On the Generation of Antisaccades in Different Conditions

To generate a saccade in the direction opposite to the stimulus site (antisaccade) takes a conscious voluntary effort: first, one needs an intact fixation system to prevent saccades to the stimulus (prosaccades) and second, one has to generate a saccade to a location with no target. While the maintenance of fixation relies on an intact tectum, the correct performance of the antitask relies on an intact frontal system. Valid peripheral precues for attention capture indicating the direction of the antisaccade increase the error rate and the reaction time of the antisaccades. In this study we investigated how different conditions of stimulus presentation influence the performance of the antitask. We varied systematically the duration of the gap (time between fixation point offset and stimulus onset) from zero to 600 ms, and the stimulus eccentricity from 1 to 12 deg. Eye movements were recorded under infrared light. We analysed the reaction time of the correct antisaccades (a-srt) and of the erratic prosaccades (p-srt), and the percentage of errors (%-err) separately for the right and the left stimulus.

Increasing the gap to 200 ms increased the %-err by 10% and decreased the a-srt by 30 ms. For longer gap durations these effects disappeared. With larger saccades the p-err rates decreased and the p-srt were reduced by 10 ms mostly staying in the range of express saccades and following the corresponding prosaccades in protasks. The a-srt decreased systematically with increasing eccentricity. The results have implications for voluntary versus involuntary control of saccades and are related to the significance of the antitask in clinical studies.