Contrast thresholds for maintained vision were determined under varying conditions of retinal image motion. The "stopped image" technique was used to eliminate normal image motion. Controlled motion at various frequencies and amplitudes was introduced by rotating one of the mirrors in the optical system. Low-frequency vibrations (1, 2, and 5 cps) of the retinal image were found to be beneficial to maintained vision while high-frequency vibrations (10, 20, and 50 cps) were found to be detrimental to maintained vision when compared to vision in the absence of normal retinal image motion.
JOHN KRAUSKOPF, "Effect of Retinal Image Motion on Contrast Thresholds for Maintained Vision," J. Opt. Soc. Am. 47, 740-741 (1957)