As you read sentences on a page your eyeballs do not move from left to right, letter-to-letter, word-to-word in a straight, steady line. If you were able to attach little lasers to your eyeballs you would see that your eyes are actually hovering and jumping about like a hummingbird. They move unevenly, go back occasionally, skip some words, and fixate on others. These small, rapid, jerky movements that your eyes make are called saccades. It only appears that you are moving them from left to right in a straight line because your brain is doing what human brains naturally do: they create order out of chaos.

Your brain tricks you into thinking that you process every word when in fact you do not. Instead your eyeballs fixate on only about 60% of the words you read. With unfamiliar material you fixate on more words; with more familiar material you fixate on fewer words. This means your eyes dance right over 40% of the words without stopping. That’s what you do when you read. It only appears as if you are reading every word because your brain is filling in the blanks.