In one sense, as you may know, we do not read with our eyes at all, but with our minds. The eyes are only a vehicle of transmission they flash the visual impulses that the brain interprets and the mind reacts to. Such interpretation and reaction may be instantaneous or halting, accurate or erroneous, easy or full of effort, depending not on the sharpness of a reader’s vision but on the clearness and richness of his understanding, and on the reflexive perception habits under which he operates.
The eyes are the camera of the mind. Like a camera, they do no more than snap the photograph. From that point on, the brain does all the work it develops the negative, prints the picture, and stores away the result. Like a camera, the eyes must focus on the subject before a photograph can be taken.
They may focus and refocus three to a dozen times on a single line of print, up to a hundred times or more on an average page, in order to continue feeding successive images to the brain for interpretation. Sit in front of a reader and peer up into his eyes as they move across a page of print.
It is a fascinating process to watch, especially if you have never observed it before. You will see his eyes focus at a point somewhere near the beginning of a line and remain there for a very brief period of time, generally a fraction of a second.
It is during this momentary pause that he is reading depending on his skill, his eyes are photographing a phrase unit, a couple of words, a single word, or maybe only a portion of a word. Then his eyes jerk sharply to the right, focus for a second time, snap a second photograph, and jerk again to the right.
These alternating jerks and pauses go on until the end of the line are reached, at which point his eyes sweep back to the left, focus on the following line, and the movement-pause, the movement-pause process starts all over again, continuing line by line, paragraph by paragraph, page by page.
Go on watching for a while. Soon you will be able to count the number of pauses made on each line. If the reader you are observing is fairly skillful you may see only three to five pauses. If he is awkward and inexperienced you may be able to count ten to a dozen or more, and on many lines, if not on practically every line, you may see his eyes suddenly reverse and jerk to the left. He is making regressions he is going back to check on the camera; the picture that his mind developed failed to make sense, or in some way his comprehension momentarily broke down.

Does all this seem vastly complicated? It is, of course. Nevertheless, these constantly alternating movements and pauses are completely reflexive and pretty nearly unconscious, controlled automatically by the ability and speed of the mind in absorbing and integrating what the eyes see.
They are as reflexive and automatic as the movements in eating, an activity in which, particularly when one is hungry, there is ordinarily little or no conscious control over, or even awareness of, the separate motions of opening and closing the mouth, raising and dropping the lower jaw, grinding the teeth, or swallowing. In a sense, such motions are directed and controlled by the stomach, which dictates the amount of food it wishes to receive and the rate at which it can comfortably receive it. So also in reading the mind dictates the portion of print it wishes to interpret at one time and the rate at which the eyes should continue feeding it these portions. Beading, then, is accomplished by a continuous alternation of ocular pauses and movements—or what we call “fixations” and “interfixation movements.” “Fixation” is the technical term for the fractional second in which the eyes focus on a portion of a line of print. During a fixation, the external movement of the eyes stops, an image is transmitted to the brain, and words are read. Then the eyes move slightly to the right, a new point of fixation is made, and another image is flashed to the brain.