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°, 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° (mean ± SD) were followed by corrective saccades, while no corrective saccades occurred following saccades with an error of 4.3 ± 4.0°. 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°. 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.