The article I'm using as a base for a lot of this is called "What Birds See", Scientific American July 2006 by Timothy Goldsmith. It's quite good.
Writing the test, in this instance, means writing questions for a midterm for undergrads.
Regarding "female tetrachromatism" -- the number of studies on it seems limited, but people who look for it seem to find it. Or, more specifically, it's a fact that some women have at least four photopigments; the actual question is whether that leads to better color discrimination. The foundational article seems to be Jameson, Highnote and Wasserman, 2001, Richer color experience in observers with multiple photopigment opsin genes, PSYCHONOMIC BULLETIN & REVIEW Issue 8 volume 2 244-261. (I haven't dug through the whole article.)
(I'm using "female" and "male" to mean people with at least two and only one X chromosome(s), respectively. I realize this is at best imprecise.)
The basic idea is that the genes for the pigments of the medium and long wavelength cones are on the X chromosome, and there's a surprising amount of polymorphism in them. When men get a "green" and a "red" gene which are too similar, they present with red-green color blindness. The mechanism proposed for female tetrachromatism is that, when one has two X chromosomes, one can have not just medium and long wavelength cones, but a medium-long wavelength cone type *in addition*. If having M and L is "normal", then having ML and L limits color perception, but having M, ML, and L can actually enhance it.
What Jameson et al did was actually genotype a bunch of subjects (typical psych-study volunteers) and found that women who had two alleles for at least one photopigment gene, and so had at least four photopigment types, performed significantly better at color discrimination tasks than women and men who had only 3 expected photopigment types.
This seems to be a non-stupid discussion of Jameson et al.
There's another article, Rodriguez-Carmona et al. 2008, Sex-related differences in chromatic sensitivity, Visual Neuroscience 25:3 433-440. It finds that women have significantly better color discrimination than men on the red-green axis but not the blue-yellow axis, which suggests again the mechanism of polymorphism in the X-linked genes for the green and red cones.
In any case, however, the added color discrimination is nothing like the degree of color discrimination in birds -- the added photopigments are within the normal human range, and, if anything, extend it only a little bit.
I am almost certainly making mistakes, confusing details, and interpolating wrong assumptions above; I'm an interested bystander in color vision theory, and the female tetrachromatism isn't even material we've presented to the students.
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branchandroot
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Date: 2009-11-17 04:29 am (UTC)Writing the test, in this instance, means writing questions for a midterm for undergrads.
Regarding "female tetrachromatism" -- the number of studies on it seems limited, but people who look for it seem to find it. Or, more specifically, it's a fact that some women have at least four photopigments; the actual question is whether that leads to better color discrimination. The foundational article seems to be Jameson, Highnote and Wasserman, 2001, Richer color experience in observers with multiple photopigment opsin genes, PSYCHONOMIC BULLETIN & REVIEW Issue 8 volume 2 244-261. (I haven't dug through the whole article.)
(I'm using "female" and "male" to mean people with at least two and only one X chromosome(s), respectively. I realize this is at best imprecise.)
The basic idea is that the genes for the pigments of the medium and long wavelength cones are on the X chromosome, and there's a surprising amount of polymorphism in them. When men get a "green" and a "red" gene which are too similar, they present with red-green color blindness. The mechanism proposed for female tetrachromatism is that, when one has two X chromosomes, one can have not just medium and long wavelength cones, but a medium-long wavelength cone type *in addition*. If having M and L is "normal", then having ML and L limits color perception, but having M, ML, and L can actually enhance it.
What Jameson et al did was actually genotype a bunch of subjects (typical psych-study volunteers) and found that women who had two alleles for at least one photopigment gene, and so had at least four photopigment types, performed significantly better at color discrimination tasks than women and men who had only 3 expected photopigment types.
This seems to be a non-stupid discussion of Jameson et al.
There's another article, Rodriguez-Carmona et al. 2008, Sex-related differences in chromatic sensitivity, Visual Neuroscience 25:3 433-440. It finds that women have significantly better color discrimination than men on the red-green axis but not the blue-yellow axis, which suggests again the mechanism of polymorphism in the X-linked genes for the green and red cones.
In any case, however, the added color discrimination is nothing like the degree of color discrimination in birds -- the added photopigments are within the normal human range, and, if anything, extend it only a little bit.
I am almost certainly making mistakes, confusing details, and interpolating wrong assumptions above; I'm an interested bystander in color vision theory, and the female tetrachromatism isn't even material we've presented to the students.