Introduction
Think about all the ways that students use their sense of sight during a typical school day.
As soon as they open their eyes in the morning, they may look at the clock to see what time
it is. Then, they might look out the window to see what the weather is like. They probably
look in a mirror to comb their hair. In school, they use their eyes to read the board, their
textbooks, and the expressions on their friend’s faces. After school, they may keep their eye
on the ball while playing basketball (Figure20.11). Then they might read their homework
assignment and the text messages from their friends. If you aren’t visually impaired, you
probably use your sense of sight in all of these ways, as well. In fact, you may depend on
your sight so much that you have a hard time thinking of anything you do without it, except
sleep. Why is sight so important?
Figure 20.11: All eyes are on the ball in this basketball game; think about how we use the
sense of sight in other games. ( 15 )
The Nature of Human Vision
Sight, orvision, is the ability to see light. It depends on the eyes detecting light and
forming images. It also depends on the brain making sense of the images, so we know what
we are seeing. Human beings—and other primates—depend on vision more than many other
animals. It’s not surprising, then, that we have a better sense of vision than many other
animals. Not only can we normally see both distant and close-up objects clearly. We can
also see in three dimensions and in color.