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Diffused throughout the organism as a whole, yet
specially seated in the skin, the sense of temperature
has claims to be grouped botli with the organic sensa-
tions and with the sense of contact proper. Some
writers have maintained that our consciousness ot
temperature is dependent on a set of nerves distinct
from those employed in tactual sensation. This is not
yet absolutely proved, but that the properties of the
nerve-fibres involved are completely different^ is shown
by the fact that either class of feelings may be almost
entirely suspended, whilst the other remains compara-
tivel}^ unaffected.

Sensations. — As our consciousness of temperature is
relative to that of our own person, this sense can afford
little assurance about the absolute heat or coldness of
an external object. When the environment is of the
same temperature with that of the part of our body
exposed, we are unconscious of it. If we pass into the
chill night air from a hot room, we are keenly aware of
the change, but even before the skin of our face and
hands is reduced to the same degree of warmth as the
surrounding atmosphere, we become habituated to the
stimulus, and consciousness of temperature almost
disappears. It has been found, however, that wdthin
a moderate range, fine variations can be noticed in
comparing the temperatures of two bodies ; and the
hand is able to detect a difference of J a degree Cent,
in two vessels of water. The effect of heat or cold
increases with the extent of the surface exposed. Thus,
water which feels only comfortably warm to the hand

'' Recent ingenious experiments by Goldscheider and other
physiologists, seem to show not merely that the nervous end-
apparatus of temperature sensations differs from that of pressure
and of pain, but even that there are in the skin distinct " heat-spots "
and "cold-spots"— minute localities sensitive to heat but not to
cold, and conversely. This appears surprising when we recollect
that to the physicist heat and cold are purely relative. (Cf. Ladd,
op. cit. pp. 34^—350)



THE SENSES. ' 71



or arm, may cause severe pain if the whole person is
immersed. In extreme heat and cold, the sensation of
temperature proper disappears, and, instead, in both
cases, a like feeling of keen organic pain ensues. In
polar voyages, the sailors speak of cold objects burning
their hands. Viewed generally, this sense is of little
cognitive, but of much emotional significance. Its
appropriate pleasure lies in moderate warmth, its
specific pain in extreme heat and cold.

Sense of Contact or Passive Touch. — Physio-
logical conditions. — The organ of this sense consists of a
system of papillcd distributed over the surface of the
dermis, or under-skin, which covers the surface of the
bod3\ Above this dermis lies the cuticle or external skin,
which acts as a protection for the papillae, nerves, and
veins lying beneath. From the papillae proceed nerve-
fibrils to the spinal column and thence to the brain.
The proper stimulus of the sense of touch is simple
pressure on the external skin. In order that a sensation
be awakened, the effect of the physical excitation at
the surface must be transmitted along a sensory nerve
to the brain. If the nerve is severed above the point
of irritation, no mental state is elicited, and if an
intersected nerve is irritated above the point of sever-
ance, the cause of the sensation aroused is judged to be
at the old peripheral extremity. From this it has been
inferred that the sensation occurs not at the surface,
but in the brain or central sensorium, and that it is by
experience we come to learn the seat of the exterior
impression.*^ If this doctrine is to be interpreted as

^ The doctrine that the true seat of sensation is a Hmited
internal centre is as old as Aristotle. (Cf. St. Thomas, Comm. De
Anima, II. 11. 22, 23.) He holds there that the heart is the proper
locus of tactual sensation, the intervening flesh being only a medium
differing from the air or other external media by the fact that it is
not an accidental but a connatural instrument. That our apparent
consciousness to the contrary does not suffice to decide the question,
he shows by pointing to the fact that if a covering or rigid substance
is placed between the skin and the excitant, we then localize the
sensation at the outer surface of the new tegument, and not in the
skin. In the De Gen. Animalium, however, he seems to pass into
the other view. (Cf. also P. S. Seewis, Delia Conoscenza Sensitiva,
pp. 368 — 372.) Dr. Stockl is among the most distinguished of



72 SENSUOUS LIFE.



implying that peripheral stimuli were originally localized
by us in the brain, or that the soul is confined within
the limits of the brain chamber, and that the action of
the excitant impinges upon it there, then it must be
rejected as warranted neither by ph3'siological nor
psychological evidence. The fact, however, may be
held to show that our ability to localize impressions
is very largely due to experience, and that our original
capacity in this respect was very imperfect.

The physiological process which is the proximate
cause of sensation contains three stages. The first is
the peculiar action set up in the exterior terminals of
the nerves of the various senses. The specialization
in structure and constitution of these apparatus, which
modern Physiology has brought into prominence,
demonstrates the significance of this moment in the
operation. The second step is the transference of
the excitation by means of a molecular change along
the nerve to the brain. Here the last item in the
physical process takes place, but of its character we
know virtually nothing. On its completion, however,
the soul which animates equally every part of the
nervous system, and, in fact, every part of the organism,
reacts in the form of a conscious sensation. The
quality of this mental state is affected by the portion
of the body in which the physiological process has
taken place ; the feeling, for instance, of an impression
on the leg or the back is different from that of a similar
impression on the arm. Nevertheless, the sensation
is not definitely localized from the beginning at the
precise spot of peripheral stimulation ; the exact site
of the starting-point of the neural change is learned by
experience. This subject will, however, be discussed
more fully in a future chapter.

Cognitional Value of Touch. — The sense of touch
stands very high as a medium of external perception,
•/et its sensations possess in many respects the vague-



modern scholastic writers who support the view that sensation is
elicited, not in the external parts of the sense-organ, but in the
brain. (Cf. Empirische PsycJwlogie, § 6, n. 12.)



THE SENSES. 73



ness and want of precision wliich cliaracterize the
faculties hitherto dealt with. Thus there is compara-
tively little variety in kind among our tactual feelings
which are mainly discriminated as rough, smooth,
gentle, and pungent. They possess, however, a delicate
sensibility to differences in the intensity and duration
of the stimulus, and still more important in this con-
nexion, they are endowed with fine local characters on
account of which they come to be referred with great
accuracy to the place of excitation. By means of this
property the mind is able simultaneously to apprehend
co-existing points, cognizing them as separate ; and in
this apprehension there is the presentation of extended
space. The simplest form of tactual sensation, such as
that of the contact of a feather, does not seem to
involve the feeling of pressure, and this is sometimes
styled the sense of contact proper, but it scarcely
passes beyond the range of the organic sensations.
The vast majority of our sensations of contact are
sensations of pressure, and this element must be
included under the sense of touch.

Discriminative Sensibility. — The sensibility of the skin
to purely tactual pressure varies in different parts of
the body. If a particular point on the hand is tested,
we can, according to some writers, notice the difference
between two successive pressures when it equals the
■^^th of the original weight. Pressures on two different
hands can only be observed when one exceeds the other
by "I. The capacity of touch for local discrimination
also varies in different parts of the skin. The method
of experiment adopted by Weber, was to place the
two points of a pair of compasses on the part to be
examined, and then to widen or narrow them until the
two points could be just felt as separate. It was found
that along portions of the back and forearm the points
of the compass required to be from two to three inches
apart in order to be distinguished, whilst on the tips of
the fingers and the tongue an interval of one twelfth
and one twenty-fifth of an inch sufficed. The spaces
within which the doubleness of the stimulus is not
observed are called "sensory circles," though the figure



74 SENSUOUS LIFE.



is not generally an exact circle. The smallness of the
circle measures the perfection of the sensibility.

The consciousness of mere contact, of tactual
pressure, and, with some writers, that of temperature,
comprise the feelings which should be grouped under
touch proper. There are, also, a few other special modes
of tactual sensation, such as tickling, and itch, which
have a very well marked character of their own.
Sensations of touch cannot be very vividly reproduced
in imagination ; yet the reality of these representations
is shown by our power of comparing a present sensation
of touch, such as that of a brush or piece of silk, wdth a
recollected experience, and also by the manner in which
ideal sensations of touch are awakened by the visual
appearance of objects. We seem io see the roughness,
smoothness, or softness of objects, although, of course,
these properties can only be apprehended by touch.
This fact, too, marks the high degree of associability
possessed by these sensations. These various qualities
of the sense of touch give it great importance in the
department of objective cognition. We have not,
however, hitherto laid stress on the fact that pressure,
revealed through tactual sensations, is an influential
agent in the generation of our conviction of the
externality of the material world, just as the apprehen-
sion of co-existing points determines our assurance of
its extension. In such sensations of pressure muscular
feelings are often implied, and though passively received
impressions of contact do really involve the apprehen-
sion of something other than ourselves, yet it is when
combined with the muscular sensations, and as con-
sequent on the effort put forth by our own energy, that
their full significance in the apprehension of the reality
of the external world is realized. As a source of
pleasure the sense of touch, apart from feelings of
temperature and other organic states, ranks low. It
has, however, been selected from the beginning as the
sense most convenient for the intiiction of chastisement,
and its capacity in this respect is indisputable.

Active Touch. — The muscular or kinesthetic sensa-
iions. — Sensations of pressure are commonly blended



THE SENSES. 75



with muscular feelings of resistance on our part, and
occasionally with those of movement. These feelings of
impeded energy and of movement constitute the mani-
festations of the so-called active or muscidav sense of
modern pS3xhologists, and it is in connexion with these
that the intellectual or cognitional importance of touch
becomes most conspicuous. The difference between
the tactual and muscular consciousness of pressure will
be realized by holding up a half-pound weight on our
hand, and then placing the same weight on our hand
whilst the latter is supported by the table. In the
former case there is in addition to the tactual impression
a feeling described as a sense of effort or strain. Again,
if we allow our arm to be unresistingly moved by
another person, we shall have the passive consciousness
of pressure or contact, with also faint tactual and
organic feelings due to the changing position of the
skin, joints, and muscles. But if we ourselves move it,
instead of the passive feeling of pressure we have the
consciousness of muscular energy put forth, accom-
panied as before b}^ the faint organic and tactual
sensations due to the varying position of the limb.



Physiolog^ical Conditions. — The analysis of this state of
consciousness and the determination of the physiological
conditions of its various elements have given rise to the
Muscular Sense Controversy, an unsettled dispute in which
psychological, physiological, and pathological evidence is
invoked on both sides.

(i) One theory holds that our muscular consciousness
consists merely of a special class of tactual sensations seated
in ordinary afferent nerves in the skin and surface teguments,
the crumpling, pressure, and strain of which excite these
feelings, 'i'o this it is objected that in cases where the skin is
rendered insensible by disease or anassihetics like cocain, the
power of movement and the feeling of effort often remain.

(2) The second theory includes among the elements of our
muscular consciousness besides those of the skin, sensations
located in sensory nerves pertaining to the muscles, tendons,
ligaments, and cartilage connexions of the joints. All these
feelings, it holds, are the concomitants of in-coming nervous
processes along aff'erent nerves. They report and measure
movement, strain, or resistance already accomplished, not



76 SENSUOUS LIFE.



something to be done. Among the advocates of this view are
W.James, Ferrier, Bastian, and Munsterberg.

(3) The third theory maintains that in addition to, and
quite distinct from these incoming or peripherally excited
feelings, our muscular consciousness includes a feeling of
innervation, oi effort put fortli, the mental correlate of centrally
initiated outgoing currents of motor energy which traverse the
efferent nerves in the execution of movement or resistance.
Its chief supporters are Bain, Wundt, Ladd, Stout, and
Baldwin.

In behalf of (3) it is argued : {a) In children and young
animals there is exhibited from the very beginning a fund ot
activity and spontaneous movements originated by a surplus
of energy rather than by external stimulation. The feeUngs
attached to such primitive activity must have for their
physical basis efferent or motor discharges. (Bain.) {b) A patient
who strives to move a paralyzed limb is conscious of effort
without any sensation of movement — which does not take
place, (c) If the muscles which move the eye to right or left
are partly paralyzed, the degree of rotation needed to fixate
an object is over-estimated and its position misjudged. This
illusion proves that our estimate of the movement is measured
by the intensity of the effort or innervation which has to be
exerted, not by incoming sensations of muscular contraction
actually accomplished in the movement. (Wundt.)

In favour of (2) it is urged by W. James : (a) The
assumption of this unique active sense or feeling of innervation,
opposed in nature to all other forms of sensation, — whicli are
concomitants of afferent nervous processes — is ^'unnecessary.''''
This feeling, were it ever present, would have vanished as a
useless link. Movements due to emotions and reflex action
occur without it. {b) There is really no introspective evidence
for its existence. An anticipatory image of the complex
feeling of muscular contractions, involved in the movement
plus the volition or fiat of the will — which is not a sensation —
is the total mental state revealed by careful introspection.
{c) To the arguments based on the seeming existence and our
apparent estimate of the feeling of effort in cases of paralysis
of certain muscles where incoming sensations from them
would be impossible, it is answered that the feeling is still
really of a purely afferent character coming from the strain
of other groups of muscles, especially those of the chest and
respiratory organs, as will be noticed if we "make believe"
of shutting our fist tight, or puUing the trigger of a gun
without really moving our fingers.

We confess the question seems to us as yet not definitely
decided. The reader will find it fully discussed in VV. James's



THE SENSES. 77



Principles of Psychology, vol. ii. pp. 189 ff. 493 ff . ; and Ladd,
Psychology Descriptive and Explanatory, pp. 115 ff. 218 ff.

Cognitional value. — The discriminative sensibility
of our muscular consciousness to varying degrees
of resisting force is very delicate. The duration of
muscular sensations is also finely felt. This latter
property, when we have acquired the power of esti-
mating velocity, is the chief instrument in our measure-
ment of space. A sweep of the arm lasting for a longer
or shorter time, velocity being equal, passes through
a greater or less space. Estimation of velocity is not
an original quality of muscular feeling, but is learned
by experience. Velocity has no meaning unless in
reference to space, and it is determined by th'j
quantity of space traversed in a given time. We
observe that, in a given time, a certain amount of
energy is required to move the arm over a definite
length of space, known by sight or touch. By
association the degree of impetus becomes the symbol
of the rate of velocity. The calculation of the quantity
of movement executed by our limbs through means
of the muscular feelings alone, unless in the case of
a familiar act, is generally very imperfect. If we
attempt to ascertain the size and shape of a strange
room in the dark, we shall find how vague are our
notions of our movement. Similarly, if the eyes are
closed and the arm is bared so that the tactual sensa-
tions of the sleeve are eliminated, the inadequacy
of motor estimation of space will become apparent ;
when the velocity is increased we invariably tmder-
value the distance moved through.^

The muscular sensations, like the other organic
feelings, cannot be vividly revived in imagination,
but our power of determining the exact degree of

^ The fact that our muscular appreciation of velocity is not
innate but acquired, and is at best vague and indefinite, constitutes
a very serious difficulty to writers like Dr. Bain, who resolve our
perception of space into the consciousness of unextended muscular
sensations varying in duration and velocity. The latter idea
involves the notions both of space and time, and should not be
assumed as an innate endowment, least of all by the empirical
school. (Cf. Mahaffy, The Critical Philosophy, pp. 138 — 144)



^S SENSUOUS LIFE.



energy to be put forth in the practice of habitual ^
actions, such as standing, walking, writing, speaking,
and the hke, is very dehcate. The sense of sight,
just as well as that of contact, is a heavy debtor to
these sensations. Not only the movements of the
licad and the eyes, but the still more minute changes
by which the convexity of the crystallme lens is
niodified to suit the varying distance of the object,
are all effected under the guidance and estimation
of muscular sensations, and it is only by means of
their acute sensibility that many of the nicest dis-
criminations of the visual faculty are possible.

Movement, moreover, enables us to multiply the
experiences of each sense, to vary the relations between
the object and the faculty, and to bring the most
sensitive part of the latter to bear on the former.
Consequently, the sensations which measure move-
ment play an important part in perfecting our know-
ledge of the properties of matter. Still it is the
consciousness of foreign resistance revealed in tactual
and muscular feelings combined, which forces upon
us most irresistibly the reality of the external material
world. In this respect the cognitional importance of
the united muscular and tactual sense exceeds that
of sight and all the other organic faculties together.^

Capacity for pleasure and pain.— l^he muscular feehngs
may give rise to a good deal of pleasure or pain.
When the body is in a healthy condition muscular
exercise affords keen enjoyment, as is established by
the general popularity of field sports. The proper
pain of muscular sensations is fatigue, _ and this can
l)e very severe when forced activity is maintained
under exhausting conditions. Besides these mental
states which we have described, the muscles, like
other parts of the body, can be the subject of the
pains of laceration or disease, but such feelings belong
rather to the general group of organic sensations,

" Amongst the qualities of matter made known by combined
muscular and tactual sensations are solidity, shape, size., hardness,
softness, elasticity, liquidity, &c. Consciousness of movement and
of variation in pressure are the main factors in such perceptions.



THE SENSES. 79



Hearing. — Physical and Physiological conditions. —
This sense is aroused by vibratory movements
transmitted from the sonorous substance through
the air or other medium to the ear. The organ
of hearing consists of three chief parts, the external
ear including the pinna and external ineatns, the
tympanic cavity, drum, or middle ear, and the
labyrinth or internal ear. The two extremities of
the tympanic cavity are connected by a chain of
small bones, and the labyrinth consists chiefly
of a number of small cavities, and contains a
liquid in which the auditory nerve is distributed.
The vibrations transmitted from the sounding object
are concentrated by the external ear, and passed on
through the middle ear by means of the chain of
small bones to the liquid contained in the labyrinth.
The disturbance of this substance excites the auditory
nerve, and this excitation is the immediate ante-
cedent of the sensation of sound.

Musical Sounds. — Sensations of hearing naturally'
divide into two great classes, those of musical, and
those of non-musical sounds. Another important
division is that into articulate sounds, or the words
of language, and inarticulate sounds. When these
last are non-musical they are called noises. The
musical character of the first class of sounds seems
to be dependent on the periodical nature of the
vibrations which excite these sensations. The chief
properties of musical notes besides intensity, are
pitch, quality, and timbre or clang. The pitch of a
sound means its altitude on the musical scale, and
is determined by the rapidity of the vibration.



8o SENSUOUS LIFE.



The terms timbre, clang, and sometimes musical
quality, designate the pecuhar feature by which the
sound of a note on one instrument differs from that
iof the same note on another. Thus the timbre of
the viohn differs from that of the cornet and of
the human voice. ^^ Particular combinations of notes
according to certain relations of pitch produce the
agreeable effect known as harmony. Notes which
sounded together produce instead an unpleasant
sensation, are said to be discordant and inharmonious.
Under certain circumstances, however, discords
may be pleasant. Groupings of musical sound in
particular time periods produce the consciousness
of melody, and skilful combinations of various in-
struments so as to secure harmony, melody, and
agreeable blending of timbre conspire to awaken the
delightful feelings of a rich symphony.

Non-musical Sounds. — Of the non-muiical sounds
the number which are classed as mere noises are
practically unlimited. The collisions of different
bodies, the cries of the various animals, the roaring
of the wind and of the ocean, are instances of such.
All forms of sound, both musical and non-musical,
are susceptible of discrimination in regard to
intensity and duration, as well as in regard to quality.
It is owing to the very great delicacy of the ear in
these several respects that articulate speech is an
instrument of such enormous value. More than
five successive excitations per second produce a

^'^ Helmholtz explains the different timbre of different instruments
as due to variations in the upper tones which accompany the
proper fundamental note. However, this theory cannot, as yet, be
held to be established



V,

V



THE SENSES. 8l



continuous sensation in the eye, while the recupera-
tive power of the auditory nerve is so perfect that
we can distinguish sixteen impressions in the same
length of time. The rapid succession of sensa-
tions, frequently discriminated by but slight differ-
ences in character and intensity, which present to
us without fatigue the long series of syllables



Online LibraryMichael MaherPsychology: empirical and rational → online text (page 8 of 63)