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Robert M. McPeek; Incomplete suppression of distractor-related activity in frontal eye field results in curved saccades. Journal of Vision 2005;5(8):581. doi: 10.1167/5.8.581.
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Saccades made in the presence of distractors show significantly more trajectory curvature than movements made without distractors. Previously, we reported that saccades curving toward a distractor during visual search are accompanied by increased superior colliculus (SC) activity at the distactor site immediately before the onset of the movement (McPeek & Keller 2003; also see Port & Wurtz 2003). On the basis of this, we speculated that curvature results when a movement is initiated before selection of the target from distractors has been fully resolved. To test this hypothesis, we recorded activity in the frontal eye field (FEF) during search. In contrast to the SC, activity in FEF is normally poorly correlated with saccade dynamics. However, the FEF, like the SC, is known to be involved in target selection. Thus, if saccade curvature is due to incomplete target selection, we expect greater FEF activity at a distractor site for curved saccades, similar to what was seen in the SC. We found that saccades that curve toward a distractor are indeed accompanied by increased FEF activity at the distractor site. This curvature-related activity appeared to persist longer in the FEF than in the SC, where it was abruptly curtailed upon saccade initiation. To verify that the activity was causally related to curvature, we microstimulated in the FEF. The stimulation was sub-threshold for evoking saccades, but when it had a temporal structure similar to that observed for curved saccades, it induced systematic movement curvature. These results support the idea that saccade curvature in search results from incomplete suppression of distractor-related activity during target selection.
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