Illusions and Zombies

Joshua at Blogosophy links to a really cool optical illusion, and offers some interesting commentary besides:

I think this kind of thing really undermines the plausibility argument for "zombies" (creatures indistinguishable from humans, but who lack qualia)--and plausibility is the only argument there is that it's a coherent notion. We think that we can imagine seeing the color red but having a completely different (in some hard-to-specify sense) feeling of what it's like to see red than someone else who also sees that color and tells us "yep, that's red." From this the argument goes that it's conceivable that someone could say "that's red" whenever we would, but who has nothing that it feels like to see red; there's just a bunch of nerves firing and chemicals changing, but nothing subjective going on. And if it's conceivable, so it is said, then it's possible.

I think, though, that it's harder (maybe even impossible) to imagine a zombie being fooled by this optical illusion; the illusion is, after all, precisely that you're losing the sense of what it is to feel like you're seeing one or more of the yellow dots, even though physically the photons are still hitting your eyes, the nerves are firing, etc. The lights are on, but you're intermittently not home to Mr. Yellow-dot Qualia. Is it conceivable that the zombie sees but isn't really aware of seeing the yellow dot, and also sees but isn't really aware of not seeing the yellow dot, and yet somehow still can distinguish objectively between the two states (so it can describe the illusion) just like someone with a mind? Or does your brain seize up in a kind of concept induced blindness trying to picture it?

I'm not entirely sure that I find his line of reasoning convincing however. It seems to me that any qualia-less 'zombie' would still have a sort of conscious/sub-conscious division to his mind. But by 'conscious' here it is only meant to refer to what information is available (i.e. directly accessible) to the central processing module (to use a computing analogy) of his mind. It is important to note that this is a distinct matter from whether phenomenological 'conscious experiences' (qualia) occur.

Given this distinction, it strikes me as entirely plausible that a 'zombie' could have sensory appartus detect the yellow dots, and yet have this information restricted to the lower sub-modules of his mind, so his central module would be entirely unaware of it. Thus a zombie could be just as fooled by the illusion as us, without any need for qualia.

P.S. For any readers with a basic knowledge of computer science, you may find it easier to follow this argument if you imagine a robot, with a specific function responsible for the parsing of perceptual input. This function would pick up all the raw data (including the light from the yellow dots), but the complicated parsing algorithm - fooled by the illusion - may fail to correctly interpret the raw data. Thus, when a different function (say, the speech one, if we want the robot to tell us what it sees) refers to this interpreted data, it will be unaware of any yellow dots.

So, yeah... it seems entirely plausible that a simple robot (let alone a full-blown zombie!) could be fooled by such illusions.