William Otterbein Krohn.

Practical lessons in psychology, by William O. Krohn .. online

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painted a gray or light stone color will seem larger and nearer to
the street (if one is looking at it from that point of view) than it
would if painted any other color.

We now come to speak of the phenomenon of color blindness.
With certain persons certain defects of vision exist of such a na-
ture that they are unable to distinguish someof the color shades.
Such individuals are said to be "color blind." A little more than
one hundred years ago it was discovered that there were persona
who could not distinguish certain colors. The first case recorded
was that of John Dalton,the celebrated English chemist. The


description he made of his defect was widely read and attracted
general notice. The defect itself was named "Daltonism." About
four per cent, of persons, or one in every twenty-jBve, are color

This phenomenon is quite frequently met with among railroad
men, especially locomotive engineers, a number of whom are
blind to the red rays. That they are "red blind" is probably
due to the fact that in their long apprenticeship as firemen their
eyes became over-stimulated by the red rays of the glaring fur-
nace grates, so that those elements of the retina whose function it
is to perceive red have simply been so fatigued and" worn out"
that they cannot " take up the burden of life again." Holmgren's
method of testing color blindness is the one ordinarily employed.
Spread the variously colored worsteds on a white cloth in good
daylight. Select any one distinct color — e. g. , a light blue — and ask
the person serving as subject to select from the mass of wor.steds
all the other skeins that seem to him to be the same in color as
the standard you have already laid to one side. If he makes
errors in putting pink, gray, green, buff, lavender, lilac, magenta,
etc., with the blue skein you selected, he is evidently color blind.
Red blindness is most frequently met with, while violet blindness
is exceedingly rare.

A person red blind sees black and white and their mixture,
which makes gray, much the same as others do. He cannot distin-
guish correctly the color 6! any red object. If the object is very
bright red, it looks like feeble green, and if feeble red, it appears
black. The explanation of this, according to the above theory is
that the waves of light from a red object on entering a red-blind
eye do not produce the sensation of red, because the red perceiv-
ing nerve elements are absent, but they fall on the green and vio-
let perceiving elements. The waves of light from green objects
are nearest the length of those of red objects, and the waves from
bright red objects excite the green perceiving nerve elements
slightly, producing the sensation of feeble green, while feeble red
is not sufficiently strong to excite them, and the sensation is
black or perhaps a brown.


Yellow, which is a combination of red and green , appears green
to the red blind, as the red part of it produces no impression
except on the green-perceiving nerve elements.

Red and green objects may appear to him of the same color,
only differing in intensity. An intense red and feeble green may
appear to him to be of the same color. "A color-blind oflBcer
once desired to purchase a blue uniform ; he chose a blue coat
and waistcoat and red breeches, which he supposed matched."

Another case is that of a person who said he could not see
any difference between the red ripe fruit on the trees and the
leaves ; a boiled lobster and a cucumber were to him of the same

Another wrote a letter, part with black ink and part with red,
without being aware of any difference. Another says a red-brick
house and the green lawn on which it is situated are of the same

A color-blind engraver says his defect is an advantage to him,
as he sees colored objects in black and white, just as he desires to
engrave them. A color blind person picked up a red-hot coal and
asked what that funny green thing was. Another, an artist,
painted a landscape with red trees. Another purchased a pair of
green pants supposing they were brown. An architect copied a
brown house in blue and green and made the sky above it rose
color. A post-office clerk, who sold the stamps, found himself in
trouble because he did not distinguish the red from the green
stamps by their color.*

Color blindness is, however, normal at the periphery of the
retina. This leads us to make mention of the fact that impor-
tant changes in the quality of our sensations are dependent upon
the portion of the retina on which the visual image falls. The
entire retina can be divided into three l)elts or zones— a central
one (the belt immediately surrounding the yellow spot), a middle
zone and an outer or peripheral one. In the zone immediately
surrounding the fovea, nearly all colors can be recognized. Out-

*Many other such examples are found In Superintendent Peckham's Interesting
article on Color Blindness— WlBCOnsln Board of Health report for 1881.


side of this is the second zone, in which blue and yellow can alone
be distinguished. Farther out at the periphery, color shades can-
not be distinguished at all, the various colors all appearing
black, white or gray. In passing from the center to the periphery
red changes at first into orange, then into violet and blue in turn,
and finally, into grey as it passes out from the field of vision.

Have you ever tried this interesting experiment? Require
the subject to fix his attention on some designated point di-
rectly in front of him. While his eyes are thus fixed on this
point, approach him from behind with a pencil or small stick, or,
better, a black piece of pasteboard, at the end of which is a small
bit of colored paper— e. g., yellow. Observe how far forward it
must be moved before he will discern its color. You will notice
that some colors must be moved much farther forward than
others in order that they may be recognized. Furthermore, you
will observe that the object is seen, no matter what be its color,
long before the color is itself recognized.

It is a disputed question as to how many colors are distin-
guishable. You remember Newton speaks of the "seven primary
colors." Some of the colors he names, however, are not any
more primary or fundamental than many he omits. At any rate,
it is certain that his classification is very unsatisfactory. Why
indigo should be given a place in his list while brown is shut out,
is difficult to conceive. We know that the number of color tones
discernible by the human eye is very large. In oil the average
person can perceive 125 colors. Herschel makes the claim that
the Avorker on the mosaics at Rome must have distinguished at
least 30,000 color tones.

It has been claimed that certain of the early nations — that is,
the human race at a certain primitive stage of culture, had no
color sensations— they were color blind. In one of his earlier
writings, Gladstone makes the claim that the ancient Greeks were
color blind to blue, and bases this claim on the fact that Homer
had no proper terms for blue. Also in describing the rainbow no
mention was made of blue. The Bongo negroes of Central Amer-
ica designate but two colors— red and black. It is interesting


to note in this connection that some insects have distinct color

If certain colors, for example green and red, are in someway
united on the retina, we have a distinct sensation of a new color
tone very unlike either of the two thus united. If red and green
are so united we have the color called "white." Two colors
which by their admixture produce white are called complemen-
tary colors. For every color there is another which, if mixed with
it, will produce a colorless combination. The complementary
colors for different persons are not always the same, and the
two eyes of the same person may differ in this respect. The sub-
joined table of Helmholtz, has some general significance as bear-
ing on this subject of complementary colors :

Color. Color.

Red Green-blup

Orangp Blue

Yellow Indigo-bhie

Green-yellow Violet

The effect of one color on another when two patches of color
are adjacent or are presented to the eye, one directly after the
other, is called contrast. You all know that a bright object ap-
pears brighter with surroundings darker than itself and darker
with surroundings brighter than itself.

We have both successive and simultaneous contrast. Select a
piece of medium gray paper from which cut four small squares
(each about one-half inch square). Then choose four differently
colored sheets of paper— e. g., bright red, yellow, blue and green,
each piece about six inches square. Lay one of your small squares
of gray on each of these colored pieces and cover them all with a
piece of white tissue paper. Your gray squares that are actually
of the same shade now appear to be of different colors. In each
case they assume a shade or color tone complementary to that
of the large color surface on which they lie. Thus thegray square
that happens to lie on the blue ground will appear yellow, the
one on the green surface will appear a deep pink, the one on the
yellow will appear blue, while that on the red will appear green.


The retinal image in the hiimau eye is, as you know, always In-
verted; the points that are at the right and upper portion of
the object are at the left and lower portion of the image, and vice
versa. Still we do not see the object inverted, corresponding to
the image on the retina, but we see it -'right side up" corre-
sponding to the object itself. That the image on the retina is
inverted is specifically characteristic of the eyes of vertebrates.
The composite image in the compound eye of the glowworm or
fly is not an inverted but an upright retinal image.

Again, how is it, having two eyes and therefore two retinal
images, that we do not see objects as double, as we do when we
push the side of the eyeball with our finger when gazing fixedly
at an object? The customary union of the two retinal images
is in the main accounted for by the crossing of the optic nerve
fibers, for by this means the excitations produced in the left half
of each retina are joined and together conducted to the right
hemisphere of the brain, and vice versa.

With a single motionless eye we could have no possible percep-
tion of solid objects. The retinal images are superficial and plani-
form, but the mind sees things as solids. The mind, then, asso-
ciates the ideas gained through movement and touch with those of
simple vision. A person that is blind from birth and receives his
eyesight later in life as the gift of supreme surgical skill, conceives
all objects to be directly in contact — in actual touch with the
outer surface of the eyeball. He only learns by degrees to pro-
ject his sensations of sight accurately with reference to both dis-
tance and solidity.

By vision ^ alone a sphere is perceived simply as a delicately
shaded disk. A cube is a flat surface bounded by converging
lines and abruptly shaded. Ruskin says : "The whole technical
power of painting depends on our recovery of what maybe called
the innocence of the eye; that is to say, of a sort of childish per-
ception of these flat stains of color merely as such, without a con-
sciousness of what they signify as a blind man would see them if
suddenly gifted with sight."

In normal circumstances sight is the leading avenue of percep-


tion or observation. The superiority of vision to the othersensee
is due to the fact that by means of this avenue of sense we can
apprehend things at a distance as well as those that are near, as
well as a great many things at the same time — for example, the
variously colored leaves of an autumn tree, or the pattern of a
wall paper or carpet. And again the eye calls forth our admira-
tion on account of the extreme delicacy with which it acts. It can
pass from one object to another with a swiftness which none of
the other end organs of sense can imitate. It thus gathers a large
amount of data in a very short time. It places these data at the
service of the intellect as quick as the intellect can use them. The
eye has always been regarded as the noblest of the sense-organs.
As all know, we are exceedingly dependent upon the acquired
perceptions of sight. Of these acquired perceptions there are sev-
eral classes. In the first place we judge of distance by size. Again,
if we know the real size of an object we estimate its distance by
its apparent magnitude. If we actually know the flying bird to
be an eagle, and yet find that it appears exceedingly small we are
sure that it is a great distance from us. If we are on the roof of
a building and know that the persons walking on the streets be-
low are full-grown men, which, however, look to us from our ele-
vation like pygmies, we judge, and judge rightly, that we are quite
a considerable distance from the ground. Likewise we judge of
magnitude by the assumed distance. If we have a correct idea of
the distance we perceive them full size. If, however, we are de-
ceived as to the distance we always make serious errors with ref-
erence to the actual size of the object. A fly skipping across the
Avindow-pane may for a moment be regarded as a la^^ge bird at a
great distance. If, however, the magnitude be unknown we judge
of distance by means of the clearness of the color, the sharpness
of the outline, and the intensity of the impression which the ob-
ject makes upon us. The traveler from the Atlantic Coast States
or the smoky Eastern city, who travels across The Plains judges
the mountains of Colorado to be far nearer than they actually are.
We hear of many laughable experiences of tourists who have at-
tempted to walk to a given mountain before breakfast, thinking


it to be but a short distance, but discovering that it is actually
several miles away. Such an illusion is due to the fact that the
atmosphere is much more transparent than that to which the
traveler is accustomed. Furthermore, intermediate objects affect
our judgments of distance and therefore our judgments of size.
This accounts for the fact that the sun and moon appear larger
at the horizon than at the zenith. The intensity of the impres-
sion also plays an important part in these judgments of distance.
If a light makes but a faint impression on us we judge it to be at
a considerable distance. When the locomotive engineer, as he
speeds his train through the darkness, perceives the lights of the
distant station which are therefore at about the same distance
from him, he knows which are the red and which are the white
lights, though they evoke no color sensations. This is because
the red light always gives rise to a more intense sensation than
a white light at the same distance.

The blind man can have no notion of what we mean when we
speak of objects appearing smaller as they move away, because
he is compelled to nlways think of them as of their constant tac-
tile size just as he recognizes them by their " tactile names " after
he has been made to see.


SENSATION (continued).

The human ear consists of three portions— tie external ear or
concha; the middle ear or tympanum ; and the internal ear or
labyrinth. (For a description of the structure of the ear the
reader is referred to any good book on anatomy. Space will not
permit a detailed description here.)*

The internal ear is really the organ of liearingand consists of a
complicated and tortuous bony tube orchamber resemblingsome-
what the interior of a snail shell. The function of the external ear
(the expansion seen on the exterior of the head, called the concha)
is to receive, convey and modify the vibratory action of the air
until the tympanum is reached. The tympanum, or "drum of
the ear," consists of a parchment-like substance which is con-
nected with a chain of bones that play upon a membranous
chamber inclosing a liquid substance.

Bodies vary in the ability to emit or convej^ sound. This is
the same as saying that their susceptibility to vibration is differ-
ent. A stick of timber or bar of iron will convey to the ear in
contact with it the sound made by a scratch of a pin, for hun-
dreds of feet. Likewise the rudely constructed toy telephone of
childhood days will convey a whisper for a long distance, though
it consists of nothing but two pasteboard collar boxes connected
by a piece of twine from 1,500 to 8,000 feet in length.

Waves that are non-periodic produce what is called a "noise;"
when these same auditory waves are periodic they constitute a
" tone " or " note." What are ordinarily called noises are really
accompanied by musical notes. The slamming door is accompa-

*The best published work thus far is that on "The Vertebrate Ear," by Dr.
Howard Avers. Pulilished in Jovrnal of Morpholony. Mav. 1892.


nied by some music. Likewise all tones are accompanied by
noises. For example, the scraping of the violin. Noises may be
compounded out of musical notes. Thus, when you strike a sin-
gle key on the piano you have a musical tone. Strike all the
keys at the same time and you have, instead of several musical
notes, a most outrageous non-musical noise.

The various efforts made by scientists to determine the lower
limit of sound for the human ear, have resulted in disagreement.
The difficulty, of course, lies in the fact that the absolute stillness
essential to the perfect working of the experiment can never be
secured. The best record of which we know up to date gives the
result of researches made by Schafhautl who fixed the lower limit
of sound as that made by a cork ball weighing one milligram
(.0154 grains), falling from a height of one millimeter (.03937
inch). The acuteness of hearing is frequently increased hy dis-
ease. " Exalted hearing," by which is meant an unduly keen per-
ception of sounds, is common to many disturbances of the nervous
system, both functional and organic. As a rule, the intoxi-
cated person has the experience of "exalted hearing," i. e., his
sense of hearing is more acute than when he is in a nor-
mal or "sober" condition. The test usually employed by
railroad corporations to discover the acuteness of the sense of
hearing in their employes serves very well as a laboratory test,
though crudeitmayseem,forthepurposeof determining the mini-
mal sounds that can be heard. The experiment should take place
in a large carpeted room, as free as possible from noise. Let the
subject be seated with his side toward the experimenter. He
should be blindfolded and have the ear opposite to the one being
tested plugged with cotton. The experimenter then endeavors
to find what is the greatest distance at which the subject can
hear the tick of a watch which is held at the level of the ear. The
distance at which the sound of the watch-tick can be heard may
be found to vary from three to seven yards.

Attention has already been called to the fact that by bringing
the finger in contact with a cogwheel revolving at agivenrate, or
atuning fork, we may have as many as 1,000 sensations in a single


second. (Seepage 116.) But if the rate be increased beyond 1 ,000
per second there results one continuous sensation. The sense
of hearing comes closest to the sense of touch. In experiments
with one ear the crack of two electric sparks may be heard as
distinct when the one sounds .002 of a second before the other;
or, to be more accurate, .00205 of a second. When the sounds
come as close together as .00198 of a second they are heard as
one sound, a little louder than a single spark would make. In
experiments with both ears the limit is higher— .064 of a second.

To recapitulate briefly, we would say that the specific physical
stimulus for the organ of hearing consists of simple sound waves
that unite sometimes as musical sound waves and sometimes as
sound waves of noise. These sound waves act as stimuli upon
the peripheral termination of the auditory nerve.

Sensations of musical sound can also be produced by electrical
stimulation of the auditory nerve. Mechanical stimuli, such as
the pressure of tumors on the auditory nerve, also produce sen-
sations of hearing.

In our psychological investigations of the sensations of sound
we must first consider their various qualities. We must, how-
ever, exclude the large class of sensations known as noises, since
they compose an especial group of sensations hardly accessible
to investigation. For our present purpose it is sufficient to de-
vote our attention to the simple sensations of tones and of music-
al sounds. Your knowledge of physics tells you that the so-called
tones of the piano are not simple but complex. Simple sounds are
most easily produced by striking a tuning fork. We get compar-
atively simple tones by blowing across the neck of an open bottle
or from a flute. The only difference in the quality of all really
simple tones lies in their pitch, to which the number of vibrations
per second on the part of the stimulating medium corresponds.
The greater the number of vibrations the higher do we perceive
the tone to be. The lowest audible note varies, of course, with
different individuals. For the average person the lower limit of
pitch is about 40 vibrations per second. Helmholtz puts the
limit at 28 vibrations, Preyer at 16, others at 19 and 23, while


Wundt claims to have heard even eight vibrations per second.
The highest audible note is made up of about 40,000 vibrations
per second. Some persons cannot hear the cry of a bat or the
chirp of a cricket, which comprise about 37,500 vibrations a

The sensitiveness of the ear to differences of pitch varies greatly
with different individuals and with the same individual for the
different octaves of the musical scale. Persons are frequently met
with, who are totally insensitive to differences in pitch — they do
not know one note from another. How terrible it must be to
have this world full of beautiful rhythmic sounds reduced to a
continuous monotone.

By an elaborate series of experiments, it has been found that
if we sound a tone of 120 vibrations and then one of 120|- vibra-
tions per second, the average person can clearly distinguish the
pitch of both tones. If we produce a tone of 960 vibrations per
second, it is found that a tone of 960i vibrations can be distin-
guished from it. But if it required i of a vibration when the rate
is 120 per second, it ought require 8 times i, or more than one
vibration, when the number is 960 per second. Therefore, the
relative discriminative ability is not constant.

We now come to define timbre. By the timbre of a note we
mean its ' ' color tone. ' ' To illustrate. The C of the piano sounds
quite different fi*om the pure C produced by the flute or tuning-
fork, despite the absolute sameness of pitch. The C of the violin
or human voice would differ still from that of either the piano or
flute. Compare the C of different makes of pianos, the same ab-
solute number of vibrations are evoked in each case, but there is a
difference between the C of the Stein way, Knabe, Chickering or
Sohmer pianos, respectively. All these differences of quality in
the auditory sensations when the pitch remains the same, are
comprehended in the conception of "timbre" or color tone.

Bearing upon the discriminative ability of the ear for the
intensity of sounds we have the interesting series of experiments
by Dr. Merkel and Professor Frank Angell. Merkel permitted
the person on whom he was experimenting to hear two stimuli


of sound that are alike in quality but different in intensity, and
then requested him to determine an acoustic stimulus that would
give rise to a sensation that could be classified as lying directly
between the first two. Experimenting in this way Merkel and
others have found that the just perceivable increment of loudness
required an increase of three-tenths of the original stimulus be-
tween 20 and 5,000 of his arbitrary scale.

The discriminative ability of the ear both for differences in
pitch and for differences in intensity is largely influenced by rep-
etition and by amount of time that elapses between the two
stimuli producing the sensations that are to be compared. Two
tones so closely related as to be just distinguishable when heard
in immediate succession appear to consciousness as one and the

Online LibraryWilliam Otterbein KrohnPractical lessons in psychology, by William O. Krohn .. → online text (page 11 of 34)