Cognitive Daily

[article originally posted September 27, 2005]

i-eca0cf2af9fc3ac4445c7dff7d8aab70-research.gifAll this talk about stereotypes can get you thinking. Perhaps some stereotypes reflect actual differences. Take color vision, for example: men often refer to themselves as “color-impaired,” letting the women in their lives make home design decisions and even asking them to match clothing for them. Maybe they’re just behaving in accordance with traditional stereotypes … but maybe there’s something more to it.

In the 1980s, vision researchers began to find some real physical differences between the eyes of many women and those of most men. “Normal” color vision is possible because we have three different types of cone cells in our eyes, each of which responds to a different wavelength of light. The process is basically the reverse of how a TV set or computer monitor works: on a TV, there are three different colored dots—red, green, and blue—and the millions of “colors” we see are based on mixtures of different proportions of those colors. In the eye, cone cells can have three different photopigments. These are usually generalized as red, green, and blue, but their actual values are closer to yellowish green, green, and bluish violet. To avoid confusion, psychologists typically refer to them to long-, medium, and short-wavelength sensitive cones. Supposing we’re looking at a yellowish-green thing, the long-wavelength cones are stimulated the most, the medium-wavelength cones are stimulated a bit, and the short-wavelength cones are not stimulated at all, and the appropriate signal is sent along the optic nerve to the brain, which then recognizes the color as “yellowish-green.”

What the researchers were finding when they actually looked at the structure of the eye is that many women—perhaps over fifty percent—possessed a fourth photopigment. Was this merely a genetic anomaly? Would the brain even be able to process this fourth input? The early research suggested that it would not. Women were no better at determining whether two very similar color patches were actually the same. They were only slightly better than men at detecting subtle spots of red light, a fact researchers attributed to individual difference.

However, Kimberly Jameson, Susan Highnote, and Linda Wasserman were not convinced by this evidence. Five- and six-year-old girls are better at naming colors than boys, and grown men are not as good at color-naming compared to women. They felt the existing measures of color sensitivity and color-matching did not capture all the differences between men and women, and devised a new experiment that they felt was more representative of real-world vision.

It’s quite difficult to examine an eye to determine if it has the fourth photopigment—the process generally involves removing the eye itself. Jameson and her colleagues might have had just a bit of difficulty recruiting volunteers to participate in an experiment requiring such extreme measures, so instead they used a genetic test to determine how many different photopigments participants were likely to possess (they estimate this process to be about 90 percent accurate—biologists will recognize this as the genotype versus phenotype problem). Of 64 participants in the study, 23 were women with 4 photopigments, 15 were women with 3 photopigments, 22 were men with 3 photopigments, and 4 were men with 2 photopigments (this is commonly called “color-blindness,” but most people with 2 photopigments can still distinguish between many colors).

Next, participants viewed a spectrum projected on a lucite window covered with tracing paper. Over the next hour and a half, they performed an array of tasks, including marking the edges of the visible rainbow, marking the locations of the “best example” of each of the major colors, and marking the edges of each “band” of color in the rainbow. Between each task, a camera flash was set off to mask the previous spectrum example, and the experimenter mounted a new sheet of tracing paper on the panel.

The most compelling results came from the number of spectral bands task:

Type of participant
Average number of spectral bands
Number of participants
Four-pigment females
10
23
Three-pigment females
7.6
15
Three-pigment males and females
7.3
37
Two-pigment males
5.3
4

Four-pigment females perceived significantly more bands of color than both three-pigment males and females. Further, three-pigment males and females are statistically indistinguishable, suggesting that the result is not due to some cultural difference between men and women.

So why were others unable to find significant results in a color-matching task when we see such dramatic results here? Jameson et al. suggest that there may be two (or more) different modes of seeing color, each processed differently in the brain. The brain may use the data from all four photopigments for some processes, but not for others. But this is still supposition. What’s clear from this study is that the stereotype of women being better with color may reflect real differences between men and women.

Jameson, K. A., Highnote, S. M., & Wasserman, L. M. (2001). Richer color experience in observers with multiple opsin genes. Psychonomic bulletin and review, 8, 244-261.

Comments

  1. #1 Agnostic
    July 20, 2006

    I’ll look up some articles when I get to the library, but off the top of your head, what’s the evolutionary story behind this difference? Women being more likely to have been gatherers & needing to distinguish more types of fruit, plant, etc.?

  2. #2 ThePolynomial
    July 20, 2006

    What wavelength range does the fourth photopigment detect? (sorry if this is in the post and I can’t find it) Thanks!

  3. #3 Coconuts
    July 20, 2006

    I stumbled across some information about human tetrachromatism a few months ago and was really fascinated by it. The best source of information I’ve been able to find (other than this post) is an article from Red Herring magazine by Glenn Zorpette.

    From that article, I’ve been led to believe that human tetrachromatism is present only in women because the red and green photoreceptors are “right next to each other on the X chromosome,” and so if you get one X chromosome with the normal red and green genes, but another with a slightly different red (or green) gene, it’s possible that you’d end up with four distinct photoreceptors: blue, green, red, and one that’s a “weird” red or green.

    Link to the magazine article, and a link to the Wikipedia page.

  4. #4 Sandeep Gautam
    July 21, 2006

    I have been interested in color vision for a while and some of my recent posting on my blog “The Mouse Trap” reflect the same. I propose that the 2 different systems that women use for perceiving colors are the normal RGB (that men also use) as well as the HSV process (that the later optical processing regions of brain use). The fourth photopigment may be the ‘yellow’ pigment, which is the opponent color for ‘Blue’in the opponent-process theory of color vision.

    Just like ThePolynomial I too would like to know the wavelength range the fourth pigmnet detects.

    Thanks!

  5. #5 Gordon Worley
    July 21, 2006

    Supposing we’re looking at a yellowish-green thing, the long-wavelength cones are stimulated the most, the medium-wavelength cones are stimulated a bit, and the short-wavelength cones are not stimulated at all

    This sounds not quite right. Red has the longest wavelength, yellow-green the medium, and blue-violet the shortest, so shouldn’t this be that that medium-wavelength cones are stimulated the most? (or that the thing is red?)

  6. #6 J. Todd Ormsbee
    July 21, 2006

    I have a question about the method of *asking* someone what they see. I’m not opposed to the idea that there are physical differences between men and women that fall within certain overlapping bell curves. But it seems that if you accept the notion that a majority of females may have better language skills than a majority of males, then it seems likely that a male might not be as adept at putting an experience such as “color” into language. That does not mean necessarily that the male isn’t perceiving or experiencing that difference.

    This was a problem in the social sciences, especially micro-sociology and social psychology, where the “hard program” of social construction used to argue that language/culture produced perception (i.e., the social construction of reality). They thought they proved this when they would ask people of different cultures without words for certain colors what colors they saw. Well, of course, if you have no word or cultural category to distinguish blue and green, how would you explain it? You would probably be confused as to why someone was even asking you to make the distinction. But ultimately it was demonstrated that all humans do actually perceive the color differences; but their cultures decide which color differences *matter*, thus serving a blow to the hard program.

    All that merely to say that a verbal test of experiential differences in the early 1980s studies is highly dubious to me. And it does point out some *possible* problems with the spectral tests. Again, it’s about what colors *matter*. If I look at a rainbow and see 7 or 8 color ‘bands’, I might also be able to perceive other bands that were pointed out to me, or if I were instructed to mark off as many as I could, I might “see” more. We are trained from birth in U.S. culture to see rainbows a certain way. Are the women who draw 10 bands actually *perceiving* something that isn’t being *perceived* by those with only three photoreceptors?

    Again, I’m not trying to be a naysayer; and I do think the study is highly suggestive that the women with 4 receptors are perceiving the spectrum differently. But I would like a better explanation of how this particular test eliminates cultural/linguistic bias, because while I think it does to a much better extent than the earlier tests, I think it mitigates and minimizes but doesn’t eliminate the cultural categories imposed on perception.

  7. #7 Heather von Stackelberg
    July 21, 2006

    I remember reading recently that a study showed that colorblind men were able to distinguish between different shades of taupe much better than non-colorblind people, with the conclusion that colorblindness may be an evolutionary adoption to be able to see through camoflage better, to aid in hunting.

    Looked at in an evolutionary sense, then, it makes sense that male hunters have color-blindness sometimes, because it makes them better hunters, and female gatherers have extra color-sensitivity sometimes, because that makes them better able to distinguish between types of fruit and vegetation, as well as healthy/unhealthy or ripe/unripe, and makes them better gatherers.

  8. #8 revs
    July 24, 2006

    What about female artists? More likely to be 4-pigment?

  9. #9 The Huge
    July 29, 2006

    I think that Mr. Ormsbees observation about the possible difference between the power of experience of colour and the ability to express the experience is important, and that this aspect is most often totally neglected in the circumstances. I will also suggest that there is a political aspect: The nowadays ever present feminists are very eager to “find” weak spots in males but are not so eager in explaining differences between men and women in more neutral terms.

    And the general method of just asking “what do you see” and take the answers for valid will always “show” that women are stronger in some area simply because women in general have a stronger urge to speak in detail about there personal experiences than men.

    The problem of course then, is to find the scientifically “neutral point” from which you can examine men and women and get neutral answers about their true nature. We are not there yet, but the search for this point is a most interesting challenge of course.

  10. #10 jeonjutarheel
    July 30, 2006

    Wait, but I didn’t see anything about speaking in this study. Didn’t they just have to mark the boundaries and the major colors? There was no naming in the most striking results, which should eliminate gender differences in language as an explanation. And as for finding “weak spots”, I don’t think anyone was claiming having three pigments to be some sort of deficiency in men. I certainly doubt I’M in the 50% of women with four.

    And the study Coconuts linked do does seem to suggest a neutral reason for the difference. I mean, I’m not an expert, and my psych degree is the undergrad variety (for now), but we read about plenty of “neutral” explanations for observed differences between men and women, especially in evolutionary terms.

  11. #11 David Harmon
    July 31, 2006

    Hmm… Something tells me this isn’t the only way people can end up with enhanced color vision. My family on Mom’s side runs to particularly sensitive color vision (we call it “artist’s eyes”), but it comes down through my grandfather, and seems to affect me as well. as my mother, aunt, and sisters. (It happens that I’m his only grandson, and the next generation isn’t old enough to query.) Ironically, *Dad* was colorblind, but of course I didn’t inherit that.