P3D Re: 3-DVG Effect

["KENNETH LUKER" <kluker@xxxxxxxxxxxxxxxxxxxxxxx>]

> I think the operative word here is EFFECT. Not true Stereo, but an optical
> illusion, I think this is another example. You think you see stereo but it
> has to be something else entirely.

     I believe it CANNOT be true stereo, since there is nothing seen 
by either eye that cannot be seen also by the other.  There is just 
no stereo information there.  Yet those who have experienced the 
effect have experienced something, and it feels like, looks like, 
(quacks like?) stereo.  I believe it has something to do with the 
sharpness of the scene, and with the way the mind processes sharp 
edges of what the eye sees.  There may also be something going on 
with the mental understanding of what the eyes are known to be 
seeing--the mind lends a stereo feeling to what it knows must be 
three-dimensional.  That is certainly part of the difficulty in 
perceiving a pseudo-stereo human face as being concave.  It is almost 
impossible to do.  

     Here's a test:  Take a monocular picture of something with 
texture--say a sheet of bubble wrap, or a piece of corrugated 
material, especially when it is something a bit different from what 
the viewer might already be familiar with.   View it using the 
3-DVG method and see  whether the apparent concavity or convexity of 
the piece, or the apparent direction of illumination, changes from 
one viewing to another, or between observers, the way a staircase or 
stack of blocks inverts itself in some optical illusions, or the way 
the dark and light profiles alternate in some gestalt experiments.  
I'd predict that there would be a relatively random orientation of 
the stereopsis among the independent observations.

Ken Luker 
_______________________________________________________________
Kenneth Luker
Marriott Library Systems and Technical Services
KLUKER@xxxxxxxxxxxxxxxx


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