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How They Eye Works

Richard Norman rnorman at umich.edu
Wed Apr 3 13:29:43 EST 2002

"BriF" <brif8 at hotmail.com> wrote in message
news:_mEq8.53999$y26.11932236 at typhoon.tampabay.rr.com...
> Greetings
> Could someone please advise me on the following statement, and correct
> necessary I'm repeating facts that I was told and would like to verify
> as accurately as possible, if for some reason this is in the wrong NG I
> apologize.
> The visual system could be likening unto a camcorder.
> The eye is simply the lens, which allows in as much light as necessary,
> is focus to a single point for it to be processed. The visual cortex of
> brain is like the viewfinder, it's function is to process the information
> from object recognition. That Yes, it has green on the top in an oval
> is supported by a brown rectangle, yes I'm looking at a tree. The visual
> cortex processes the image and what it is, without paying much attention
> the specific details, colors etc. this is performed at a rate of 28 frames
> per second. Much like the viewfinder is Black & White and is worried about
> what is in picture and what is out of picture.
> The visual subconscious is like the cassette tape. It records everything
> very clear details specific colors shapes etc.. It does not do the image
> processing, it simply records what is seen and is not worried about what
> is. Due to the less processing done it is capable of performing at a rate
> 30 frames per second. Much like the cassette it just records what is fed
> into the lenses, for latter use.
> Is this accurate, or where are the flaws. (perhaps terminology) I'm not
> sure. What was of real interest to me was that two parts of the brain
> visual images from the eye, and that each brain functions at different
> rates. If this is the case I would love someone to please explain this to
> me, in basic understanding, I'm not into neurobiology, but this is non the
> less quite fascinating.
> Any direction to online material that covers this issue would be more
> appreciated.
> I thank you all for your patience and to those willing to help, I thank
> in advance
> Barry

I am not sure where you are getting this informtion, but it is an amazing
combination of pieces some of which are just plain wrong, some of which
are rather inaccurate interpretations of things that are sort of true, and
some of which are just drastic over-simplifications of things that are true.

The eye is far more than a "lens" that gathers light and somehow sends an
image in some form to the brain (where a little person inside watches the
viewfinder).  In fact, there is a rather complex set of neural circuits in
the retina of the eye that does preprocessing of the visual information so
the information carried in the optic nerve is already an interpretation of
the optical image that falls on the retina.

You talk of two other levels, visual "cortex" and visual "subconscious".
these are entirely different concepts -- one deals with specific brain
involved in processing information, the other deals with whether the
at any particular level can be brought into our "conscious" perception or

The visual cortex is very complex, containing many different centers of
None of them deals with notions of "viewfinder".  You may be thinking of a
separate visual center in the midbrain (superior colliculus and other
which are involved in things like direction of gaze, visual attention, eye
and such, but that is not visual cortex.  Also, some parts of the visual
do "attend" to general features and others do attend to fine details.  The
 of processing at 28 or 30 frames per second seems somewhat off-the-wall.

And you confuse "subconscious" visual processing with visual (or other)

The whole notion that the visual system is a camcorder begs the whole
question about what visual processing is. The purpose of a camcorder
is simply to record the image without "understanding" what it is recording.
The whole notion of the visual system is to "understand" what it is looking
without necessarily recording the result.

An excellent review of visual processing (although now a little old) is
Brain, and Vision" by D.H. Hubel, Scientific American Library, W.H. Freeman,
1988.  There have been developments in the last 20 to 25 years, but this
captures the important ideas specifically written for a non-specialist by
one of
the leaders in the field.

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