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Shrinking Spot

Source Institutions

    The Exploratorium

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Shrinking Spot

In this activity, learners control the (apparent) size of a hole with their brain. This illusion occurs due to an automatic reflex that causes light entering one eye to change what is seen in the other eye, demonstrating one of the many idiosyncrasies of the human visual system. Activity includes step-by-step instructions, and an explanation of the science behind the activity.

Quick Guide

Preparation Time:
Under 5 minutes

Learning Time:
5 to 10 minutes

Estimated Materials Cost:
1 cent - $1 per student

Age Range:
Ages 11 - 18

Resource Type:


Materials List (per student)

  • 2 1/2 x 4 1/2 inch (6 x 11 cm) rectangle of black card stock or construction paper
  • Tape
  • One 2 x 2 inch (5 x 5 cm) square of aluminum foil
  • Pushpin


  • Life Sciences
    • Human Senses and Perception
      • Vision
      • Perception
  • Physical Sciences
    • Light and Optics
      • Sunlight and Color


Includes alignment to state and/or national standards

This resource is part of:

Access Rights:

  • Free access