So, I've been thinking a lot about qualia, and trying to get a paper together on why they shouldn't be seen as such a problem for materialism. It seems to be generally accepted that features of mental life which can be analyzed functionally are not problematic for materialism, so my line is that, contrary to superficial appearances, qualia can actually be adequately characterized by their functional role in our minds. I propose that what is characteristic of qualia is something like what Hume called "force and vivacity"; their tendency to bring associated ideas to mind, and enliven ideas in the sense of making them more believed or plausible.
First, some of the reasons for thinking this could be the place to look to understand qualia. There does seem to be a connection between phenomenal experiences and something like Humean vivacity. The psychologists Nisbett and Ross report, on the basis of a wide variety of studies, that people's beliefs are much more heavily influenced by what they call "vivid" evidence, which usually involves some kind of experience or detailed imagining (sometimes literally vivid personal observations or photographs), than by objectively much more informative evidence presented in a non-vivid form (e. g. statistical data).
Furthermore, when there is more than one path to the same vivacious awareness, we don't seem to distinguish different associated qualia. It seems clear to me that perceptions of distance have a phenomenal feel to them, but we cannot tell introspectively whether something we observe seems distant because of binocular vision, focus, perspective, or any of the other clues our perceptual systems integrate into our depth perception (if we could, it would be easier to see through depth illusions, as we'd be aware of the various conflicting evidence present in such cases, instead of just having a seeming as if the most powerfully active of the clues were right).
Conversely, mental activity with a high level of vivacity is inevitably associated with phenomenal feels. The products of reasoning are, sadly, lacking in vivacity most of the time, but when reasoning is particularly clear and well-understood, it seems almost universal for people to start employing metaphors with the phenomenal; the skilled mathematician or logician almost always "sees" the truth of some striking theorem.
So, what are the obvious problems with equating phenomenal content with vivacity? Obviously, I can think of some lines of objection myself (and lines of response to those objections), but I'm curious as to where others think this goes astray.