The Disappearing Disks

Click the picture above to start the Flash illusion.
Stare at the disks in the center of the picture as you set the background in motion. What happens to the disks when the background is moving?

When the background is in motion, the disks disappear and reappear.

In a motionless situation, the brain analyzes all the details as a single picture, and that is how we see it. When the background is moving, it is the movement that draws our attention, and the disks - which are actually there all the time - are "erased" from our field of vision. The brain has limited attention resources. When it focuses on processing the movement, it does not simultaneously process the three stationary disks.

This illusion was discovered in 2001 by brain researchers at the Weizmann Institute.

Link:
Read more about this illusion on the website of its discoverers: http://www.weizmann.ac.il/home/masagi/MIB/mib.html