A limit to the speed of vision

Recent years have witnessed a great increase of interest in the relation of illumination to effective vision and efficient work. Better lighting makes it possible to see more quickly and more accurately than under poor lighting conditions. Although there are many other factors involved in vision and its relation to production, the speed of vision is one of great interest. It has been known for a long time that the retinal image must be stationary if it is to be seen clearly or even at all. Just what the minimum exposure time of the stationary image must be has been only approximately known. The eyes are always more or less in motion, and often they are engaged in trying to discriminate details which are moving. In reading, for example, the movement of the eyes consists chiefly of rapid sweeps with brief pauses between them. During the sweeps it is impossible for the details to make a sufficient impression, since the image is rushing across the retina. It is only during the fixational pauses in the eye movements, when the image is nearly or quite at rest on the retina, that an adequate impression is made.