All Resources

Numb Fingers

In this activity, students confuse their brains as they explore a phenomenon known as perceptual disjunction in this tactile illusion.

Sometimes our brains fail to take all factors into account when processing sensory information. The sensation we think we feel is therefore incomplete, this is a perceptual disjunction. For example, in the activity below, our brains "forget" that there is another object (your partner's finger) blocking us from feeling both sides of our index finger. Stroking only one side of our finger results in the feeling that our finger has gone numb.

Objectives

  • Understand that tactile information is processed in the brain.

Materials

  • Per Pair:
    1 pairs of hands

Key Questions

  • How does your finger feel?
  • Which sides of your fingers are being touched? Which sides do you FEEL as being touched?
  • How are you confusing your brain?

What To Do

  1. Pair up with a partner.
  2. Place the palm of your left hand against the palm of your partner’s right hand, making sure that all the fingers line up.
  3. Use the thumb and index finger on your right (other) hand to simultaneously stroke your and your partner’s index fingers (i.e. your right thumb should be touching your index finger, and your right index finger should be stroking your partner’s left index finger).
  4. Swap roles with your partner.

Extensions

  • How is this illusion similar to optical illusions?
  • Try the Aristotle Illusion, another variation on a tactile illusion.

Other Resources

New Scientist |Tactile Illusions: The Aristotle Illusion