SOME NEW ASPECTS IN STEREOSCOPIC VISION 
by C. A. J. von Friyrac Drasse, Delft, Holland. 
Introduction. 
The aim of the following study is to afford a deeper insight into the problems 
of stereoscopy. 
This cannot be attained without first considering how we “see” the mental 
image of the outside world when looking with one eye. 
Experience has taught us that when seeing binocularly, the rules of obser- 
vations show a typical deviation with relation to the observation with one eye. 
The following considerations should therefore be taken into account, which in 
their turn, illustrate that when seeing binocularly, the mental images of each of 
our retinal images may occur separately. Let us examine this property more closely, 
thus obtaining a clear insight into the ways and means of fusing these separated 
images. 
We then find that by one of these ways the so-called stereoscopic observation 
will become possible. At the same time the position as to where we subjectively 
“observe” the stereoscopic image may be approximately determined. 
This problem where we observe the stereo image has never, to our knowledge, 
been quite definitely solved, neither with regard to the distance of observation, 
nor with regard to its position. 
Monocular vision or vision with one eye. 
When closing one eye and focusing the other upon an object, we get an 
image of the object on which the eye is focused. This lies for us unchangeable on 
one spot, viz. in the exact direction where the object is. 
Without special means we are not able to see the image anywhere else than 
in that place. 
By this we get the impression as if we see the object itself in its place in the 
outside world. 
Yet this is only apparent. What is the case, however? We focus our eye on 
the object and we get on our retina a strongly reduced and at the same time an 
inverted image. Until this point the relation between us and the object is still 
merely of an optical nature. The retinal image itself is formed, after the rays 
coming from the object have passed our eye-lens, according to the normal optical 
rules (fig. I). 
After that, the retinal image we caught from the outside world, comes to our 
consciousness by a neurological and psychological way by means of a process 
which has nothing to do and obviously cannot have anything to do with optics. 
We ourselves take possession of the retinal image and what we make of it 
need not be completely analogous to reality. 
Nobody exactly knows, at least with regard to the colour, how our outside 
world looks. We see a red colour, but is that the very same colour the object 
reflects indeed? We do not know this; we only know that the average man 
experiences this colour as red; but at the same time we know that there are 
others, viz. the colourblind, who do not experience this colour as such. So 
becoming aware of the colour is already something subjective. But so 1s 
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