I am not a computer
- Shadows of the Mind: A Search for the Missing Science of Consciousness by Roger Penrose
Vintage, 457 pp, £17.99, September 1995, ISBN 0 09 958211 2
Years ago, a colleague of limited intellectual powers accosted me with the charge that I had been telling students that the ‘mind was meat’. This was my colleague’s way of putting things. I then fell for the question which the charge led up to: ‘So you’re a materialist?’ ‘Yes,’ I answered. To which my normally witless interlocutor responded: ‘Pray tell, what is the nature of the material world?’
Witless was right. We naturalists don’t remotely understand what makes up the world, let alone the world itself. Our materialism is promissory. If the world can be explained, it can be done without introducing non-natural or supernatural properties, phenomena or processes. But what principles demarcate natural properties, phenomena and processes from those too weird to be natural is not something that is much discussed, let alone agreed on. Whoever calls for a ‘deeper physicalism’, whether it be Witless or a leading mathematical physicist like Roger Penrose has got to be right. Deep physicalists look to biology, chemistry and physics for depth. They are sceptics – and rightly – about the resources of both a priori philosophy of mind and computer science to explain nature and mind.
Computationalism continues to grip the academic and popular imaginations, however. A recent issue of the New York Times led its science section with an article called ‘The Brain Manages Happiness and Sadness in Different Centres.’ Immediately beneath the first paragraphs of text were pictures of PET scans showing the different areas of the brain that are active when people are happy or sad. The pictures were introduced in large, boldface type with this headline: ‘How the Brain Computes Tears and Laughter.’
This might seem innocuous, but if so, it can only be because talk of the brain computing things is the dominant way of speaking about the mind. But in this case, at least, the pictures decidedly did not show the brain computing anything, let alone tears and laughter. What PET scans show are blood-flow patterns. So what the pictures showed were areas where blood flows; and thus oxygen, and thus, we presume, activity, were increased or decreased. The maps were correlated with phenomenological reports of the relevant feelings, and the plausible inference that such and such areas of the brain are importantly implicated in the relevant emotions is made. Nothing was revealed, however, about how anything was being computed.
Why do we speak this way? The simple answer is because the computer is the dominant metaphor for mind. For Penrose it is a metaphor which has overstepped its bounds. We forget that it is a metaphor, and take the claim literally, so that the mind/brain is a computer. Colin McGinn calls this view ‘pan-computationalism’. In its most extreme version the universe becomes a computer, whose parts run their own particular programs or sub-routines.
Penrose defines computation as the action of a Turing machine, a perfectly idealised computer, and takes ‘algorithm’ to be completely synonymous with ‘computation’. The appeal of ‘pan-computationalism’ comes both from the success of computer modelling across disciplines and from the construction of machines which display ‘intelligence’. But just because we can model chemical reactions, photosynthesis, genetic transmissions, the weather and so on, computationally, it seems absurd to say that any of these things are computers or the computational children of the mother of all computers, the universe.