causing it to become more or less convex, thus affecting the con-
vergence of the rays of light upon the fovea. In monocular vision
differences in distance up to a few feet can be estimated fairly acai-
rately in terms of the kinaesthetic sensations arising from the ciliary
muscle. These estimations are, how-ever, unconsciously made.

DEFECTIVE VISION.

Myopia and Hyperopia. In the normal eye the distance from the
cornea to the fovea is 20 millimeters {^/\ of an inch). If now the
eye is so constructed that this distance is greater than 20 mm. the image
of distant objects is formed in front of the retina and only near objects
can be clearly seen (near-sightedness or myopia). On the other hand,
if this distance is less than 20 mm. then the image of objects will be
formed behind the retina and the refractive power of the eye must be
increased to permit of clear vision (long-sigtitedness or hyperopia).
*'The hyperopic eye must consequently exert an effort of accommoda-



198 INTRODUCTORY PSYCHOLOGY FOR TEACHERS

tion in order clearly to see objects at a distance, while for near work
this effort must be excessive. The result is that the hyperopic eye is
under constant and abnormal strain from the incessant demands upon
its ciliary muscle, and that, in consequence, numerous secondary symp-
toms or resultant effects appear, some of them obvious, others unex-
pected, many of them serious. Local symptoms appear in inflammation,
redness, or soreness of the eyes, lids or conjunctiva, and in twitchings
and pain within the eye ball. Aside from these local disturbances,
periiaps the most constant symptom of hyperopia is frontal or occi-
pital headache."*

Both myopia and hyperopia may be counteracted by the use of
glasses.

Astigmatism. "In a perfectly normal or ideal eye the refractive
surfaces, cornea, anterior and posterior surfaces of the lens, are sec-
tions of true spheres, and, all the meridians being of equal curvature
the refraction along these different meridians is equal. Such an eye will
bring the cone of rays proceeding from a luminous point to a focal
point on the retina, barring the disturbing influence of chromatic and
spherical aberration. If, however, one or all of the refractive surfaces
have unequal curvatures along different meridians, then it is obvious
that the rays from a luminous point cannot be brought to a focal
point, since the rays along the meridian of greater curvature will be
brought to a focus first and begin to diverge before the rays along
the lesser curvature are focused. Such a condition is designated as
astigmatism."t

In a person afflicted with astigmatism there must be a ceaseless
activity of the ciliary muscle as first one point and then another of a
scene is focused. In normal vision many of such points can be focused
at the same time thereby requiring less effort of this muscle and also
providing fuller and richer vision. Astigmatism can ordinarily be
corrected by wearing properly fitted glasses.

Color-blindness. About 4% of men and less than 0.5% of women
are color-blind. Most of these are red-green blind which means that
they do not see any difference between these two colors. "Total color-
blindness, while well-authenticated, is rare, and is presumably a path-
ological defect." "It is obvious that many callings are, or should be,
closed to the color-blind, e. g., railroading, marine and naval service,
medicine, chemical analysis, painting and decorating, certain branches
of botany, microscopy, mineralogy, the handling of dry goods, mil-
linery, etc. In some phases of school work, the color-blind pupil is
likewise at an evident disadvantage. The color-blind test should, ac-
cordingly, be regularly instituted in the early years of school life, in

*C. M. Whipple, Manual of Mental and Physical Tests, 2nd edition, 1914, p. 164.
tW. H. Howell. A Text-Book of Physiology, 1907, p. 302.



LESSON 36 199

order that the existence of the defect may be made known to the child
as soon as possible."*

FUSION OF VISUAL AND TACTUAL SENSATIONS.

Professor Stratton carried on some experiments a number of years
ago, as follows. He wore constantly for a week a pair of glasses with
two lenses so constructed that every object appeared upside down.
"The results showed that an experience coming from such an image
would in time be indistinguishable from our normal experience. The
first effect was to make things, as seen, appear to be in a totally dif-
ferent place from that in which they were felt. But this discord be-
tween visual and tactual positions tended gradually to disappear; not
that the visual scene finally turned to the position it had before the in-
version, but rather the tactual feeling of things tended to swing into
line with the altered sight of them. The observer came more and
more to refer his touch impressions to the place where he saw the ob-
ject to be ; so that it was clearly a mere matter of time when a com-
plete agreement of touch and sight would be secured under these
unusual conditions." As Stratton points out "harmony of touch and
sight can grow up under the greatest variety of circumstances, pro-
vided merely that the experience remains uniform long enough to de-
velop fixed expectation. t

Undoubtedly this is exactly what has happened to each of us in in-
fancy. The child is engaged in early life in receiving a maze of sensa-
tions and as certain combinations occur over and over they become
fused together and finally become thought of as an object. A rattle,
for example, is at first a hodgepodge of tactual, kinaesthetic, visual,
and auditory sensations. Eventually it is a rattle having all of these
various characteristics, and moreover when it is touched in the dark
the tactual stimulations bring to mind not only tactual notions of the
rattle but also visual, kinaesthetic, and auditory sensations all fused
logether into the percept of a rattle.

SUMMARY

The eye is merely a mechanism for adjusting physical light
\ ibrations so that they will arouse physiological chan2:es in the retina,
\' hich, in turn, will be conveyed to the brain and interpreted in terms
of cur past experiences. A visual situation must be thought of, not
in terms of the object itself, but in terms of the nervous processes
which are aroused by it.

ORGANIC, GUSTATORY, OLFACTORY, AUDITORY AND STATIC SENSATIONS

In addition to cutaneous, kinaesthetic and visual sensations, we have



•G. M. Whipple, op. cit.. p. 189.

tG. ^\. Stratcon. Experimental Psychology and Culture. 1903. p. 146-149.



200 INTRODUCTORY rSVCIIOLOGY FOR TEACHERS

several others. Organic sense-organs are similar to cutaneous and
kinaesthetic, but are located not in the skin or about the muscles, but
in and about the internal organs. From these sense-organs we obtain
the little information that we do receive as to the working of these
organs. They arouse such sensations as thirst, hunger, nausea, heart-
burn, suffocation, pain of a general, massive, agony type, and general
bodily feelings of well or ill. Gustatory sense-organs are located in
the mouth, and olfactory in the upper portion of the nasal cavity.
Sensations of taste and odor are too familiar to need discussion here.

Organic, gustatory and olfactory sensations are similar to cutaneous
and kinaesthetic. A specific stimulus affects a very simple sense-
organ consisting apparently of not much more than a nerve ending
and we obtain the sensation characteristic of that sense-organ.

Auditory situations, on the other hand, are received and affect
consciousness by means of an elaborate receiving mechanism similar
to the eye in complexity. It is not essential that the anatomy of the
ear be mastered. It is sufficient that one realizes that a physical
stimulation — vibration of the air — is converted within the ear into a
physiological stimulation which is transmitted over the auditory nerve
to the brain and that there the air vibration is expressed in con-
sciousness in the form of different tones and noises and their
combinations.

Still another type of situation which affects us is known as the
"static." We are not directly conscious of it, but only indirectly
through its influence upon other sense-organs, particularly the organic
stnse-organs. Within the semi-circular canals of the ear and two
adjacent small bodies are little hairs projecting into the liquid filling
these organs. Whenever the head is moved, the liquid is disturbed,
just as water in a glass is disturbed if the glass is moved. The liquid
in turn disturbs the hairs, which in turn excite the nerves connected
with them. These stimulations are transmitted to the mid-brain
and from thence to various sense-centers which control the move-
ments of the body. Here is the mechanism, for example, which starts
the movement to regain our equilibrium when we slip on a banana
peel. Excessive stimulation of these static sense-organs, as in
swinging in a swing, whirling around, being tossed alx)ut in a ship,
etc., brings about changes in the bodily organs. These changes in turn
affect the organic sense-organs therein situated and we feel dizzy,
or seasick.

REFERENCES

W. H. Howell, Texi-book of Physiology, 1907, pp. 286-362.

J. R. Angell, Psychology, 1909, pp. 131-145.



LESSON 2,7 20I

Ladd & Woodvvorth, Physiological Psychology, 191 1, pp. 182-196.
\\\ B. Pillsbury, Essentials of Psychology, 191 1, pp. 82-95.
J. D. Lickley, The Nervous System, 191 2, Chap. X.
G. M. Whipple, Manual of Mental and Physical Tests, 1914,
pp. 164-200.

LESSON 37— HOW DOES ONE ESTIMATE DISTANCE?

SPACE-PF.RCEl<riON.

The first few minutes of the laboratory hour will be devoted to a
Jenionstraton of a model of the eye. Be prepared to clear up any
difficulties you had in obtaining a general idea of the constnuction
of the eye.

We have seen in Lesson 35 that there are four cutaneous sensa-
tions which are simple experiences and cannot be resolved into any
simpler sort of consciousness. We have also seen that there are a
great many other so-called sensations which appear at first thought
to be equally simple, such as hardness, softness, dryness, smoothness,
etc. But, on closer study, these can all be resolved into simpler sen-
sations. These so-called sensations have been referred to as com-
pound sensations. Compound sensations have been developed thru
experience — have been learned. Another term of somewhat similar
meaning is "percept." When we use the expression "compound sen-
sation" we have reference primarily to the abstract quality, say of
sharpness ; when "percept" is employed we are thinking of the par-
ticular object which is sharp. Actually, it is very improbable if we
ever experience "sharpness" as a compound sensation in this sense,
but rather always think not only of sharpness but also of the object
which occasions the sharpness. That is, the combination of elementary
sensations gives us directly the perception of a sharp object.

But a percept can be and usually is much more complex that a com-
pound sensation. The percept of an apple includes sensations of
vision, touch, taste, smell and hearing (sound of crunching a piece of
apple) whereas a compound sensation has reference to combinations of
sensations from the same sense-organ.

Apparently the estimation of any distance is a perception, due to
the combination of certain sensations experienced together and from
experience known as "this object" "so far from us." Now we want
to discover in this lesson and in Lesson 39 some of the factors in
terms ot which we perceive that a certain object is nearer than a
second object and farther away than a third object. For example,
how do TOW know that the tree you see is outside the window instead



202 INTRODUCTORY PSYCHOLOGY FOR TEACHERS

of inside? How do you know this telephone pole is nearer than
that one?

This problem is assigned not only because it is worth while in
itself, but because it will ilustrate to some extent how we have built
up thru experience such notions as distance, time, space, height,
weight, etc. In fact, the fundamental principles of how we have learned
It. estimate distance underlie the development of all our perceptions
of objects, as a cow, horse, barn, book, etc.

This problem is also assigned because it illustrates the analysis
teachers must make of the processes they are to teach. The more
aetailed a grasp of the separate processes involved in using a plane,
cr saw, or ])en, or typewriter he has, the better can the teacher teach
their use. For when the complex whole has been analyzed into its
component parts, then the teacher can call the student's attention to
the parts and aid him in mastering each part and performing them in
their proper sequence. Otlierwise the learning must be entirely a
"trial and error" performance — the most irritating and inefficient
way of learning.

ESTIMATION OF DISTANCE.

The problem before us primarily is the determination of the relative
distance of one object in reference to other objects, i. e., is it nearer
or farther away than some other object? The conversion of this
idea of relative distance into measurements of distance, such as stat-
ing its distance in feet, is another matter and will not concern us
in this experiment.

If we close one eye and move our finger back and forth toward the
nose and then away from it, it is clear that we can determine its position
with regard to our nose very well. How we do this with one eye
(monocular vision) is one problem.

If we look with both eyes at near objects and then objects farther
away (but less than lOO feet), it is again clear that we can determine
their relative position very well. How we do this with both eyes (binoc-
ular vision) is a second problem.

And if we look at distant objects thru the window, it is also clear
that we can determine their relative distance, although possibly not
so well. How we do this is a third problem.

The second problem of binocular vision under loo feet distance will
be tackled in this lesson ; the first and third problems in Lesson 39.

EXPERIMENT

Problem: What are the factors underlying the Perception of
Distance of Objects zvithin 100 feet unth Binocular Vision f



LESSON 37 203

Apparatus: A number of small objects; a stereoscope and views
of the Titchener Series.

Procedure:

(i) Selvct some narrow object (A), as the strini^ attached to the
curtain in the window, or the wooden strip between two panes ct
glass in the window, or a drop cord supporting an electric light. Seat
yourself so that you can look past the object to some other object (B)
some distance away. Now alternately focus on A and B fifteen to
twenty times. Note that A appears first as one string and then as
two strings. Note the change in the strain felt in the eyes. And note
also changes in the position of your partner's eyeballs when he is
thus focusing back and forth,

(2) Select two Imoks (C and D). Stand book C on end upon
the table with its side about three feet away (placed at three feet to
exaggerate the phenomenon). Stand book D a few inches nearer and
with its back towards you. Book D now stands more or less perpen-
dicular to lx»ok C. Now note the difference in the details which can
be seen of book D as you look at it alternately with the rigkt eye and
the left e\ e. Also observe the differences which can be seen in book C
under the two conditions — book C acting as a background for the view
of hook D. (If you do not discover such differences in book C, move
your position slightly. But be very careful not to move the head from
side to side as you look alternately with one eye and the other.)
Note the following points: (a) The two views are different; (b) the
points on the back of the book D are displaced more from right to left
than the points of book C; (c) the view seen by the two eyes together
is a fusion of what both eyes see — not an average of what the two
see — and one is not conscious of whether he sees a detail with
one eye or with the other (not until he has experimented).

Confirm these points and add any others that are discovered thru
studying these and other objects about the room. Draw what is seen
with each eye separately when looking at the two books.

(3) Carefully note the differences in the details of the two
photographs which comprise a stereoscopic picture (use, for example.
Nos. 15, 17, 37, etc., of the Titchener series). Choose two points in
the picture, one of which is in the very near foreground and the other
far back in the background. Measure carefully the distance from
these two points to the right hand edge of the picture in which they
occur. Note whether a near-point varies more to the right and left
in the two photographs than a distant point.

(4) Xote slide No. i. Here are two views composed of two dots
each. In the right hand view, however, the dots are spaceil farther



204 IMROULCTOUV PSVCHOLOGY FOR TEACHERS

ipart than in the left liand \icvv. Why, when seen in the stereoscope,
does one dot appear nearer than the other? Would this occur if the
spacing between the two dots was the same in the two views?

Results: Carefully compare your findings in the four experiments.
What relationship do they bear to one another? Answer the following
questions, after reading over the section in Lesson 36 on "Convergence,
Divergence and Accommodation":

(i) How do the differences in what is seen by the two eyes of a
near object differ from what is seen of a distant object? How do the
differences in objects in the foreground of two stereoscope pictures
ci-'ffer from the differences in objects in the background? Explain.

(2) Is there any relationship between the differences in the view
of a book as seen by the two eyes and the differences between two
stereoscopic pictures? Explain.

(3) Is it correct to state that when the two views of an object, as
recorded on the retina of the two eyes, differ, then those points which
differ most are seen as nearby while those points which differ only a
little are seen as far away? Explain your point of view.

Application. What general relationship is there between the results
discovered here and learning in general?

ASSIGNMENT FOR NEXT CI.ASS HOUR

1. Write up the above experiment.

2. Be prepared to discuss Lesson 36 in class.

3. During the next few days be gathering data on how you are
able to determine the relative distance of objects, both of which are
more than 100 feet away. Jot down every clue that comes to mind.
(The answers to this problem are very simple, so simple that most
students overlook them in endeavoring to discover some profound
proposition.)



LESSON 38. THE MECHANISM BY WHICH RESPONSES

ARE MADE""

In Lesson 34 a bird's-eye view of the whole physiological explanation
of behavior was presented. This was expressed under three general
Leadings: Stimulation of a sense-organ (the situation), movement
of a muscle or muscles (the response), and the connection of sense-
organ and muscle (the bond). In Lessons 35 and 36 we have studied
typical mechanisms by which situations affect us. We have seen that
certain kinds of stimulations arouse a sense-organ to activity and that
that activity is passed on over nerve pathways to the spinal-cord or
brain. We now shall consider how the response is made to these
situations.

In order to have before us a proper perspective, consider again
the example given in Plate XXX. There is illustrated the simplest
lossible type of situation and response (reflex action). A pin is
stuck into the skin. One or more pain and touch spots are stimulated.
A nervous discharge from thes(e sense-organs proceeds over the
nervous pathway to the spinal-cord. This current then jumps a gap
to another nerve-cell along whose fibre it proceeds until it reaches
the muscle C. This muscle then contracts and the arm is pulled away.
(Actually, the case is more comj^lex, involving more than one muscle
and more than one pathway.) This example illustrates a complete
situation-response functioning. The problems before us are: Just
how does a stimulated muscle move a portion of the body, and, second,
how does a nervous current stimulate the muscle and cause it to react ^

HOW DOES THE CONTRACTION OF A MUSCLE MOVE A PART OF THE BODY?

In Plate XXXIII is shown a diagram of the two major muscles of
the upper arm and their relation to the bones of the arm, forearm, and
shoulder. The biceps ("4" in the diagram) is attached to the shoulder
and to the bones of the forearm. In the latter case it is attached j
short distance beyond the elbow end of the bone. The bones of the
forearm and upper arm are jointed together somewhat after the
fashion of a door-hinge. If tlie biceps should contract, it is clear that
it would pull the shoulder blade and the bones of the forearm. Either
the shoulder or the forearm bones would have to move. As the
shoulder is fastened, the forearm has to swing up. The forearm acts
like a lever here.



•CLASS-HOUR


IN CLASS WRITE UP


READ


38
39
40


Discuss. Les. 36, 37

Experi. Les. 39 Lesson 39

Discuss, Les. 38, 39


Lesson 3 8



205



206 INTRODUCTORY PSYCHOLOGY FOR TEACHERS




Plate XXXIH. Motor Mechanism. I. The humerus. 2. The muscle by which the
joint is straightened (the triceps). 3. Its insertion. 4. The muscle by which the elbow
ia bent (the biceps). 5. Its origin. 6. Its insertion. When the muscle 4 contracts
by an amount represented by 7 to 8, the amount of motion of the ball wiU be rep-
resented by 9 to II. There is a loss of power which is compensated by an increase of
motion. (D. J. Hill, The Elements of Psychology, 1888, p. 401).

A slight pull on it at 6, where the biceps is attached to it. results in
a large movement at the finger ends. In compensation for the increase
in motion at 12 over that at 7, there is a corresponcJing loss in
power. Contraction of the biceps results, then, in movement of the
forearm.

Muscles which have to do with movements of the body are attached
lo the bones of the body. They are normally in a state of elastic
tension. In most cases, they are in pairs, as in the case of the forearm.
One pulls the arm up, the other down. The elastic tension is con-
ducive to a sm(X)th and very prompt movement. When the biceps is
stimulated so as to contract, the triceps are stimulated so as to relax,
and vice versa.

i;OW DOES THE NERVOUS CURRENT STIMULATE THE MUSCLE AND

CAUSE IT TO REACT.?

Before answering this question, a few facts need to be considered
concerning the structure of the muscle. There are two kinds of
):iuscles: (i) Striated skeletal muscle, and (2) plain muscle. Muscles
which move the body belong to the first group, while muscles which
have to do with the blood vessels, alimentary canal, glands of the
body, etc., belong to the second group. We shall consider here only
the former group. A skeletal muscle is made up of many fiber.s
composed of a single cell, enclosed in an elastic membrane. When
the motor nerve enters the muscle, it subdivides and subdivides until
t'lere is at least one nerve fibril attaching itself to each fibre of the
ruiscle. The point of attachment is near the middle of the fibre.
This point is called a motor end-plate. Returning to our main
question now, we can see that when a nervous stimulation is trans-
mitted from the spinal cord to the muscle it reaches, by way of these
motor end-plates, every fibre in the muscle. The effect of this stimu-



LESSON 38 207

lation on the muscle is to produce a chemical change (as yet not very
well understood) which causes the fibre to contract. Consequently,
the whole muscle contracts, and its attached bone is moved.

When a muscle contracts, it gives off heat and electrical energy
and produces work. In other words, the chemical change caused by
the stimulation of the muscle can be likened to the case of a gas-
engine, where heat and work result from the combustion of gasoline.
But the human muscle is a very much more efficient engine than a
steam or gasoline engine. Only 10 to 15 per cent, of the energy con-
tained in coal is converted into work by a steam engine, 15 to 25
]'er cent, of the energy in gasoline in the case of a gasoline engine,
wliereas from 25 to even 40 per cent, is utilized in the case of a muscle.
The remainder of the stored-up energy is wasted mainly in the form
cf heat. In the case of an engine, this is all pure waste, but in the
case of the animal, much of this heat is utilized in keeping the
organism warm.

FATIGUE

The contraction of the muscle is due to chemical changes. As a
result of these changes, carbon dioxide gas (CO2), lactic acid
(C3H6O3), and acid poassium phosphate (KH2PO4) are liberated,