Abstract
Saccade trajectories are modulated by the presence of an irrelevant distractor. These modifications have been attributed to competitive interactions of activation patterns in the superior colliculus, a midbrain structure involved in encoding stimuli as potential saccade targets. Variations in the balance between target and distractor activations in different saccadic paradigms may therefore be reflected in differential effects of distractors on the saccadic trajectory.
To explore this, we investigated the effect of distractors in prosaccade, antisaccade, and memory-guided saccade tasks. We hypothesized that target activation would be reduced in antisaccades (where there was never a stimulus at the target location) and in memory-guided saccades (where the stimulus at target location has disappeared). If so, a model of competition between target and distractor activations would predict that distractors would induce greater distortions of saccadic trajectory in antisaccades and memory-guided saccades, than in prosaccades.
In the same set of 8 subjects we measured vertical prosaccades, antisaccades and memory-guided saccades (using a 1500 ms interval) with and without a distractor. The results showed that deviation away from the irrelevant distractor was larger in an antisaccade than in a prosaccade. Still more deviation away was observed in the memory-guided saccade paradigm. These results confirm the hypothesis that a distractor evokes more competition when there is a weaker target representation. They also illustrate the potential of using saccade deviations as a probe of saccade-related activation patterns in the ocular motor system.