Phenomenal CharacterTo know that some organism or system id p-conscious does not yet tell us anything about the specific, fine-grain character of their phenomenology.
There are different phenomenal modalities (types, kinds).
We can describe a subject's phenomenology at differing levels of specificity. (i.e. "color experience" vs "red experience" vs "crimson experience")
Two Kinds of FunctionalismConceptual functionalism (Analytic functionalism, a priori functionalism): That mental states are individuated by their functional roles can be read off from the way we talk/think about the mind.
Empirical Functionalism (Psychofunctionalism. a posteriori functionalism): That mental states are individuated by their functional roles is a finding of empirical science. It could have turned out differently, but our best science says that phenomenal differences need to be ground out/explained in terms of functional differences.
Two skeptical challenges to functionalism...Absent qualia: "I can conceive of a functional duplicate that is not p-conscious..."
Inverted qualia: "I can conceive of a functional duplicate that has phenomenal-green experience where I have phenomenal red experience..."
Under conceptual functionalism, such cases are supposed to be incoherent.
If there were real cases of inverted qualia, empirical functionalists would look to vision science for a functional explanation of this difference...
Nita-Rumelin's "Pseudonormal Vision"Pseudonormal vision: "red" cones and "green" cones swap pigments, so what would have been a "red" signal becomes a "green" signal and what had been a "green" signal becomes a "red" signal...
These cases aren't just conceivable, they really exist! Or, at the very least, our best science seems to take the hypothesis of red/green phenomenal inversion seriously.
Either empirical functionalists would need to rule out this hypothesis a priori, which would turn them into conceptual functionalists. Or they would have to distrust empirical science, which which violate the "empirical" part of "empirical functionalism".
This is all supported by the "plausible prima facie constraint": "No hypotheses accepted or seriously considered in colour vision science should be regarded according to a philosophical theory to be either incoherent or unstatable or false."