Mark O’Brien gives a good statement of the computationalist case here; clear, brief, and commendably mild and dispassionate. My impression is that enthusiasm for computationalism – approximately, the belief that human thought is essentially computational in nature – is not what it was. It’s not that computationalists lost the argument, it’s more that the robots failed to come through. What AI research delivered has so far been, in this respect, much less than the optimists had hoped.
Anyway O’Brien’s case rests on two assumptions:
- Naturalism is true.
- The laws of physics are computable, that is, any physical process can be simulated to any desired degree of precision by a computer.
It’s immediately clear where he’s going. T0 represent it crudely, the intuition here is that naturalism means the world ultimately consists of physical processes, any physical process can run on a computer, ergo anything in the world can run on a computer, ergo it must be possible to run consciousness on a computer.
There’s an awful lot packed into those two assumptions. O’Brien tackles one issue with the idea of simulation: namely that simulating something isn’t doing it for real. A simulated rainstorm doesn’t make us wet. His answer is that simulation doesn’t produce physical realities, but it does seem to work for abstract things. I think this is basically right. If we simulate a flight to Paris, we don’t end up there; but the route calculated by the program is the actual route; it makes no sense to say it’s only a simulated route, because it’s actually identical with the one we should use if we really went to Paris. So the power of simulation is greater for informational entities than for physical ones, and it’s not unreasonable to suggest that consciousness seems more like a matter of information than of material stuff.
There’s a deeper point, though. To simulate is not to reproduce: a simulation is the reproduction of the relevant aspects of the thing simulated. It’s implied that some features of the thing simulated are left out, ones that don’t matter. That’s why we get the different results for our Parisian exercise: the simulation necessarily leaves our actual physical locations untouched; those are irrelevant when it comes to describing the route, but essential when it comes to actually visiting Paris.
The problem is we don’t know which properties are relevant to consciousness, and to assume they are the kind of thing handled by computation simply begs the question. It can’t be assumed without an argument that physical properties are irrelevant here: John Searle and Roger Penrose in different ways both assert that they are of the essence. Even if consciousness doesn’t rely quite so brutally as that on the physical nature of the brain, we need to start with a knowledge of how consciousness works. Otherwise, we can’t tell whether we’ve got the right properties in our simulation – even if they are in principle computational.
I don’t myself think Searle or Penrose are right: but I think it’s quite likely that the causal relationships in cognitive processes are the kind of essential thing a simulation would have to incorporate. This is a serious problem because there are reasons to think computer simulations never reproduce the causal relationships intact. In my brain event A causes event B and that’s all there is to it: in a computer, there’s always a script involved. At its worst what we get is a program that holds up flag A to represent event A and then flag B to represent event B: but the causality is mediated through the program. It seems to me this might well be a real issue.
O’Brien tackles another of Searle’s arguments: that you can’t get semantics from syntax: ie, you can’t deal with meanings just by manipulating digits. O’Brien’s strategy here is to assume a robot that behaves pretty much the way I do: does it have beliefs? It says it does, and it behaves as if it did. Perhaps we’re not willing to concede that those are real beliefs: OK, let’s call them beliefs*. On examination it turns out that the differences between beliefs and beliefs* are nugatory: so on gorunds of parsimony if nothing else we should assume they are the same.
The snag here is that there are no robots that behave the way I do. We’ve had sixty years of failure since Turing: you can’t just have it as an assumption that our robot pals are self-evidently achievable (alas). We know that human beings, when they do translation for example, extract meanings and then put the meanings into other words, whereas the most successful translation programs avoid meanings altogether and simply swap text strings for text strings according to a kind of mighty look-up table.
That kind of strategy won’t work when dealing with the formless complexity of the real world: you run into the analogues of the Frame Problem or you just don’t get really started. It doesn’t even work that well for language: we know now that human understanding of language relies on pragmatic Gricean implicatures, and no-one can formalise those.
Finally O’Brien turns to qualia, and here I agree with him on the broad picture. He describes some of the severe difficulties around qualia and says, rightly I think, that in the end it comes down to competing intuitions. All the arguments for qualia are essentially thought experiments: if we want, we can just say ‘no’ to all of them (as Dennett and the Churchlands, for example, do). O’Brien makes a kind of zombie argument: my zombie twin, who lacks qualia but resembles me in all other respects, would claim to have qualia and would talk about them just the way we do. So the explanation for talk about qualia is not qualia themselves: given that, there’s no reason to think we ourselves have them.
Up to a point: but we get the conclusion that my zombie twin talks about qualia purely ex hypothesi: it’s just specified. It’s not an explanation, and I think that’s what we really need to be in a position to dismiss the strong introspective sense most people have that qualia exist. If we could actually explain what makes the Twin talk about qualia, we’d be in a much better position.
So I mostly disagree, but I salute O’Brien’s exposition, which is really helpful.