Hacker News Reader

Comment by joe_the_user | Hacker News Reader

It seems like basic materialism to claim that the brain could be simulated by a large enough Turing machine. But that claim would not necessarily imply that a Turing machine is a useful model for brain. A Turing machine isn't necessarily even used as the working model of a computer though it conceivably could be.

Edit: My comment is basically asking what saying "the mind is a Turing machine" really means. It seems like the main implication someone would take away from that statement is that it's reasonably practical to describe mental processes with a computer but given that the question is formulated as a binary is/is-not. The mind "is" a Turing machine given ordinary physics which I believe say everything can be approximated by a large enough Turing machine. But this sense of "is" doesn't imply the Turing machine mind model is useful.

View on HN

Nobody claims that Turing machines in particular are well-suited to the task. What we claim is something more open-ended: Turing-complete languages can simulate each other given a universal encoding (a program we typically call an "emulator") and the simulation is only polynomially slower and larger.

To the details: We don't want just one tape on the Turing machine. It's fine but slow, like using unary Church numerals instead of binary Cantor numerals. We usually assume at least two tapes. Similarly, we often ignore tapes and use a random-access memory instead.

Edit: I guess that this is how we're talking today? From the article:

> It is common to summarize CCTM through the slogan “the mind is a Turing machine”. This slogan is also somewhat misleading, because no one regards Turing’s precise formalism as a plausible model of mental activity. The formalism seems too restrictive in several ways.

The article then lists senses, finite memory, concurrency, and determinism as four ways in which the brain might differ from idealized Turing machines.

Finite memory just means a limited subset of what a Turing machine can do.

Concurrency doesn't make Turing computable processes capable of anything beyond what they can already do. At best it buys them speed, maybe some expressiveness for the programmer, and bugs.

Nondeterminism is useful for some algorithms but it also doesn't make it possible for Turing computable processes to go beyond Turing computability. See for example https://arxiv.org/pdf/cs/0401019.pdf.

The most interesting item in that list would be the senses of organisms, as some of those might indeed involve processes that are not computable.

Also, some aspects of the brain's activity may not be computable. See Roger Penrose's books for details, such as p. 377 of Shadows of the Mind (a section about possible noncomputability in some physical processes).

Nobody claims that Turing machines in particular are well-suited to the task. What we claim is something more open-ended: Turing-complete languages can simulate each other given a universal encoding (a program we typically call an "emulator") and the simulation is only polynomially slower and larger.

Well, that's the Church-Turing Thesis, which most people accept but isn't being discussed by me or the OP - the topic being "theories of the mind", I think.

I'm still reading through the paper/article, but a Turing machine would be the substrate in this case, not the model. I think the question is whether we can model the brain's way of computing in a Turing machine, and then it will follow we can also model the brain. Turing machines are a model of computation, and if the brain's computational model is Turing complete, it will follow that we can simulate a brain inside a Turing machine.

> if the brain's computational model is Turing complete, it will follow that we can simulate a brain inside a Turing machine

I don't believe this is correct. If the brain's model/the brain itself is Turing-complete, that doesn't mean a Turing machine can simulate; it means that the brain's model can simulate any Turing machine qua Turing machine. This does not imply the reverse, that any Turing machine can simulate it.

I think a Turing Machine is an infinite state automaton with the capability that you can remotely access state information. [1]

Maybe someone can clarify whether this is correct.

If you phrase it that way, then it seems more intuitive that the brain could be described as a Turing machine. The definition of a Turing machine is deceivingly simple and cause us to question what we perceive of as complex. The transition function (and the tape) actually make magic happen if you compare it to any "dumb" mechanical or electrical device.

This is correct w.r.t the formalization of Minsky.

Further, there is a conflation among models and implementation from the parent commenter. Minsky propounds in his automaton theory that a machine may be implemented in any way and it is only its formal history of signals and responses to states which determine the machine. In this sense a biological machine made of organic bases can be considered the same to that of gears and another of semi-conducting transistors assuming their states are described by the same histories.

More so, in the same automaton theory any environment which interacts with a machine in itself must be a machine by symmetry. The classification of each is arbitrary for consideration of the states you’re interested in.

The author of the article remains correct as we must be able to model at least one faculty of the mind as Turing complete because we can also compute by the nature of computation itself. This remains useful as then we can project the guarantees of a Universal Turing machine onto that specific faculty of the mind which is Turing complete. This then allows us to explore those novel guarantees of the mind, those which are also of the Universal Turing Machine since by that faculty having the properties of UTM, it is to be considered a UTM, as opposed to having no guarantees.

[1] https://en.wikipedia.org/wiki/Finite-state_machine

It might seem like basic materialism, but a lot of philosophers suddenly loose their simple and clear-cut ontological stance as soon as the mind gets involved.

>> Edit: My comment is basically asking what saying "the mind is a Turing machine" really means.

The article clarifies that "the mind is a Turing machine" is not what the Classic Computational Theory of Mind claims. See section 3 "The classical computational theory of mind":

https://plato.stanford.edu/entries/computational-mind/#ClaCo...

To summarise, the article suggests that, while: "It is common to describe CCTM as embodying “the computer metaphor”. This description is doubly misleading." (first because nobody claims that the mind is a computer and second because the comparison to Turing machines is not a metaphor).

The article concludes that: "CCTM claims that mental activity is “Turing-style computation” [snipped for relevance]".

In short, nobody really claims that the mind is a computer, a digital computer, a Turing machine, a metaphorical Turing machine, etc etc. The idea, if I'm not misrepresenting it myself, is that the mind can think like Turing machines can compute.

> Edit: My comment is basically asking what saying "the mind is a Turing machine" really means.

It means that if we internalise this idea we can use all the language we have developed to say precise things about computers/software/hardware to also say precise things about our minds.

After all “computer” was a human job description...

All descriptions (theories) are, fundamentally symbolic/linguistic.

Are you absolutely convinced that you can build a sentient mind out of clockwork parts?

Because that's what your interpretation of basic materialism implies.

Clockwork parts? No. Parts that select from a combination of inputs? Yes.

Computability theory demands repeated combination/selection and memory. It doesn’t otherwise care how this is accomplished.

In principle? No question.

In practice? No chance.

How would a clockwork model of the mind explain the phenomenon of consciousness (as opposed to computation)?

The idea is that consciousness is what a planning algorithm feels like from the inside. A planning algorithm requires representations of the entities relevant to planning, e.g. various objects in the world, relevant laws, internal states such as emotions, motivations, etc. It is these representations from an internal perspective that have something it is like to have them. But the fact that this planning algorithm is constructed out of mechanical components is irrelevant.

Computation is just an abstract description of the behavior of some classes of systems. But it doesn't exhaust the set of possible descriptions for a system. Some subset of computational systems might also have a description in terms of consciousness.

Your apparent consciousness is the illusion of control over your subconscious mind.

Your comment makes more sense if we replace “useful” with “practical”

Reply on news.ycombinator.com