Schroeder Reversing Stairway

This reversing stairway illusion was first published by H. Schroeder in 1858. Seen in wireframe mode, most viewers can "flip" this between two alternative interpretations of 3d shape.

You're viewing this page with a browser that doesn't understand the APPLET tag. If you were using a Java-enabled browser that understood the APPLET tag, you would see an interactive figure here.

Experiment with the depth cue and flat shading modes to see whether they clarify the figure. Can you still force your brain to see both 3d shapes?

Then try rotating the figure around by holding the mouse button down as you move your mouse in the area of the figure. Can you still make the figure alternate between two shapes?

Can you find a position in which flat shading does not help you -- and one where it leaves only one interpretation? Which method helps you more often -- depth cues on the lines, or the shading?

Because Java does not yet support three-dimensional drawing on its own, the method we are using to decide what to shade first is quite a simple one. Can you notice when it fails to sort the 'faces' of the stair object correctly?

This applet draws heavily on work by Daeron Meyer of the Geometry Center at the University of Minnesota.