Don: Say you're looking at an object on a table in front of you. How long do you think your eyeballs stay in one position?

Ya?l: You mean, how long before they move? I'm going to guess... a minute.

D: More like less than a second.

Y: Yow!

D: Though we feel as if our eyes stay completely still when we focus on something, researchers have found they only stay still at most for a couple seconds--often just a few milliseconds. What's fascinating about this is that every time our eyes move, we are momentarily visually impaired. We aren't seeing anything but a blur. So if we're always moving our eyeballs, and are always impaired, why don't we experience the world as a confusing rush?

Y: I bet you have an answer.

D: Researchers at the University of Delaware have a good guess. They have done studies that show the brain is always extending the boundaries of what it sees-- adding in made-up information along the edges. This process is called "boundary extension," and it seems to be going on all the time. Say you're looking at a brick wall. You really only see a small section of it, but your visual processing system essentially says, "I can assume that beyond my visual field on either side are more red bricks, so for now I'll just add them in until I get better information." That process of constantly extrapolating on what you see may be what allows you to experience a calm and consistent visual world, even though the actual data coming in is much more fragmented.