The child is shown these forms one at a time and he is simply asked to copy them. It is amazing to see some of the distortions that a child will make in attempting to copy these forms. If a child can't perceive and copy these simple geometric forms, it is unreasonable to assume that he will be able to perceive the wiggly lines which make up letters which in turn make up words, which in turn make up sentences which stand for abstract ideas. We see children often who can't tell the difference between a square and a rectangle or a circle and an oval. This is also a skill which can be improved through vision therapy.
Many children see just one word at a time with each eye fixation.
Reading speed can be improved by learning to see two, three, or more words with each eye fixation. This could be compared to reading through a straw. It is easy to see the difference in reading for meaning when the span of perception is wide. The ultimate visual skill is visualization. This is similar to being able to see things in the mind's eye.