As sensation is the basis of knowledge, the sensory process must be the
basis of the correctness of legal procedure. The information we get from
our senses and on which we construct our conclusion, may be said, all in
all, to be reliable, so that we are not justified in approaching things
we assume to depend on sense-perception with exaggerated caution.
Nevertheless, this perception is not always completely correct, and the
knowledge of its mistakes must help us and even cause us to wonder that
we make no greater ones.
Psychological examination of sense-perception has been going on since
Heraclitus. Most of the mistakes discovered have been used for various
purposes, from sport to science. They are surprising and attract and
sustain public attention; they have, hence, become familiar, but their
influence upon other phenomena and their consequences in the daily life
have rarely been studied. For two reasons. First, because such illusions
seem to be small and their far-reaching effects are rarely thought of,
as when, e.g., a line drawn on paper seems longer or more inclined than
it really is. Secondly, it is supposed that the influence of sensory
illusions can not easily make a difference in practical life. If the
illusion is observed it is thereby rendered harmless and can have no
effect. If it is not observed and later on leads to serious
consequences, their cause can not possibly be sought out, because it can
not be recognized as such, and because there have been so many
intermediate steps that a correct retroduction is impossible.
This demonstrates the rarity of a practical consideration of
sense-perception, but does not justify that rarity. Of course, there are
great difficulties in applying results of limited experiments to
extensive conditions. They arise from the assumption that the conditions
will be similar to those which the scientist studies, and that a
situation which exhibits certain phenomena under narrow experimental
conditions will show them, also, in the large. But this is not the case,
and it is for this reason that the results of modern psychology have
remained practically unproductive. This, of course, is not a reproach to
the discipline of experimental psychology, or an assault upon the value
of its researches. Its narrow limitations were necessary if anything
definite was to be discovered. But once this has been discovered the
conditions may be extended and something practical may be attained to,
particularly in the matter of illusion of sense. And this possibility
disposes of the second reason for not paying attention to these
illusions.
Witnesses do not of course know that they have suffered from illusions
of sense; we rarely hear them complain of it, anyway. And it is for this
very reason that the criminalist must seek it out. The requirement
involves great difficulties for we get very little help from the immense
literature on the subject. There are two roads to its fulfilment. In the
first place, we must understand the phenomenon as it occurs in our work,
and by tracing it back determine whether and which illusion of the sense
may have caused an abnormal or otherwise unclear fact. The other road is
the theoretical one, which must be called, in this respect, the
preparatory road. It requires our mastery of all that is known of
sense-illusion and particularly of such examples of its hidden nature as
exist. Much of the material of this kind is, however, irrelevant to our
purpose, particularly all that deals with disease and lies in the field
of medicine. Of course, where the nature of the disease is uncertain or
its very presence is unknown, it is as well for us to consider the case
as for the physician. But above all, it is our duty to consult the
physician.
Apart from what belongs to the physician there is the material which
concerns other professions than ours. That must be set aside, though
increasing knowledge may require us to make use even of that. It is
indubitable that we make many observations in which we get the absolute
impression that matters of sensory illusion which do not seem to concern
us lie behind some witnesses’ observations, etc., although we can not
accurately indicate what they are. The only thing to do when this occurs
is either to demonstrate the possibility of their presence or to wait
for some later opportunity to test the witness for them.
Classification will ease our task a great deal. The apparently most
important divisions are those of “normal” and “abnormal.” But as the
boundary between them is indefinite, it would be well to consider that
there is a third class which can not fall under either heading. This is
a class where especially a group of somatic conditions either favor or
cause illusory sense-perceptions, e.g., a rather over-loaded stomach, a
rush of blood to the head, a wakeful night, physical or mental
over-exertion. These conditions are not abnormal or diseased, but as
they are not habitual, they are not normal either. If the overloaded
stomach has turned into a mild indigestion, the increase of blood into
congestion, etc., then we are very near disease, but the boundary
between that and the other condition can not be determined.
Another question is the limit at which illusions of sense begin, how,
indeed, they can be distinguished from correct perceptions. The
possibility of doing so depends upon the typical construction of the
sense-organs in man. By oneself it would be impossible to determine
which sensation is intrinsically correct and which is an illusion. There
are a great many illusions of sense which all men suffer from under
similar conditions, so that the judgment of the majority can not be
normative. Nor can the control of one sense by another serve to
distinguish illusory from correct perception. In many cases it is quite
possible to test the sense of sight by touch, or the sense of hearing by
sight, but that is not always so. The simplest thing is to say that a
sense-impression is correct and implies reality when it remains
identical under various circumstances, in various conditions, when
connected with other senses, and observed by different men, with
different instruments. It is illusory when it is not so constant. But
here again the limit of the application of the term “illusion” is
difficult to indicate. That distant things seem to be smaller than they
are; that railway tracks and two sides of a street seem to run together
are intrinsically real illusions of sense, but they are not so
called--they are called the laws of perspective, so that it would seem
that we must add to the notion of sense-perception that of rarity, or
extraordinary appearance.
I have found still another distinction which I consider important. It
consists in the difference between real illusions and those false
conceptions in which the mistake originates as false inference. In the
former the sense organ has been really registering wrongly, as when, for
example, the pupil of the eye is pressed laterally and everything is
seen double. But when I see a landscape through a piece of red glass,
and believe the landscape to be really red, the mistake is one of
inference only, since I have not included the effect of the glass in my
concluding conception. So again, when in a rain I believe mountains to
be nearer than they really are, or when I believe the stick in the water
to be really bent, my sensations are perfectly correct, but my
inferences are wrong. In the last instance, even a photograph will show
the stick in water as bent.
This difference in the nature of illusion is particularly evident in
those phenomena of expectation that people tend to miscall “illusions of
sense.” If, in church, anybody hears a dull, weak tone, he will believe
that the organ is beginning to sound, because it is appropriate to
assume that. In the presence of a train of steam cars which shows every
sign of being ready to start you may easily get the illusion that it is
already going. Now, how is the sense to have been mistaken in such
cases? The ear has really heard a noise, the eye has really seen a
train, and both have registered correctly, but it is not their function
to qualify the impression they register, and if the imagination then
effects a false inference, that can not be called an illusion of
sensation.
The incorrectness of such classification becomes still more obvious when
some numerical, arithmetical demonstration can be given of the presence
of faulty inference. For example, if I see through the window a man very
far away clearing a lot with an ax, I naturally see the ax fall before I
hear the noise of the blow. Now, it may happen that the distance may be
just great enough to make me hear the sound of the second blow at the
moment in which I see the delivery of the third blow. Thus I perceive at
the same moment, in spite of the great distance, both the phenomena of
light and of sound, just as if I were directly on the spot. Perhaps I
will wonder at first about these physical anomalies, and then, if I have
made my simple mistake in inference, I shall tell somebody about the
remarkable “sensory illusion” I had today, although no one had ever
supposed me capable of being deceived in this way. Schopenhauer calls
attention to the familiar fact that on waking after a short nap all
localizations are apparently perverted, and the mind does not know what
is in front, what behind, what to the right, and what to the left. To
call also this sensory illusion, would again be wrong, since the mind is
not fully awake, and sufficiently orientated to know clearly its
condition. The matter is different when we do not properly estimate an
uncustomary sense-impression. A light touch in an unaccustomed part of
the body is felt as a heavy weight. After the loss of a tooth we feel an
enormous cave in the mouth, and what a nonsensical idea we have of what
is happening when the dentist is drilling a hole in a tooth! In all
these cases the senses have received a new impression which they have
not yet succeeded in judging properly, and hence, make a false
announcement of the object. It is to this fact that all fundamentally
incorrect judgments of new impressions must be attributed,--for example,
when we pass from darkness into bright light and find it very sharp;
when we find a cellar warm in winter that we believe to be ice-cold in
summer; when we suppose ourselves to be high up in the air the first
time we are on horseback, etc. Now, the actual presence of sensory
illusions is especially important to us because we must make certain
tests to determine whether testimony depends on them or not, and it is
of great moment to know whether the illusions depend on the individual’s
mind or on his senses. We may trust a man’s intellect and not his
senses, and conversely, from the very beginning.
It would be superfluous to talk of the importance of sensory illusion in
the determination of a sentence. The correctness of the judgment depends
on the correctness of the transmitted observations, and to understand
the nature of sense-illusion and its frequency is to know its
significance for punishment. There are many mistakes of judges based
entirely on ignorance of this matter. Once a man who claimed, in spite
of absolute darkness, to have recognized an opponent who punched him in
the eye, was altogether believed, simply because it was assumed that the
punch was so vigorous that the wounded man saw sparks by the light of
which he could recognize the other. And yet already Aristotle knew that
such sparks are only subjective. But that such things were believed is a
notable warning.[309]