Effect of stimulus probability on anti-saccade error rates.

Subjects sometimes fail to suppress a reflexive saccade towards the flashed stimulus in an anti-saccade task. Here, we studied how error rates in the anti-saccade task varied as a function of saccadic probability. Ten subjects performed 200 anti-saccade trials for each of three saccade-direction probability conditions (20%, 50%, and 80%). We found that as the likelihood of a saccade in a given direction increased, the percentage of pro-saccade errors also increased for stimulus presentations in this direction. These results provide support for the hypothesis that errors in the anti-saccade task are the result of an increased level of motor preparation.