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Random Dot Stereogram

In this demonstration, students discover how the structure and placement of the eyes creates depth perception.

Depth perception occurs as your brain compares the pictures received in each eye to figure out how far objects are from you. Each eye sees a slightly different picture because they're in slightly different places.

If you use first one eye then the other to view an object, nearby objects tend to jump back and forth more, whereas faraway objects hardly seem to move at all.

In the first part of the demonstration, one eye sees the object covered by the index finger. The other eye has an unobstructed view. This demonstrates that each eye is getting a different picture of the world.

Single image random dot stereograms are the original versions of the popular 'Magic Eye' pictures in which a 3D image pops out from what appears to be a sheet of random dots. The dots are arranged in repeating pattern, with slight differences in each repetition. Each eye sees a slightly different pattern because of the different angles between the page and each eye. Your brain tries to overlap the two patterns, and creates the virtual 3D object.

If you want to view movies or pictures in 3D, you have to show a different picture to each eye. That's why they give you glasses with 2 lenses of different colours (or let through light of different polarities.)


  • Describe how depth perception affects how the brain forms an image.


  • a selection of single image random dot stereograms, printed on either an overhead sheet or on a large sheet of paper
    overhead projector (optional)

Key Questions

  • Do both eyes have the same point of view of the objects before them?
  • If you bring your finger closer to your face, do you find it jumps back and forth more or less than when it’s farther away?
  • What was your method for “seeing” the image?

What To Do

Part 1: Depth Perception

  1. Focus on a person or object.
  2. Hold up your index finger at arm’s length.
  3. Close your left eye. Looking only with your right eye, move your finger so it covers the object.
  4. Now look with just your left eye.

Part 2: Stereograms

  1. Show random dot stereograms to students.
  2. Try and see what image is “hidden” in the stereograms.

Note: Stereograms are difficult to make out on computer screens


  • How would being blind in one eye affect your depth perception? Why?
  • How are random dot stereograms created?