[Beowulf] Go-playing machines

Robert G. Brown rgb at phy.duke.edu
Wed Jun 25 13:28:23 EDT 2008


On Wed, 25 Jun 2008, Vincent Diepeveen wrote:

> His answer was very surprising (apologies to not know the English word for
> it) that the central part at where all the brain cells connect to, is at far 
> higher
> speed than what i assumed it is taking decisions. Something in the order
> of 200 kHz to 400 Mhz. The thing unknown in how it exactly works to 
> researchers
> is this high speed central nerve system.

????

I'm deeply, deeply skeptical.  The rate of synapse firing is well known
and long since measured.  However, many synapses fire in parallel --
webs of cascading fires ripple around all the time.  The aggregate rate
of synapse firing may well be very high, then, but the clock per synapse
very low (and synapses do other odd things, like saturate if you drive
it too hard, get "tired", and so on).

> Thousands of times faster than i assumed it worked at, which was my big 
> surprise.
>
> If we multiply that speed by a few billion brain cells then obviously we 
> should revisit
> our idea on how the brain works. Maybe a new entry in wiki is needed for them 
> as well :)

No, you can't multiply it out.  This is already aggregated over those
hundred billion cells, each with all of those synapses.  Think about the
energetics of it.  Your brain is already using roughly 1/3 of your total
energy budget as it is.  100 billion 400 Mhz clocks, with biological
switching energies of any reasonable magnitude would cook your brain.

> So to get back on the original brain question: "how are humans doing it"
> My answer is that the majority messes up so bigtime, that it is unclear how 
> *some* are doing it.

Humans probably do it lots of ways, starting with pursuing simple trees.
The "messing up bigtime" is the people who are still trying to think
linearly, the way we are programming the computers.  Then suddenly they
gain experience, and prune 90% of the trees away from the very
beginning, and are a bit better.  Then they develop elaborate pre-pruned
trees -- a repertoire of "openings" -- and from them abstract some very
nonlinear patterns that become a mix of "intuition" that causes them to
not even glance at all the "obviously stupid" moves in any given
situation and an ability to "guess" how certain very long sequences will
play out even without working out ALL of the possibilities, and they
suddenly become a decent player.  Then they gain a lot more experience,
and can "see" very far indeed down the relevant tracks, and see enough
alternatives that they can be deceptive with people that can see less
far or who still have a flawed intuition about certain sets of tracks.

The same question applies to the Ramanujans and Riemanns.  Some people
can just "see" two numbers to know what their product is.  They don't
"compute it" by using a serial algorithm.  They don't memorize it.  They
just know.

I think that this is a really, really interesting question, BTW.  An
equally interesting one is whether or not we can "learn" this kind of
intuition, and if so what would the training/learning process look like?
Probably NOT teaching people long ways of algorithmically multiplying.
Probably NOT asking them to memorize large tables.  Something different.
We probably don't even have the right task decomposition to begin to
experiment.

    rgb

-- 
Robert G. Brown                            Phone(cell): 1-919-280-8443
Duke University Physics Dept, Box 90305
Durham, N.C. 27708-0305
Web: http://www.phy.duke.edu/~rgb
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