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Posted by: brian0918 Mar 12, 2007, 05:20 AM

Quick summary: There is a person whose eyes don't allow him to see certain colors (color-blindness), but who can perceive those colors due to a condition (grapheme-color synesthesia) that makes him see colors when he sees numbers. Evidence for/against existence of qualia?


I recently read an article on SciAm about an individual discovered by V.S. Ramachandran with the following ability:

"We also observed one case in which we believe cross activation enables a colorblind synesthete to see numbers tinged with hues he otherwise cannot perceive; charmingly, he refers to these as "Martian colors." Although his retinal color receptors cannot process certain wavelengths, we suggest that his brain color area is working just fine and being cross-activated when he sees numbers."


He also discusses it further here:

"The effect is most obvious and pronounced in the colorblind synesthetes, but occurs in "regular" synesthetes as well. The colors evoked by cross activation in the fusiform gyrus "bypass" earlier stages of color processing in the brain, which may confer an unusual tint to the colors evoked. This is important for understanding the phenomenon of synesthesia, because it suggests that the qualia label--that is, the subjective experience of the color sensation--depends not merely on the final stages of processing but on the total pattern of neural activity, including earlier stages."


What do you think of this individual's ability to "see" colors that he can't - and presumably never could - physically see. Is this evidence for/against qualia? Is it simply evidence for the fact that our brains utilize some sort of "spectrum of interpretation" for colors, so that even though these individuals have never seen the colors elsewhere, their brains will interpolate from other data?

Any other thoughts?

Posted by: lucid_dream Mar 12, 2007, 12:37 PM

I don't believe it

Posted by: Rick Mar 12, 2007, 01:22 PM

I believe it, but I also think that anyone who needs "evidence" for the existence of qualia must be a philosopher's zombie.

I also don't think philosopher's zombies can exist, so those apparent zombies must be merely inept at observing their own consciousness.

Or maybe what I call "consciousness deniers," like Daniel Dennett, really are zombies.

Posted by: lucid_dream Mar 12, 2007, 01:27 PM

this has nothing to do with the existence of qualia and everything to do with whether conscious experience of completely novel sensations can be evoked without receptors for said sensations. I do not believe it possible. It's like asking someone congenitally blind to imagine what it's like to see.

Posted by: Rick Mar 12, 2007, 01:34 PM

Astronauts see flashes of light when cosmic rays intersect their brains. I think an astronaut born blind would also see those flashes.

Posted by: brian0918 Mar 12, 2007, 08:31 PM

Why shouldn't it be possible? These two things are known to be true:

1. The sensory receptors are just the beginning of the process of evoking a color in the brain.

Ramachandran has shown that cross-activations (numbers evoking colors) can occur at multiple points in this process.

2. In grapheme-color synesthetes, colors are being evoked at those points in the brain, without their eyeballs receiving any external light from those wavelengths of light.

I'm not saying that the color-blind synesthete is necessarily experiencing what he would definitely experience if his eyeballs could receive the colors they currently can't; maybe his brain is doing some sort of interpolation based on colors he's already familiar with... who knows... anyways, it doesn't seem unreasonable that regions of the brain that can trigger colors without having any external stimulus from those wavelengths can also trigger colors that we believe the person shouldn't be able to perceive, for whatever contrived reason...

Posted by: lucid_dream Mar 12, 2007, 09:25 PM

interpolating between subtle shades or hues of similar colors is one thing that many of us have experienced or can experience, but extrapolating to completely different types of colors that have never been perceived before is something completely different. There is a wealth of evidence that our perception is dependent on our sensation, and our sensation is dependent on our senses. If you lack the sensory apparatus for sensing certain fundamental qualities, then it is not possible to perceive or imagine these things. Everything we can imagine is anchored in our direct sensations (the idea of which dates back to at least Hume). You cannot imagine anything completely separated from your sensations. So the idea that anyone can do this, I do not believe, or at any rate am extremely skeptical until compelling objective evidence is presented, and that doesn't just rely on subjective reports which are prone to error.

Posted by: brian0918 Mar 13, 2007, 05:03 AM

What's so hard to believe about this? It's not as if the light that hits your eyes is directly involved in your brain's functions; your brain has all the necessary components for creating perception. Assuming that one's only defect is in their eyes, what makes you think their brains would be equally defective at perceiving certain colors, real or imagined.


What is this based on? Synesthetes perceive colors without any specific wavelengths hitting their eyes. Astronauts perceive flashes of light without any light hitting their eyes. People on drugs can perceive colors that aren't there. What is this strong evidence you have to be able to say definitely "it is not possible to perceive or imagine these things"?


Just because the external component of sensation (the eyes, nose, tongue) might not work doesn't mean those same areas of the brain don't work, and as has been clearly shown, those areas can be cross-activated by other areas, leading to the perception of colors associated with numbers. Nothing about your brain requires that your eyes/nose/ears/whatever be connected to it for its individual components to function or potentially function in the future.


These reports are anything but subjective. Ramachandran and others have thought up clever ways to determine for certain what these people are perceiving, and in a way that they could not, on average, fake (well, unless there is a world-wide conspiracy among synesthetes). You may want to read some of the literature on this........

Posted by: Rick Mar 13, 2007, 08:01 AM

Didn't you know that musical tones have color? I assume blind people can see them too. Consider this thought experiment:

A person is born with complete color blindness from a genetic defects: the person's retina has only rods, no cones. The person learns all there is to know scientifically about color, obtaining a PhD and becoming the world's foremost expert on color vision. Then through a new genetic engineering procedure, the person's retinal cones are restored and she can see color. Is there any information content she has access to now that she didn't before? If so, is there any way to convey this information to another person?

If not, then qualia are ineffable. If so, then she wasn't quite the expert we supposed.

Posted by: brian0918 Mar 13, 2007, 09:57 AM

That's how the thought experiment breaks down. It requires that there be no limit on the person's ability to comprehend/know what it's like to perceive light (without having the light actually pass through her eyes), but then requires there to be some contrived limit on her knowledge - a limit that is more the result of our current lack of understanding than anything else.

It's essentially saying:

1. Assume Mary can attain perfect knowledge of colors without light actually hitting her eyes (that's fine).
2. Expose her to light.
3. (Because our current understanding isn't perfect,) She will experience some new knowledge, and therefore qualia exist.

Posted by: lucid_dream Mar 13, 2007, 06:21 PM

No, but it evokes complex patterned neural activity that is very unlikely to be evoked without ever having said sensations. It's the same reason we can't imagine geometry in 4 spatial dimensions, because we do not possess the sensory apparatus that enables us to see in 4D. No matter how hard you try to imagine, you can't imagine in 4 spatial dimensions. That's why I don't believe that a congenitally color-blind synesthete could ever imagine colors that they do not have the sensory apparatus to have ever seen. Also, Ramachandran's claim is based on a single color-blind synesthete; One single person that he believes is a color-blind synesthete. This is not compelling.

Posted by: brian0918 Mar 14, 2007, 06:02 AM

It's only irreproducibly complex if you follow the brain activity from beginning (information going into the brain from the optic nerve) to the end (the "realization" of the color in your mind); but if something in the beginning step can be triggered in the same way that the optic nerve initially triggers this process, it should have the same effect. This is exactly what is seen in synesthetes. The shape of numbers/letters causes cross-activation in the fusiform gyrus, early in the process of visual perception. This results in the perception of colors that aren't really there. So your argument from complexity can't possibly be valid, as I've shown a well-observed counterexample.


Those situations are no analagous. First, in this case, nothing is being imagined, unlike in your case. Second, our brains have evolved in a 3D world, so it makes some sense that we shouldn't be able to truly imagine a 4D world. On the other hand, our brains have also evolved in a world of color; even if you're blind, the color areas of your brain are intact, so you still have the ability to have an initial trigger that results in the perception of color. I don't understand what's so hard to believe about this; grapheme-color synesthetes do it all the time (perceive colors where there aren't any), so why shouldn't color-blind synesthetes do the same (as has been documented)?

The only reason you believe there is a problem is that you believe they are imagining something, which isn't the case. They are getting triggers from their senses in the same way as anyone else experiencing reality; they just have their triggers cross-wired.

I'm sure if a blind man went into space, he would perceive the same flashes of light astronauts perceive when cosmic rays hit their optic nerve or retina (at least in the case of people with cataracts, uveitis, trachoma, or any massive defects to the front of the eye). He may not be able to explain it in words - simply because he hasn't had the benefit of someone by which to calibrate his observations ("This is red." "That is blue." "That is green."), but that doesn't make the observation any less real.

So what's hard about believing that the same process that triggers colors in the brain when looking at uncolored characters can trigger colors in the brain of someone with defective eyeballs and an intact color-region of the brain?

Nowhere in my explanation do I require that someone "imagine" something, unlike in your 4D situation.


They are not imaging anything. Nowhere in my explanation do I require anyone to imagine anything. It's simply the case that numbers/letters are triggering the color areas in their brain in the same way that light of specific wavelengths triggers color areas in their brain. This has already been clearly shown to be true in grapheme-color synesthetes.


This one person has the same effects as thousands of others; he just has defective eyeballs (also remember that the color-receptors of the eye aren't even involved in this perception at all.

The only reason you're having trouble with this is that you believe these people are imagining things, which is clearly not the case.

There's a good review of the current research in:

Ramachandran, V. S. and E. M. Hubbard (2001). "Synaesthesia--a window into perception, thought and language". Journal of Consciousness Studies, 8, 3-34.

Just google for: "Synaesthesia--a window into perception, thought and language", it's the first link.

Posted by: lucid_dream Mar 14, 2007, 07:39 AM

This is incorrect on two fronts. First, cross-wiring does not reproduce the same sensations since the neural activation patterns will be different. For example, simply stimulating primary visual cortex with electrodes certainly evokes neural activity, but it is not the same as stimuli received from the retina; hence, you cannot evoke realistic sensations via stimulating primary visual cortex using electrodes. You assume that cross-wiring produces the same 'trigger' as visual stimuli, and elicits identical neural activation patterns, but this is nonsense. Read the neurophysiological literature on crossing-wiring in ferrets (M. Sur).

Second, I never referred just to synesthetes but to color-blind synesthetes, who have never experienced certain sense modalities, and which you expect me to believe are able to experience them (these never experienced before sensations) via cross-wiring. Have you ever heard of experience-dependent plasticity? How do you expect the brain to form it's intricate circuitry for computation and representation in the absence of environmental interaction? It doesn't.

Posted by: brian0918 Mar 14, 2007, 10:35 AM

Grapheme-color synesthetes see numbers in color, and report that those colors match to other colors they normally perceive; this is currently our only source of evidence, but assuming they are correct, this would seem to disagree with your claim.



I think you meant experience-expectant plasticity, which has sensitive periods in which the senses must be stimulated for best development (Note: this still allows for less-perfect development outside of the window of opportunity). Vision in general may be experience-expectant, but the color-blind synesthete has always had vision, so that isn't an issue. The problem is whether or not you believe that creating/maintaining the connections necessary for perceiving every color in the brain is experience-expectant or -dependant. Is there research either way?

Posted by: lucid_dream Mar 14, 2007, 11:44 AM

I mean that I believe that what we perceive is dependent on previous interactions with the environment. Since it is plasticity, and since it is experience-dependent, I referred to it simply as experience-dependent plasticity and avoided nuances and jargon that are not widely accepted.

The central issue is whether the "Martian colors" of the colorblind synesthete correspond to colors his retinal receptors cannot process. I believe that Ramachandran would like to believe that this is the case, as it makes the story sensational. I am not convinced, and have not seen any convincing evidence for this.

Posted by: brian0918 Mar 14, 2007, 12:41 PM

It would indeed be very interesting if that were the case. I'm not sure what evidence he could get from the person. Maybe if he asked the person if the color is closer to one end of the spectrum or another... or if some sort of correlation could be found between numbers and colors among a much larger sampling of synesthetes (color-blind or not)... who knows. It's still very interesting.

Posted by: Rick Mar 14, 2007, 02:55 PM

I have never seen music colored with colors outside my normal visual range, and I am not color blind. However, if I were color blind, I would not be surprised to see colors in music outside my visual range. My brain would be able to see the full range that music can stimulate, but my eyes would be defective.

Posted by: Layman_Sam Aug 04, 2007, 06:24 PM

Ramachandran gave a speech at IBM Almaden Inst. last year.

It includes this topic, and can be found at googlevideo: " The Uniqueness of the Human Brain"

Posted by: cerebral Aug 05, 2007, 11:04 AM

Cool. Thanks. Btw, have you read "Phantoms in the Brain"?

Posted by: Layman_Sam Aug 06, 2007, 10:30 AM

No, but I've gotten a fair share of it trough diff. articles/sources including the "Reith lectures" (BBC radio).
Hes a funny guy

Posted by: Layman_Sam Aug 09, 2007, 07:38 PM

scientificblogging com/news/seeing_the_colors_in_music

So by finding the "opponent incongruent" color, and apply it to the 2's in the 5's and 2's experiment.
Or in other words whatever color (if any) that makes it hard for the colorblind grapheme-color synesthesic person to see the pattern in it should show what arbitrary value the "martian-color"(opposite) he is perceiving has.....?

I guess theres a question of what type of colorblindness the subject had, and if his photo receptors would be acceptable to the stimuli of the wavelength of the opponent incongruent color...

I'm probably reading to much into this...