Color-blind synesthesia, Evidence for/against the existence of qualia? Options

[brian0918]

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?

[lucid_dream]

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.

[brian0918]

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.

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...