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Re: comparative color vision
I am glad to see so many people interested in color vision. My own two
1. Wrasses occur in so many color variations and it does appear that
species may be distinguished principally by color pattern, that I would find
to believe that they are colorblind.
2. My interpretation of cladistics is that if a trait is found in a
clade and in a contained clade it is presumptive in the intermediate clade.
If tetrapods are the containing clade and birds are the contained clade,
then theropods are presumptively capable of color vision.
3. There is considerable evidence that human perception of color vision
involves higher brain centers: I offer as evidence the experiments
of Edwin Land on mondrian patterns, in which the human perception of
a particular patch of color is shown to depend on a comparison with
the colors around it. ("Spectral Brown" could equal "Perceptual Green".)
This is believed by some to enable humans to perceive color as a constant
under varying light intensities.
My daughter did a science fair experiment on Cyclopean vision (Bela Julesz's
term for fusion of images perceived by the two eyes to create a single
perceived image) in which she used computer-generated random dot patterns
(Julesz patterns) and used color shifts as the discriminator that caused a
pattern to appear. Most viewers were able to perceive a stereo image.
This required that left-right comparisons of dot color were integrated
in the brain.
I don't know whether Land mondrians have been used in bird color
but it would be interesting to find out.