[Comp-neuro] The sniffing brain - and free will

Bryan Bishop kanzure at gmail.com
Tue Aug 26 07:47:51 CEST 2008


On Friday 15 August 2008, Asim Roy wrote:
> This is very insightful. If I understand you correctly, you are
> saying that the brain has nothing to do with "learning" as is
> generally understood by most in these fields. And you could be right
> on this. I am not questioning the theory. However, the traditional
> belief is that "much" of the brain comes as a blank slate ("tabula

Yes, but what is a "blank slate" in this context? Traditionally it 
implies that it is something that could be written on, as easily as I 
write characters on tty7. But we can hardly paint on dendrites so 
analogously.

> rasa"). And that "learning" implies writing to the slate. I hope you

There's a few too many layers of folk psychology here, I suspect. 
Writing to the slate might mean the simple stimulation you're providing 
via simulation of action potentials and the synaptic dynamics. But 
traditionally writing to the slate would mean "knowledge", which --

> are not contesting the "tabula rasa" idea. If you contest the "tabula
> rasa" idea, you are claiming that all knowledge comes predefined and
> prewired and that might be a hard thing to prove.

Yeah, so you're trying to make a direct connection between "writing to 
the brain" via experience/stimulation, to "knowledge" which is not 
something I've seen an information theoretic analyses wrt the brain on. 
You're trying to go full circle (your working, conscious conception 
of "knowledge") to connect it back to the neurobiological reality 
(however it's actually done in the brain) and if you had that then 
you're already done, no? How do you know that "knowledge" is the right 
idea/heuristic? And so on.

> >From what I read, you are questioning the idea that the "brain" is
> > somehow  "free" to design a special type of network (e.g. a
> > multilayer network) to solve some "odd unknown problem" - e.g. to

Special in a graph theory sense? Violating rules of plasticity? I don't 
understand.

> > learn mathematics or music or a language. You can obviously prove
> > this part of your theory by showing that certain standard network
> > structures, the ones that are actually found in biological systems
> > (say in the olfactory system), can solve other types of odd unknown
> > problems too, such as learning mathematics, music or a language.

That smells more like a hack of a use of neurons than anything else. 
While I can write an ANN to play chess, this is hardly evidence that 
the real things are meant to play chess. In fact, ironically, Wikipedia 
says the function of a neural network is, I quote, "given a specific 
task to solve, and a class of functions F, learning means using a set 
of observations, in order to find f^* \in F which solves the task in 
an /optimal/ sense." [[Personally, I'm investigating the origins 
of 'optimal', in the sense of computer science (compiler optimization 
strategies) and, one of the reasons why I'm here*, computational 
neuroscience.]]

* besides compulsive mailing list reading:
http://heybryan.org/mailing_lists.html

> > That way, you can be consistent with the "tabula rasa" idea and say
> > that "learning" is just adjusting some very standard structures
> > found in our brains. I would venture to say that if you can do
> > that, that would be a huge step forward for this field because you
> > have simplified the "learning" task. But contesting the "tabula
> > rasa" idea itself might be a bit difficult.

It's difficult because the /context/ of the tabula rasa. It's not 
whether or not the brain receives inputs from outside the system, but 
the folk psychology attached to the idea of "upload knowledge here -- 
press button to continue". It doesn't seem to be that way. 

There's some literature worth citing here that I am completely 
neglecting.

> b) -- the question of what we already "know" and how it governs our
> behavior, or even the extent to which what looks like 'learning'
> might actually be a different fixed read out, with changing context,
> is seldom considered by computational neurobiologists, or the neural
> network community.

And what about the wet experimentalists?

> c) Experimental evidence that the olfactory system might "know" a
> great deal about bio-metabolism is also only published in thesis form

Do the genetic regulatory networks (GRNs) constitute 'knowing' in the 
olfactory system? Just wondering.

- Bryan
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