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Matthew Heath, Jeffrey Weiler, Kendal Marriott, Timothy Welsh; The antisaccade task: dissociating stimulus and response influences online saccade control. Journal of Vision 2011;11(11):549. doi: 10.1167/11.11.549.
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Antisaccades require the suppression of a stimulus-driven response (i.e., response suppression) and the computation of a movement plan mirror-symmetrical to the location of a target (i.e., vector inversion). The goal of the present study was to determine whether response suppression, vector inversion, or both, contribute to previously reported differences in the online control of pro- and antisaccades (Heath et al. 2010: Exp Brain Res). Pro- and antisaccades were completed in separate blocks (i.e., blocked schedule) and a block wherein the spatial relation between stimulus and response was provided at response cuing (i.e., random schedule). Notably, the random schedule provides a relative means for equating response suppression across pro- and antisaccades. To examine online trajectory amendments, we computed the proportion of variance (R2 values) explained by the spatial location of the eye at early, middle and late stages of saccade trajectories relative to the saccade's ultimate movement endpoint. The basis for this analysis is that between-task differences in R2 values reflect differences in trajectory control: small R2 values are taken as evidence of an online mode of control whereas larger R2 values are taken to reflect a trajectory that unfolds with reduced online and error-nullifying amendments. Prosaccade reaction times were faster than antisaccades; however, this difference was reduced when tasks were equated for response suppression (i.e., the random schedule). Additionally, antisaccades yielded larger R2 values than prosaccades from early to late stages of saccade trajectories and this finding was consistent across blocked and random schedules. In other words, the spatial location of the eye during antisaccade trajectories was more predictive of the response's endpoint. Thus, we propose that the intentional nature of vector inversion disrupts the normally online control of saccades and results in a cognitive mode of control that is not optimized for trajectory amendments.
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