Saccadic adaptation is not done by halves B Dillenburger, S Raphael, M Morgan |
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Visual Perception Group, Max-Planck-Institute Neurological Research, Germany
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| Saccadic adaptation has been shown to intermediate locations in mixed shift-size trial experiments. But does saccadic adaptation also occur if only 50% of trials contain a shift? Do saccades then also adapt to an intermediate position? We recorded eye movements (Eyelink2000) in 5 subjects. After central fixation subjects had to saccade to a target. We randomly interleaved 50% shift trials in which targets were displaced by 0.7 deg during saccade with 50% no-shift trials. In a second experiment, central fixation was colored to condition shift vs. no-shift trials. In all experiments, subjects had to indicate whether they had perceived a shift or not. We analyzed average fixation locations to compare shift and no-shift trials. We found no saccadic adaptation in no-shift trials. Fixations landed on different locations in shift and no-shift trials, even though trials differed only during saccade. In color-coded experiments we found the same result, indicating that no conditioning of the saccadic adaptation process occurred using the color information. In mixed shift/noshift experiments saccades are not adapted to intermediate locations, but are in-flight corrected in each trial. The data suggest that error signals in more than 50% of trials are necessary for saccadic adaptation. |
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