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The amazing staircase

 

This is a hands-on illusion you can build yourself.

[PDF] 63kb

 

Instructions

  • Print out this illusion onto paper or onto acetate for use on an over-head projector
  • This is an ambiguous figure that flips when the image is turned
  • Hold the paper with the spotted area at the top right
  • How many stairs do you see? 4 with the spotted wallpaper at the back?
  • Rotate it 90 degrees clockwise. Does the image flip so the spotted wallpaper is now at the front and there’s only 3 stairs?
  • Rotate another 90 degrees – what do you see?
  • Another 90 degrees – do the stairs come from the attic?
  • Try blinking to make the ambiguous figure flip.

This amazing hands-on illusion is used with kind permission of the science magician Richard Robinson

 

What’s happening in your brain?

The picture doesn’t change, but your brain interprets it in two different ways.

 

When you look at something, your eye and brain must decide what it is in a split second. Your brain makes a ‘best guess’ and usually gets it right.

 

But this picture is ambiguous in different orientations. Your brain can’t decide which is the best ‘best guess’, so the picture appears to flip between the two options.

 

Whether you see 3 or 4 stairs partly depends on where you look and which way up the picture is. Your brain weighs the evidence and decides which is the most likely option.

 

For more illusions click here