What's happening?

Because our eyes are set apart from each other, they see everything from slightly different angles. So the images your brain gets from each eye are a little different from one another.

By comparing the images, your brain can give you a three-dimensional picture that helps you judge distances. This is called stereoscopic vision. When you cover one eye, you no longer have stereoscopic vision and you see things in two dimensions, like a photograph. This makes judging distances much more difficult.

Fortunately, there are other clues to help you judge depth in real life, such as size, brightness, and position compared to other familiar objects. These are the clues that people use if they lose the sight in one eye. You can improve your one-eyed depth perception too. Try the penny drop test several times. You'll soon be hitting the cup quite easily.

• Return to the experiment.
  

Excerpt from The Jumbo Book of Science by the Ontario Science Centre, used by permission of Kids Can Press Ltd., Toronto.