I combine, for the sake of simplicity, the senses of location, pressure,
temperature, etc., under the general expression: sense of touch. The
problem this sense raises is no light one because many witnesses tell of
perceptions made in the dark or when they were otherwise unable to see,
and because much is perceived by means of this sense in assaults,
wounds, and other contacts. In most cases such witnesses have been
unable to regard the touched parts of their bodies, so that we have to
depend upon this touch-sense alone. Full certainty is possible only when
sight and touch have worked together and rectified one another. It has
been shown that the conception of the third dimension can not be
obtained through the sense of sight. At the beginning we owe the
perception of this dimension only to touch and later on to experience
and habit. The truth of this statement is confirmed by the reports of
persons who, born blind, have gained sight. Some were unable to
distinguish by means of mere sight a silver pencil-holder from a large
key. They could only tell them to be different things, and recognized
their nature only after they had felt them. On the other hand, the
deceptive possibilities in touch are seen in the well-known mistakes to
which one is subjected in blind touching. At the same time practice
leads to considerable accuracy in touch and on many occasions the sense
is trusted more than sight--e.g., whenever we test the delicacy of an
object with our finger-tips. The fineness of paper, leather, the
smoothness of a surface, the presence of points, are always tested with
the fingers. So that if a witness assures us that this or that was very
smooth, or that this surface was very raw, we must regularly ask him
whether he had tested the quality by touching it with his fingers, and
we are certain only if he says yes. Whoever has to depend much on the
sense of touch increases its field of perception, as we know from the
delicacy of the sense in blind people. The statements of the blind
concerning their contact sensations may be believed even when they seem
improbable; there are blind persons who may feel the very color of
fabrics, because the various pigments and their medium give a different
surface-quality to the cloth they color.
In another direction, again, it is the deaf who have especial power. So,
we are assured by Abercrombie that in his medical practice he had
frequently observed how deaf people will perceive the roll of an
approaching wagon, or the approach of a person, long before people with
good hearing do so. For a long time I owned an Angora which, like all
Angoras, was completely deaf, and her deafness had been tested by
physicians. Nevertheless, if the animal was dozing somewhere and anybody
came near it, she would immediately notice his steps, and would
distinguish them, for she would jump up frightened, if the newcomer was
unknown, and would stretch herself with pleasure in the expectation of
petting if she felt a friend coming. She would sense the lightest touch
on the object she occupied, bench, window-seat, sofa, etc., and she was
especially sensitive to very light scratching of the object. Such
sensitivity is duplicated frequently in persons who are hard of hearing,
and whom, therefore, we are likely to doubt.
The sense of touch is, moreover, improved not only by practice, but also
by the training of the muscles. Stricker asserts that he has frequently
noticed that the observational capacity of individuals who make much use
of their muscles is greater than among persons whose habits are
sedentary. This does not contradict the truth established by many
experiments that the educated man is more sensitive in all directions
than the uneducated. Again, women have a better developed sense of touch
than men, the space-sense and the pressure-sense being equivalent in
both sexes. On these special forms of the touch-sense injections of
various kinds have decided influence. The injection of morphine, e.g.,
reduces the space-sense in the skin. _Cannabinum tannicum_ reduces
sensibility and alcohol is swift and considerable in its effects.
According to Reichenbach some sensitives are extreme in their feeling.
The best of them notice immediately the approach and relative position
of people, or the presence of another in a dark room. That very nervous
people frequently feel air pressure, fine vibrations, etc., is perfectly
true. And this and other facts show the great variety of touch
impressions that may be distinguished. The sense of temperature has a
comparatively high development, and more so in women than in men. At the
lips and with the tips of the fingers, differences of two-tenths of a
degree are perceived. But where an absolute valuation and not a
difference is to be perceived, the mean variation, generally, is not
much less than 4 degrees. E.g., a temperature of 19 degrees R. will be
estimated at from 17 to 21 degrees. I believe, however, that the
estimation of very common temperatures must be accepted as correct.
E.g., anybody accustomed to have his room in winter 14 degrees R. will
immediately notice, and correctly estimate, the rise or fall of one
degree. Again, anybody who takes cold baths in summer will observe a
change of one degree in temperature. It will, therefore, be possible to
believe the pronouncements of witnesses concerning a narrow range of
temperatures, but all the conditions of perception must be noted for the
differences are extreme. It has been shown, e.g., that the whole hand
finds water of 29 degrees R. warmer than water of 32 degrees R. which is
merely tested with the finger. Further, Weber points out,[186] “If we
put two adjacent fingers into two different warm fluids the sensations
flow together in such a way that it is difficult to distinguish
differences. But if we use two hands in this test, it is especially
successful when we change the hands from one fluid to another. The
closer the points on the skin which receive contemporary impressions,
and perhaps, the closer the portions of the brain to which these
impressions are sent, the more easily these sensations flow together;
while again, the further they are from one another the less frequently
does this occur.” In the practice of criminal law such matters will
rarely arise, but estimations of temperature are frequently required and
their reliability must be established.
It is important to know what a wounded man and his enemy feel in the
first instant of the crime and in what degree their testimonies are
reliable. First of all, we have to thank the excellent observations of
Weber, for the knowledge that we find it very difficult to discover with
closed eyes the angle made by a dagger thrust against the body. It is
equally difficult to determine the direction from which a push or blow
has come. On the other hand we can tell very accurately in what
direction a handful of hair is pulled.
With regard to the time it takes to feel contact and pain, it is
asserted that a short powerful blow on a corn is felt immediately, but
the pain of it one to two seconds later. It may be that corns have an
especial constitution, but otherwise the time assigned before feeling
pain is far too long. Helmholtz made 1850 measurements which proved that
the nervous current moves 90 feet a second. If, then, you prick your
finger, you feel it a thirtieth of a second later. The easiest
experiments which may be made in that regard are insufficient to
establish anything definite. We can only say that the perception of a
peripheral pain occurs an observable period after the shock, i.e., about
a third of a second later than its cause.
The sensation of a stab is often identified as contact with a hot
object, and it is further asserted that the wounded person feels close
to the pain which accompanies the push or the cut, the cold of the blade
and its presence in the depths of his body. So far as I have been able
to learn from wounded people, these assertions are not confirmed.
Setting aside individuals who exaggerate intentionally and want to make
themselves interesting or to indicate considerable damage, all answers
point to the fact that stabs, shots, and blows are sensed as pushes. In
addition, the rising of the blood is felt almost immediately, but
nothing else; pain comes much later. It is asserted by
couleur-students[187] who have occasion to have a considerable number of
duels behind them, that “sitting thrusts,” even when they are made with
the sharpest swords, are sensed only as painless, or almost painless,
blows or pushes. Curiously enough all say that the sensation is felt as
if caused by some very broad dull tool: a falling shingle, perhaps. But
not one has felt the cold of the entering blade.
Soldiers whose shot wounds were inquired into, often just a few minutes
after their being wounded, have said unanimously that they had felt only
a hard push.
It is quite different with the man who causes the wound. Lotze has
rightly called attention to the fact that in mounting a ladder with
elastic rungs one perceives clearly the points at which the rungs are
fastened to the sides. The points at which an elastic trellis is
fastened is felt when it is shaken, and the resistance of the wood when
an axe is used on it. In the same way the soldier senses clearly the
entrance of his sword-point or blade into the body of his enemy. The
last fact is confirmed by the students. One can clearly distinguish
whether the sword has merely beaten through the skin or has sunk deeply
and reached the bone. And this sensation of touch is concentrated in the
_right_ thumb, which is barely under the hilt of the sword at the point
where the grip rests.
The importance of the fact that the wounder feels his success lies in
the possibility it gives him, when he wants to tell the truth, to
indicate reliably whether and how far he has wounded his opponent. The
importance of the testimony of the wounded man lies in its influence on
determining, in cases where there were more than one concerned in the
assault, which wound is to be assigned to which man. We often hear from
the victim who really desires to tell the truth, “I was quite convinced
that X dealt me the deep stab in the shoulder, but he has only pushed
and not stabbed me--I did not perceive a stab.” Just the same, it was X
who stabbed him, and if the examining judge explains the matter to the
victim, his testimony will be yet more honest.
There are still a few other significant facts.
1. It is well known that the portion of the skin which covers a bone and
which is then so pulled away that it covers a fleshy part, can not
easily identify the point of stimulation. Such transpositions may be
made intentionally in this experiment, but they occur frequently through
vigorous twists of the body. When the upper part of the body is drawn
backwards, while one is sitting down, a collection of such
transpositions occur and it is very hard then to localize a blow or
stab. So, too, when an arm is held backward in such a way as to turn the
flat of the hand uppermost. It is still more difficult to locate a wound
when one part of the body is held by another person and the skin pulled
aside.
2. The sensation of wetness is composed of that of cold and easy
movement over surface. Hence, when we touch without warning a cold
smooth piece of metal, we think that we are touching something wet. But
the converse is true for we believe that we are touching something cold
and smooth when it is only wet. Hence the numerous mistakes about
bleeding after wounds. The wounded man or his companions believe that
they have felt blood when they have only felt some smooth metal, or they
have really felt blood and have taken it for something smooth and cold.
Mistakes about whether there was blood or not have led to frequent
confusion.
3. Repetition, and hence summation, intensifies and clarifies the
sensation of touch. As a consequence, whenever we want to test anything
by touching it we do so repeatedly, drawing the finger up and down and
holding the object between the fingers; for the same reason we
repeatedly feel objects with pleasant exteriors. We like to move our
hands up and down smooth or soft furry surfaces, in order to sense them
more clearly, or to make the sensation different because of its duration
and continuance. Hence it is important, every time something has to be
determined through touch, to ask whether the touch occurred once only or
was repeated. The relation is not the same in this case as between a
hasty glance and accurate survey, for in touching, essential differences
may appear.
4. It is very difficult to determine merely by touch whether a thing is
straight or crooked, flat, convex or concave. Weber has shown that a
glass plate drawn before the finger in such wise as to be held weakly at
first, then more powerfully, then again more powerfully seems to be
convex and when the reverse is done, concave. Flatness is given when the
distance is kept constant.
5. According to Vierordt,[188] the motion of a point at a constant rate
over a sizable piece of skin, e.g., the back of the hand from the wrist
to the finger tips, gives, if not looked at, the definite impression of
increasing rapidity. In the opposite direction, the definiteness is less
but increases with the extent of skin covered. This indicates that
mistakes may be made in such wounds as cuts, scratches, etc.
6. The problem may arise of the reliability of impressions of habitual
pressure. Weber made the earliest experiments, later verified by
Fechner, showing that the sensation of weight differs a great deal on
different portions of the skin. The most sensitive are the forehead, the
temples, the eyelids, the inside of the forearm. The most insensitive
are the lips, the trunk and the finger-nails. If piles of six silver
dollars are laid on various parts of the body, and then removed, one at
a time, the differences are variously felt. In order to notice a removal
the following number must be taken away:
One dollar from the top of the finger,
One dollar from the sole of the foot,
Two dollars from the flat of the hand,
Two dollars from the shoulder blade,
Three dollars from the heel,
Four dollars from the back of the head,
Four dollars from the breast,
Five dollars from the middle of the back,
Five dollars from the abdomen.
Further examinations have revealed nothing new. Successful experiments
to determine differences between men and women, educated and uneducated,
in the acuteness of the sense of pressure, have not been made. The facts
they involve may be of use in cases of assault, choking, etc.
Topic 2. PERCEPTION AND CONCEPTION.