Saccades

The eye can move in a rapid motion called a saccade, which lasts less than $45$ms with rotations of about 900$^\circ$ per second. The purpose is to quickly relocate the fovea so that important features in a scene are sensed with highest visual acuity. Figure 5.15 showed an example in which a face is scanned by fixating on various features in rapid succession. Each transition between features is accomplished by a saccade. Interestingly, our brains use saccadic masking to hide the intervals of time over which saccades occur from our memory. This results in distorted time perception, as in the case when second hands click into position on an analog clock. The result of saccades is that we obtain the illusion of high acuity over a large angular range. Although saccades frequently occur while we have little or no awareness of them, we have the ability to consciously control them as we choose features for fixation.