of feedback the oculomotor system receives. We conclude that a global saccadic correction occurs rapidly whereas directional selectivity is probably implemented by slower and later stages of adaptation.
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