Re: Perceptual symbol systems

From: Sergio Navega (snavega_at_intelliwise.com)
Date: 08/10/04 

Date: Tue, 10 Aug 2004 11:24:29 -0300

"Eray Ozkural exa" <erayo@bilkent.edu.tr> escreveu na mensagem
news:fa69ae35.0408080356.32b6c42c@posting.google.com...
> "Sergio Navega" <snavega@intelliwise.com> wrote in message
news:<4113f221$1_3@news.athenanews.com>...
> > "Traveler" <traveler@nospam.com> escreveu na mensagem
> > news:v4g5h01i294h931ca0ji6ss9pnltg6j4hn@4ax.com...
> > > In article <4112b4dc_6@news.athenanews.com>, "Sergio Navega"
> > > <snavega@intelliwise.com> wrote:
> > > It is a good thing you saw fit to put "internal symbols" between
> > > quotes because there are no such things. What I mean is that a neural
> > > spike may be considered a symbolic event from the point of view of an
> > > outside observer looking in, but from the point of view of the brain
> > > itself, it is just another spike. So the mechanism of the brain could
> > > not possibly be thought of as manipulating symbols.
> >
> > The big jump we have to give here is not to consider a single spike as
> > representing one "symbol", but to look at the dynamical (and transient)
> > behavior of a group of neurons as standing for some external stimuli
> > (or at least standing for some specific properties of that external
> > stimuli).
>
> The single spike does not necessarily correspond to a single symbol of
> communication, there are phrases in the spike code... Though, I think
> a spike train seems to correspond to a string of symbols, and it seems
> to be an adaptive discrete code. (I couldn't tell it better, my
> explanation looks inaccurate now as well. Please search for flypapers
> on comp.ai.philosophy archives and ai-philosophy archives. Michael
> Olea has written some good descriptions of it.)

Those who try to model the spike behavior of single neurons have
been puzzled trying to decipher what is the "code". I find the
study of populations of neurons much more promising.

> Your characterization is closer. In sensory processing, the symbols
> will correspond to properties in external stimuli (motion, rotation,
> color, etc.), so these could be numerical (implementing large
> alphabets, number systems and so forth!). The "dynamical behavior of a
> group of neurons as standing for some external stimuli" can be
> characterized as the computation performed by them, but we do not yet
> know the kinds of computation in actual sensory systems, I think.

That's the point, no one has found the "coding system" of single neurons.
In some cases, neurons seem to code temporal relations between spikes.
In other cases, what's important is the average timing in a train
of spikes. The third hypothesis (which is what I think is more interesting)
considers the "code" to be a synchronous behavior of groups of neurons.
The olfactory system of locusts has been investigated and a pattern
of oscillations coding specific odors has been found. In another
important study, it has been found that these patterns of oscillations
are affected by the learning of new associations (during conditioning).

Sergio Navega.

Relevant Pages

  • Re: Why do we need definitions?
    ... > train, which suggests that a train carries two bits. ... observed relationship between stimulus ensemble and neural response (the ... displacements into spike trains. ... and primary afferent neurons innervating the sacculus. ...
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  • Re: Perceptual symbol systems
    ... it is just another spike. ... > behavior of a group of neurons as standing for some external stimuli ... a spike train seems to correspond to a string of symbols, ...
    (sci.cognitive)
  • Re: Perceptual symbol systems
    ... In article, Sergio Navega ... there are phrases in the spike code... ... >> a spike train seems to correspond to a string of symbols, ... >study of populations of neurons much more promising. ...
    (sci.cognitive)