[photo-3d] Re: Re: 3d vision again

[Jim Crowell <jcrowell@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

>> I am not an ophthalmologist, but as a pediatrician I do know a little
>> about strabismus and amblyopia ("lazy eye" etc). I am curious as to
>> whether someone (older child or adult) who has never seen
>> stereoscopically could actually fuse and "process" the images into 3D
>> even if they are delivered appropriately to each eye by correcting the
>> visual axes of the input tomatch the eyes. If so, would this be an
>> immediate "skill", or acquired/improved with practice? Or is there a
>> developmental time window after which the brain would be unlikely to be
>> able to do this?
> 
> I'm not an ophthalmologist  either, but what I've read is, if they haven't
> learned to view in 3-D from an early age, they never acquire it later in
> life. I'll try to find some reliable sources on this, but I believe this is
> pretty
> much common knowledge among ophthalmologists, at least.

I'm not an ophthalmologist either, but from spending several years working
with people who study visual development I'm pretty sure Gabriel is right.
I don't remember exactly when the sensitive period (the period during which
you need to experience stereo vision in order to have it in later life) for
stereo vision ends, but I think it's 5-7 years.

This happens because the brain cells in visual cortex get wired up partly by
means of experience with stereoscopic inputs.  A given cell will start out
at birth by firing in response to inputs from a relatively broad region of
both retinas and to a range of binocular disparities.  In order to encode
image disparities accurately, that has to get narrowed down to a fairly
small area of each retina.  This happens through experience; as a child
looks around at three-dimensional scenes, various brain cells will tune in
to various levels of image disparity, and stop responding to parts of the
scene that don't give rise to their preferred disparities.

If a child's eyes aren't aligned properly during the period when this is
going on, then the parts of the two retinas that a given cell gets its
inputs from may not even be pointing at the same part of the scene.  In this
case, that cell will probably gradually lose the input from one of the eyes.

It doesn't sound good, I know.  But except for stereo photographers (or
potential stereo photographers), I don't think the loss of stereo vision is
too serious.

-Jim C.

-------------------------------------
Jim Crowell, Ph.D.
Dept. of Psychology
Cognitive/Experimental Group
Townshend Hall
1885 Neil Ave. Mall
Ohio State University
Columbus, OH 43210
mailto:crowell@xxxxxxxxxxxxxxxxx
mailto:crowell@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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http://vision-lab.psy.ohio-state.edu/crowell/