Visual Cortex Columns Question

Richard Vickery Richard.Vickery at unsw.edu.au
Wed Nov 22 17:59:10 EST 2000


Richard Norman wrote:

> > >  I am not sure how i want to phrase this question, but what purpose do
> the
> > > Ocular dominance, and Orientation columns in the visual cortex serve?
 
> I seem to recall on old paper (ca. the 60's) of D. MacKay (sp?) pointing out
> that disparity in the orientation vector between the two eyes is an
> important
> component of depth perception.  That is, if you look at a stick, you see a
> straight line at some orientation angle.  However, if one end of the stick
> is
> closer to you than the other, the orientation angle varies between the two
> eyes.  (Try it, it's true!)> 
> Therefore, keeping the orientation angle information separate from the
> ocular dominance information allows the appropriate processing to
> detect the depth effect.


That orientation difference can contribute to depth perception has
been known for some time - Wheatstone devised stereographic images in
the 1830s that demonstrated this.

I was attempting to answer what the "purpose" of the columnar
structure was.  It seems to me that as the neuron is the basic unit of
information processing, it is easy to imagine cortical structures that
function without columns as it is only the connections between the
neurons that matter (the neural connectivity specifies the separation
of orientation and dominance info).  It may well be however, that
columns provide the simplest wiring solution.  This would make their
"purpose" something like "efficient use of space and energy" as
opposed to "keeping the orientation angle information separate from
the ocular dominance information".  Certainly generating distinct
information streams and combining them at the right time and place is
a key part of cortical function.

Cheers
Richard


-- 
Dr Richard Vickery                  
School of Physiology & Pharmacology, UNSW, Australia, 2052
ph. 61 2 93851676,  fax 61 2 93851059              
http://www.med.unsw.edu.au/Physiology/School/staff/vickery/Welcome.html






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