Optical Illusions are things that make us see something that doesn't exist, make us see something in way that we shouldn't see it or otherwise trick our visual perception.

After Images, etc
This illusion is a classic. The little gray dots that bounce around don't really exist. Its all in your mind.

Stare at the flag for 30 seconds. After that, stare at a white wall, piece of paper or a white point on this webpage. You should see an after image with the inverse colors of the original. This happens becasue the rods and cones in yours eyes that percieve the colors in the first image get tired. This is why if you glance at the sun (and we do NOT recommend that you do) you have a bright spot in your field of vision for a short amount of time.

Perception Illusions
Which figure has a larger middle circle? It seems pretty obvious that the answer is B, but if you measure them, you will find that they are both the same.

Do you see the triangle in the image below? There is no triangle... It's just three circles with little pieces taken out. You just assume that there's a triangle.

What effect does music have on the brain?
How is the brain effected by visual art?
Why are we fooled by optical illusions?
What are some other forms of art?