Accuracy of memory-guided saccades.

Accuracy of saccades toward a remembered target positions in the dark (memory-guided saccades) was studied in 11 normal subjects. The subjects were instructed to execute saccades with amplitudes of 20, 40, 60, and 80 degrees, centering on the primary position. Saccades were initially performed for 30 s with visual fixation targets. The targets were then switched off. The subjects continued saccades in the dark with the given amplitude. Most memory-guided saccades overshot the target. Saccades with an amplitude error of 12.7 +/- 7.3 degrees (mean +/- SD) were followed by corrective saccades, while no corrective saccades occurred following saccades with an error of 4.3 +/- 4.0 degrees. The accuracy of initial memory-guided saccades decreased with time. However, the amplitude of the memory-guided saccades was corrected when the error was beyond about 5 degrees. These results suggest that memory-guided saccades are not repetitions of visually guided saccades, but nonvisual error signals relate to the control of eye movements in the dark.