William Otterbein Krohn.

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with movement) gives quite a different sensation than mere simple
contact or passive touch. It is also more discriminative. The



116 PRACTICAL LESSONS IN PSYCHOLOGY.

carpenter who desires to tell whether the board is planed smoothly
or not, does not simply lay his hand on the board, but rubs it
over the surface, the smoothness of which he desires to judge.
Likewise as to the grinder of lenses for optical instruments. Com-
pare for yourself the sensation received from merely resting the
tip of the finger on the rough surface of a piece of sandpaper, or
even a rough book cover, with the sensation you receive when
you move the finger over such a surface. The bank teller cannot
tell a counterfeit five-dollar bill or the spurious lead coin by
simply touching it passively. He rubs it between his fingers, or
rubs his fingers over it. The merchant in buying cloth depends
largely upon the "feel of it," as he rubs it between his thumb and
finger to determine the quality of its texture. You probably do
the same thing in comparing several varieties of writing paper
as to their smoothness and thickness.

Sergi, the Italian Psychologist, and others have made some
extended experiments with reference to ascertaining theacuteness
of his skin's power in making time discriminations when a num-
ber of stimulations follow in close succession. In other words,
his attempt was an endeavor to find how much of an interval
there must be between successive touch stimulations to prevent
their being fused into one continuous sensation. As apparatus
he used six tuning forks, each of which could be set into vibra-
tion electrically, and which were, respectively, capable of 30, 100,
250,435,500 and 1,000 vibrations per second. Various locations
on the skin are then brought into direct contact with each of these
forks after they are set into vibration. After a large number of
careful tests, Sergi finds that different portions of the dermal
surface are by no means equally capable of perceiving successive
stimulations and of making time discriminations. He did find
tjome localities exceedingly sensitive — e. g., the tips of the fingers
where the beats of the fork do not blend into a continuous sen-
sation of touch, even when the vibrations are 1,000 or more a
second.



LESSON X.

SENSATION (continued).
THE MUSCLE SENSE.

By muscular sensations are meant all those sensations which
arise from the varying condition of the muscles whether in action
or at rest ; therefore they depend upon the contraction and re-
laxation of the muscular fibers or the varying relative position
of the muscles. When we slowly stretch or violently jerk the arm ,
when we snap the finger, when we rotate the wrist, when we tread
or kick with the foot, when we strain and tug with the whole
body to lift a heavy weight or push against a resisting obstacle,
we experience a corresponding variety of muscle sensations.

The muscle sense is among the first, if not itself the very first,
to furnish data by means of which the child becomes able to dis-
tinguish himself — his body — from the rest of the material uni-
verse. Through a large variety of movements the infant first
explores every part of the organism, and as a result derives that
standard by which he measures the material world without. You
see, then, by the expression "muscular sensation " is meant those
feelings of which we are conscious when we voluntarily exercise or
refrain from exercising our muscles.

While the real muscular sensations would comprise those of
pain, effort, fatigue and the like, it should be observed that the
term ** muscle sense " has come to receive a more restricted, defi-
nite and special meaning in Psychology, and it is now used to des-
ignate more particularly that sense by which lifted weights are per-
ceived. For experiments upon sensations belonging to this class,
it is necessary to have a series of weights for the purpose of test-
ing one's discriminative ability with reference to this special
sense. The most available weights for such purposes are made
by loading paper gunshells with shot. A convenient series would

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118 PRACTICAL LESSONS IN PSYCHOLOGY.

consist of the following weights: 100, 101, 102, 102.2, 102.5,
103 arid 103.4 grams. Also a carefulh' graduated series of
smaller weights beginning with a weight of ten grams, and run-
ning as high as fifteen grams. The experiment should be made
something as follows: Let the person whose discriminative abil-
ity for lifted weights you wish to test, stand at a table of conven-
ient height. He should be blindfolded. Place within easy reach
of his right hand and near together two weights, one of which
sliould be the standard weight of 100 grams, and the other a
weight to be compared with it, either one that is equal, heavier
or lighter. Let the subject lift them one after the other, being
careful that he lift them the same way, to the same height and at
the same rate, giving a decision as to which of the weights he
thinks is the heavier or the lighter. If he thinks the two of equal
weight, record this judgment also. The fac^t of the matter is
that when the two are of equal weight he will be apt to say that
the second one lifted is the heavier. The difference between the
two weights must be considerable if it is to be perceived. If we
should close our eyes and a friend should lay a weight of 300
grams, then one of 312 grams, on our hand and we are called
upon to state which of the two is the heavier it would be seen
that the additional weight of twelve grams more than the orig-
inal 300 grams is so small that the difference is not constantly
perceived with thoroughgoing certainty. Fechuer, the first to
innovate this test, found that in one hundred such trials as the
one just indicated, in which sometimes the lighter and sometimes
the heavier weight was first lifted, the correct answer was given
sixty times. Therefore the number of correct cases amounted to
60 per cent.

Now a second series of trials is made, the initial weight being
600 grams, the additional weight remaining 12 grams for the
time being. It is then soon found that the number of false esti-
mates has been greatly augmented, the number of correct cases
being not more than 40 percent. In order to attain 60 per cent.
of correct cases, as in the case of 300 grams and 312 grams, we
have to raise the additional weight to 24 grams if our initial



SENSATION. 119

weight remain 600 grams. If the beginning weight is doubled,
the additional weight must also be doubled in order that the
probability of a correct discriminative judgment remain con-
stant.

Closely allied with the muscular sensations are what is known
as the orgnnir sensations. When the stomach, lungs, heart and
other visceral organs are entirely healthy and their functions are
normally performed, they are attended with no very positive or
distinct sensations. If, however, they be injured or diseased,
very clearly recognized disturbing and unpleasant sensations re-
sult. The hale, hearty, healthy man does not know that he has
a stomach; the dyspeptic person hardly knows that he hns nny-
thing else. These organic sensations are often blended with tlie
muscular, and are experienced in constant connection with nor-
mal or abnormal muscular sensations.

But more intimately related to the muscular than are these
organic sensations are those of the joints and tendons — sensa-
tions, which are often experienced in the passive motion of the
various bodily members, especially brought into prominence in
the flexion of the elbow. The surfaces of the joints are organs
which become intensely painful when the least bit inflamed. The
motion of the articulated joints upon each other gives rise to n
peculiar sensation. To this sensation is due the perception wo
have of the position of our limbs at a given moment. If these
joint surfaces are rendered angesthetic the perception of the
movement, and consequently the position of the limbs, becomes
exceedingly obtuse. If you place the forearm of a person flat upon
a hinged board and raise one end of the board so that tlie fore-
arm is slowly and gradually elevated, and require the person to
pronounce when he first perceives the motion of his forearm, it
will be found that the chief data upon which he bases his judg-
ment is the peculiar sensation of motion which he localizes in
the elbow joint. At least this is what happens with health}^
persons in normal condition. But when the feelings of such pas-
sive movements as well as other sensations which furnish us a
clue to the position of our limbs are lacking, we get such results



120 PRACTICAL LESSONS L\ PSYCHOLOGY.

as are related by Professor Striinipell of his wonderful aneesthe-
sic boy, whose onl}- sources of sensation were the right eye and
left ear. The principal features of the case are thus quoted by
Professor James : * " Passive movements could be imprinted on
all the extremities to the greatest extent, without attracting the
patient's notice. Only in violent forced hyperextension of the
joints, especially of the knees, there arose a dull vague feeling of
strain, but this was seldom precise! 3^ locahzed. We have often,
after bandaging the eyes of the patient, carried him about the
room, laid him on a table, given to his arms and legs the most
faiitastic and apparently the most inconvenient attitudes with-
out his having a suspicion of it. The expression of astonishment
in his face, when all at once the removal of the handkerchief
revenled his situation, is indescribable in words. Only when his
head was made to hang away down he immediately spoke of
dizziness, but could not assign its ground. Later he sometimes
inferred from the sounds connected with the manipulation that
something special was being done with him. . . . He had no
feelings of muscular fatigue. If, with his eyes shut, we told him
to raise his arm and keep it up, he did so without trouble. After
one or two minutes, however, the arm began to tremble and
sink without his being aware of it. He asserted still his ability to
keep it up. . . . Passively holding still his fingers did not
nffect him. He thought constantly that he opened and shut his
hand, whereas it was really fixed." Goldscheider found that a
swing of the arm, amounting to .22° to .42°, is sensibly perceived
in the shoulder joint. Such small displacements as these can hardly
be detected by the eye. Of course the velocity with which the mem-
ber is moved plays an important part. The minimum velocity for
the shoulder joint has been found to be about .3° in a second of
time. All these facts prove that the joint surfaces constitute the
chief seat of the impressions by which the movements and posi-
tion of our bodily members are immediately perceived.

Mention must also be made of the sensations of resistance. To



*Wllllam James. Psychology— Briefer Course. New York, 1892. _ The German
account is not in our possession.



SENSATION.



121



demonstrate what is meant let us take a five-pound weight to
which is attached a strong piece of ordinary string. With the
arm extended hold the weight by the string so that it hangs just
a few inches above the floor. Lower the weight rather rapidly
until it strikes the floor. Just as it strikes, a sensation of resist-
ance to further motion is clearly perceived.

We now come to speak of those sensations by means of which
we recognize the position of the body as a whole. That there are




tW. /7.



such sensations can be very easily verified by a simple experiment.
The most clear demonstration occurs in connection with the "tilt-
ing board " shown in the cut. (See Fig. 17.) This consists of a
board seven feet long and two feet wide balanced over a support
somewhat resembling a sawhorse. At one end there is a footboard
secure enough to bear the weight of a man when the tilting board
is in a vertical position. At the other end should be attached a
plumb-line and a semicircular scale so adjusted that the inclina-
tion of the tilting board can be read off at any moment. To pre-



122 PRACTICAL LESSONS IN PSYCHOLOGY.

vent the person from falling when the head is downward, shoul-
der and body straps are provided which securely bind him to the
board. Cause the person who is to serve as subject in this exper-
iment to place himself on the tilting board and have him close
his eyes. Begin with the board vertical, his head up. On ques-
tioning him you will find that he will probably announce that he
is leaning slightly forward. Tilt him slowly backward and re-
quire him to announce when he is at an angle of 45° from the
vertical, when at an angle of 90°, and when at an angle of 180°.
In most cases the subject will probably say that he is vertical,
head downward, when he is from 30° to 60° from the designated
position.

In this connection reference must be made to the t^ensations of
rotation. The nature of these sen.sations is also best determined
by appeal to actual experiment. Some of these experiments can
be performed by twisting the rope of an ordinary swing in which
a person is seated. It is better, however, 1o have a board kiid
across a screw stool or ordinary rotating office chair without a
back ; seat the person and rotate him rapidly for about half a
turn, then stop him suddenly, A distinct sensation of rotation
in the opposite direction will be clearly perceived. This experi-
ment must be performed with the eyes closed, for if the eyes be
open, the sensation immediately ceases. Close the eyes again
and it returns. When a person is turned in one direction and
then in the other for quite a little period of time and for different
distances, he will finally lose all knowledge of direction in which
he is subsequently rotated. These totally wrong judgments with
reference to the direction of rotation are quite common, and are
made use of in a number of children's games. The "donkey
game " is a familiar example. A figure of a donkey minus a tail
is cut out of colored paper and fastened to a sheet or screen hung
up on the wall at one end of a room. Each member of the company
is then required to locate the proper place for the tail standing at
the opposite end of the room with his eyes open. Then he is
blindfolded, turned about by another person, first in one direc-
tion, then in the other, and finally told to pin the detached tail,



SENSATION. 123

which has been cut out separately, to the donkey at what he
thinks is the proper place. Much merriment is caused by the
striking mistakes with reference to direction and locality.

It ought also to be mentioned here that deaf and dumb per-
sons are, as a rule, quite insusceptible of being made dizzy by ro-
tation. The semicircular canals located in the labyrinth of the
ear are, as it were, six little spirit levels, which seem calculated
to be organs of the sense of rotation.



LESSON XL

SENSATION (continued) .
VISION.

The organ of vision is the eye. It is not necessary in this
place to give a detailed description of the structure of the eye.
Such a description can be found in any book on anatoIn3^ It is,
however, always an interesting observation for one to verify
Buch descriptions by dissection of the eye of a beef or sheep. For
such examination the specimen should be first frozen or hardened
in alcohol.

The following general points in reference to the eye's structure
ought, however, be noticed in passing. With the exception of the
ear, the eye is by far the most complicated end organ of sense.
The eye is an optical instrument, witli a self-adjusting lens, and
supporting, on its inner circular wall, a delicate membrane of
nervous matter which acts as the sensitive plate of the camera
(for such the eye is) on which the image is formed. On examin-
ing the eye you find it to be a flattish sphere formed by an outer
tough membrane which incloses a nervous surface and refracting
media. The parts of the eye are shown in the schematic draw-
ing of Gegenbaur (Fig. 18).

Of the three coats of the eye the inner one (retina) is by far
the most significant. As stated above, it is the sensitive plate,
and is a delicate membrane consisting of ten layers. Of these
layers, the structure of the ninth (counting from the inner sur-
face) — the layer of the rods and cones — is the most interesting.
It consists of a multitude of elongated bodies arranged side by
side in a sort of mosaic. These bodies are of two kinds; one,
the cylindrical " rods," the others, more flask-shaped, are
called "cones." The rods are longer than the cones. In the
adult human eye they are about -^ of an inch in length. It is a
(124)



SENSATION.



125



peculiar fact that these end organs are not pointed forward to-
ward the light as it streams through the pupil, but backward
toward the outer or sclerotic coat. The cones seem to be the
most sensitive to light. Certain it is that in the center of the eye




Figure 18.— Horizontal section through the left eye.
Gegenbaur.)



RETINA
CHOROID
SCLEROTIC



(.Schematic, from



only cones appear, and they are exceedingly numerous, over
1,000,000 being found in a -^^ inch square.

The optic nerve fibers cannot be directly stimulated by light.
The place on the retina where the optic nerve enters tlie eye is in



126 PRACTICAL LESSONS IN PSYCHOLOGY.

fact entirely blind, because nothing but fibers (and no rods and
cones) exist there. This spot is wanting in all nervous elements
sensitive to light. To prove the existence of the blind spot, close
the right eye and look steadily with the left at the cross in Fig.
19, holding the book in front of the face, moving it to and fro.
At about one foot from the face the black disk entirely disap-
pears; when nearer than this or farther from the face it is seen.
In this simple experiment it is absolutely necessary to keep the
left eye focused on the cross. The blind spot is about ji^ of an
inch long in the average human eye.

Aside from the blind spot the sensibility of the eye varies
greatly. The place of clearest vision is the " yellow spot " which
is oval in shape, with a central depression called the fovea. This
yellow spot is about 1-16 of an inch in length and lies at a dis-




FlQURB 19.

tance of 1-6 of an inch from the middle of the blind spot. As Dr.
Sanford suggests, the yellow spot may be projected and seen in
the following manner : Close the eyes for about thirty seconds
and then look with one of them through a flat-sided bottle, con-
taining a saturated solution of chrome alum, at the clear sky. In
the blue-green solution of the chrome alum a rose-colored spot
will be seen which corresponds to the yellow spot of the eye.

We see single with two eyes, just as we hear single with two
ears and smell single with two nostrils. We can, however, see
double under certain conditions, though we can never hear double
or smell double. An easy and clear demonstration of this fact is
to roll a sheet of paper so as to have a tube an inch or two in
diameter and a foot long. Keep both eyes open, and hold with
your right hand one end of the tube to your right eye (with



SENSATION. 127

which you are to look through the tube) to restrict its field, and
leave the left eye unrestricted as to its field of vision. Place the
open left hand (palm side toward you) against the left side of
the tube directly in the field of vision for the left eye. With both
eyes look straight ahead. With your right eye you see the hole
of the tube and with the left you see your hand. Your mind super-
imposes the image of the one on that of the other, consequently
3'ou see your hand with a hole in it just the diameter of the tube.
Again, take the same tube and hold it over one eye and then with
both eyes look at a finely figured wall paper or carpet. To the eye
whose retinal field is restricted by the tube the object looked at
will appear further away than it does to the other eye. Another



Figure 20.

interesting experiment in this direction would be for the reader
to gaze fixedly at Fig. 20 with the black spots directly in front
of the right and left eyes, respectively. After looking at it for
a little time, as if the paper were at an infinite distance, or as if
he were looking through it, the reader will see the two black dots
fusetogether and combine into one. This combined spot is located
directly in front of his nose on a line between thetwoactualspots.
This combined spot results from seeing the two spots in front of
each eye with the same part of the fovea.

If instead of two identical spots we use two different figures or
two differently-colored spots or areas as objects for the same two
fovea to focus upon, they cannot appear as a single object but al-
ternate/j displace each other from view. This is the phenomenon



128



PRACTICAL LESSONS IN PSYCHOLOGY.



known as retinal rivalry. If one looks with each eye upon a differ-
ent image, as in Fig. 21, sometimes the one sometimes the other
will be perceived. A piece of cardboard or paper ought to be
placed in a vertical position on the middle dividing line so as to
confine the vision of each eye to the figure or system of lines imme-
diately in front of it. As Helmholtz puts it, we find that we are
able "to attend voluntarily now to one and now to the other sys-
tem of lines ; and then that system remains visible alone for a cer-
tain time, while the other entirely vanishes. This happens, for ex-
ample, if one attempts to count the lines first of one and then of




Figure 21.



the other system ; but it is extremely difficult to chain the atten-
tion down to either one of the systems, for long," etc.

That the rods and cones of the retina are arranged in a mosaic
is indicated in Bergman's experiment. Place the system of lines
in the left portion of Fig. 22 in a good light and gaze fixedly
at it from a distance of about 5 feet. You will notice an appar-
ent bending of the lines, as shown in the portion A, of the same
figure. This is, of course, explicable on the basis of the mosaic
arrangement. The retinal elements on which one of the white
lines happens to fall are stimulated according as they are more
or less touched, give rise to corresponding sensations.



SENSATION.



129



If, after looking intently at any bright object with a reasona-
bly clear outline, we close our eyes, it is found that an image of
the object remains for some time and only fades out of sight
gradually. This phenomenon is known by the name of "after-
image." After-images in which the arrangement of light and
shade found in the original object is preserved are called posi-
tive after-images — i. e., the bright and dark parts correspond to
those of the original object. Those after-images in which this
relation is reversed are called negative after-images. The posi-
tive after-image has a color like that of the original object. In
the negative the opposite or complementary colors are evoked.




Figure 22.



It some moi-uing you look steadily for a minute at the win-
dow of your room and then direct your eyea so as to look on a
whited wall or screen the dark parts of the window will appear
light, and vice versa. The arrangement of light and shade are
here reversed just as in a photographic negative. If we look at
a green surface for some time and then fix the eye upon a white
sheet of paper or screen we find that the latter will contain an
image of red color corresponding in size and outline to the orig-
inal green surface. For example, if you look for a moment at a
small green circle and then fix your eyes upon the white surface
you will see within the bounds of the white surface a red circle as
the negative after-image. Negative after-images are really a
L. p.— 9



130 PRACTICAL LESSONS IN PSYCHOLOGY.

form of retinal fatigue, but the positive are in all probability
due to the inertia of the retina .

Bright surfaces are alM-ays enlarged at the expense of dark
surfaces by which they may happen to be surrounded ; this is
called the phenomenon of irradiation. With Fig. 23 in a good
light, notice that the white squares seem larger than the black,
though they are actually of the same size.

In the same connection it should be mentioned that color in-
fluences the apparent size of an object. Every woman knows that
her hand looks smaller in a. black than in a white glove. The so-
ciety belle declines to wear a white slipper to the ball or german
because it makes her foot appear larger and less dainty than




Figure 23,

would a red slipper. The gray shades of suiting make a man ap-
pear larger than when he wears a soft black. You have observed
the same thing with reference to the colors of dwellings. A house



Online LibraryWilliam Otterbein KrohnPractical lessons in psychology, by William O. Krohn .. → online text (page 10 of 34)