Gray Step

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In this activity, learners discover that it's difficult to distinguish between two different shades of gray when they aren't separated by a boundary. Learners will be surprised when two slightly different shades of the same color look different if there is a sharp boundary between them. But if the boundary is obscured, the two shades appear indistinguishable. Use this activity to help learners explore how the eye-brain system condenses information through a process called lateral inhibition.

Quick Guide

Preparation Time:
10 to 30 minutes

Learning Time:
5 to 10 minutes

Estimated Materials Cost:
$1 - $5 per group of students

Age Range:
Ages 8 - 14

Resource Type:


Materials List (per group of students)

  • A sheet of Pantone™ 404 u-g graduated paper, uncoated (available at art supply stores in 20 x 24 inch sheets)
  • Cardboard or masonite
  • A horse tail made of a length of hanging yarn, twine, or rope
  • A sheet of white paper
  • A hole punch
  • Scissors or paper cutter
  • Glue or tape
  • Adult help


  • Life Sciences
    • Human Body
      • The Brain and Nervous System
    • Human Senses and Perception
      • Vision
      • Perception
  • Physical Sciences
    • Vibration and Waves
      • Light and Optics
    • Light and Optics
      • Reflection and Refraction
      • Sunlight and Color


To use this activity, learners need to:

  • see
  • see color
  • touch

Learning styles supported:

  • Involves hands-on or lab activities


Components that are part of this resource:

This resource is part of:

Access Rights:

  • Free access



Funding Sources:

  • National Science Foundation
  • California Department of Education
  • NEC Foundation of America