From: Ben Houston (ben@exocortex.org)
Date: Wed Apr 10 2002 - 17:06:07 MDT
Hey Eliezer,
Sorry for the late reply. This is exam and essay writing season. :-/
> Eliezer Yudkowsky wrote:
> Ben Houston wrote:
> > I've seen some truly amazing things done in the computational
> > pharmacology field dealing with cheap, but massive parallelization.
> > Basically, a lot of short cuts are available in the parallelization
of
> > an algorithm once you've solidified it. In order words making a
> > parallel problem solving is difficult and cost in the general case
but
> > in a specific case it can be quite cheap. The field of
computational
> > pharmacology is working with special purpose multi-teraflop machines
> > that cost less than $1,000,000 US for a year or so now.
>
> If you can run exactly the same algorithm on each of a billion pieces
of
> data with no interaction between instances of the algorithm, naturally
> parallelization is easy.
If you glanced at any of the sites or papers I referenced you wouldn't
be able to dismiss it so quickly. Basically the particular special
purpose computer I was referring to is made for QM/MM problems. These
are N-body problems in which the next state of every particle (usually
numbering at least in the millions) depends on the previous state of
every other particle. Thus these problems are about as interdependent
as possible -- and quite the opposite of what you describe above.
> One serial bottleneck is enough to render overall consciousness
serial.
> The
> human brain, having been rendered serial, is adapted as a whole to
serial
> deliberation, no matter how many subprocesses are massively parallel.
> Sequiturs may run massively parallel searches to find thoughts, but
it's
> only one thought that wins.
I guess we are just working with different terminology. I guess your
use of "the overall flow of cognition" probably can be mapped to my
concept of "specific cognitive flows".
> > >>>>>>>>>>>>>>>>>>>>>>>
> > We know it is possible to evolve a general intelligence that runs on
a
> > hundred trillion synapses with characteristic limiting speeds of
> > approximately 200 spikes per second.
> > <<<<<<<<<<<<<<<<<<<<<<<
> >
> > 200 spikes/sec is probably the median for the brain. Some neurons
I've
> > studied in my courses have upper limits around 1000 spikes/sec.
>
> Hence "approximately".
Cool stuff. :-)
> > Neglect the sensory and motor systems I believe that in the CNS 'S'
> > would be upwards of at least 5 as a result of the DAG-like
arrangements
> > of the signal processing pathways -- ignoring backwards, regulatory
> > projections.
>
> 'S' is measured with respect to signal propagation speed measured in
clock
> ticks, not the characteristic number of links. Maybe I should clarify
> this
> in the text. Or just check out Anders Sandberg's original paper.
I understood originally from your paper that a "clock tick" for the
brain was one 200th of a second. I still think that the point applies
since a chain of 4 neurons will most likely require more than 1/200th of
a second to transmit a signal. But overall I guess I find this
"brain/cognitive clock tick" concept sort of strange -- I'm probably
just boring.
> > It seems plausible that the brain uses a resonance-like compare
> > function. Basically, a match may be recognized when a neural
assembly
> > finds its group-firing greatly facilitated as a result of the
> > presented/remembered stimulus. Sort of like how a glass will
vibrate
> > when exposed to its natural resonance frequency.
>
> It's easy to postulate "resonance", and in fact, I actually did. But
you
> have to explain the specific similarity metric, before postulating
> "resonance" as "a compare/similarity/clustering operation of some
kind,
> implemented on a neural substrate using feedforward and feedback
> connections, and synaptic computing in those huge dendritic trees to
> establish long-term potentiation with the memory's proper cues" really
> says
> anything more than "a compare operation implemented in the same
hardware
> devoted to storing the memories"; everyone knows what neural hardware
> looks
> like.
I guess I wasn't trying to explain how "resonance" is realized in the
neurons but was just mentioning it as a term that you could use.
> > Actually, there is quite a collection of papers in PubMed discussing
the
> > evidence that the corticothalamic feedback projections play a role
in
> > image contrast control.
>
> Why do you need ten times as many reciprocal feedback connections as
> feedforward connections to do contrast control? I'm not saying that
there
> are no proposed explanations for the massive feedback connections or
that
> there are no known functions that require the neuroanatomical
backlink,
> just
> that the *massiveness* of the feedback connections has no *standard*
> explanation, and the greater computational complexity of feature
> controller
> structure relative to feature detector structure may have something to
do
> with it.
Well, I'm just going from the empirical evidence. I have seen some
evidence that these feedback projections play a role in modulating
contrast, low level attention, and possibly in short-term "sensory
memory". During "visual working memory" I suspect that if there is any
activation of the LGN it is only secondary to the activation of high
areas -- possibly as a result of the activation of attentional networks.
> > It is an accepted fact that working memory, both verbal and spatial,
is
> > maintained by mutual stimulation between the lateral prefrontal
cortex
> > and certain posterior association areas:
>
> The existence of working memory is an accepted fact. That working
memory
> is
> depictive is an absolutely established fact that is still not entirely
> accepted in some GOFAI circles. Whether depictive mental imagery is
> governed by the concepts that appear in our internal narrative is
another
> fight entirely.
Interesting additions... getting into this over email is really
difficult and though.
> > I'm not sure if you mentioned it but did you know that 'verbs' seems
to
> > be stored in a different brain region that 'nouns'? And that 'noun'
> > storage in the brain seems to be organized in a categorized spatial
> > manner? Neat stuff eh?
>
> Yes, I know.
I guess I only made the point because it seems in my quick reading that
the concept of "concepts" in your hierarchy had become somewhat
homogeneous. This concern is probably minor though.
> I'm afraid I didn't have room to mention, in the section on
> coevolution of thought and language, how cognitive selection pressures
for
> different treatment of verbs and nouns based on the different
perceptual
> structure of verbs and nouns could be responsible for the emergent
> existence
> of Chomskian deep grammar before its evolutionary fixation - as
Terrence
> Deacon points out, the evolutionary emergence of Chomskian grammar
from
> strictly linguistic selection pressures is a puzzle because Chomskian
> grammar has so many different surface forms; you would expect purely
> linguistic selection pressures to fix the computationally simpler
surface
> structures first. But now I'm saying things that don't make any sense
> unless you've read Deacon's "The Symbolic Species" as well as DGI, so
I'd
> better shut up.
I enjoyed Deacon's stuff as well. :-) I choose to review Deacon's book,
M Donald's "Origins of the Modern Mind" and W Calvin's "How the Brain
Things" for one of my core cognitive sciences courses back in early
2000. Although, I found Deacon's work was worthwhile and interesting I
found I preferred Donald's work.
> > In your section on "thought" why don't you mention the cognitive
> > psychology construct of "working memory"? You seem to describe its
two
> > part structure perfectly: (1) phonological loop and (2) visuospatial
> > sketchpad.
>
> There are a thousand things that DGI does not mention, so don't feel
> slighted just because some of your favorite things were left out...
I mention it because it seemed so central to your sections on "thought"
and "deliberation." It is a very hot topic (if not the hottest) in
cognitive neuroscience with over +500 papers published on the topic in
last year.
Recently, I've been researching on my own time how the VTA and the NAc
interact with the PFC (and vice versa) in the modulation of attention in
regards to the perception of rewards or the expectation of reward.
Haven't gotten too far but this system seems like it may play a central
role in both "deliberation" and "thought".
> As it
> happens, though, the phonological loop in working memory is just the
> prefrontal refreshment of workspace in the auditory cortex.
Correct. :-) That's what the evidence has been suggesting since at
least 1993.
> the internal
> narrative may manifest in the same workspace but the phonological loop
> does
> not in itself implement an internal narrative, otherwise tape
recorders
> would be sentient.
Interesting. :-) I've never had many problems with understanding the
neural substrates of the phenomena of "internal narrative." I guess I
has just assumed that it was realized by the same systems that were
responsible for the phonological loop and normal linguistic output with
the exception of the [phonological-code to motor-plan] and [motor-plan
to movement] "modules". (I am just regurgitating the seminal Levelt
framework.)
Take care,
-ben
http://www.exocortex.org
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