|MadSci Network: Neuroscience|
The afterimage effect occurs when you stare at a color for a while and then look at something white - like a blank piece of paper or a wall. You will then see colors that are "opponents" to the original colors in the image. Green's opponent color is red. Yellow's opponent color is blue. The reason for this is that some neurons in the retina and thalamus are turned "on" by red but turned "off" by green. Others are turned "on" by green and turned "off" by red. (The same thing goes for the blue/yellow combo.) (If you detect these colors at a particular point on the retina, you cannot simultaenously detect the opposing color at the same point; you therefore cannot see a greenish red.) The afterimage comes into play when you "tire out", say, your green response by staring at green. When you then stare at white (which contains all colors, including red), only the red part of the green/red pairing will fire normally. Put another way - 1. Stare at green and the green/red neurons (neurons that are turned on by green and off by red) will fire until they get tired. 2. Stare at white and the red wavelengths in the white light will turn on the red/green neurons (those that are turned on by red and off by green). The green wavelengths in the white light won't be able to turn on your green/red neuronsm because those guys are tired. Hope this helps.
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