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In this article, about an unfinished book by von Neumann (he died in 1957 before he could finish it), one can read:

After stating that he himself is neither a neurologist nor a psychiatrist, but a mathematician, Von Neumann embarks upon the first part of this essay by explaining the components of a computer in the language of a computer scientist. First, the difference between analog and digital computers is explained. This distinction will have some relevance for the discussion of the brain because—as stated in the second part—the brain can prima facie be considered as a digital computer. However, upon further reflection, some elements of analog computing (e.g., the chemistry) will also become relevant in understanding the functioning of the brain.

Is he saying the brain is an analogue computer? What does he even mean with that?

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  • $\begingroup$ Can you come up with an argument to justify the opposite (the brain being a digital computer)? $\endgroup$
    – Mauricio
    Aug 10 '21 at 16:59
  • $\begingroup$ @RodrigodeAzevedo I think the brain is only an analod computer. But thats not the question. I wanna know what von Neumann's thoughts on this are. $\endgroup$ Aug 10 '21 at 18:49
  • $\begingroup$ @Mauricio No. The brain is an analoge computer. Thats why I was surprised. $\endgroup$ Aug 10 '21 at 18:50
  • $\begingroup$ No, he is saying it is primarily a digital computer with analog elements mixed in, an analog–digital hybrid. Isn't "the brain can prima facie be considered as a digital computer. However, upon further reflection, some elements of analog computing (e.g., the chemistry) will also become relevant" clear enough? $\endgroup$
    – Conifold
    Aug 10 '21 at 22:24
  • $\begingroup$ @Conifold No. Thats why I asked. Isnt the whole brain chemistry? So all analog? Pulse conduction, etc. $\endgroup$ Aug 10 '21 at 22:38
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Von Neumann makes the distinction between chemistry and, well, non-chemistry. In fact, the whole brain is chemistry. There are no power sources like that of a digital computer. All power is inherent to the processes. There is no external source pushing the events. Nor is there an external program. The fact that there are pulsed currents is the only reason he makes the comparison with digital computers. It looks as if zeros and ones are manipulated. In a digital cimputer though the ones and zeros are, again, pushed by external potentials. Declaring himself to be no expert on neurons it is understandable he makes the comparison. The spikey potentials in the brain run completely different though from those in a computer.

I read in a comment:

It doesn't matter what it is, it matters how it functions. Digital and analog computers function differently, but can be combined.

This comment shows the same naive view. The processes in the brain all function differently from a digital computer. The brain fuctions like an analog computer as a whole. An analog of external processes in the external world is internally given form inside huge chemical processes. Huge numbers of neurons play in concert to internally form representations of the world outside. Von Neumann came close. His genius had not enough knowledge of the brain to extend the notion of an analog computer to the whole brain.

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