• Background
  • Instructions
  • Illustration
  • Quiz


The Fraser-Wilcox spiral staircase illusion (Fraser & Wilcox, 1979), also called the escalator illusion, is an early version of the class of illusions called peripheral drift. In peripheral drift when you look at an object it is still, when the same object is in the peripher it appears to be moving. Fraser & Wilcox developed their illusion using a sprial stimulus giving it is name.

See the text for an explanation of the illusion and the more complicated rotation snakes illusion which is baed upon this illusion.=.

In this activity, you can not only view the illusion but change various parametes of the illustration to see how they impact the strength of the illusion.


Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab


Below is a list of the ways that you can alter the illustration. The settings include the following:

Colors: select from some preset color sets to see how they alter the strength of the illusion. Gray Scale is the default.
Contrast: change the contrast among the colors of of the stimulus.
Spiral Size: change the size of the two spirals.
Left Spiral: change the direction of the left hand spiral.
Right Spiral: change the direction of the right hand spiral.


Pressing this button restores the settings to their default values.