The time of secondary saccades to primary targets

When a first saccade is made in response to a single, suddenly appearing stimulus it often misses the target. The retinal error may be very large, in particular in those cases where the subject anticipates the target location and initiates a saccade to a wrong position. We have analyzed the time of the occurrence of the secondary saccades by which the subject corrects these errors. Using the gap task with random target locations we found that large errors after anticipatory saccades--especially those after direction errors--can be corrected very fast. The latencies of these corrective saccades (being measured from target onset, not from the end of the primary saccade) form bimodal distributions with a first peak at 100 ms. It is therefore concluded that large errors can be corrected by express secondary saccades.