Sorry for the long delay in responding, I've not had a chance to get back to this and respond intellegently.
I guess the contention that our qualia are identical (per #1, post 28 above) bothers me. It seems to suggest #2 is also true which seems like a rather radical suggestion. I could accept that they are very similar, just as our brains are similar but not identical in ability or configuration.
H said: As for "function"-- it's an ambiguous word, and you seem to be taking a very coarse-grained view of what it might refer to. I leave the word ambiguous somewhat intentionally, but in theory it could be something as fine-grained as specifying a particular kind of neural algorithm instantiated by particular kinds of neurons in particular kinds of arrangements.
I'd agree the concept of functionalism is ambiguous, I'd disagree my analogy was 'course-grained'. If I'd suggested a car or a bus serves the same function when traveling from NY to LA - then tried to suggest sensory function that resulted in qualia can similarly be different, then yes, that would be "course-grained".
People on the other hand are unique so I would think our brains would be structured differently also which would result in very different 'algorithms' used to decipher sensory inputs. Looking at a range of IQ exams, differences in interests and abilities between individuals, etc… surely suggests that our brains are NOT wired the same. Thus the "mental states" which correspond to "red" are likely to be equally varied and if those mental states correspond to qualia then from a functionalist's perspective one would have to conclude the resulting qualia was as different as the individual's "algorithms". Ok, so the "function problem" might be refined, I'd agree it isn't refined and besides, we seem to agree that qualia such as "red" can be less than identical.
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I found a variety of interesting info regarding eyes and interpretation. As I'm sure many of you already know, humans have 3 different light sensing cones in our eyes, hence we are called "trichromats".
Humans with normal color vision are called trichromats. Their color vision is based on cones with three different visual pigments, each responding to a different part of the spectrum.
Why three? Why not four?
As it happens, three photopigments may be a popular design, but there are others. Let's consider some animals.
1. monochromats
Dogs - probably
2. dichromats
most mammals - In addition to rods, they have only middle and short wavelength cones.
Cats
New World Monkeys
Squirrels
Rabbits
Tree Shrews
some Fishes
3. trichromats
Birds
Fish
Old World Monkeys
Humans - usually
4. tetrachromats
Turtles - cones: red, green, blue, yellow, UV; plus rods
Chickens - cones: violet, blue, green, red; plus rods
Goldfish
Japanese Dace
pentachromats
Pigeons
Ducks
Papilio Butterfly - has at least five different photoreceptors, many of them in long wavelengths
Interesting notes:
The Mantis Shrimp has ten types of photoreceptors.
In at least three species of New World Monkey (squirrel monkey, spider monkey, marmoset) most are dichromats, but a sex-linked color vision factor makes about one-third of the individuals trichromats.
In addition to different colors, the photoreceptors of bees are sensitive to polarized light.
Ref:
http://wolfstone.halloweenhost.com/TechBase/litadv_AdvancedLightingConcept.html
My conclusion from that is there is no reason to believe in identical qualia across the animal kingdom.
One study seems to indicate women see color differently or more vividly than men.
Because females can have two different versions of this gene, but men can have only one, females may be able to perceive a broader spectrum of colors in the red/orange range. "Men and women may be literally seeing the world differently," Tishkoff said.
Ref: http://www.psycport.com/stories/ascribe_2004_07_14_eng-ascribe_eng-ascribe_014026_988726893508805748.xml.html
While another study found that although there is a large difference in the number of cones in the eye, there is no significant difference in how we percieve color.
Researchers at the University of Rochester have found that the number of color-sensitive cones in the human retina differs dramatically among people—by up to 40 times—yet people appear to perceive colors the same way.
…
Each subject was asked to tune the color of a disk of light to produce a pure yellow light that was neither reddish yellow nor greenish yellow. Everyone selected nearly the same wavelength of yellow, showing an obvious consensus over what color they perceived yellow to be. Once Williams looked into their eyes, however, he was surprised to see that the number of long- and middle-wavelength cones—the cones that detect red, green, and yellow—were sometimes profusely scattered throughout the retina, and sometimes barely evident. The discrepancy was more than a 40:1 ratio, yet all the volunteers were apparently seeing the same color yellow.
"Those early experiments showed that everyone we tested has the same color experience despite this really profound difference in the front-end of their visual system," says Hofer. "That points to some kind of normalization or auto-calibration mechanism—some kind of circuit in the brain that balances the colors for you no matter what the hardware is."
Ref:
http://www.sciencedaily.com/releases/2005/10/051026082313.htm
I'd have to argue the volunteers didn't necessarily percieve color the same way. The number of different photoreceptors varied by as much as a factor of 40! So what could the volunteers be doing to identify the color? They all were asked to identify "yellow" and they did, but that doesn't mean their qualia were identical, only that they were able to percieve what was asked of them. The article further points out that people's perception of a given color can change without their knowing further supporting IMHO that we don't necessarily have identical qualia experiences regarding color.
In a related experiment, Williams and a postdoctoral fellow Yasuki Yamauchi, working with other collaborators from the Medical College of Wisconsin, gave several people colored contacts to wear for four hours a day. While wearing the contacts, people tended to eventually feel as if they were not wearing the contacts, just as people who wear colored sunglasses tend to see colors "correctly" after a few minutes with the sunglasses. The volunteers' normal color vision, however, began to shift after several weeks of contact use. Even when not wearing the contacts, they all began to select a pure yellow that was a different wavelength than they had before wearing the contacts.
"Over time, we were able to shift their natural perception of yellow in one direction, and then the other," says Williams.
Another article pointed out that people with a form of color blindness called "deuteranomalous" were able to distinguish differences at certain wavelengths that "normal" people couldn't.
Indeed, the researchers found that some color pairs were only seen to be different by deuteranomalous individuals. The finding suggests that although these individuals may be blind to some colors accessible by color-normal individuals, they also have a sensitivity to a "color dimension" that is inaccessible to those with normal color vision. In their paper, the researchers remark that "[f]or a color-normal experimenter, it was striking to watch a deuteranamolous subject giving large difference ratings to apparently identical stimuli, and doing so without hesitation."
Ref:
http://www.medicalnewstoday.com/medicalnews.php?newsid=34581
From reading all this, I'd say it isn't likely we all percieve exactly the same color. Our qualia may be very similar but I tend to doubt it is identical. Qualia may be dependant on our eyes but it must also be dependant on the 'processing' our brain does with that stimulus. This processing isn't something that can presently be guaged in any way. I rather like this conclusion better than suggesting we have identical qualia experience (as I defined in post #28) which leads to a rather nasty second conclusion I think. Not sure if we can avoid the second conclusion if we make the first.