APPLIED STEREOSCOPY 203
grid (bar-screen) or a lenticular grid (grid). In each instance
there is a sharp differentiation into two distinct and different
images.
FREE VIsroN.-The aim, of course, has been to introduce some
system which would make the viewer unnecessary, and to a cer-
tain degree success has been achieved, but this degree is slight.
All of these experimenters have overlooked the essentially vital
factor that the full realism of true stereoscopy can never be real-
ized in free vision nor by any system which dispenses with the
stereoscope for viewing.
The essential factor involved is that of visual-psychological iso-
lation. This factor is so fundamentally important that it is in-
credible that it could ever be overlooked. The only excuse is that
those who work toward this goal seek only an appearance of solid
relief, not the realistic recreation which is the sum and substance
of stereo.
Visitors to New York (for example) often take home as sou-
venirs, small metal models of the Empire State Building. One of
these small models is the full equivalent of the free-vision stereo-
gram of the same building. Both are tiny, solid appearing models,
nothing more. The dual stereogram viewed in the stereoscope is
not anything like this. It provides the visual isolation which gives
to the spectator every visual stimulus he would receive in looking
at the real thing. In short, provided with a good stereo outfit, the
spectator does not look at a picture, he sails away upon a magic
carpet to New York and actually looks at the building itself. He
sees the original, not a picture.
This is not an exaggeration for emphasis, because when you
view a stereogram, you really do see the real original, even though
you are not in its physical presence. The explanation has been
called metaphysical. It is not. It is based upon an accepted fact
of vision which is not widely known.
You say that you “see an automobile,” inferring some kind of
direct physical contact with the automobile. What actually hap-
pens is that you do receive a direct optical image of the automo-
bile in the eye. That image is perceived, as is the one from the
other eye. But in the brain these two images are mixed and from
the mixture is produced a third synthetic image, which is pro-
duced wholly within the brain itself. This image is then psycho-