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Comment by linschn | Hacker News Reader

The only serious counter-argument I've heard against the hypothesis that the brain goes further than a Turing machine is that the brain does not implement an algorithm, with one input, some processing steps, and one output.

Instead, it processes information as it comes, this information comes during the processing of previous information and the output partly loops back to the input. Short-circuits everywhere, no clock, etc. I'm unconvinced but I could not refute the argument formally.

Note that this does not contradict the Church-Turing Hypothesis : if you restrict the brain to one input, some processing steps with a pen and paper without arrival of new information, and an output, then it is very possible that the brain can only work out Turing-computable problems.

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'information comes during the processing of previous information and the output partly loops back to the input"

Computers do this all the time. Simplest example is "cancel" button everywhere.

The point is that out definition of the computability of a function is too narrow, and does not take into account the real-time all connected nature of the computation the brain does.

Therefore, we lack formal way of satisfactorily compare the brain to a Turing Machine.

I don't see why. Your computer reacts to keyboard and mouse in the real time, also for network packets going in and out. And it's plain turing machine. It does so by regarding every input as they become available, one by one.

Information comes to brain via neurons, and those have finite speed, it's not as they had quantum-like properties. Signal in; signal out, with delay and altered magnitude.

The important word is : formal.

I, too, think that the brain is 'a computer'. But the formal definitions of computation we have today require the computer to be left alone for some time between the moment the input is given and the moment the output is due. The brain does not work like that, ergo we lack a formal model of how the brain operates, and thus the definition of 'computable function' -which is based on our model of computation- is less general than what the brain can do.

e.g. We have no proof that the only way neurons communicate with one another is via the synapses.

Brain, too, needs some time to react to any incoming event.

I fail to capture the difference.

I don't think that we are in the territory of having that argument at all to be honest. We don't know what the processes that the brain self evidently generates are - for example Intelligence, Consciousness. It isn't possible to discuss how these are executed (or not, depending) until we have some understanding of what they really are.

And we don't, and worse, we may not ever have access to these concepts, as Hofstadter and others have argued. It may not be possible to represent the idea of ideas in an idea.

That of which we cannot speak that thereof we must remain silent, or something.

> The only serious counter-argument I've heard against the hypothesis that the brain goes further than a Turing machine

I'm confused... is the counter-argument AGAINST the brain being BEYOND a Turing machine (if I am to interpret your sentence literally)?

Or by this double negative do you actually mean the counter argument is AGAINST the brain being ONLY a Turing machine? (Because that's what the rest of your post sounds like.)

> and the output partly loops back to the input.

So? Turing machines have no issues with feedback loops; what would lead you to think they do?

The counter argument to the CT hypothesis, i.e. the argument against, sorry for my ambiguous phrasing.

I'm a dualist but for the sake of argument, one approach is to claim that however the brain functions, it should be explainable by physics, and if physics is computable, then it should in principle be simulable by a Turing Machine.

The question of whether physics is computable is a fascinating one I'd really like to see solved before I die.

Physics is most probably computable, since people created it; the real question is whether the world is (Turing) computable, and from my point of view it is clearly not. I find it remarkable that most people believe it is or that it might be.

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