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Optical Illusions

Description Goes Here

Try This at Home: Fish Out of Water

Illustrated Concepts

A persistence of vision illusion occurs when several discrete images are quickly flashed before the eye. These individual images are melded together by the eye and the brain to form a continuous image. This is the same sort of illusion that makes movies and cartoons appear as moving images.

What You Need

  • 2 index cards
  • Crayons or markers
  • Clear tape
  • 1 pencil

What To Do

1. Make sure you have an adult with you to supervise this experiment.

2. Draw and color a fishbowl, without any fish in it, on one index card.

3. Draw and color a fish, without a fishbowl or water, on the other index card. Make sure that the fish is the right size, and in the right place on the index card, to fit inside of the fishbowl.

4. Place the index cards back to back, so that both drawings are showing and are right-side up, and tape the top and sides of the cards together.

5. Stick the pencil in between the cards so that it is perpendicular to the bottom of the cards. Tape the pencil to the cards in this position.

6. Make a hypothesis! The fish and the bowl are not together. By spinning them quickly, do you think the fish will ever appear in the bowl?

7. Spin the cards by rolling the pencil in between both hands quickly. Do you see the fish in the bowl?

8. Clean up.

What’s Happening

As you spin the pencil, each index card will flash before your eyes. The cells in the back of your eye, on the retina, will retain this image for just a little longer than you actually see it. The next image will flash so your cells will see this image as well. Your brain helps to combine the two images into one image; the fish looks like itís inside the fishbowl! You can also do this experiment using two different images, such as a bird in a tree or a puppy in a window. Similarly, many discrete images flash before your eyes when you watch television or go to a movie. The combination of your eyes and your brain work to form the images into one continuous image.

Fun Fact

All humans are born colorblind–our color-seeing cells don’t start working until we are 4 months old.