Does Colorblindness Discriminate?
Have you ever wondered how others might experience the world? Have you ever wondered if others see things through different lenses? How do you know that red for your friend is not green for you? These certainly are good questions, for many conditions seem to suggest that perceptual experience is not objective as we might want to think. Consider, for example, synesthesia, a condition where stimulation to one sensory or cognitive stream gives rise to an associated experience in an unstimulated sensory or cognitive stream. Many synesthetes see things the rest of us don’t: colored music, flavored words and motion tinted with sound. Many of these individuals don’t learn that their experiences are unique until well into adulthood.
The same might go for color perception in general. Many people believe that color perception is objective, that is, that visual color experience has accuracy conditions. Under this view if you look at a heart and tell me it’s red, you’re correct. Likewise, if you look at a heart and tell me it’s green, you’re incorrect. Or are you? What is it about color that entitles it to having accuracy conditions? The answer to these questions are more difficult than they might appear.
The initial problem for color objectivism as well as any other theories of conceptual objectivity is espoused in the philosopher W. V. Quine’s famous indeterminacy of translation thesis. The thought experiment used to establish the thesis goes like this: Imagine that you are a field linguist who studies newly discovered languages. As part of your job, you travel to a distant part of the world to observe the language of a small, recently discovered tribe. The tribespeople speak a language unlike anything you’ve ever heard, so you’re eager to learn how the language operates in their environment. The tribespeople catch onto what you’re doing and are more than happy to help teach you their language.
At some point, while on a hunt, the tribespeople discover a rabbit, point in its direction and say ‘gavagai’. At first, it may seem natural to assume that ‘gavagai’ just means rabbit. And that’s a reasonable assumption. But how can you really know what the tribespeople mean by uttering ‘gavagai’? How can you rule out other possible translations of gavagai such as “a momentary rabbit stage” or “undetached rabbit parts”? Here the distinction is subtle, but it’s a real distinction. A rabbit is not the same as a momentary rabbit stage or a set of undetached rabbit parts, yet, according to Quine, you have no way to ever adjudicate between the two possibilities.
In most cases, this inability may not seem to make a significant difference, for you and the tribespeople might perform all of the same tasks even though your concepts behind ‘gavagai’ are a bit different. But the fact remains that you’re concepts are not the same.
Now a problem creeps in. You admit that you can’t really say exactly what the meaning of gavagai is because there’s nothing you can observe that quite gives you that information. But meaning for words in your own language suffer from the same worry. Since your first language was also learned through observation as well, your native linguistic concepts suffer from the same indeterminacy as well.
So how do you (and others) get out of this problem? One possible way to do so is to consider terms that are so basic that it would be hard to create a case such that their meaning isn’t clear to all individuals. Color experience seems like a good candidate. Color is a low-level perceptual property, meaning that the experience associated with is not much more than a calculation based on the frequencies of light striking the retina. So long as everyone’s brain makes the right calculation you all will have the same color experience, right? Not quite. The problem is that even our conception of color experience is highly variable.
Color objectivism holds that there is a fact of the matter as to which perceivers and viewing conditions are normal. From this it follows that there is a perceptual norm that is satisfied by some perceivers but not others. Those who don’t satisfy this norm are mistaken about the colors of objects.
But how do we decide what type of perceiver is normal? Some cases are clearer than others. For example, it’s obvious that you cannot satisfy the perceptual norm if you can’t see. A tree, a cup of coffee and a blind man do not satisfy the perceptual norm. One might think that a normal perceiver is similar to a uniform majority group, but this view is problematic, for there doesn’t appear to be a uniform majority group. Even if there were a uniform majority group, being a member of that group would not necessarily mean the individual satisfies the perceptual norm. Suppose that a natural disaster killed off all but 5% of the global population, which includes the 8% of colorblind males. In this scenario, the number of color blind individuals would exceed that of non-colorblind individuals, yet we wouldn’t say that colorblindness is the perceptual norm.
Rather, our idea of normality is connected with optimality. When we say someone is a normal perceiver of color, we are really saying that the perceiver’s color vision works optimally. There are problems with this view as well. First off, the number of photoreceptors in the human retina is not constant. Different parts of the retina have different concentrations of photoreceptors. This suggests that there are mechanisms in the brain responsible for adjusting input of the retina. So variations in color perception are not merely a matter of the number of photoreceptors of the retina.
Studies have shown color judgments and color discrimination abilities vary among even those individuals who pass tests for color vision normality. This variability may depend on gender, national origin and ethnicity. For example, on group reported a difference in spectral sensitivity to the blue regions of the color spectrum between Africans and Caucasians.
Recent studies indicate that a significant variance in a gene located on the X-chromosome may effect how some perceivers detect light in the long-wavelength (red/orange) regions of the color spectrum. Given that women have two copes of the X-chromosome, it’s possible for them to have two different versions of this gene and therefore possible that they may be better at discriminating red and orange light. So it is possible that women perceive a broader spectrum of colors in the red/orange region than men.
Another research group speculates that up to 40% of women have what’s known as tetrachromatic color vision. Most humans are trichromats, that is, they have three cone types each dedicated to absorbing light in different regions of the spectrum. About 8% of males and a small number of females are dichromats, that is, they have only two cone types, making them colorblind. This type of colorblindness results when a genetically mutant red or green photopigment gene on the X-chromosome fails to express retinal photopigment.
The women who carry this gene may not be colorblind, but her male offspring are likely to be. The mothers and daughters of dichromats and the mothers and daughter of males with deviant red/green photopigment genes may have a typical X-chromosome along with an X-chromosome that caries one of the deviant red or green photopigment genes. If the normal red and green photopigments and a highly altered variant are all expressed together with the blue photopigment, then the woman could have tetrachromatic color vision. There appears to be evidence for the possibility of tetrachromacy in the animal kingdom. While most female spider monkeys are dichromats, some possessing an extra photopigment gene are trichromats. These females can experience colors that others can’t.
Variation in color categories across languages also occurs. Many languages—including Vietnamese, Kuku-Yalanji, Tswana, and Zulu—don’t have words that distinguish blue from green but have a term for the color in between the two. Other languages—including Chinese, Korean and Japanese—do distinguish between blue and green but have mixed color terms for other regions of the color spectrum. Some languages don’t distinguish blue from gray or black and others have only two words, one for dark and one for light. Other languages, such as Russian, have more color terms than English.
This variation in color terms suggests that color experience is variant as well. If our color terms do what we think they do—that is, if they track our perceptual experience—then differences in color terms should reflect differences in perceptual experience. The fact that linguistic differences occur across languages is an indicator of the variability of color experience.
The evidence for the variation of color experience provided by experiments as well as language differences poses a problem for color objectivism. According to objectivism, normal individuals detect the same color properties when exposed to the same stimulus in the same viewing conditions. But the evidence shows this is false.
One way to respond to this argument is to say that normal individuals see the way Mother Natureintended. The problem with this argument is that variation occurs even among individuals who pass standardized tests of normality, suggesting that Mother Nature didn’t intend for color perception to work in one way. The other problem is that, under this view, tetrachromats could not be considered optimally normal despite having better vision than trichromats. A better strategy might be to defend color universalism, which holds that there is fixed number of basic color categories. But doesn’t completely explain why some languages lack the color terms that others have.
The problem lies in figuring out who is right and who is wrong. It turns out that, under the color objectivist view, most individuals who may be classified as “optimum” viewers are white males. This shouldn’t be surprising. White males traditionally have had the greatest access to proper healthcare, so it might be expected that doctors who discover certain conditions pick up on the irregular traits of less commonly seen black and female patients. The idea of colorblindness only exists relative to the normal white male viewer. But we’ve already seen that being a member of the majority perceptual group doesn’t mean your vision is optimum. So who’s to say that this conception of color vision should be the privileged one?