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UBC Theses and Dissertations

The global effect for antisaccades Viswanathan, Jayalakshmi


In the global effect, prosaccades are deviated to a position intermediate between two targets or between a distractor and a target, which may reflect spatial averaging in the collicular map. Antisaccades differ from prosaccades in that they dissociate the locations of the stimulus and goal, and generate weaker collicular activity. We used these antisaccade properties to determine whether the global effect was generated in stimulus or goal computations, and if the global effect would be larger for antisaccades, as predicted by an origin of the effect in collicular averaging. In the first two experiments, human subjects performed antisaccades while distractors were placed in the vicinity of either the stimulus or the saccadic goal. Global effects occurred only for goal-related and not for stimulus-related distractors, indicating that this effect emerges from interactions with motor representations. In the last experiment, subjects performed prosaccades and antisaccades with and without goal-related distractors. When the results were adjusted for differences in response latency, the global effects for rapid responses were three to four times larger for antisaccades than for prosaccades. These results were consistent with predictions of spatial averaging in a collicular model. We conclude that the antisaccade global effect shows properties compatible with spatial averaging in collicular maps, and if so, originate in layers with neural activity related to goal rather than stimulus representations.

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Attribution-NoDerivs 3.0 Unported