optical header

Ready to try a do-it-yourself optical illusion? Check out the games below.

hole in the hand
dotted lines
games paper

What you need:
A piece of paper

cylinder
1.

Roll up a piece of paper in the shape of a tube.

cylinder eye
2.

Hold the tube up in front of one eye. Keep both eyes open and look forward.

hand cylinder
3.

Take your free hand (the one not holding the tube), and hold it up in front of the eye that is not looking through the tube. Keep this hand open with your palm facing your face. Place your open hand against the side of the tube.

games paper

What you should see:
It should look like there’s a hole in your free hand. The objects in the distance should be visible through this hole.

cylinder

What happened?
Your brain takes information from both of your eyes to make one image. One eye sees a hole, and the other sees a hand. When the brain adds the images together, you see a hand with a hole in it.

Pencil Test
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Pencil dotted lines

What you need: Two pencils

eyes shut
1.

Close one of your eyes.

pencil tips
2.

Hold the two pencils horizontally out in front of your face and try to touch the pencils ends together, keeping one eye closed.

hand cylinder
3.

Now, try it again with both eyes open.

games paper

What you should experience:
It should be harder to touch the pencil ends together with one eye closed than it is with both eyes open.

cylinder

What happened?
Having two eyes helps you judge depth and distance. Can you think of some other activities that would be hard with just one eye?

Ask a ScientistWhat do your eyes do when you’re sleeping? Find out with Dr. Wiggs.

first aid video
Last updated: June 2019