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What Are Optical Illusions?

What are optical illusions? Optical illusions are when the way we perceive what we see does not actually correspond to what is there.

There are three main types of optical illusions:

  • literal illusions – The image created is different from the object that created it. Think of seeing a horse in the clouds or the face on Mars.
  • physiological illusions – The eyes and the brain are affected by over stimulation. Think of the illusions where you have to stare for some period of time to have it take effect.
  • cognitive illusions – When there is some sort of interference in the processing of the image. Think of the images of never ending staircases. The brain is trying to make sense of the nonsensical by providing information which isn’t really there.

Optical illusions are sometimes called visual illusions.

I’ll provide some illusions from time to time. Students usually enjoy them and they are fun, quick activities.

A favorite illusion with kids is the sausage finger illusion. Hold your hands together with your fingers pointing at each other as shown below. Now, leave about 2cm (one inch) between the fingertips. Adjust your focus, so you are looking through your fingers, beyond them. Most people will see a “finger sausage” as shown at the bottom of the illustration.

Sausage Finger Optical Illusion

This is a cognitive illusion. By focusing beyond the fingers, you prevent the image from each eye from coming together. Instead, the images overlap to create the strange sausage floating between your fingers.

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