6J11.56 - Perception - Shades of Gray

See paragraph one in the procedure section.
Code Number:
Demo Title:
Perception - Shades of Gray
Depth Perception by the Eye
Area of Study:
Optics, Human Biology
Gray shade illusions

Show the shades of gray illusion that is desired.  Most of these follow the same format in that a light area of gray is partially surrounded by a much darker border.  The area of gray inside the border appears to be lighter than that outside.  This can be more easily distinguished by putting a pencil across the lighter gray area.  Removing the pencil and in some cases even covering the dark border reveals that the light gray area is uniform.

  • Martin Gardner,  "Two Shades of Gray?",  TPT, Vol. 35, # 2, p. 119, Feb. 1997.
  • Paul Doherty, Don Rathjen, "Gray Step", The Cheshire Cat, p. 61.
  • Martin Gardner, "61, The Two Shades of Gray?", Smart Science Tricks, p. 94.
  • Ron Hipschman,  "Gray Step 4",  Exploratorium Cookbook III, p. 158.1.
  • Ron Hipschman,  "Green Tomatoes",  Exploratorium Cookbook II, p. 106.4
  • Raymond Bruman,  "Horse's Trail", Exploratorium Cookbook I, p. 43.1.
  • Raymond Bruman,  "Rotating Gray Step", Exploratorium Cookbook I, p. 44.1.
  • Raymond Bruman,  "Mondrian", Exploratorium Cookbook I, p. 45.1.

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