left-right reversal of CNS: Why?
kenneth paul collins
KPCollins at postoffice.worldnet.att.net
Sat Sep 14 01:08:30 EST 1996
dantso at cris.com wrote:
> In <322E5EEF.73E9 at postoffice.worldnet.att.net>, kenneth paul collins <KPCollins at postoffice.worldnet.att.net> writes:
> :> Cajal put forward a very plausible explanation based on the
> :> fact that images on the retina are left/right inverted.
> :> Without the visual and motor decussations it would need peculiar
> :> and complicated circuitry to make a movement of one side of the
> :> body that related to something in the ipsilateral visual field.
> :> See his "Recollections of my Life" for a concise explanation
> :> with diagrams.
> :Cajal was right, but he didn't carry the idea to fruition... the
> :information-processing problems that are addressed by all of the twists
> :and turn that exist within the neuroanatomy are much-more-generalized
> :than hand-eye coordination... although such is included...
> You are confusing image inversion with visual field representation.
> The optics of the eye have nothing to do with crossed CNS
> Humans are among the few species that have an appreciable binocular
> overlap, perhaps to provide stereopsis, or whatever.
> Crossed CNS representations are ancient, many species having very
> poor or no vision, or no single retinal image. Many species in which other
> senses far dominate vision. The visual *field* (not image) representation
> crossing followed the previous cross of the rest of the CNS. It did not
> drive it.
There is some confusion... if you look above, you'll see that I said:
"the information-processing problems that are addressed by all of the twists
and turn that exist within the neuroanatomy are
-->much-more-generalized than hand-eye coordination...<--
although such is included..."
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