(十三)

What actually happens when we read? Some people think that we read one word at a time, understand it and then go on to the next. Other people think that our eyes smoothly move over each line from left to right, then back to the beginning of the next line, and so on. In fact, the physical action of reading usually doesn't work in either of those ways.
Suppose you do this experiment with a friend. Get hold of a book with a large page size and with lines that go right across the page. Get your friend to hold the book up and to read it with the top of the book just below his eye level. This means that you can watch the movement of his eyes as he reads the page. If you do this, you will see that your friend's eyes do not make a continuous forward sweep. Instead they progress(向前)by little "jumps", moving, then stopping, as they progress along the line.
There has to be this starting and stopping movement because the eye can see only when it is not moving. Every time the eye pauses it sees a phrase or even a sentence, then jumps to the next part of the line, and so on.
There is another interesting fact about eye movement. You will notice that, from time to time ,the reader goes back and looks again at something he has read before, in other words, he returns to an earlier part of the text probably because he realizes he is not understanding it properly. Then he comes back where he stopped and continues reading.
简析：说明文文体，主要阐述阅读的准确动作。