Have them read for one minute out of the book. Compare with how many lines they read at the beginning of the lesson. Interesting to the reader. NOW have them read for one minute from the ook that they have chosen. Write down how many lines they have read.
Most people see the whole tree in one or two glances.
This is what we call Natural Vision. When we are seeing almost anything, we are using Natural Vision, except when we are looking at a page of print. You see, in first grade we were taught how to have tunnel vision. Most people can only see one word at a time. You may as well read through a straw.