P3D Re: Dark Vergence (was: Curious eye defect)

[Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Thu, 01 Jan 1998
>From: Linda Nygren writes:
>............................ I have "exophoria"
>meaning my eyes tend to wander "out" if one of my eyes is blocked, for
>example if I am sitting behind someone at a theatre and I can only see
>with one eye, the other eye loses its "fixation". It feels weird.
>Anyway, I find that I can easily parallel view but I can't cross view at
>all because my eyes just won't do it! Doctors check for "phorias" by
>doing a cover/uncover test where one eye is covered while the other
>looks straight ahead; then when the eye is uncovered, it may be seen
>moving back into a normal fixation position from where it wandered in
>(esophoria) or out (exophoria). You can check yourself with the help of
>an observer if you are not sure whether your eyes tend to do this.
>-Linda
>
>

****  All natural tendencies aside, *exophoria* will NOT prevent you from
cross viewing. It may make it more difficult to learn, but not so as to
prevent learning. Consider that you probably read books or magazines. You BY
DEFAULT converge your eyes to the page you are reading. That exact
convergence IS crossed viewing, for some set of points more distant. Should
there just happen to be a cross viewable image or pattern located a bit
farther away from you than your comfortable reading distance, you in fact
would be cross viewing. 

The single most significant factor in the difficulty of learning cross
viewing when you already know parallel is that your automatic  eye response
which generally helps you hold a convergence, tends to correct for the
parallel or wide eyed mode. If you attempt cross viewing, the slightest
misalignment of your eyes, causes them to jump into wide eyed mode, losing
all possibility of the cross viewed results. 

That's why the finger method of crossed viewing is so effective a learning
tool. You can force your eyes to remain converged on your finger and
literally WAIT until the cross viewable images farther away than your finger
becomes noticeable. At first, your response will be to shift your focus and
convergence to the distant place, the stereo disappears, and it seems that
you'll never learn. However, keep trying WITH a concrete point to hold your
attention. Gradually you can train your eyes to correct their alignment and
convergence back to the finger.

The trick is to find the right distance for your finger. It should be
exactly at the convergence point for the two cross viewable images. (four
images becomes three, and the center one is stereo, so ignore the outside
ones) When you finally GET the stereo view, your finger is right in the
middle of the virtual image!!!  That's what makes it work.

If your exophoria is so extreme as to prevent you from normal vision and
reading convergence, that's a different story. Under those conditions you
might not even have stereo vision. Otherwise there should not be any problem
learning crossed viewing. Probably most of the population could learn it,
given the right opportunity and the motivation to try. It's literally as
easy as reading, once you train your eyes to cooperate instead of fighting
you...

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/
http://3dzine.simplenet.com/


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