As a change of pace, Brad DeLong has a simply stunning optical illusion. It demonstrates very clearly just how much vision is a cognitive process.

[via Brink Lindsey]

I read once (Scientific American?) that the natural resolution of the human eye is only about 200x130 pixels, operating at about 24 images per second. The eyes are moved rapidly over small distances, and the mind interpolates the images to get our normal perception of vision. In other words, seeing is almost all software. (This, by the way, also explains why we should be very sceptical of images purporting to show "how a fly sees" - we don't know the software.)

I had to open the JPEG in Paint Shop Pro and check the colors to believe it. The RGB values for both squares are R107G107B107.

Jeff, I find it hard believe the numbers you are quoting, either for resolution or refresh. Some people are known to be able to see the flicker in 60 cycles per second flourescent lights, for instance. Some marksmen with better than 20/20 vision are able to track bullets in flight with the naked eye. On a personal level, I can discern the difference between a 30FPS and 60FPS refersh rate for a video game.

One thing I know for sure is that if there are numbers, they're not the same for everyone.