Illusions | Page 9

performing an act of mental synthesis,
or imaginative construction. To the sense-impression[5] which his eye
now gives him, he adds something which past experience has
bequeathed to his mind. In perception, the material of sensation is acted
on by the mind, which embodies in its present attitude all the results of
its past growth. Let us look at this process of synthesis a little more
closely.

When a sensation arises in the mind, it may, under certain
circumstances, go unattended to. In that case there is no perception.
The sensation floats in the dim outer regions of consciousness as a
vague feeling, the real nature and history of which are unknown. This
remark applies not only to the undefined bodily sensations that are
always oscillating about the threshold of obscure consciousness, but to
the higher sensations connected with the special organs of perception.
The student in optics soon makes the startling discovery that his field of
vision has all through his life been haunted with weird shapes which
have never troubled the serenity of his mind just because they have
never been distinctly attended to.
The immediate result of this process of directing the keen glance of
attention to a sensation is to give it greater force and distinctness. By
attending to it we discriminate it from other feelings present and past,
and classify it with like sensations previously received. Thus, if I
receive a visual impression of the colour orange, the first consequence
of attending to it is to mark it off from other colour-impressions,
including those of red and yellow. And in recognizing the peculiar
quality of the impression by applying to it the term orange, I obviously
connect it with other similar sensations called by the same name. If a
sensation is perfectly new, there cannot, of course, be this process of
classifying, and in this case the closely related operation of
discriminating it from other sensations is less exactly performed. But it
is hardly necessary to remark that, in the mind of the adult, under
ordinary circumstances, no perfectly new sensation ever occurs.
When the sensation, or complex sensation, is thus defined and
recognized, there follows the process of interpretation, by which I mean
the taking up of the impression as an element into the complex mental
state known as a percept. Without going into the philosophical question
of what this process of synthesis exactly means, I may observe that, by
common consent, it takes place to a large extent by help of a
reproduction of sensations of various kinds experienced in the past.
That is to say, the details in this act of combination are drawn from the
store of mental recollections to which the growing mind is ever adding.
In other words, the percept arises through a fusion of an actual

sensation with mental representations or "images" of sensation.[6]
Every element of the object that we thus take up in the act of perception,
or put into the percept, as its actual size, distance, and so on, will be
found to make itself known to us through mental images or revivals of
past experiences, such as those we have in handling the object, moving
to and from it, etc. It follows that if this is an essential ingredient in the
act of perception, the process closely resembles an act of inference; and,
indeed, Helmholtz distinctly calls the perception of distance an
unconscious inference or a mechanically performed act of judgment.
I have hinted that these recovered sensations include the feelings we
experience in connection with muscular activity, as in moving our
limbs, resisting or lifting heavy bodies, and walking to a distant object.
Modern psychology refers the eye's instantaneous recognition of the
most important elements of an object (its essential or "primary"
qualities) to a reinstatement of such simple experiences as these. It is,
indeed, these reproductions which are supposed to constitute the
substantial background of our percepts.
Another thing worth noting with respect to this process of filling up a
sense-impression is that it draws on past sensations of the eye itself.
Thus, when I look at the figure of an acquaintance from behind, my
reproductive visual imagination supplies a representation of the
impressions I am wont to receive when the more interesting aspect of
the object, the front view, is present to my visual sense.[7]
We may distinguish between different steps in the full act of visual
recognition. First of all comes the construction of a material object of a
particular figure and size, and at a particular distance; that is to say, the
recognition of a tangible thing having certain simple space-properties,
and holding a certain relation to other objects, and more especially our
own body, in space. This is the bare perception of an object, which
always takes place even in the