Learning to see in 3D

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Tue, 14 Jan 1997 22:57:05 -0600
>From: P3D Larry Berlin  <lberlin@xxxxxxxxx>
>Subject: Re: Dominating eye

>It may be very advantageous to your child's health to provide them with
>ViewMaster reels or other stereo tools while young so that at a minimum they
>become aware of this particular faculty. The use they make of it is their
>own choice, but at least it won't be as strange a phenomenon later should
>they try to FV. Children provided only with 2D images, may bypass this
>awareness and develop observation habits that shuts out *difference*
>information instead of using it.

I agree that all of this is likely to be beneficial, but there's a
physiological factor that comes into play at a very early age, probably
too young for Viewmasters. It has been reported in the past on this list
that vision researchers state that there's a certain critical age at which
small children either develop the inherent ability to see in 3D, or they
don't. If something interferes with this process (for instance a vision
problem that isn't corrected until a later age), then these people will
never develop full stereoscopic perception, no matter how hard they work
at it.

I came across an interesting article in Scientific American several years
ago, which may shed some light on how this could be. The article was about
the vision systems in young cats. Cats have visual centers for processing
the incoming left and right views, but when they are very young, the visual
signals from both eyes go to both processing centers. (The "left view"
processing center receives input from both the left and right eyes, and
so does the "right view" processing center.) As a cat gets older, and
providing that the cat has full use of both eyes, the cross-connections
are gradually shut down, so each processing center pretty much receives
signals only from the corresponding eye. Above a certain age, the ability
to shut down these cross-channels appears to go away.

If this also applies to humans, then it looks like one reason for extreme
stereo blindness could be the wiring in the brain. If for some reason
your brain didn't rewire itself for stereo vision at that critical age,
then the left and right processing centers are getting the *same image*
(a composite of the inputs from both eyes), so the stereo processing portion
of the brain doesn't get the *differences* in the two inputs from which to
derive depth information. (That doesn't mean the person can't figure out
distances using other cues - just that one particularly powerful perception
mechanism isn't working properly.)

Maybe sometimes some of the cross-connections are shut down,
but the job isn't completed - perhaps that could cause some people to
perceive depth less intensely than others.

As to why the the brain should start with the cross-connections and then
rewire them as the visual system is used, perhaps there's an evolutionary
advantage - if something's wrong with one eye or part of the brain, it
provides the best chance to provide the best possible visual processing
with what's available.

John R


------------------------------