chapter  4
43 Pages

The Work of the Eyes

When we read we have the impression that our eyes (and mind) sweep continuously across the text except for a few places in which we encounter diffi culty, and at those points we pause to consider what we have just read or regress (go back) to reread earlier material. However, that impression is an illusion. First, the progress of the eyes across the page is not continuous. The eyes come to rest for periods that are usually between 150 and 500 ms; these periods when the eye is close to immobile are called fi xations. Between the fi xations are periods during which the eyes are moving rapidly. These eye movements are called saccades after the French word for jump. Saccades are ballistic movements (i.e., once they start, they cannot be altered). When we read our eyes generally move forward about seven to nine character spaces with each saccade. The duration of a saccade in reading varies with the distance moved, with a typical saccade taking about 20-35 ms. Since, for all practical purposes, no visual information is extracted from the printed page during saccades because of saccadic suppression (Matin, 1974), all visual information is extracted during fi xations. The pattern of information extraction during reading is thus a bit like seeing a slide show. You see a slide for about a quarter of a second, there is a brief off time, and then a new slide of a different view of the page appears for about a quarter of a second. This pattern of fi xations and saccades is not unique to reading. The perception of any static display (i.e., a picture or a scene) proceeds the same way, although the pattern and timing of fi xations differs from that in reading (Rayner, Li, Williams, Cave, & Well, 2007). An exception is when the eyes track a moving target (i.e., a pursuit movement). In this case the eyes move relatively smoothly (and much slower than during saccades) and useful visual information is extracted during the eye movement.