338 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vou. VIII. 
face and nothing else; of course it must of necessity be a plane, for a curved 
surface would pre-suppose depth perception. Perhaps one could accept 
also the surface of an infinite sphere. ‘Then all things which we perceive, 
including our own body, and consequently the mind’s standpoint of obser- 
vation should be within that surface. Though we cannot say the ego is 
definitely located in the body or in the brain, we nevertheless give at any 
point of time a definite location in space to the standpoint of observation. 
In monocular vision we put the standpoint of observation into 
one point of the axis of the eye and in binocular vision it is a point some- 
what behind the middle point of the straight line which combines the centres 
of the two eyes. Now if the visual space were originally given as a sur- 
face in no distance, we, 2. e., our standpoint of observation would neces- 
sarily be in that surface too, and then arises the question, could we see 
a surface at all? It must be answered in the negative, for we would only 
be able to see lines, in other words even the second dimension would 
already be a product of inference, not something really given. So much 
is certain, one cannot perceive a plane from a point within that plane. 
The conditio sine qua non for the perception of a surface is to be outside 
of that surface. Thus the perception of two dimensional space structures 
silently involves what is usually called the third dimension, but what, 
as we Shall see later on, should better be designated ‘‘extension in all 
possible directions.” 
As everywhere else, so also in case of the perception of a surface, 
Wundt’s doctrine of the presentation-object, according to which the 
distinction of subject and object is the outcome of abstraction, is valid. 
At the moment when I perceive a surface I am the perceived surface. 
I am not only the perceived surface but I am a great many other things. 
If now the other things which I am or experience are not within that first 
surface, then it is clear that I must have immediately more than a two 
dimensional space. It is claimed that man has in his early childhood 
no perception of depth, for, so it is argued, the child grasps for the moon 
as well as for an apple. This proves only that at this age no measuring 
exploration of the depth has as yet taken place, so that the child, though 
he puts the moon and the apple in indefinite distances, has not yet learned 
to apply magnitude to distance. It is perfectly correct that our light 
and colour sensations are of a surface nature, but the perception of a Sur- 
face is only possible in fully extended space. A seen surface is only the 
far limit of a perceived part of space extended in all directions ; we might 
say the basis of a transparent pyramid the apex of which is in the eye. 
Even our memory images and the products of imagination are not excepted 
here. Though they have no definite localization in the vision field, they 
