todd (03/12/83)
Subject: 3-D Movies and Pulferich's Pendulum
3-d movies, so-called, make use of visual illusions in one form or another.
The red/blue approach to 3-d movies specifically makes use of
the human visual system's differential response latencies in processing
red versus blue (low frequency versus high frequency) input.
Pulferich (I believe in the 19th century) first noticed this when he viewed
the motion of a pendulum with red and blue filters over his eyes (one
each). The pendulum motion appeared to be circular in depth rather than
merely back and forth.
We now know that the "red system" in the retina and the
visual cortex processes lightwave stimuli in the red visible region of the
spectrum faster than the corresponding response of the "blue system"
processes lightwaves in the blue region. However, since the visual input of
both eyes eventually gets processed as one object at some
higher cortical center, that object has a red input arriving faster than a
blue input from the other eye.
Now comes the clincher: The mammalian visual system is hard-wired
to construe such inter-ocular delays as information about depth.
Thus, your red/blue delay induced by colored glasses is evoking (albeit
artifically) a highly adaptive mechanism of binocular vision for which
mammals are well known.
The color (hue) of the screen is really a mixture of reds and blues
roughly overlaid and designed to feed separate color "channels" to each eye
when you have the "magic" glasses on. For viewing without glasses, the
producers may have allowed full color. However, the other colors are not
relevant to the 3-d effect. Now, when you view the screen through a
red/blue set of filters, reds and blues are effectively washed out of the
color percept, leaving shades of grey and yellow (green from the full color
movie print plus red from your one eye's filter make yellow).
Hope that answers the questions.
I'm sure you also noted limitations in the red/blue method. Wait
until they perfect true 3-d cinema with full-color holography. That is no
trick on the visual system!!
Todd Tieger
pyuxss!todd