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From: jxh@cup.portal.com (Jim - Hickstein)
Newsgroups: comp.graphics
Subject: Re: 3-D perceptual abilities
Message-ID: <14825@cup.portal.com>
Date: 19 Feb 89 05:28:38 GMT
References: <6382@thorin.cs.unc.edu> <6511@cadnetix.COM> <14496@cup.portal.com>
Organization: The Portal System (TM)
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While we're on the subject of human visual perception, specifically
stereopsis, has anyone else noticed that their *perception* of 3-d,
not just stereopsis, occasionally "goes flat", especially when under
stress of, say, sleep deprivation?  I have several times experienced
driving along a "projected" road, that is, projected on a flat screen
in front of my (moving) car.  Once I managed (suffered?) quite a long
episode of this, over half an hour.  One friend of mine, upon hearing
that I had had this experience, was much relieved to know that he wasn't
losing his marbles: he, too, had experienced this.

Now, I don't scour the medical literature, so maybe this "astereopsis"
(a misnomer, I now realize) is common; yet, I haven't heard more than
this one other report.  How many of you have had this experience?  How
long does it last?  Can you make it come and go at will (I'm approaching
this)?  Is it related to stress, or visual fatigue?  I gather that a
significant number of readers share my habit of voluntary sleep deprivation,
related to their work: are you a programmer, or do you often stay up late
for some reason?  Does watching TV or reading (close-up tasks) exacerbate
or trigger this condition?  (Contrast my half hour tour-de-force in the
car; luckily the road was quite empty.)  I find that reading with one eye
closed (face distorted due to propping head on bent arm) triggers it
after about half an hour.  (I get lots of practice with reading in bed:
I'm almost through my chemistry text, which I seldom see in 3-d :-).

Also, my new prescription sunglasses (80 per cent, color neutral) cause
a temporary loss of steropsis (not 3-d perception entirely) when I
put them on.  I gather this has something to do with how they grind lenses
these days, and what, precisely, is the density of the lens along the
viewing axis at a given instant; I have been told that if the two lenses
are not precisely the same density (i.e. a sidelong glance) that an
illusion occurs related to stereopsis.  I have seen this at the Exploratorium
in the "Professor Pulfrich's Universe" exhibit, but I'm not convinced this
is the reason I have trouble: after a few minutes acclimatization, the
effect is gone and I can drive normally.  Let's hear from those of
you with prescription sunglasses, too.

-Jim Hickstein
jxh@cup.portal.com
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