Re: [photo-3d] Stereo vision and eye spacing

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

----- Original Message -----
From: "William Gartin" <william_gartin@xxxxxxx>
To: <photo-3d@xxxxxxxxxxxxxxx>
Sent: Sunday, March 11, 2001 8:45 AM
Subject: [photo-3d] Stereo vision and eye spacing
> Has
> anyone ever done any kind of study on how eye spacing affects depth
> perception?

There have been some studies on this as well as several aspects of human
vision perception (there were some related P3D threads not too long ago).
The general technique is to replicate the condition with external optics.
In the case of eye spacing special eyewear that prismatically widened or
narrowed the stereo base were worn by volunteers.

As with the previously noted experiments, the subjects became used to the
new perception after a while.   Then, when they removed them, the real world
viewed normally appeared abnormal.  People seemed larger or smaller than
they should have (the opposite of the effect that the artificial stereo base
gave them).

Although these tests were done about forty years ago, more recently similar
tests were done with HMDs that also had a pair of head mounted miniature
video cameras with an adjustable stereo base.  This made for a less
cumbersome rig in which the wearer could (after getting used to it) perform
normal functions, including walking up and down stairs, and even one brave
individual who rode a bicycle while wearing it.

The cameras were mounted on a horizontal rod that was in turn mounted to the
front of the helmet in front of the person's eyes.  Thus, they could be
adjusted over a reasonably wide range.  I don't have the measurements, but
from the picture that I saw of a person wearing it, I would guess that the
range was from about 1-1/2 to 12 inches.  The person would be looking at the
pair of LCD monitor screens as with most HMDs, and the sides and top and
bottom were shielded such that none of the real world could be seen around
the edges, only the video images.

I don't recall what the timing was, but after a while at a particular
setting the images once again seemed normal, and again they seemed abnormal
immediately after the HMD rig was removed.

Most human beings with a reasonably good memory will experience a similar
effect during their lifetime if they revisit places where they were as a
child.  If you saw something as a child, when your eye spacing was slightly
smaller than it is now, and returned years later as an adult, everything
will appear somewhat smaller than your memory leads you to recall.  This is
a common observation that I have heard from many people.

Of course, this is a combination of two effects.  You are taller as well, so
your POV is from a higher point (to which this is usually attributed).
However, I believe that stereoscopic vision has as much or more to do with
the impression, since apparent size difference works with all objects,
regardless of their height relative to your eye height.  Stereoscopic
"giantism" or "liliputionism", as a result of a narrower or wider stereo
base, is independent of the POV.

JR


 

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