There were a few amateur experiments at emulating three-dimensional vision
prior to the classic 1838 lecture of the then Professor Charles Wheatstone.
Nobody, however - not even Leonardo da Vinci - had realised that stereoscopic
perception relies on the fusing of two DISSIMILAR images.
If you hold a hand up at about forty degrees to your left eye, and at the level
of the eye, it might be eight inches away. It will be ten or so inches away
from the other eye, and at an angle of about thirty degrees to the plane of
your face.
Thus, both the SIZE and the GEOMETRY will be radically different.
We now know that we fuse the image with the mind by STOCHASTIC methods.
We perceive two lines, one per eye, that are ROUGHLY the same - even
though there may be a slight blurring due to focus. This is an IMPRESSION.
Using pulse-frequency modulation, the brain CANNOT evaluate such a situation
to better than about twenty percent - for example, match the lengths of the lines
to over twenty percent.
However, under stochastic laws, the precision of the perception rises as the
SQUARE ROOT of the number of observations.
So in the multiple, parallel SUPERCOMPUTER that is the brain, where there
are about ten billion neurones, or brain cells, a FLOOD of such
IMPRESSIONS is used to raise the accuracy of perception.
This has the merit that although the brain is being seemingly wasted by millions
of cells attending to the same task, when minor damage occurs to the brain it
continues to be unaffected because there are always other channels that can deliver
the required impression.
In 1838, Wheatstone not only anticipated modern neurological knowledge by refuting
that two identical images are simply overlapped, but devised an ingenious experiment
to prove his point.
The eyes do not NEED to play over the image to measure the distance by
triangulation. This was NEW to the world, at the time when he said it.
He "GLUED" images to his retinae, simply by dazzling himself by their
brightness. The afterglow - which he called "SPECTRA" - created a stereoscopic
impression even though it was IMPOSSIBLE to play his eyes over the images.
Today we know that we peceive depth in the REAR OF THE LIMBIC SYSTEM.
The limbic system is the part of the brain that turns data into "FEELINGS".
At the back of the brain is the monochrome vision centre, and the CEREBELLUM
which contains the "DEVICE DRIVERS" - the reflex actions to steer the eyes and limbs.
So we steer the eyes into stereopsis, and the monochrome centre feeds to the limbic
system a flood of reassurances that the shape has been understood.
The limbic system then "FEELS" the shape.
So Wheatstone's observations are supported by modern neurological knowledge.
Beyond this, Wheatstone made an exact study of the geometry - using mathematical
structures such a regular cube or the frustrum of a pyramid.
For the first time, each of the two images was tailored to its eye.
The lithographer J. Basire - or perhaps Wheatstone himself - then playfully created
an image of an arch. The draughtsmanship was guided by the exact geometrical knowledge
that Wheatstone had amassed.
It was perhaps the first of the stereoscopic images that were purely for entertainment
that were now to flood the world, as the craze for this new novelty spread.
Twenty years later, photography arrived - and the Victorians rushed to buy. It was as
if the boom would never end.
Then another craze arrived - the "What the Butler Saw" machine, and MOTION
pictures. Stereoscopy faded - but never went away.
