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Stephanie M. Shorter-Jacobi, Jeffrey D. Schall; Microstimulation of frontal eye field samples the state of saccade preparation during visual search. Journal of Vision 2004;4(8):641. doi: 10.1167/4.8.641.
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The frontal eye fields (FEF) are involved in visual selection and saccade selection. Previously we used FEF microstimulation to explore the evolution of these processes in macaques performing a search task with prosaccade or antisaccade responses based on the shape of a color singleton (Juan et al., SFN 2003 Abstract 180.4). A key result was that on antisaccade trials evoked saccades reliably deviated toward the saccade endpoint and not toward the singleton that was opposite this endpoint. This finding provides evidence that FEF stimulation effectively samples the current state of saccade preparation. In the current report we manipulated the aspect ratio of the rectangular singleton to change the difficulty of categorizing which response was required on each trial. Microstimulation was delivered at variable times subsequent to array presentation on half of the randomly intermixed prosaccade and antisaccade trials. Microstimulation usually evoked a saccade that disrupted the natural saccade preparation, but a second corrective saccade shifted gaze to the correct target location. Greater elongation of the singleton resulted in faster reaction times. Also, as aspect ratio increased, the magnitude of the deviation of evoked saccades increased. Evoked saccades landed progressively closer to the prosaccade or antisaccade target. The present results are consistent with the hypothesis that the initial neural selection of the singleton of a search array does not necessarily influence the production of the upcoming saccade. More generally, these results support that visual selection and saccade selection are distinct processes.
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