What is the cause of this optical illusion?
The circular region seems to jitter around, as if my eyes are trying to make it come into focus but cannot quite get it.
Boy that’s really creepy.
I thought the image might be animated online to look like an optical illusion (imagine that, a fake optical illusion) but I copied the image into my editor, and displayed it several times as big on my screen, and it still has that effect.
I notice if I move my head left and right, the image seems to tilt.
I don’t think I’m seeing anything like what you two are… the blurry area is a bit tiring to look at, but it’s nothing special otherwise. If it has to do with focusing, perhaps the fact that I can see about 6" w/o my glasses has something to do with it?
Try the following: Move your head closer and further from the screen while staring at the circle. Notice what happens to the things in the circle.
Your eyes are never still - they make little jerky movements, called saccades, all the time (apparently, this is necessary to keep your visual system stimulated) - it may be that this illusion exploits that phenomenon, somehow.
The blurriness of the interior circle mimics what we are accustomed to seeing if an object in our field of vision is a lot closer to us than a different object that our eyes are currently focused on. Or, alternatively, farther away. At a very different focal length, either way.
The little muscies in your eyeball plus the voice of experience in your brain contrive to make sense out of that, treating the fuzzy dots in the inside circle as sharply-defined checkerboard pattern that is either close to your nose or down about one flight of steps from the grainy surrounding area that your eyes are focused on.
Seconded.
Whoa! Now THAT is freaky.
What I find most striking is the depth illusion. It looks like a circular hole, with the blurred area behind it.
Yes, but if you move up close to it, it looks like a ball in front of a mottled background.
Hmm. Didn’t notice anything much again until I tried it with my glasses off, at which point the colours in the circle seem to invert about 3’ away from the screen. (I’ve got a 21" CRT FYI).
My brother has better vision and LCDs. Think I’ll ask him.