by Bruce E.R. Thompson.
A question that sometimes comes up in a philosophy class is this: how do you know that the red you see is the same red that I see? If the professor doesn’t ask this question, then surely one of the students will. This is the kind of question that gives philosophy a bad name. It is supposed to one of those unanswerable questions that philosophers take too much time trying to answer, when the answer, to quote Gertrude Stein, is “There ain’t no answer. There ain’t going to be any answer. There never has been an answer. That’s the answer.” The question is raised only to prove that it is impossible to have someone else’s experiences.
But, in this case, Gertrude Stein is wrong: we know the answer to the question. The answer is that they are very possibly not the same! This is especially likely to be true if I am a man and you are a woman. Of course, no one can have someone else’s experiences, so I cannot directly compare my experiences to your experiences. But we can report what we see, and we can find instances in which different people report having different experiences. I once asked a girlfriend whether turquoise was blue or green. She reported that she thought it was greenish blue—more blue than green. I objected that I thought it was bluish green–more green than blue. We debated for a while on the theory that we were having a disagreement over terminology. We were not. The only conclusion we could draw was that we were literally having different experiences: the color she saw was not the same as the color I saw! Many years later I came to understand that we had reached the correct conclusion. People do experience colors differently—not radically differently, perhaps, but differently enough that the discrepancies are noticeable. Fortunately, this can be explained, and part of the explanation has to do with gender.
The biological mechanisms that make color vision possible are complex. The first perceptual psychologist to propose a theory that was (mostly) correct was Christine Ladd-Franklin. She was one of those brilliant women whom history has forgotten and whose biography is a study in the systematic neglect and psychological abuse to which women of her era were subject.
Miss Christine Ladd was admitted to Johns Hopkins University only because she signed her application “C. Ladd,” so the admissions board assumed she was a man. When they discovered their mistake, they tried to withdraw their offer, but the mathematician James J. Sylvester (who had encouraged her to apply in the first place) refused to permit this. Her presence at Johns Hopkins caused so much dissention that one governing board member actually resigned over the matter. The other faculty member who appreciated Miss Ladd’s brilliance was the philosopher, Charles S. Peirce, who served as her dissertation advisor. It was because of her work with Peirce, and her contributions to syllogistic logic, that she first came to my attention. My own work in logic is largely founded on her preceding work.
Although she completed all the requirements for a Ph.D. in mathematics and logic—obviously the first woman to do so—the university refused to award her the degree. It was only with great reluctance that they allowed her to graduate at all. They had previously done her the indignity of refusing to list her among the university fellows, even though she held a fellowship. Hence, it was not until 1926, when she was seventy-eight years old, that Johns Hopkins finally awarded her the Ph.D. that she had earned forty-four years previously.
Meanwhile Christine Ladd married Fabian Franklin and had two children with him. Not content to be just a wife and mother, she became a leading researcher in the field of color perception and figured out the basic mechanism behind color vision.
The retina of the eye has two types of light detectors called rods and cones. Rods are easily stimulated by any light of any frequency. Hence, nocturnal animals that need to see well in dark conditions will have retinas consisting almost exclusively of rods. Cones are, in effect, stunted rods: they are mutated in ways that make them less sensitive to light—bad for night vision. But their misshapenness makes them sensitive to different frequencies of light, and this is what makes color vision possible. In human eyes there are three kinds of cones. One kind is sensitive to high-frequency (blue) light. The other two are sensitive to lower-frequency light. One type is sensitive to light in a range that stretches from mid-range (green) to lower-range (yellow) while the other type is sensitive from lower-range (yellow) down to the lowest-range (red).
When we see color on an object, what we are seeing is the light that bounces off that object. Some light will be absorbed by the object, while some light will be bounced back. An object that absorbs most of the light will bounce little back, so it will stimulate few of our rods and cones. That object will appear to us to be black. The more light that is bounced back, the brighter the object will appear to us to be. An object that bounces back nearly all the light will stimulate all our cones, so it will appear to us to be white. Notice that two types of cones are sensitive to yellow light, which explains why yellow appears to us to be brighter than the other (non-white) colors.
Here is where gender comes into it. The genes that code eyes to be sensitive to blue light are on one chromosome; the genes that code for green light and red light are on another. Specifically, they are on the X chromosome! Women typically have two X chromosomes while men typically have only one. Red-green colorblindness is rare in men, but it is much rarer in women because people with more than one X chromosome have a better chance to develop vision that discriminates between red and green. We are slowly coming to realize that gender is more complex than we had previously believed, but here is the bottom line: if you have more than one X chromosome, then there is a good chance that you can see a richer palate of colors than I can see. So, the red you see may not be precisely the same red that I see. Indeed, it probably isn’t.
I’m okay with that. I let my wife pick out my clothes, but she always asks me to drive after dark. My night vision is much better than hers.