Saccadic eye movements after extremely short reaction times in the monkey.

Monkeys were trained to change their direction of gaze from one point (fixation point) to another (target). If the fixation point was extinguished at the same time when the new target occurred the saccadic reaction times (SRT) were in the order of 200 ms. If the fixation point disappeared 150-250 ms before the new target occurred (gap with no visible stimulus) monkeys made regular saccades after shorter reaction times of about 140 ms. In addition animals in the gap situation made saccades that had reaction times of no more than 70-80 ms measured from the onset of the new target (Express-Saccades). The reaction times of the E-saccades have standard deviations of only +/- 3 ms. E-saccades occurred with a frequency of up to 80% for gaps of 200-240 ms. If the gap was shorter than 180 ms increasingly more regular saccades were made with reaction times of 140-160 ms. With gap duration decreasing from 140 ms to zero all saccades were regular with SRTs increasing linearly to more than 200 ms. In one animal almost all E-saccades fell short and were corrected after less than 250 ms depending on the size of the error: large errors were corrected faster than small ones.