Hemispheric control....

Andrew T. Austin slightlynervous at NOSPAMbtinternet.com
Tue Jan 23 10:46:49 EST 2001


I have often wondered about the supposed "upside down image on the visual
cortex" thing.  Just because the lense will invert the image, doesn`t
necessarily mean that this is how it is represented on the visual cortex,
surely?

A quick `twist` in the optic nerve would surely solve this problem.

Plus, it doesn`t seem to me that the image is `projected` as though onto a
viewing screen.

Can anyone provide further elucidation?

Thanks,

Regards,

Andrew "likes to use long words unnecessarily" Austin.

Richard Norman <rsnorman at mediaone.net> wrote in message
news:Ef2b6.40322$ft6.843643 at typhoon.mw.mediaone.net...
> The image reversal in the visual system  is certainly not the source
> of contralateral control.  Consider the contortions that the optic nerve
> must undergo at the optic chiasm to ensure that retinal ganglion cells
> originating on the nasal half of each retina cross, but those originating
> on the temporal half stay ipsilateral.  And consider that most vertebrates
> don't have much bilateral vision -- their eyes are on the sides of their
> heads and all axons must cross.  Squid, which also have camera eyes,
> and inverted images, don't have this silliness.  No, the "upside down
> and backwards" image on the retina is not really related to anything.
> Neurons don't care about which way is "up".
>
> "MS" <marshmallow5 at yahoo.com> wrote in message
> news:LLXa6.3717$mo2.429194 at news1.news.adelphia.net...
> > I'm assuming what you mean by contralateral control is that the left
> > hemisphere governs motor and sensory functions for the right side of the
> > body and vice-versa. The only explanation that I have found suggests
that
> > it's a result of the visual system.  All of the other sensory and motor
> > systems could hypothetically be represented ipsilaterally (i.e. left
side
> of
> > the body on the right side of the brain, etc.)  However, an optical
> property
> > of the visual system is that the images reaching the retina are upside
> down
> > and backwards, so that the left visual field reaches the right
hemisphere,
> > etc.  The rest of the senses (and motor systems) have to be aligned
> > accordingly, so that things seen in the left visual field are also felt
in
> > the left visual field, and reached for the same visual field. So
> basically,
> > the reversed visual system causes everything else to need to be
reversed.
> >
> > Marcello Spinella, Ph.D.
> >
> >
> > Andrew T. Austin <slightlynervous at NOSPAMbtinternet.com> wrote in message
> > news:942lop$5j14 at eccws12.dearborn.ford.com...
> > > This might be a silly question, but can anyone tell me what the
> advantage
> > of
> > > having contra-lateral control is?
> > >
> > > What benefit IS there by having the left hemisphere controlling the
> right
> > > side and vice versa?
> > >
> > > Thanks in advance,
> > >
> > > Andrew "clicking his amygdala" Austin.
> >
> >
> >
>
>







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