Re: Convergence as a Depth Cue

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Date: Sun, 22 Jun 1997
>From: P3D  LeRoy Barco writes:
>......
>
>     IMO, convergence is exceptionally weak as a depth cue.
>
>     Experiments have been suggested on the question... though not terribly
>scientific, I present the following for your consideration:
>..... The projection room was very large with high ceilings and walls which
>were dark and non-reflective.............
>     As he moved the controls, I could feel the convergence happening to my
>eye muscles, but the image didn't seem to move forward and back or otherwise
>change.
>
>     So I must queque(:=)) with those who think the self-contained image
>disparaties are the overwhelming contributors to the mental stereovision
>construct.

*****  While I fully understand the situation you describe it is also
possible to be more aware of the absolute depth of the screen just as you
are aware that a tree is in the foreground and a bridge in the background.
If you have spatial relative awareness of the tree and bridge, you can
develop an awareness of how they move forward or back with chip placement,
without seeing the screen itself, though that certainly helps. Projection
distance and where you are sitting will strongly affect the situation.

I draw a distinction between characteristics that exist but aren't often
recognized and those that can't be recognized for some concrete reason. If
skill building dramatically increases the awareness of one of the
characteristics, whether it be convergence or any other, then it's not
appropriate to claim the effect is missing or weak just because so many
don't see or use it. Take a better sample from those who have learned a
skill to a moderate degree and then determine where the more realistic
limits exist. For example, just because someone falls off a bicycle on the
first few tries doesn't mean that most people are unable to learn the skill
of riding one. 

If you felt the convergence happening, it is then theoretically possible to
learn to interpret those sensations accurately with more experience at doing
so. The demonstration you mention was effective due to a general lack of
experience with that factor isolated in that way.  In a way it's like seeing
a moon crater as a bump instead of a crater. It sounds like a fun thing to
do at stereo clubs, viewing skill building. Get out the trick projectors....
or maybe an inventive optical illusion assignment?  :-)

I feel that the self contained image disparities are sensed to a large
degree by convergence factors on a comparitive level in the mind. Perhaps
not always consciously recognized as convergence factors, but effectively
convergence anyway, or at a minimum available for interpretation as such.

Larry Berlin

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


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