"What do the Colorblind See?"
March 18, 2008, 4-6PM
Note-taker: E. I.
Last Updated: April 18, 2008
[Q = Question, A = Answer, C = Comment, R = Response]
This particular talk has almost nothing to do with neuroscience, but is about equally a work in cognitive science, psycho-physics, and with slight stretching philosophy of mind/psychology.
Basic question I am interested in: What do the colorblind see?
There is a theoretical answer that was made into a systematic theory in the 1950s by Helmholtz and Maxwell and a little bit of help from Grassmann.
Three color channels imputing from the retina into a three dimentional color space. Red-green axis, yellow-blue axis, and white-black axis form basis of representations for hue, saturation and brightness.
I will focus on study of dichromats (if you only have two cone receptor types in the retina instead of three).
Helmholtz and Maxwell conducted tests with spinning color disks. Asked “is this distinguishable with. Concluded that dichromats lose red-green axis completely and only have blue-yellow axis. i.e. Green and red experiences collapses onto red-blue and dark-bright axis.
This is a very elegant theory that has been dominant for 150 years, but probably cannot be true. It is interesting that in c. 1854, 1905, 1940s, 1970s, 1980s, there has been evidence by distinguished people that this “standard theory” could not be right, but no one has been able to incorporate it in a new theory. Thus, the standard theory (though it does not cohere with the evidence) has been
Q. This theory will say that there are only two hues—yellow and blue. In other words, there is no hue experience except for two?
A. Yes.
14.00
Dalton (great chemist of late 18th century, gave name for “colorblindness” in many European languages) was colorblind (confused reds, greens) and wrote about the characters of his confusions. 1798: “Crimson by day has a blue tinge, but by candlelight it becomes yellowish red. Pink seems to me three parts yellow and a reddish yellow…etc”
Here, we have a source of skepticism of the standard theory of colorblind vision—he talks as if he has more sensations than just yellow and blue.
17:30
Experiments have been done that seem to show that the colorblind have more sensations that what the standard theory will predict.
Nagel developed the gold standard test (Nagel anomaloscope) for determining the type of colorblindness that a person has.
20:00-explanation of test
However, Nagel noted that dichromats will never confuse reds and greens if the stimuli is very large (e.g. 70cm radius as opposed to 1cm in radius).
Suppose we are talking about different quantities of R, G, B light.
The standard theory predicts that if you are a protonope (missing red receptor), then addition or subtraction of red will not make a difference to the viewer.
30:00
Judd reviewed approx 100 cases unilateral dichromacy, and concluded that the standard theory was correct. However, when we examine the articles that Judd reviewed, it appears that Judd’s generalization is unwarranted.
e.g. Example of vonHippel & Hongren’s disagreement about phenomenology of 18 year old patient (35:00-)
Contrary to what the standard theory predicts, colorblind patients DO seem to experience a variety of sensations under a variety of conditions.
40:45
Nagel (1910) “Among thirty dichromats of both types…I have found none that experience dichromatic vision also in large field vision.” With area .5-.75m and distance .5-.75 meters, dichromats can distinguish reds, greens and
43:51
James & Hurvich Experiment
“Dichotomous 15 test”—Subjects must assemble caps (of 15 different colors) in the order of similarity. Protonopes may mix up reddish/greenish ones. Deuteronopes
Stage 1. Ask them do order the caps.
Stage 2. Then ask them to name the caps.
They get far more right than they should—they mix up the ordering, but
Stage 2’. Order the caps again. (They are just as inaccurate as stage 1)
Stage 3. Give color names in order of apparent similarity. (Linguistically, they know perfectly well what the color sequence is)
Conclusion by H&J→ The subjects use a rule-of-them where they call dark appearing things “red” and call light appearing things “green”. They do not actually experience the colors.
This conclusion by H&J does not seem likely.
49:30
Prof. Broakes’ First Rival Hypothesis: Different colors have a unique way of changing (in appearance) as a function of the type (intensity, hue, saturation) of incident light. This function may be what the dichromats detect as different “kinds” (colors) of light. The information is there in the stimulus, but is to be recovered through this method.
Prof. Broakes’ Second Hypothesis: The macula may be used. (Pigmented yellow filter that we see through when we look at things directly but not when we see via peripheral vision.) The effect of this yellow filter is similar in character to seeing objects in direct sunlight.
Prof. Broakes modeling: What happens to colors when the incident light changes from direct yellowish sunlight to blueish skylight?: Reds are proportionally darker and Greens are lighter. With a particular mathematical modeling (that makes a projection taking into account how the greens and reds will shift in darkness according to shifts in the incident light), greens will be projected to the green area, reds will be projected to the red area, while blues and yellows would not be affected too much.
The macula acts in an incredibly similar way. Transmittance of macula is 100% for RG light, but 40% of B light. Effective sensitivity of the receptors is different with and without the macula. The macula adds an extra dimension to vision.
1:03
It is perfectly possible that the R-G colorblind patients get only Y and B in their experience, but are also in some way able to distinguish R and G from each other by saying that if the color changes in this way, it is R and if it changes in that way it is G.
Do we have any evidence that the color blind actually “see” these colors?
I think there is evidence. It comes from the fact what we might call “aspect shift in color appearance”. There are cases where red things can look red and instead come to a green to a color blind person. This is an almost unrecognized phenomenon about color vision (top researchers, major literature/theorists in the field have not recognized it), so let me tell you about it.
I am a color-blind person. I am not a person who has only two receptor types. I am probably a person who has two medium wave length receptors and no long wave receptor. (e.g I have no R receptors but have two versions of G receptors)
The title of this book is written in red and green alphabet symbols (alternating in color). When I first showed this book [shows image of book cover. Title is printed in red and green letters, colors alternating at each letter], my friend delighted in the fact that the book on colorblindness had the title printed in red and green. I felt a little uncomfortable because until he pointed that out, I was unaware that the title was printed in two different colors. All the letters just look dark to me. But later, as I held it under a bright light, eventually, the colors began to emerge. The red letters went forward a little, and the green went backwards. I wondered whether there was a pattern to the colors, and I initially thought that perhaps the first three letters were red, but as I looked at it more closely, I realized that the second letter was green, not red, after all. But I could think of the green letter as red if I wanted to. If I told myself that it was red, it came to look a little different. But it looked different. I think this is a phenomenon not unlike the well-known “aspect shift” situations with the rabbit-duck, the necker cube, etc. What you have is a 2-D input, which is in some sense thought into a 3-D space. When you take 2-D input and you think it into a 3-D space, then obviously there are ambiguities—you can think it this way into a 3-D space, or you can think it that way. Is your internal space merely two dimensional? No. Your internal space is three dimensional, but you are projecting two dimensional information into it, in a way that will occasionally make you wrong about it and sometimes you will have to shift since you thought it was such-and-such layout but actually it’s a different layout. You were wrong on the third dimension. You quickly have to jump and change your mind on it. Now, if I make those mistakes being an anomalous dichromat, it seems very likely that a real dichromat makes those mistakes too. Other people have reported to me that they have experienced the same thing. So I’m not the only person that this happens to, it’s quite common, it seem (although it has to be backed up by a lot of concrete evidence) to me that we do have real evidence that it is not the case that the vision of the colorblind just collapses to yellow and blue. The colorblind have shown that they are capable of making discriminations of reds and greens—we’ve seen that from Hurvich and Jameson example, we’ve seen that from the Nagel reports on the people with large samples—they do not prove insensitive to the difference between red and green. And as for the difference, I mean, do they see reds as red and greens as green, I can’t immediately provide evidence that clearly they have the experiences of reds and greens, but it seems that it is very possible that they do have experiences that are not quite as saturated, but it seems to me very likely that even if their input corresponds to something without determinacy on the red-vs-green, and given a certain hue you may, in a sense, push it out and see it as red, or instead if you enter here/counterweight it [refers to diagram], then you’ll end up seeing it as green. Down here, it can come to look green-ish or it can come to look red-ish according to the stimuli and the character of the surrounding hues. There are philosophical implications and future experiments that I would like to see done, but [as we are running out of time] I will leave it at that and will be very happy to take questions.
1:09:26
Q: Could you briefly talk about the philosophical conceptions?
A: There’s a variety of philosophical views of what colors are. If we go back to a very crude view, then you could imagine somebody saying, “colors are only experiences of the mind and sensations in the mind.” A more advanced view would be, “That’s not what we’re talking about, when we talk of this thing as red, we know that it’s not always not going to look red, at any one moment, it would look a whole variety of different kinds of red, as the light that falls upon it is slightly different.” So it would be a step forward to say “Redness is not just a sensation, it’s a power of a particular thing, or a disposition, to produce a certain kind of sensation/experiences of red under a normal circumstance.” But it would be better yet to say “it would be a disposition to produce a whole range of experiences under a range of different conditions, so with this kind of light it looks this way, with that kind of light it looks very different and so on.” That seems to me, so far, all helpful/taking steps forward. There’s yet another conception that one might think of, that the dispositional power that we should be interested is not the power of the thing to produce a certain experience in us, but rather a power in the thing to transform the light that falls upon it in a certain way, which then of course will in turn have an effect upon the eye. Think about what we mean by “shiny surface.” It is a surface which has a certain kind of specular reflectance pattern. A matte surface obviously does reflect light, but it doesn’t reflect light in such a way that you could see the shapes of objects when they are reflected upon it, but a shiny surface does enable you to see the shape of the object reflected on it. What is the difference between a shiny surface and matte surface? It’s a matter of the pattern of reflectance—what it does with the light that falls upon it. Now what’s a white surface? A white surface is one that give roughly 100% back of the light that falls upon it. But of course the same is true for a mirror. A mirror gives back 90-100% but in a different way. It reflects the light in such a way that you can see the forms, whereas a white thing has an entirely diffuse reflectance so you can’t see the forms. It’s the way in which the thing changes the incident light—that, I think is the characteristic of what a surface kind is. A blue thing would be something that substantially reflected back the blue part of the spectrum, a red object would be one that very much reflects the red part of the spectrum, and so on. And if we have that conception of what the difference between a red thing and a green thing is, then it may not matter so much precisely what the sensation of a person is in order to perceive the color of the thing. Picture a person wearing sunglasses, if you’re wearing sunglasses, in some ways your sensations change, but would you have any difficulty identifying white things, black things, brown things—no, actually you would be pretty good at least in black and white and the basic color categories and so on. You see the colors because what you’re doing is identifying these kinds of reflective surface in the world perhaps through the deployment of slightly different sensations from the ones you get when you take your glasses off, but in actual fact of course our eyes are subject to varying kinds of illumination all the time, (e.g. as the sun changes, the character of the sky changes, and artificial light in some sense compensates for all this), so this is not so puzzling if what you think of as a thing you are tracking as being these reflectance patterns, these reflectance kinds. And in that case, you can imagine a person if you were stuck on the idea of what is really different of a red thing versus a green thing was a particular sensation, then you might well say “well, a person who always has sunglasses on would have different sensations so they’ll never know what redness really is.” I prefer to say that the really characteristic thing about the red/shiny/white thing is not which particular sort of sensations it produces but what pattern of variation it produces in one’s experience. And that pattern of variation can be just as a cue for the person who always wears sunglasses as the person who doesn’t wear sunglasses, and similarly for color blind person—even if the sensations are slightly different, you might well say that they’ve kept the ability to see the external character. But that is of course, jumping over a whole lot of fine distinctions that have yet to be made and details to be thrown in there, but that is the general area that I wanted to work in, and that is the general direction I wanted to take the argument.
Q. Can we summarize your view in a few points: One point is that the dispositional power plus the reflection power plus the illumination will uniquely determine what is your perception of light. The second point is that even if there is a lot of variation, with glasses or whatever, there is a pattern. In the scope of this pattern, no matter what, we will call this red. That’s the categorization of our experience. Would this summary be correct?
A. I think that’s just about right. If you think of a person learning to identify shiny things, they do it obviously by using their eyes. But it’s not very important when the light is bright yellow, or bright green, or whatever, you can see that constant feature which is the way of changing the incident light, whether its reddish/incidental bluish/yellowish light, there is a pattern of change. In actual fact, however, I would like/am tempted to go one stage beyond in my own interpretation of this, it also seem to be quite possible that in a certain sense people “correct” their sensations—I mean, there is a sense of normalization in the sensation. It seems to be also that we may end up wanting to say that the sensations of the color blind are not as far off as the sensation of the normal person as one might first think. What my argument is is that we would need to get people to talk a bit more about the structure of our experiential space. Now, one thing you could think of is ordinary/normal observers—how do you know that the difference between red and green is like the difference between blue and yellow. It’s a difference in hue, and it’s not like the difference between blue and pale blue (i.e. same hue different saturation), but when you move from blue to red, it’s not that kind of change (i.e. change in saturation), it’s a different kind of change. How do we know this? Well, the answer is you can get people to talk about what’s similar to what, and in what respect is it similar. We did this—if you ask people to arrange solid colors in terms of their similarity, they would arrange this in a three dimensional space. People know how to follow instructions such as “could we have the wall two shades lighter than the ceiling?” And for ordinary people there are three dimensions of variation: saturation, hue, brightness. Now, could we work with the same network of patterns of similarity of variation and so on, with the color blind too? I think we need to ask question of dichromats—when they’re shown a large red thing and asked if they’re seeing it, then they describe it as being genuinely red. Then if you say “can you give me something else in this room that is like that but a little more yellow-er?” Can they identify an orange thing as being fairly similar to this red but a little bit closer to the yellow? You can easily find out that the structure of experiences was the same for them, or it wasn’t the same for them as it is for other people. Obviously if this dimension has completely collapsed, then the transition here from blue to red (call it T1), would effectively be the same as transition 2 from blue to gray. And you could show with a series of large samples, take them through T1 and T2 and say “How do you describe this…?” And if they say “this is looking a little paler, this is a bluish red…etc “ then they no doubt know that this doesn’t look the same as that to them, and for that kind of thing we can say “Clearly, they’ve got a sense in which there is a different hue involved here from what’s involved there”—this is one of the experiments I would like to see done. We need to look at the structure of color experience. But with all of that, I think we might get us to a position where we have to say, “It wouldn’t be very surprising if the color blind had the same sensations as the normally sighted, after all, they have the same brain as the normal sighted. What they haven’t had is the very same input from the retina but they’ve had other cues from the retina which might have stimulated the very same experiences through the activity of the brain.
Q. I think your idea is good but I also detect some determinism in it. The subject’s sensation is completely determined with some collapse of some structure so there are various different kinds of projections. If these structures/inputs are the same, then your sensations should be exactly the same—is this your assumption?
A. Yes.
C. Actually, there is some neurophysiological evidence about color sensitive cells to different hues. And what you suggested actually, that some how colorblind signals get transformed into hue coordinates otherwise colorblind people wouldn’t be able to experience a whole range of hues, as you suggested. But on the other hand, there were experiments with similarities and dissimilarities of our sample with color blind people, and those experiments were using only one dimension—they do not distinguish between colors.
A: Who is reporting that?
C. Sokoloff and Parami(?) tried to reconstruct the ??? space from the matrix of similarities and dissimilarities between color samples. And for color blind people that come up with disused shut up dimension.
A: Okay, Shepard has come up with this. (C. Yes, Shepard was one of them.) I have to say I have some difficulty reconciling—with the other evidence that we have here. It seems to me that it is very likely that there are wide individual variations here. It seems to me that there are dichromats who care very much about what they are missing and work very hard to make up for it and they manage to compensate very well. There are dichromats who don’t seem to care very much, and they might not develop all the usage of all the cues that are around. So it seems to me that it’s possible that the experiences of these two groups after 5, 10, 50 years, may be very different. It is not a very trendy topic now to talk about how to train the color blind to improve their vision. But there have been times where it was quite trendy to claim that there were people who managed to get the number of errors on such-and-such a test down from 95% to 32%. This suggests (although we should be skeptical) that training does make a real difference.
C: Yes, colorblindness will not make anyone disabled (people are able to navigate in the world even if they are color blind), so maybe that is why there is not a demand for training.
A: I also think that it’s interesting that many colorblind people do have interest in what they’re missing out on, and try to do better. I think that those who learn and make the effort to recover missing dimensions so-to-speak, may end up with something close to the normal experience. Not of course for tiny samples only seen very briefly, only with relatively large samples. Actually, I would love to know whether the neurological studies that you’re talking about—did they involve large samples? I mean, when Nagel says “I cannot find a dichromat who does not identify with complete accuracy samples that are 70cm by 70cm—if he says that, it would be very weird if the neurologists can come along and say “they get the exact same sensation with gray.” How in the world are they doing it then? This is a puzzle. The fact is, it is very likely that the neurological studies show that they get the same sensations as they get from gray—using relatively small samples…I don’t know what they’re doing. The tradition has been not to take seriously the idea that the colorblind might have a wider range of sensations than the Maxwell-Helmholz theory says. The popular wisdom is, experience collapses to two dimensions. So people in the adjacent areas say “Wouldn’t it be nice if I link my research with that” and you get some things that are just false in that area. And I have no idea whether these reports are false with respect to what they are talking about—maybe they are entirely accurate with what they are talking about but different if you use large samples. But let me give you of things that are genuinely false. I’ve seen people who have done long studies on Benham’s top: Shown the top, they claim that dichromats have no color experience outside of yellow and blue. I’m not a dichromat, but very close to one. I was asked by a researcher to look at a Benham’s top for the very first time—and I saw pink. greenish, yellow and blue…and I saw exactly the same colors in exactly the same places as he did. I was rather pleased! I don’t know whether my sensations were exactly the same has his, and he said “Look, I tested a number of pure dichromats and they’re reporting exactly the same thing.” Now it’s just a puzzle that there are other people who have published exactly the opposite on this. And I just have to say there is an element of fashion involved here, an element of experimental technique that is no 100% unchallengeable among all of us.
Q: Is anything you’re saying about compensation for deficits or aspect shifts call to question the traditional distinction between judgment and sensation altogether in general?
A: In a way no, but in a way I’m open to doing that. If you take the duck-rabbit, you can see it as a duck or a rabbit. There’s one description of this phenomena, which is: whichever total set of mind you’re in, you got the same sensation but a different judgment. In one case you think here is a rabbit image, and in the other you think here is a duck image. Two different judgments but only one sensation.
C: Are you sure?
A: This is somebody else’s description, not mine. I’m not sure that’s the right way to describe it, because so-to-speak patterns of similarity…if people are shown 20 photographs and are told to pick out the one that is most similar to that, you’ll chose a different set of things depending on whether you’ve seen it as a duck or as a rabbit. I don’t think judgment is in play there. There seems to be some not-very-well understood level of pictorial representation that is different in the case of seeing it as a rabbit or seeing it as a duck. That is, pictorially they are different even if the sensations of where you see white marks and where you see black marks is exactly the same. This is still a puzzle to me—I’ve spent weeks reading what people have to say about this and I still do not know what I should say about this. The particular case that I am interested in (color shift), though, will be a challenge to the standard description, or it would be a phenomenon that went outside the range of cases of the standard mode of descriptions as usually applied to. The standard mode of description is that you got the same sensation but a different judgment. Whereas in my case it’s clear that you got a different sensation. Sometimes you get a red sensation, sometimes you get a green sensation from this thing. The case I’m describing has got to be a case of variation in sensation.
C: Yes, and the introspective case that you described about yourself, seems to be saying that “as I change my judgement, my sensation of the color changes”.
A: That top-down view was never denied by the sensation-distinct-from-judgment theorists, I’m not a fan of that view, but I want to show respect to how it was developed. They are fine with the idea that the input can change as a result of the judgment you make. I heard long time ago when Christopher Peacock was defending his sensational representational distinction—that was a version of the modern day sense datum theory and he was certainly explicitly ready to say “and sensations can be influenced by judgments.”
[15:00]
Q: I wanted to know how far you will take your view that color perception is related to the effort that you put in. Specifically, I am thinking of the example like Mary the neuroscientist. We can perhaps take a stretched version of your view and say that the Mary case is impossible because the type of brain that we have regardless of whether your input is black and while, or RGB, you will experience color.
A: I’m not unsympathetic to that, but it’s also not something I’d like to be a consequence of my views. It could be that humans are built so that if they close their eyes and push their eyeballs that they’re going to get color sensations, but anyway, what I wanted to say was that you’re going to get color experiences from colored things even if you have somewhat of a reduced input. I didn’t want to say you’re going to get color experiences from black and white things even if there’s a reduced input. If Mary is brought up in a room where there are only black and white things and her body is painted in black and white, then I have no particular view.
C: If she uses her yellow macula filter—it seems as if she could see color in a black and white room.
A: I’d like to be encouraging to that, but it in some ways it points to the opposite direction from where I’m generally going. Where I am generally going is that color is a phenomenon in the world and we have a brain that is training itself to the identification of—the key thing about color is that there is a difference between these/those things. So in a certain sense the sensations don’t matter too much if the things we are interested in are the kinds, the features out there. Now, what you’re focusing on are the oddities in the processing mechanism—could those give us a conception of an external kind, even if you don’t come across the external kind.
C: I was trying to see whether your view would collapse into the view that colors just don’t exist in the world. You said that you don’t view that, but I can imagine someone ungenerous to your view saying if you’re going to say that we know that these people experience color, when they seem to not have the normal input of color they have the same experience of color, isn’t this just taking it further away from thinking that colors are real things rather than things that are created by our brains.
A: I think it’s exactly the opposite way around, actually. I would say that by taking the color as exactly the sun reflectance pattern, kind of spectral reflectance, that we made it most plausible that the colorblind can get the same perception of the thing and I don’t want to say “and their sensations are radically different from normal people.” I actually want to say “and their sensations are largely the same as normal people.” So I’m not against sensation (some people seem to have bad conceptions of sensations), I’m rather in favor of sensations.
Q: But in your view, where is the location that the sensation is created? In the retina? Cortex? At what stage?
A: Certainly not the retina. It seems to me it’s better to say that the sensations are in the mind, rather than saying that they’re in V1, V2… The activity in the V1, V2, V4…is going to result in patterns of experience which are in the mind. I’m not suggesting an immaterial Cartesian mind, I’m suggesting that there’s a certain way of talking about the whole activity of a human being, thanks to what’s going on in the brain, the sensations don’t have a physical location…
C: You mean [inaudible]
A: When I feel a pain in my toe, there is some sense in which the pain’s in my toe, there’s some sense that the pain is due to something going on in the brain, but I don’t want to say that the pain is really in this part of the pain, not in my toe.
C: It is projected in the brain?
A: This is a very complicated issue that I do not have a pat answer.
C: But at least you agree that the sensation is not in the retina, right? This gives you a ??? view to accommodate very many difficult things because the it would require the process with a lot of filters, so what sensation is is not just the ??? of the hues/brighness/saturation, but it’s more than that. It also depends on the processing mechanism there, and a lot of filterning out, a lot of characterizations. Are you sympathetic to that?
A: I have no special objection to that.
Q: My first question is a clarifying question—I thought that you had said that the sensation of red is in the pattern variation that the object…that it’s in the object, it is the way that the object changes according
A: I don’t actually want to say that the sensation is in the object
C: So color…what would you say is in the object?
A: The first way we talk about colors is, “I would like to have the wall to be painted in a darker shade of blue that it is in right now.” What do we want? We want a paint with a particular property.
C: Right, so you want more pigments of this type.
A: It’s obviously true that if ask “What is this thing we are talking about?” we have to fix upon the institution, the conceptual scheme within which we first fix upon it, so we say things like…if you said the colors are sensations, there would immediately be a problem of this from the fact—suppose someone asks for a red tie, and if I say “well, no, because all my ties are currently covered because it’s dark” you notice at some level it’s just a silly thing to say. Because what does the person mean when they say they want something red, they want something that looks red under normal circumstances—they don’t mean that they want something that is currently producing a sensation of red. They obviously know that things remain red whether or not they’re being sensed. So of course I do not want to say that a color is a sensation. Color is a characteristics of surfaces, lights etc that is when I happen to be looking at it in the light is good enough, able to produce experience in me.
C: So there is two senses of color in some sense. Sometimes I’ll be talking about the thing in the object and sometimes I’ll be talking about how it appears.
A: But I would say that the same is true of shapes and sizes, too. You can be asked “pick out from these photographs the things that are really elliptical” or you can be asked “pick out the things that look elliptical”, so yes, there are two things (being vs looking elliptical), but there is also being a horse and looking like a horse. For every characteristic that we can perceive at all, there is also looking that way. I would say it comes with the fact that the mind is a representational system. That doesn’t mean that there are two senses of the terms, no, the only sense of a horse is a four-legged, member of such-and-such a species. That’s what horses are, and there’s looking a horse. A donkey might be dressed up to look like a horse, it’s not like there is one property of being a horse and one property of having the sensation of a horse. You got horseness and the appearance of horseness. In the first place you got the property in the world, and we got the representation of it.
Q: I don’t think there is anything black and white in biology—everything comes in gradiations. So you can have twins but they will be slightly different, and you can have cone receptors and I think that even though they may be produced in the same way during embryonic development, I don’t think that every cone receptor is going to be exactly the same. So in some sense even if we have one type of cone only, you would have a gradiation (I think) and so you would be able to triangulate somehow, and you would have more than one color. Do you think that could possibly explain why the colorblind can see different hues?
A: That seems to be extremely interesting and at some level quite possible. What we do know is that there are many varieties of long-wave receptors among the normal population if you’re normal trichromat, it doesn’t mean there are only one kind of L-receptor found in every person. But whether you get variety within one person, I haven’t seen much reported but it seems to be very conceivable, I’d love to know.