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| quote: | Originally posted by MERTON
why does it do that? |
It is the way the eye is setup. each gangleon cell codes a certain portion of the image projected on the retina. It is thought that they code a circle with a smaller circle in the middle of it. These two circles react to opposites, so if the center is looking for light to make a response, the outside is looking for no light to make a response. SO when you have light in the middle and no light on the outside it fires.
Also when a cell responds to an area it tells adjacent cells to not fire, therefore contrast is formed. This effect, simultaneous color contrast, makes the lighter portions look darker. this happens because responding is at its greatest at the edge of the dark portions where the center is filled with light and half of the outside circle is filled with dark. so adjacent cells do not fire therefore darkenning the light areas and making it look as if the object is moving.
It stops moving when you focus on it because of the concentration of cells in your fovea. Each ganglion cell there codes a very small part of the visual field as opposed to other regions that code larger areas.
This picture also supports a view that we look for invariance to detect motion. So we look at those red things on the outside as a refernce to tell us, this thing is not moving. However there is nothing like that on the inside so we think it is moving.
It is really hard to explain for two reasons, its so much easier when you can draw the cell's receptive field, and I just learned this in class yesterday. I only go into this much detail because I will put money on the fact that this question is on my final. If it was and this was my answer....I would fail.
But I hope it helps a little...
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Nifty illusion
