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Kitty Xu, Jay Edelman; Disruption of voluntary saccade commands by abruptly appearing visual stimuli. Journal of Vision 2008;8(6):639. doi: 10.1167/8.6.639.
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Saccades can be made both reflexively in response to a sudden appearance of a sensory stimulus as well as voluntarily to an object of interest in the visual field. However, there has been little study of how the interaction of voluntary and reflexive systems depends on the timing of their commands. We studied the ability of a suddenly appearing distractor to disrupt a voluntary saccade command, and how this ability depended on the spatial and temporal relations between the visual stimulus and the voluntary saccade plan. Two subjects' saccades were monitored at 500 Hz using an Eyelink II video eye tracker. They first fixated a central arrow, which pointed either left or right. 500–800 ms later the fixation stimulus disappeared, cuing the subject to make a saccade of 8° to a blank space in the direction the arrow pointed. A 2°×2° distractor appeared at a time 40–130 ms before the saccade. The distractor could appear at the saccade goal (0° separation), or else at the same eccentricity, separated in direction by 22.5°, 45°, 90°, or 180°. Subjects were instructed to ignore the distractor. As a control, in 1/6 of trials no distractor appeared. Trials with differing distractor/saccade goal separations were run intermixed. We found that for large distractor/saccade goal separations (90°, 180°) there was a large notch in the saccade timing histogram, such that virtually no saccades occurred from 80–100 ms after distractor appearance. When this separation was small (0°, 22.5°), more saccades were elicited 80–100 ms after distractor appearance (i.e. “express saccades”) than in control trials when no distractor was present. These results strongly suggest that the transient component of a visual response has a much stronger impact on voluntary saccade generation than does the sustained visual response, thus elucidating the time course of the remote distractor effect.
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