From Jamie:
Why does your brain do what it does with this thing? What is going on there?
Now, if you're who I think you are, you're smarter than all of us, and know full well what is going on there. But I'll be glad to play along.
What is going on there is a good ole' fashioned optical illusion: more specifically, your brain trying to fill in the missing pieces.
When you think about how a brain works, it's kinda scary how much data it processes almost instantaneously very second just to keep you functioning and communicating and not getting run over by rickshaws.
And, truth is, you don't observe as much as you think you do. There are big gaps in our observation, due to our senses being inferior to pretty much everything. Birds have better sight, bats have better hearing, dogs have better smell . . . et cetera.
What is going on specifically in the illusion above is your brain is compensating for what it
expects to see -- a symmetrical circle of evenly-sized, evenly-spaced dots of a uniform color. The movement of the dots and the speed of the movement don't give your brain enough time to accurately process the information.
If this were a stationary circle of pink dots, with one missing, you'd see it as such. But in the fraction of a second that each image is there, your brain tries to complete it.
But why is the dot green?
That has to do with the rods and/or cones in your eye. (Biology, like auto mechanics, is not my strong suit.)
But I did study theatrical lighting design (did you know that color mixes with lights are different than pigments? That'll mess you up when you're trying to do a lighting plot) and I know a thing or two about the:
Color Wheel!
(Color wheel courtesy of www.prosperity.com/myers/artlessons/graphics/colorwhel.jpg)
If you find the magenta-ish color (around M) that is similar (or as David Letterman says,
simular) to the dots in the illusion, look directly across the color wheel and you'll find the green-ish color of the phantom dot (around G). The rods and/or cones in your eye see the "inverse" of the missing pink dot: a green dot.
Interesting fact: This is the precice reason that hospital scrubs and OR walls are greenish-blue. When surgeons would look up from a bloody gash against a brightly-lit white wall, they'd see the inverse of the image -- a big greenish bloody gash on the wall. Blech.
So they started making such things greenish-blue, the inverse of
fresh human blood . . . mwa ha ha ha!Helpful?
(By the way, this optical illusion and many others be located at:
University of Maryland Physics Dept.)
UPDATE:
I've been starting at the floating pink dots for about 2 hours now (no, not really).
But here's an answer to the second half of the puzzle (which I hadn't scrolled down to see before): Why do the pink dots eventually disappear?
Once again, your mind starts seeing the "moving object" -- in this case the imaginary green dot, which is not really there (whoa) -- as the focal point. Once again, your mind knows (even if your brain does not) that magenta is the complimentary color for green. As one of its methods for not completely melting down due to overstimulation, your brain filters out needless information.
If you look quickly at a green dot and then look away, you'll see the faint pink "shadow" (see operating room, above). Your brain knows this, and starts compensating for it. After seeing the green dot move around the circle a couple of times, it senses the regular pattern and speed. Focusing on just the green dot, your brain perceives the pink as this "shadow" and starts disregarding it as irrelevant information. Obviously, a green dot is going to leave a pink shadow. But the pink shadow is not important, so your brain cuts it out of your sense so it doesn't get in the way.
Freaky.
UPDATE 2:
I have to say, it's a good thing you didn't ask me about
these, because then you'd totally have me stumped.
FINAL NOTE:
This all seems to be variations on the Troxler Effect, or Troxler's Fading.
As Susan Sarandon's character Annie says at the end of
Bull Durham, "You can look it up!"
