Thanks to Thoughts, Arguments and Rants for the link
Anyway, the central point to note is that any simple robot (as could be built today), could easily have 'hidden' information (e.g. raw visual data) which is not made available to its other decision-procedures. That is, its camera would capture the photons (same as our eyes)... but the interpreting algorithm could be fooled into not noticing any yellow dots (same as our brain).
The thing about Zombies, though, is that they do considerably more than this robot; by posit, they are indistinguishable from human beings in their behavior. This means that Zombies not only have to be fooled by the illusion, but to notice that it is an illusion, and to say "Neat!" So more is going on than just the information getting hidden by a sub-system (which is presumably what it happening even in humans); there also has to be an ability to note and act on the fact that not only that certain information is present to the decision procedures but that other information ought to be present but is not (which requires not only a model of the world, but a model of your "mental states"), to infer that the reason this is so is due to an optical illusion and not some other kind of failure (Zombies don't look at it and say, "Augh! I've gone partially blind!") and to decide, despite the absence of anything subjective going on, to express a faux-emotional reaction: "that's cool."
Perhaps that's still easy to picture (I don't really find it so, but I may be deficient in this regard).
Suppose we flip it around, though. According to the logic underlying the Zombie hypothesis, if it's conceivable, then it's possible. Isn't it conceivable that the simple robot has qualia? After all, in the Zombie hypothesis qualia don't attach to a mental state by virtue of the behavior that state induces, not even the behavior of being able to note and act on that mental state, nor are qualia the cause of any mental state. (If they were, then there would in principle be some way of distinguishing Zombies from Realies.) Is there a reason that it's inconceivable that the robot that falls for the Motion Induced Blindness illusion has qualia as it does so? If not, then there is a possible world where such robots do have qualia...but if a robot, why not a rock? Can we imagine that there's something that it's like to be a rock?
I am a rock,
I am an island,
and a rock feels no pain,
and an island never cries
It might be that the Zombie proponents would say, "Sure. That proves that consciousness has nothing to do with that lump of meat in your head." I'll stick with my brain, though. I'm very fond of it, you know. We grew up together.
You could slice it another way, as well. Imagine that there are some beings who have qualia, just as we do, but they don't experience emotions the way we do. Call them Vulcans. Unlike people who actually don't experience emotions (such people really exist), and unlike Star Trek Vulcans, these Vulcans are indistinguishable in their behavior from normal people (Feelies). They laugh, they cry, when asked why they laugh or cry they give perfectly consistent and lucid explanations of their behavior in terms of emotions, their physiology changes exactly as humans do in the grip of emotions (bloodpressure, galvanic skin response, etc.)...they have all the normal sensory qualia, but they don't actually have any emotional qualia.
Is this conceivable? If Zombies are conceivable, then Vulcans certainly are.
Have we just proved that the soul, or whatever metaphysical thing provides the qualia, is bipartite, and the question of having sensory qualia is completely distinct from having emotional qualia? Seems so. Whatever "the answer" is to how people can have qualia, it's possible (in the Zombie-possibility sense) to have an entity in that same situation who's a Vulcan.
Why stop there? Is it conceivable that the qualia of thinking are severable from the qualia of perceiving and emoting? What about specific sensory qualia? Can you imagine an entity who has qualia when perceiving visually, but is a Zombie when it comes to auditory perception? What about one who is a Feelie with respect to all emotions except, say, lust, where he's a Vulcan? (Note that he would still act as if he experienced lust, he just would have no lust qualia; it's not the same as having no sex-drive.) I'm reminded of Daffy Duck, who once explained, "I'm different from other people. Pain hurts me." What about someone who is only a Zombie part-time...say every other day. Does that prove the detachability of souls (or whatever)? Or does it prove a new type of metaphysical entity: the every-other-day-qualia-inducer?
It seems like you can multiply the necessary metaphysical entities to explain qualia endlessly. The conceivable => possible argument is an anti-Occam's Razor.
What I'm really arguing is that what's imaginable or conceivable is a really loose constraint if it's wide enough to admit Zombies, and so by imagining Zombies the Zombie-hypothesizers haven't really proved anything possible--let alone proved that there must be something metaphysically or spiritually other going on in our brains or we wouldn't have qualia.
I'm now A Wiggly Worm. Woohoo!
There's some interesting back and forth at The Panda's Thumb about the TTLB ecosystem rankings, and whether the "progress" that higher rankings in TTLB represent is antithetical to the proper understanding of the evolutionary relationship of organisms. I think that some of the people, in order to deny teleology in evolution, are bending over backward too far in denying that there's anything interesting going on at all in terms of complexity and specialization over time. There's a pretty strong sense in which organism A is "more evolved" than organism B if organism A could be the decendant of organism B, but not vice-versa, and I think that sense carries over to organisms C and D where C is a descendant of A that shares the features that make A later than B and D is a descendant of B that lacks those features, even if C and D are both equally removed in time from A and B. Evolution is a tree, not a field of grass, and time's arrow is stamped all over organisms if you know how to look. That doesn't mean that more evolved is somehow better in some moral sense, or even in terms of fitness, any more than having a lot of inbound links (the measure in TLBB rankings) makes a blog better or even more "fit" in the blogosphere.
I suppose it depends on whether you're buying or selling.
% increase in average suggested retail price of a scholarly book 1989-2000,
commercial scholarly presses: 23
% increase in average suggested retail price of a philosopy book 1989-2000, commercial scholarly presses: 120
A new philosophy blog, by "Richard." His comments on my recent optical illusion post are well worth reading.