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From: jwtlai@watcgl.waterloo.edu (Jim W Lai)
Subject: Re: The Bandwidth of the Brain
Message-ID: <1990Dec19.001519.25006@watcgl.waterloo.edu>
Organization: University of Waterloo
References: <37034@cup.portal.com>
Date: Wed, 19 Dec 90 00:15:19 GMT
Lines: 29

In article <37034@cup.portal.com> mmm@cup.portal.com (Mark Robert Thorson)
writes:
>There is a common myth that the brain is capable of enormous computational
>bandwidth -- for example that the retina sends gigabauds worth of data to
>the brain.  I believe the computational bandwidth of the brain is quite low,
>low enough that we could simulate a brain on today's computers if only we knew
>how to do it.

[test of experiments deleted]

>So it seems like the whole brain, engaged in a task which undeniably involves
>thinking, might be modeled as a pipeline of 10 stages with no more than
>1200 baud bandwidth each -- an astoundingly low amount of computational
>bandwidth.  Of course, this doesn't mean the same 10 stages are used for every
>problem, merely that most sorts of thinking don't involve many layers of cells
>or much bandwidth.

Not so.  If it is a pipeline of "agents", you only know the maximum speed of
any individual filter along the pipeline.  (A chain is only as strong as its
weakest link.)  Each agent can encode data minimally for compactness in
theory, but that doesn't mean that the brain is therefore optimal and actually
only uses 50 bits per second bandwidth.  There's nothing wrong with a model
that assumes the sending gigabits per second down the pipeline.  In the agent
paradigm, each agent can feed output to many agents.  A tree ten levels deep
can still be quite wide, and be particularly nasty if when cycles are added.

My gripe with experiments that claim to measure the bandwidth of the brain
is the validity of their measurement criteria, which may have already
assumed a fair amount of preprocessing to have taken place.