Re: Mental Imaging

From: HARNAD Stevan (
Date: Fri Mar 08 1996 - 20:36:27 GMT

> From: "HOLMES Sharon" <>
> Date: Fri, 8 Mar 1996 11:56:35 +0000
> We could think of ourselves as walking organic computers. Neurons have
> an 'all or nothing' on/off state and will only fire (switch on) if the
> stimulus reaches a specific level of intensity. In that sense, we are a
> walking collection of on/off switches. However, this does not
> necessarily explain HOW the mechanism works. Yes, at a neural level,
> all information is processed as a series of 1's and 0's - neurons
> firing and not firing. It is how this is organised and how this action
> translates from 1's and 0's to speech, memory, language, conscious
> awareness etc. which is the unknown.

There is also a level of activity below the threshold for neural firing,
called "postsynaptic potentials." At this level, neuronal activity is
not all-or-none but gradual. Also, the neuronal code may be at the level
of the FREQUENCY of firing (how fast and often a neuron fires), which
can also vary gradually. Moreover, there are molecular processes in the
brain that are more chemical than electrical. No one knows at what
level the cognitive "action" in the brain takes place. So the analogy
between on/off firing of neurons and on/off activity of computer
flip-flops may or may not be significant.

> For example, imagine we found an item of alien machinery (as you do!).
> Scientists and engineers could spend years studying this machine,
> detail the components in minute detail, but still be none the wiser for
> HOW it works, or what it is for.

In other words, the only way to reverse-engineer the brain is to model
it; just peeking and poking at it will not reveal how it works. Once
you have a working model, one that can do what the brain can do, then
you finally have some clue as to what to look for when you peek and

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