SteveKlinko wrote: ↑December 16th, 2021, 4:53 pmConsul wrote: ↑December 16th, 2021, 2:56 pm
It doesn't produce the redness because it is (identical to) it: Certain (dynamic patterns of) electrochemical processes in your brain are your color experiences.
You have to be able to show HOW Redness is Electrochemical Processes in the Brain. Saying it does not Explain it. It's ok as a Speculation but it is not an Explanation.
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Sensory Coding: Taste
On one’s tongue, there are four distinct kinds of chemically sensitive receptor cells. (There are recent indications of a fifth type, but for simplicity’s sake I’ll leave this aside.) Cells of each kind respond in their own peculiar way to any given substance that makes contact with them. A peach, for example, might have a substantial effect on one of the four kinds of receptor cell, a minimal effect on the second kind, and some intermediate level of effect on the third and fourth kinds. Taken altogether, this exact
pattern of relative stimulations constitutes a sort of neural ‘fingerprint’ that is uniquely characteristic of peaches.
If we name the four kinds of cells a,b,c, and d, respectively, then we can describe exactly what that special fingerprint is, by specifying the four levels of neural stimulation that contact with a peach actually produces. If we use the letter S, with a suitable subscript, to represent each of the four levels of stimulation, then the following is what we want: <S_a , S_b, S_c, S_d> . This literal
list of excitation levels is called a
sensory coding vector (a vector is just an ordered list of numbers, or magnitudes). The important point is that there is evidently a
unique coding vector for every humanly possible taste. Which is to say, any humanly possible taste sensation is just a pattern of stimulation levels across the four neural channels that convey news of these activity levels away from the mouth and to the rest of the brain.
We can graphically display any given taste by means of an appropriate point in a ‘taste-space’, a space with four axes, one each for the stimulation level in each of the four kinds of sensory taste cell. Figure 7.13 depicts a space in which the positions of the various tastes are located. (However, in this diagram, one of the four axes has been suppressed, since it is hard to draw a 4D space on a 2D page.) What is interesting immediately is that subjectively similar taste-sensations turn out to have very similar coding vectors. Or what is the same thing, their proprietary points in taste-space are very
close together. You will notice that the various types of ‘sweet’ tastes all get coded in the upper regions of the space, while sundry ‘tart’ tastes appear in the lower center. Various ‘bitter’ tastes appear close to the origin of the space (the ‘bitter’ axis is the one we dropped), and ‘salty’ tastes reside in the region to the lower right. The other points in this space represent all of the other taste sensations it is possible for humans to have. Here there is definite encouragement for the identity theorist’s suggestion that any given sensation is simply identical with a set or pattern of spiking frequencies in the appropriate sensory brain area.
Sensory Coding: Color
A somewhat similar story appears to hold for color. There are three distinct types of color-coding neurons distributed uniformly throughout cortical area V4, just downstream from the primary visual cortex. These three types of cells are ultimately driven by the wavelength-sensitive cells in the retina, via a clever tug-of-war arrangement involving the axons between the two cell populations. (I’ll spare you the details.) Here also, a (
three-dimensional) neuronal activation space, embedded in area V4, displays simultaneous activation-levels across those three types of cells for each small area of the visual field, an activation space for each of the possible colors perceivable by humans. Figure 7.14 portrays that space, and you will notice that it contains a special double-coned or spindle-shaped
subvolume, within which
all of the familiar objective colors are systematically placed according to their unique
similarity (i.e., proximity) and
dissimilarity (i.e., distance) relations to all of the other objective colors. Orange, for example, is tucked closely between red and yellow, as you would expect, while green is a maximal distance from red, as is blue from yellow, black from white, and so forth. This neuronal coding system recreates, in complete detail, the internal qualitative structure of human phenomenological color space, as displayed in introspection. One might even say that it
explains it, especially since it predicts, with equal accuracy, the qualitative character of the many thousands of possible
after images one can induce in the human visual system by temporarily fatiguing the neurons involved. Indeed, it even predicts the weird qualitative characters of certain unusual visual activation-vectors outside the central spindle of the familiar objective colors. That is, it correctly predicts the qualitative characters of sensations you have never even had before. Evidently, phenomenological qualia are not quite so inaccessible to physical theory as was originally advertised."
(Churchland, Paul M.
Matter and Consciousness. 3rd ed. Cambridge, MA: MIT Press, 2013. pp. 227-231)
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