P3D Reality of Seeing

[jacob@xxxxxxxxxxxxxx (Gabriel Jacob)]

Paul writes (in another post):
>Great post, Bruce.  Stereo slides appear "more realistic" than flat
>images to me, but I've never felt them as being "real" to the same
>extent that many others do.

It looks like you and I are the only ones. Seriously I think there
are others with this affliction! ;-) I think I have commented on
that in the past and I know you have.

My guess as to why is because of accommodation (eye focusing far or
close). Even though it is a very weak way of determining absolute
distance, I think certain individuals are more sensitive to it's
effects. This is not to say they can resolve distances very well
but they can tell if it is close or far away. Therefore in the
case of viewers (2-D and 3-D) I (as also Paul does) doesn't get
fooled that the distance is at the place the image suggests it
is. For people that are not sensitive to accommodation they sense
the image as if it was in reality. 

In my informal experiments I had tried viewing one side of a stereo
pair (can be done with a 2-D slide for that matter) and looked at
it with one eye and with the other eye stared at a blank wall far
away. Superimposing the image onto the wall, so that the eye looking
at the blank wall also "sees" (brain actually sees this image) the
image, what happens is that the brain is getting two different 
accomodation signals. One where the eye viewing the image is sending
a tensed muscle signal and the other eye sending a relaxed state. In
this case the brain has a hard time determining the overriding one,
but when the relaxed state was predominent I sensed that the image
was actually far away and huge instead of a few inches away and 
small. It is quite breathtaking when this happens!

This is all very similiar (and might shed light to 3-D perception)
to a paper that studied the effect of distance and television
screen sizes had on the perception of overall size. From what I
remember reading, it seems that it is not only simple geometry but
also involves other psychological and physiological factors.    

Gabriel



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