[Neuroscience] Re: Mirror, Mirror .... You Bloody Liar

Benjamin via neur-sci%40net.bio.net (by Benjamin At verizon.net)
Thu Jan 25 08:51:16 EST 2007


<raipanello At gmail.com> wrote in message 
news:1168931407.577719.15720 At v45g2000cwv.googlegroups.com...
>
> John H. wrote:
>> When I look in the mirror right\left is inverted. Why do I not appear
>> upside down?
>
> because a mirror is a reflecting surface, not a focal point

If everything's planar you are [of course] correct, but John was
addressing a much deeper question -- an important one
that exists at the most-fundamental level of neuroscience.

To see its stuff, take mind's eye to your local amusement park's
funhouse, paying careful attention to the non-planar mirrors.

Bring some gedanken shaving cream and have a go at shaving.

It's still "reflection", but the waviness of the mirrors make it
necessary for one to impose a complementary transformation
between the information that reaches the retina from the mirror
and the activations of the muscles that control the motion of
the 'razor'.

See the difference? Invoking reflection from, say, a bathroom
mirror as one shaves, without addressing the 3-dimensionality
of the ambient "forces" in one's external experiential environ-
ment leaves necessary stuff out of the picture.

It was this stuff that John was addressing.

Once the general necessity of accounting for such stuff is
realized, it's possible to rapidly converged upon its details.

Using the "mirror" you invoked, for instance, get out your
gedanken glass cutter and score it vertically [relative to
a standard horizon] so that it's divided into two equivalent
halves, crack it [there's no such thing as 'bad luck' :-],
and, "hinging" along the cracked edge, set the two halves
at various angles relative to each other . In this way, one
can flip-flop the reflected image at will -- and it's all still
reflection.

It's this sort of manipulation, which is inherently topological,
that John was addressing, in particular, with respect to how
and why the visual image, which passes through the eyes'
lenses and is, by them, everywhere "inverted", still yields
"upright" images, with faithfulness to all external optics.

What John was getting at is that a lot happens between
the physical mirror and "mind's eye' -- all of which is
the province of neuroscience, most of which is fund-
amental neuroanatomy. There are great wonders in-
herent -- that a plane-mirror is totally-unbiased with
respect to light's directionality,  yet when we "look
into" one, "left" and "right" are reversed, but "up" and
"down" are not -- even though all light that we perceive
passes through the lenses of our eyes, there, everywhere
"inverted" as it travels to the retina.

So there's 'reflection' involved, but invoking simple
reflection is insufficient.

A superficial part of it is due to the fact that our eyes
are oriented in a horizontal plane, but most of what's
involved is founded at exceedingly-deeper levels of the
neuroanatomy. To address all that's entailed, one has to
literally address every "twist and turn" that exists
within the neural pathways.

For instance, no matter where one looks in a 'normal'
nervous system, everything one sees is precisely-
ordered with respect to the way the eyes' lenses
invert all the light that passes through them. The
great fiber crossings in the medulla, for instance, all
exists solely in order to achieve the stuff that evoked
John's comments.

This because, if the nervous system is to be able
to converge upon activations of an individual's
musculature that will, say, enable the individual to
successfully use a tool in the presence of 'gravity',
or to walk through a doorway without banging her
arm, there must be an overall order that enables
the nervous system to 'know' how to achieve the
necessary muscle activations.

See the big problem inherent?

How does the nervous system ["the brain"] 'know'
how [and even why] to so orchestrate its activations
of its host organism's muscles so that the result
will be behavior that is, more or less, 'appropriate'
with respect to environmental necessities upon
which survival of the organism [even us] depends?

That is really what John was addressing.

And, although there's a lot that's involved, it's
all ordered in an awesomely-simple way that
enables a nervous system to 'know' how [and
even why] to activate all of the body's musculature,
practically no matter what routine external stim-
ulation is experienced [is encountered by; im-
pinges upon] the nervous system.

Nervous systems achieve this very-useful [ab-
solutely-survival-essential] end by doing only
one thing -- they 'strive' 'blindly' and auto-
matically to minimize the topologically-distrib-
uted ratios of excitation to inhibition that are
occurring within themselves. The easiest way to
begin see this is to study the way that all neuro-
anatomical twist, turns and lateral-crossings are
ordered with respect to the cerebellum's entirely-
inhibitory outputs [which arise solely from the
cerebellar Purkinje cells]. Because all of the out-
puts of the cerebellum are inhibitory, when, say,
one's arm brushes against an object in the external
environment, such results in an increase of the
excitation that the brushed surface of the arm
passes to the cerebellum. And all the cerebellum
does is take that little 'mountain' of excitation
and transform it into a 'valley' of excitation,
with the topography pereserved, and project
that 'valley' of excitation back to the muscles
that control the orientation of the arm. Because
the topography is, in fact, preserved, a Truly
wonderous thing happens -- the muscles that
were most active -- and, so driving the body
into its encounter with the environmental obstacle -- 
rapidly become relatively least-activated and
the muscles that were formely weakly-activated
rapidly become relatively most-activated -- 
and the arm 'moves away from' its contact with
the environmental obstacle, thus [typically] saving
the body from injury.

Take this simple, extremely-low-level example
and extend it everywhere within a nervous system.

It's all exactly the same simple stuff that nervous
systems are everywhere-organized to achieve:
minimization of the topologically-distributed ratios
of excitation to inhibition.

Every neuroanatomical twist, turn, and crossing
occurs within 'normal' nervous systems solely
to establish the means to achieve this one end.

And all of this was in John's splendid post [even
his already knowing it, eh John? :-]

The eyes -- "vision" -- are completely subservient
to this one simple ordering principle. They do
nothing that's discordant with respect to it.

So, if, for instance, it was the case that we were
not fixed in space with respect to the directed
force of 'gravity', the left-right/up-down differ-
ential that John addressed would not be as it is.

What would exist within nervous systems would,
then, be whatever it would be that would enable
them to achieve TD E/I-minimization, and the
resultant beings, although not like us, would
survive in their different world just as capably
as we do in ours, even though there would be no
"left" or "right", "up" or "down". [Octopusses
come to mind as and at least partial example.]

"Reflection" from the planar surface of the mirror
is actually artifactual with respect to what happens
within nervous systems.

This is what John was actually addressing in his post.

Cheers, folks

[Yes, it's ken. I'm using this 'funny' UserID in the
hope that it'll allow me to just be with folks for a
while before this [9th] machine is rendered useless
by folks who, for whatever reason, don't like me
being with you folks.]











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