Full context:   When reading, the eye moves continuously along a line of text but makes short rapid movements (saccades) intermingled with short stops (fixations). There is considerable variability in fixations (the point at which a saccade jumps to) and saccades between readers, and even for the same person reading a single passage of text. When reading, the eye has a perceptual span of about 20 slots. In the best-case scenario and reading English, when the eye is fixated on a letter, four to five letters to the right and three to four letters to the left can be clearly identified. Beyond that, only the general shape of some letters can be identified.