Visual illusions can give us insight into how the brain processes visual information.

• Viperlib includes many copyright free illusions
• Illusion forum
• Gallery of illusions
• Richard Gregory's web pages
• The barber pole illusion
• Many static images that appear to move.
• Perception demonstrations (require Shockwave plugin)
• Donald Hoffman's illusion page
• Motion induced blindness is a recently discovered but very powerful illusion.
• Change blindness is a very striking effect. Daniel Simons also has some real life examples on his web site.

The middle cube on the left either appears to look like the one on its right or the one on the left. If you stare at it for a while, it will spontaneously switch between these two appearances.

Is the image on the right of a vase, or the profile of two faces? Again, you tend to only see one of these two competing perceptions at a time.

Are the dots moving left-right or up-down? Keep looking at the dots and you will notice that the direction of motion appears to switch.

'Filling in' the blind spot

Each of our eyes has a region where it is blind. If we close our left eye, we have no visual input from a small region directly to the left of our fixation. If we close our right eye, we are blind in a region to the right of fixation. The illusion is that we are not consciously aware of this blindness - our brain fills in this region. Surprisingly, our brain is pretty sophisticated in this illusion. My favorite example is on the right, and comes from Robert Ornstein's book "The Evolution of Consciousness". Close your right eye, and look at the 'x' in the figure. Move either closer or further away from the screen until you notice the that circle with the dot inside vanishes altogether. Notice that you do not simply fail to see the dot, you actually perceive the pattern filling the location.