superimposition(redirected from color key)
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The ability to see two similar images superimposed but not mentally fused. Examples: seeing a bird in a cage with both eyes in a synoptophore when one eye is presented with a bird and the other with a cage; seeing the letter E in a synoptophore when one eye is presented with the letter F and the other with the letter L. See Worth's classification of binocular vision.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann