P3D Curious eye defect

[JNorman805 <JNorman805@xxxxxxx>]

     Yesterday I went to the eye doc for a routine checkup.  I asked him to
check the alignment in my glasses (I have astigmatism) because I sensed that
when I wore my reading glasses, for text, the line of type perceived by the
right eye seemed to run uphill, left to right, relative to the same line seen
by the left eye.  He asked how I could possibly sense this, and I confessed
that as a stereo photographer, I was able to "free view" stereo images, and
when I did the same with text, I saw a difference between right and left eyes
while using my glasses.  So he gave me a test involving the use of polarized
glasses and transparency overlays to check just how good my stereo perception
really is.  The first involved a macro picture of a fly, enlarged to perhaps
three inches long.  The doc asked me to reach for the wing of the fly, which
protruded, I sensed, about a half-inch from the "window".  Then he asked me to
state which of about six little figures stood out from a line of about six
such figures.  On line "C"  I perceived only a flat line of figures.  On line
"B" I perceived one figure very slightly ahead of the others, whereas on line
A, one figure stood out prominently.  "I've got news for you, " he said.
"Your stereo perception is really rather poor.  I'd suggest you get another
hobby!"  He said that people with normal stereo vision reach for the fly's
wing as if it were six ot eight inches off the page, and have no trouble
seeing one figure in each of the three lines of figures standing way out in
front.
      As you can imagine, this was pretty amazing news to a person who always
thought he had pretty teriffic stereo vision, and of course I have no
intention of giving up stereo photography!  
      But it got me to thinking.  Could it be that I really do have poor
stereo vision, and the reason I like stereo images so much is that the
slightly hyper quality of many such images allows me to see the world in three
dimensions as people with normal vision see it all the time?  I know that the
stereo base that I routinely use is a little wider than normal eye placement,
since I use two 35 mm SLRs mounted bottom to botom; and I often get closer to
the foreground than the 30/1 rule of thumb should permit.  On the other hand,
I have no trouble perceiving stereo images that their makers claim are truly
"ortho," whatever that means.
      Does anyone know if there have been any controlled studies of ability to
perceive stereo among stereo nuts, as compared with normal people in the
population at large?  Might be an interesting project.  Perhaps over time,
during routine eye exams, P3Ders might ask for a stereo perception test, and
(honestly) report the results here for tabulation.
       Another thought: do you suppose there might be a correlation between
poor stereo vision and accident proneness?  How about between good stereo
vision and excellence in sports such as basketball?  
      I find all this intriguing.  Anyone else interested?
      (BTW, the doc found nothing wrong with my prescription and couldn't
explain why text perceived by my right eye runs uphill.)

       Jim Norman (who still thinks he has pretty good stereo vision and has
no
                           intention of giving up stereo photography)


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End of PHOTO-3D Digest 2462
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