ust be rich with meaningful information
In fact, the question of whether computation involves meaningful representation can bear on the question of what it is for a system to ‘normally perform’ a computation. If the Arabic numerals ‘1’, ‘2’, ‘3’, … represent the numbers one, two, three and so on, and if some machine or organism takes any two of those numerals and typically churns out a numeral denoting its sum, then there’s good reason to think that this thing normally performs addition, even if it occasionally hiccups out the wrong sum when it is tired or distracted. If the system is just swishing around meaningless symbols, it is much more difficult to say what should determine that the system normally performs one computation rather than another one.
Many have thought that computation must involve meaningful representation or information. Far from saying that we are meaningless machines, the claim that our brains are computers would require that our mental lives are rich with meaningful information. Yet if computation requires giving meaningful answers to meaningful problems then, in order to say what it would be for the brain to be a computer, one must also say what it would be for activity in the brain to be meaningful. One difficult question begging another. There are a number of dissenting and intermediate positions about whether computations must be meaningful.
It’s not so clear that there is any single answer to what a computer is. Computation might not be a uniform kind of thing in nature. Many things are said to compute: household PCs, analogue machines, looms, brains and even DNA and quantum-mechanical systems. These are quite different pieces of nature (or, in the case of PCs, looms and analogue machines, human artifice – itself a piece of nature). What it is for one sort of thing to compute might turn out to be quite different from what it is for another sort of thing to compute. The features of a Navy fire-control system that make it distinctively computational might differ from the features of the brain that make it distinctively computational. It gets worse: the features of single neurons or networks of neurons that make them distinctively computational might differ from the more high-level features of our mental capacities – our abilities to perceive the direction of a sound source or the depth of a surface – that make those capacities distinctively computational.
There is just no consensus on what it is to be a computation or for a piece of nature to perform a computation. Neither question might have a general answer. The common claim that the brain is a computer is not, at the moment, a concrete, precise, well-understood scientific hypothesis.
Still, the claim is almost certainly true.
Earlier I said that the cognitive sciences are full of concrete, well-understood hypotheses that the brain computes such-and-such in so-and-so way. Now I am saying that the claim that the brain computes is not a concrete, well-understood hypothesis. Worse, I am still insisting that the claim is almost certainly true. Bananas?
The concrete, well-understood hypotheses are the specific hypotheses that the brain performs specific computations. Many of these hypotheses have lots of evidence. Each of these specific hypotheses entails that the general claim that the brain computes, full stop, must be true. (Note: they do not imply that the brain only computes! It certainly does other things.) The thing is, none of this means that the general claim that the brain computes is itself a concrete and well-understood hypothesis. The hypothesis that the brain computes X can yield testable predictions and insightful explanations. The claim that the brain computes, full stop, doesn’t on its own do much predicting or explaining at all – or at least, I suspect, not nearly so much as is advertised.
Many research articles begin, in the introduction, with: ‘We are interested in whether the brain computes X,’ and then: ‘If it does compute X, then upon conducting such-and-such experiment we should see this-or-that result.’ And while scientist