PERSONALITY 552
Factors in Personality 553
The Self 555
Integration and Disintegration
of the Personality 558
The Unconscious, or,
the Subconscious Mind 561
Unconscious Wishes and Motives 565
Exercises 571
References 571
INDEX 573
{1}
PSYCHOLOGY
CHAPTER I
WHAT PSYCHOLOGY IS AND DOES
THE SUBJECT-MATTER OF THE SCIENCE, ITS PROBLEMS AND ITS METHODS
Modern psychology is an attempt to bring the methods of scientific
investigation, which have proved immensely fruitful in other fields,
to bear upon mental life and its problems. The human individual, the
main object of study, is so complex an object, that for a long time it
seemed doubtful whether there ever could be real science here; but a
beginning was made in the nineteenth century, following the lead of
biology and physiology, and the work of the investigator has been so
successful that to-day there is quite a respectable body of knowledge
to assemble under the title of scientific psychology.
Psychology, then, is a science. It is the science of--what shall we
say? "The science of the soul"--that is what the name means by
derivation and ancient usage. "The science of the mind" has a more
modern sound. "The science of consciousness" is more modern still.
"The science of behavior" is the most recent attempt at a concise
formula.
None of these formulas is wholly satisfactory. Psychology does not
like to call itself the science of the soul, for that has a
theological tang and suggests problems that have so far not seemed
accessible to scientific investigation. Psychology does not like very
well to call itself the science {2} of the mind, as _the_ mind seems to
imply some thing or machine, and there is no such thing to be observed
(unless it be the brain and body generally), and, anyway, psychology
is distinctly a study of actions rather than of things. Psychology
does not like to limit itself to the study of consciousness, but finds
it necessary to study also unconscious actions. As to "behavior", it
would be a very suitable term, if only it had not become so closely
identified with the "behavioristic movement" in psychology, which
urges that consciousness should be entirely left out of psychology, or
at least disregarded. "Behavior psychology", as the term would be
understood to-day, means a part of the subject and not the whole.
[Footnote: A series of waggish critics has evolved the following:
"First psychology lost its soul, then it lost its mind, then it lost
consciousness; it still has behavior, of a kind."]
The best way of getting a true picture of psychology, and of reaching
an adequate definition of its subject-matter, would be to inspect the
actual work of psychologists, so as to see what kind of knowledge they
are seeking. Such a survey would reveal quite a variety of problems
under process of investigation, some of them practical problems,
others not directly practical.
Varieties of Psychology
Differential psychology.
One line of question that always interests the beginner in psychology
is as to how people differ--how different people act under the same
circumstances--and why; and if we watch the professional
psychologist, we often find him working at just this problem. He tests
a great number of individuals to see how they differ, and tries to
discover on what factors their differences depend, how far on
heredity, how far on environment. The "psychologist" in such a place
as the children's court {3} is a specialist whose duty it is to test
the delinquent children that are brought before the court, with the
special object of measuring the intelligence of each individual child
and of helping in other ways to understand the child's peculiar
conduct and attitude.
The "psychological examiner" in the Army, during the Great War, had the
same general object in view. It was desirable to measure the
intelligence of each recruit as he entered the service, since military
experience had shown that men of low intelligence made poor soldiers,
while those of high intelligence made the best officers and
non-commissioned officers, provided they also possessed good physique
and certain less measureable mental qualifications, such as courage
and leadership.
Applied psychology.
The Army psychologists, like the court psychologist, were engaged in
applying scientific knowledge to the practical problems of life; and
there are many other applications of psychology, to education, to
medicine, to business and other occupations, as well as to the art of
right living. Scientific knowledge enables you to _predict_ and
_control_. Having devised scientific tests for intelligence, you can
predict of a six-year-old boy who tests low, that he will not get much
good from the regular classes in school; and thus you are in a
position to control the education of this boy for his own best
interests. In the Army, it happened during the earlier part of the war
that some companies or regiments made much slower progress in training
than others; and a whole Division was delayed for months because of
the backwardness of a single regiment. When the psychological tests
were introduced, these slow-learning units were found to contain a
disproportionate number of men of low intelligence. From that time on,
it was possible by aid of the tests to equalize the intelligence of
different units when first formed, and thus insure equal {4} progress
in training. This was a good example of "control".
Most of us are attracted by the practical use of a science, and some
have no patience with any study that does not seem immediately
practical. But really any science, however much it is applied, must
remain fundamentally a pure science; that is, it must seek most of all
to know and understand. Practical scientific knowledge was usually
first obtained without any inkling of how it might be used. The
science of electricity is the most striking example of this. It began
as an attempt to understand certain curious phenomena, which seemed to
be nothing but curiosities; yet when the knowledge of these phenomena
had progressed to a certain point, abundant use was found for it. Much
the same is true of psychology, which began as a pure science and only
recently has found ways of applying its discoveries to practical
affairs. So the student beginning the science, though properly
desirous of making practical use of what he learns, should let himself
be governed for the present by the desire to know and understand,
confident that the more scientific (which is to say, the more
complete, systematic and reliable) his knowledge is, the more
available it will be for practical application.
General psychology.
Our science is not concerned entirely with differences between people,
but asks also in what ways people are alike, and this is indeed its
central problem. How do "we" observe, learn, remember, imagine, think?
What sensations and feelings do we have, what emotions, what
instincts, what natural and acquired impulses to action? How are our
natural powers and impulses developed and organized as we grow up?
Psychology is concerned with the child as well as the adult, and it is
even concerned with the animal. It is concerned with the abnormal as
well as the normal human being. So you will find books and {5} courses
on animal psychology, child psychology, abnormal psychology. Now
general psychology--or just plain "psychology"--has to do with the
main laws and principles that hold in all these special fields.
Psychology as Related to Other Sciences
A good definition of our science would distinguish it from other
sciences, especially from those neighboring sciences with which it is
in closest contact.
Psychology and sociology.
There is no difficulty in framing a good logical distinction here.
Sociology studies the activities of a group of people taken as a
whole, while psychology studies the activities of the individuals.
Both might be interested in the same social act, such as an election,
but sociology would consider this event as a unit, whereas psychology
would break it up into the acts of the several voters. The distinction
is clear enough theoretically, but breaks down often in practice, as
sociology would like to know the motives that swayed individual
voters, while psychology on its side is interested to know what
decision was reached by the majority. All the social sciences,
including economics and politics, have a psychological side, since
they evidently are concerned to know the causes that govern human
conduct. Social psychology studies the individual in his social
relations.
Psychology and biology.
Biology, being the science of living creatures, includes psychology,
which studies these creatures on the mental side. The science of life
includes the science of mental life. We may call psychology a part of
biology, or we may call it one of the biological sciences. It has very
close contact with several other branches of biology. Animal
psychology overlaps that part of zoology which studies the behavior of
animals. Genetic psychology, as it is sometimes called, i.e., the
study of mental heredity. {6} and development, dovetails with the
general biological science of genetics, so that we find biologists
gathering data on the heredity of feeble-mindedness or of musical
ability, while psychologists discuss the general theory of heredity.
Psychology and physiology.
That one of all the sciences that has the closest contacts with
psychology is human and animal physiology. Broadly defined, physiology
is that part of biology that studies functions or activities; and, so
defined, it includes psychology as part of itself. In practice,
psychology devotes itself to desire, thought, memory, and such "mental
functions", while physiology concentrates its effort upon "bodily
functions" like digestion and circulation. But this is only a rough
distinction, which breaks down at many points.
Where shall we class sensation? Is it "mental" or "bodily"? Both
sciences study it. Physiology is perhaps more apt to go into the
detailed study of the action of the sense organs, and psychology to
concern itself with the classification of sensations and the use made
of them for recognizing objects or for esthetic purposes. But the line
between the two sciences is far from sharp at this point.
Speech, also, lies in both provinces. Physiology has studied the
action of the vocal organs and the location of the brain centers
concerned in speech, while psychology has studied the child's process
of learning to speak and the relation of speech to thought, and is
more apt to be interested in stuttering, slips of the tongue, and
other speech disturbances which are said to be "mental rather than
physical".
It would be hard to mention any activity that is mental without being
physical at the same time. Even thinking, which seems as purely mental
as any, requires brain action; and the brain is just as truly a bodily
organ as the heart or stomach. Its activity is bodily activity and
lies properly within the field of physiology.
{7}
But it would be equally difficult to mention any function that is
exclusively bodily, and not mental at the same time, in some degree.
Take digestion for example: the pleasant anticipation of food will
start the digestive juices flowing, before any food is physically in
the stomach; while in anger or fear digestion comes to a sudden halt.
Therefore we find physiologists interested in these emotions, and
psychologists interested in digestion.
We do not find any clean separation between our science and
physiology; but we find, on the whole, that psychology examines what
are called "mental" activities, and that it studies them as the
performances of the whole individual rather than as executed by the
several organs.
The Science of Consciousness
Typically, the activities that psychology studies are conscious
performances, while many of those falling to physiology are
unconscious. Thus digestion is mostly unconscious, the heart beat is
unconscious except when disturbed, the action of the liver is entirely
unconscious. Why not say, then, that psychology is the study of
conscious activities?
There might be some objection to this definition from the side of
physiology, which studies certain conscious activities itself--speech,
for example, and especially sensation.
There would be objection also from the side of psychology, which does
not wish to limit itself to conscious action. Take the case of any act
that can at first be done only with close attention, but that becomes
easy and automatic after practice; at first it is conscious, later
unconscious, but psychology would certainly need to follow it from the
initial to the final stage, in order to make a complete study of the
practice effect. And then there is the "unconscious", or the
"subconscious mind"--a matter on which psychologists {8} do not wholly
agree among themselves; but all would agree that the problem of the
unconscious was appropriate to psychology.
For all the objections, it remains true that the _typical_ mental
process, the typical matter for psychological study, is conscious.
"Unconscious mental processes" are distinguished from the unconscious
activity of such organs as the liver by being somehow _like_ the
conscious mental processes.
It would be correct, then, to limit psychology to the study of
conscious activities and of activities akin to these.
The Science of Behavior
No one has objected so strenuously to defining psychology as the
science of consciousness, and limiting it to consciousness, as the
group of animal psychologists. By energetic work, they had proved that
the animal was a very good subject for psychological study, and had
discovered much that was important regarding instinct and learning in
animals. But from the nature of the case, they could not observe the
consciousness of animals; they could only observe their behavior, that
is to say, the motor (and in some cases glandular) activities of the
animals under known conditions. When then the animal psychologists
were warned by the mighty ones in the science that they must interpret
their results in terms of consciousness or not call themselves
psychologists any longer, they rebelled; and some of the best fighters
among them took the offensive, by insisting that human psychology, no
less than animal, was properly a study of behavior, and that it had
been a great mistake ever to define it as the science of
consciousness.
It is a natural assumption that animals are conscious, but after all
you cannot directly observe their consciousness, and you cannot
logically confute those philosophers {9} who have contended that the
animal was an unconscious automaton. Still less can you be sure in
detail what is the animal's sensation or state of mind at any time; to
get at that, you would need a trustworthy report from the animal
himself. Each individual must observe his own consciousness; no one
can do it from outside. The objection of the behaviorist to
"consciousness psychology" arises partly from distrust of this method
of inner observation, even on the part of a human observer.
Indeed, we can hardly define psychology without considering its
_methods of observation_, since evidently the method of observation
limits the facts observed and so determines the character of the
science. Psychology has two methods of observation.
When a person performs any act, there are, or may be, two sorts of
facts to be observed, the "objective" and the "subjective". The
objective facts consist of movements of the person's body or of any
part of it, secretions of his glands (as flow of saliva or sweat), and
external results produced by these bodily actions--results such as
objects moved, path and distance traversed, hits on a target, marks
made on paper, columns of figures added, vocal or other sounds
produced, etc., etc. Such objective facts can be observed by another
person.
The subjective facts can be observed only by the person performing the
act. While another person can observe, better indeed than he can
himself, the motion of his legs in walking, he alone can observe the
sensations in the joints and muscles produced by the leg movement. No
one else can observe his pleased or displeased state of mind, nor
whether he is thinking of his walking or of something quite different.
To be sure, his facial expression, which is an objective fact, may
give some clue to his thoughts and feelings, but "there's no art to
read the mind's construction {10} in the face", or at least no sure
art. One may feign sleep or absorption while really attending to what
is going on around. A child may wear an angelic expression while
meditating mischief. To get the subjective facts, we shall have to
enlist the person himself as our observer.
Introspection
This is observation by an individual of his own conscious action. It
is also called subjective observation. Notice that it is a form of
observation, and not speculation or reasoning from probabilities or
from past experience. It is a direct observation of fact.
One very simple instance of introspection is afforded by the study of
after-images. Look for an instant at the glowing electric bulb, and
then turn your eyes upon a dark background, and observe whether the
glowing filament appears there; this would be the "positive
after-image". This simple type of introspection is used by physiology
in its study of the senses, as well as by psychology; and it gives
such precise and regular results that only the most confirmed
behaviorists refuse to admit it as a good method of observation.
But psychology would like to make introspective observations on the
more complex mental processes as well; and it must be admitted that
here introspection becomes difficult. You cannot hope to make minute
observations on any process that lasts over a very few seconds, for
you must let the process run its natural course unimpeded by your
efforts at observing it, and then turn your "mental eye" instantly
back to observe it _retrospectively_ before it disappears. As a matter
of fact, a sensation or feeling or idea hangs on in consciousness for
a few seconds, and can be observed in this retrospective way. There is
no theoretical objection to this style of introspection, but it is
practically difficult and {11} tricky. Try it on a column of figures:
first add the column as usual, then immediately turn back and review
exactly what went through your mind in the process of adding---what
numbers you spoke internally, etc. Try again by introspecting the
process of filling in the blanks in the sentence:
"Botany could not make use of introspection because ______ have
probably no ________ processes."
At first, you may find it difficult to observe yourself in this way;
for the natural tendency, when you are aiming at a certain result, is
to reach the goal and then shift to something else, rather than to
turn back and review the steps by which you reached the goal. But with
practice, you acquire some skill in introspection.
One difficulty with introspection of the more complex mental processes
is that individuals vary more here than in the simpler processes, so
that different observers, observing each his own processes, will not
report the same facts, and one observer cannot serve as a check upon
another so easily as in the simpler introspection of after-images and
other sensations, or as in the observations made in other sciences.
Even well trained introspectionists are quite at variance when they
attempt a minute description of the thought processes, and it is
probable that this is asking too much of introspection. We mustn't
expect it to give microscopic details. Rough observations, however, it
gives with considerable certainty. Who can doubt, for example, that a
well-practised act goes on with very little consciousness, or that
inner, silent speech often accompanies thinking? And yet we have only
introspection to vouch for these facts.
Objective Observation
But to say, as used to be said, that psychology is purely an
introspective science, making use of no other sort of observation, is
absurd in the face of the facts.
{12}
We have animal psychology, where the observation is exclusively
objective. In objective observation, the observer watches something
else, and not himself. In animal psychology, the psychologist, as
observer, watches the animal.
The same is true of child psychology, at least for the first years of
childhood. You could not depend on the introspections of a baby, but
you can learn much by watching his behavior. Abnormal persons, also,
are not often reliable introspectionists, and the study of abnormal
psychology is mostly carried on by objective methods.
Now how is it with the normal adult human being, the standard subject
for psychology? Does he make all the observations on himself or may he
be objectively observed by the psychologist? The latter, certainly. In
fact, nearly all tests, such as those used in studying differential
psychology, are objective. That is to say that the person tested is
given a task to perform, and his performance is observed in one way or
another by the examiner. The examiner may observe the _time_ occupied
by the subject to complete the task, or the _quantity_ accomplished in
a fixed time; or he may measure the correctness and _excellence_ of
the work done, or the _difficulty_ of the task assigned. One test uses
one of these measures, and another uses another; but they are all
objective measures, not depending at all on the introspection of the
subject.
What is true of tests in differential psychology is true of the
majority of experiments in general psychology: the performer is one
person, the observer another, and the observation is objective in
character. Suppose, for example, you are investigating a memory
problem; your method may be to set your subject a lesson to memorize
under certain defined conditions, and see how quickly and well he
learns it; then you give him another, equally difficult lesson to be
learned under altered conditions, and observe whether he {13} does
better or worse than before. Thus you discover which set of conditions
is more favorable for memorizing, and thence can infer something of
the way in which memorizing is accomplished. In the whole experiment
you need not have called on your subject for any introspections; and
this is a type of many experiments in which the subject accomplishes a
certain task under known conditions, and his success is objectively
observed and measured.
There is another type of objective psychological observation, directed
not towards the success with which a task is accomplished, but towards
the changes in breathing, heart beat, stomach movements, brain
circulation, or involuntary movements of the hands, eyes, etc., which
occur during the course of various mental processes, as in reading, in
emotion, in dreaming or waking from sleep.
Now it is not true as a matter of history that either of these types
of objective observation was introduced into psychology by those who
call themselves behaviorists. Not at all; experiments of both sorts
have been common in psychology since it began to be an experimental
science. The first type, the success-measuring experiment, has been
much more used than introspection all along. What the behaviorists
have accomplished is the definitive overthrow of the doctrine, once
strongly insisted on by the "consciousness psychologists", that
introspection is the only real method of observation in psychology;
and this is no mean achievement. But we should be going too far if we
followed the behaviorists to the extent of seeking to exclude
introspection altogether, and on principle. There is no sense in such
negative principles. Let us accumulate psychological facts by any
method that will give the facts.
{14}
General Laws of Psychological Investigation.
Either introspective or objective observation can be employed in the
_experimental attack_ on a problem, which consists, as just
illustrated in the case of memory, in controlling the conditions under
which a mental performance occurs, varying the conditions
systematically, and noting the resulting change in the subject's
mental process or its outcome. Psychologists are inclined to regard
this as the best line of attack, whenever the mental activity to be
studied can be effectively subjected to control. Unfortunately,
emotion and reasoning are not easily brought under control, and for
this reason psychology has made slower progress in understanding them
than it has made in the fields of sensation and memory, where good
experimental procedure has been developed.
Another general line of attack worthy to be mentioned alongside of the
experimental is the _comparative method_. You compare the actions of
individuals, classes or species, noting likenesses and differences.
You see what behavior is typical and what exceptional. You establish
norms and averages, and notice how closely people cluster about the
norm and how far individuals differ from it. You introduce tests of
various sorts, by which to get a more precise measure of the
individual's performance. Further, by the use of what may be called
double comparison, or "correlation", you work out the relationships of
various mental (and physical) traits. For example, when many different
species of animals are compared in intelligence and also in brain
weight, the two are found to correspond fairly well, the more
intelligent species having on the whole the heavier brains; from which
we fairly conclude that the size of the brain has something to do with
intelligence. But when we correlate brain weight and intelligence in
human individuals. {15} we find so many exceptions to the rule (stupid
men with large brains and gifted men with brains of only moderate
size) that we are forced to recognize the importance of other factors,
such as the perfection of the microscopic structure of the brain.
Tests and correlations have become so prominent in recent
psychological investigation that this form of the comparative method
ranks on a par with the strict experimental method. A test is an
experiment, in a way, and at least is often based upon an experiment;
but the difference between the two lines of attack is that an
experiment typically takes a few subjects into the laboratory and
observes how their mental performances change with planfully changed
conditions; whereas a test goes out and examines a large number of
persons under one fixed set of conditions. An experiment belongs under
what we called "general psychology", and a test under "differential
psychology", since the first outcome of a test is to show how the
individual differs from others in a certain respect. The results may,
however, be utilized in various ways, either for such practical
purposes as guiding the individual's choice of an occupation, or for
primarily scientific purposes, such as examining whether intelligence
goes with brain size, whether twins resemble each other as much
mentally as they do physically, whether intellectual ability and moral
goodness tend on the whole to go together, or not.
The _genetic method_ is another of the general lines of attack on
psychological problems. The object here is to trace the mental
development of the individual, or of the race. It may be to trace the
development either of mentality in general, or of some particular
mental performance. It may be to trace the child's progress in
learning to speak, or to follow the development of language in the
human species, from the most primitive tongues up to those of the
great {16} civilized peoples of to-day. It may be to trace the
improvement of a performance with continued practice.
The value of the genetic method is easily seen. Usually the beginnings
of a function or performance are comparatively simple and easy to
observe and analyze. Also, the process of mental growth is an
important matter to study on its own account.
The _pathological method_ is akin to the genetic, but traces the decay
or demoralization of mental life instead of its growth. It traces the
gradual decline of mental power with advancing age, the losses due to
brain disease, and the maladaptations that appear in insanity and
other disturbances. Here psychology makes close contact with
_psychiatry_ which is the branch of medicine concerned with the
insane, etc., and which in fact has contributed most of the
psychological information derived from the pathological method.
The object of the pathological method is, on the one side, to
understand abnormal forms of mental life, with the practical object of
preventing or curing them, and on the other side, to understand normal
mental life the better. Just as the development of a performance
throws light on the perfected act, so the decay or disturbance of a
function often reveals its inner workings; for we all know that it is
when a machine gets out of order that one begins to see how it ought
to work. Failure sheds light on the conditions of success,
maladaptation throws into relief the mental work that has to be done
by the normal individual in order to secure and maintain his good
adaptation. According to the psychiatrists, mental disturbance is
primarily an affair of emotion and desire rather than of intellect;
and consequently they believe that the pathological method is of
special importance in the study of the emotional life.
{17}
Summary and Attempt at a Definition
Having now made a rapid preliminary survey of the field of psychology,
and of the aims and methods of the workers in this field, we ought to
be in a position to give some sort of a definition.
We conclude, then: psychology is a part of the scientific study of
life, being the science of mental life. Life consisting in process or
action, psychology is the scientific study of mental processes or
activities. A mental activity is typically, though not universally,
conscious; and we can roughly designate as mental those activities of
a living creature that are either conscious themselves or closely akin
to those that are conscious. Further, any mental activity can also be
regarded as a physiological activity, in which case it is analyzed
into the action of bodily organs, whereas as "mental" it simply comes
from the organism or individual as a whole. Psychology, in a word, is
the science of the conscious and near-conscious activities of living
individuals.
Psychology is not interested either in dead bodies or in disembodied
spirits, but in living and acting individuals.
One word more, on the _psychological point of view_. In everyday life
we study our acquaintances and their actions from a personal
standpoint. That is, we evaluate their behavior according as it
affects ourselves, or, perhaps, according as it squares or not with
our standards of right and wrong. We always find something to praise
or blame. Now, the psychologist has no concern with praise and blame,
but is a seeker after the facts. He would know and understand human
actions, rather than pass judgment on them. When, for example, he is
introduced into the school or children's court, for the purpose of
examining children that are "problems", his attitude differs
considerably from that of the {18} teacher or officer of the law; for
while they almost inevitably pass judgment on the child in the way of
praise or blame, the psychologist simply tries to understand the
child. The young delinquent brought into the laboratory of the court
psychologist quickly senses the unwonted atmosphere, where he is
neither scolded nor exhorted, but asked to lend his coöperation in an
effort to discover the cause why his conduct is as it is. Now, this
psychological attitude is not necessarily "better" than the other, but
it is distinctly valuable in its place, as seen from the fact that the
young delinquent often does coöperate. He feels that if the
psychologist can find out what is the trouble with him, this may help.
Nothing, indeed, is more probable; it is when we have the facts and
trace out cause and effect that we are in a fair way to do good.
Nothing is more humane than psychology, in the long run, even though
the psychologist may seem unfeeling in the course of his
investigation.
To the psychologist, conduct is a matter of cause and effect, of
natural law. His business is to know the laws of that part of nature
which we call human nature, and to use these laws, as fast as
discovered, for solving the problems presented by the human individual
or group. For him, even the most capricious conduct has its causes,
even the most inexplicable has its explanation--if only the cause can
be unearthed, which he does not pretend he can always actually
accomplish, since causes in the mental realm are often very complex.
No one can be a psychologist all of the time; no one can or should
always maintain this matter-of-fact attitude towards self and
neighbor. But some experience with the psychological attitude is of
practical value to any one, in giving clearer insight, more
toleration, better control, and even saner standards of living.
{19}
EXERCISES
1. Outline the chapter. A sample outline of the briefer sort is
here given:
A. Subject-matter of psychology: mental activities.
(1) A sub-class under vital activities.
(2) Activities of individuals, as distinguished from
(a) Activities of social groups (sociology).
(b) Activities of single organs (physiology).
(3) Either conscious, or closely related to conscious activities.
(4) May be activities of human or animal, adult or child,
normal or abnormal individuals.
B. Problems of psychology:
(1) How individuals differ in their mental activities.
(2) How individuals are alike in their mental activities.
(3) Practical applications of either (1) or (2).
C. Methods of psychology:
(1) Methods of observing mental activities.
(a) Introspective, the observing by an individual of his own actions.
(b) Objective, the observation of the behavior of other individuals.
(2) General lines of attack upon psychological problems.
(a) Experimental: vary the conditions and see how the mental
activity changes.
(b) Comparative: test different individuals or
classes and see how mental activity differs, etc.
(c) Genetic: trace mental development.
(d) Pathological: examine mental decay or disturbance.
2. Formulate a psychological question regarding each of the following:
hours of work, genius, crime, baseball.
3. Distinguish introspection from theorizing.
4. What different sorts of objective fact can be observed in psychology?
5. What is the difference between the physiology of hearing and the
psychology of hearing?
6. State two reasons why it would be undesirable to limit psychology
to the introspective study of consciousness.
{20}
7. What is the difference between an experiment and a test, (a) in
purpose, (b) in method?
8. Compare the time it takes you to add twenty one-place numbers,
arranged in a vertical column, and arranged in a horizontal line,
(a) Is this introspective or objective observation? Why so? (b) Is
it a test or an experiment? Why?
9. Write a psychological sketch of some one you know well, taking
care to avoid praise and blame, and to stick to the psychological
point of view.
REFERENCES
Some of the good books on the different branches of psychology are
the following:
On animal psychology:
Margaret F. Washburn, _The Animal Mind_, 2nd edition, 1917.
John B. Watson, _Behavior_, 1914.
On child psychology:
Norsworthy and Whitley, _The Psychology of Childhood_, 1918.
On abnormal psychology:
A. J. Rosanoff, _Manual of Psychiatry_, 5th edition, 1920.
On applied psychology:
Hollingworth and Poffenberger, _Applied Psychology_, 1917.
On individual psychology, parts of:
E. L. Thorndike, _Educational Psychology, Briefer Course_, 1914,
Daniel Starch, _Educational Psychology_, 1919.
{21}
CHAPTER II
REACTIONS
REFLEXES AND OTHER ELEMENTARY FORMS OF REACTION,
AND HOW THE NERVES OPERATE IN CARRYING THEM OUT
Having the field of psychology open before us, the next question is,
where to commence operations. Shall we begin with memory, imagination
and reasoning, or with will, character and personality, or with motor
activity and skill, or with feelings and emotions, or with sensation
and perceptions? Probably the higher forms of mental activity seem
most attractive, but we may best leave complicated matters till later,
and agree to start with the simplest sorts of mental performance. Thus
we may hope to learn at the outset certain elementary facts which will
later prove of much assistance in unraveling the more complex
processes.
Among the simplest processes are sensations and reflexes, and we might
begin with either. The introspective psychologists usually start with
sensations, because their great object is to describe consciousness,
and they think of sensations as the chief elements of which
consciousness is composed. The behaviorists would prefer to start with
reflexes, because they conceive of behavior as composed of these
simple motor reactions.
Without caring to attach ourselves exclusively to either
introspectionism or behaviorism, we may take our cue just here from
the behaviorists, because we shall find the facts of motor reaction
more widely useful in our further studies than the facts of sensation,
and because the facts of {22} sensation fit better into the general
scheme of reactions than the facts of reaction fit into any general
scheme based on sensation.
A reaction is a _response_ to a _stimulus_. The response, in the
simplest cases, is a muscular movement, and is called a "motor
response". The stimulus is any force or agent that, acting upon the
individual, arouses a response.
If I start at a sudden noise, the noise is the stimulus, and the
forcible contraction of my muscles is the response. If my old friend's
picture brings tears to my eyes, the picture (or the light reflected
from it) is the stimulus, and the flow of tears is the response, here
a "glandular" instead of a motor response.
The Reaction Time Experiment
One of the earliest experiments to be introduced into psychology was
that on reaction time, conducted as follows: The experimenter tells
his "subject" (the person whose reaction is to be observed) to be
ready to make a certain movement as promptly as possible on receiving
a certain stimulus. The response prescribed is usually a slight
movement of the forefinger, and the stimulus may be a sound, a flash
of light, a touch on the skin, etc. The subject knows in advance
exactly what stimulus is to be given and what response he has to make,
and is given a "Ready!" signal a few seconds before the stimulus. With
so simple a performance, the reaction time is very short, and delicate
apparatus must be employed to measure it. The "chronoscope" or clock
used to measure the reaction time reads to the hundredth or thousandth
of a second, and the time is found to be about .15 sec. in responding
to sound or touch, about .18 sec. in responding to light.
Even the simple reaction time varies, however, from one {23}
individual to another, and from one trial to another. Some persons can
never bring their record much below the figures stated, while a few
can get the time down to .10 sec, which is about the limit of human
ability. Every one is bound to vary from trial to trial, at first
widely, after practice between narrow limits, but always by a few
hundredths of a second at the least. It is curious to find the
elementary fact of variability of reaction present in such a simple
performance.
What we have been describing is known as the "simple reaction", in
distinction from other experiments that demand more of the subject. In
the "choice reaction", there are two stimuli and the subject may be
required to react to the one with the right hand and to the other with
the left; for example, if a red light appears he must respond with the
right hand, but if a green light appears, with the left. Here he
cannot allow himself to become keyed up to as high a pitch as in the
simple reaction, for if he does he will make many false reactions.
Therefore, the choice reaction time is longer than the simple reaction
time--about a tenth of a second longer.
The "associative reaction" time is longer still. Here the subject must
name any color that is shown, or read any letter that is shown, or
respond to the sight of any number by calling out the next larger
number, or respond to any suitable word by naming its opposite. He
cannot be so well prepared as for the simple, or choice reaction,
since he doesn't know exactly what the stimulus is going to be; also,
the brain process is more complex here; so that the reaction time is
longer, about a tenth of a second longer, at the best, than the choice
reaction. It may run up to two or three seconds, even in fairly simple
cases, while if any serious thinking or choosing has to be done, it
runs into many seconds and even into minutes. Here the brain process
is very {24} complex and involves a series of steps before the
required motor response can be made.
These laboratory experiments can be paralleled by many everyday
performances. The runner starting at the pistol shot, after the
preparatory "Ready! Set!", and the motorman applying the brakes at the
expected sound of the bell, are making "simple" reactions. The boxer,
dodging to the right or the left according to the blow aimed at him by
his adversary, is making choice reactions, and this type is very
common in all kinds of steering, handling tools and managing
machinery. Reading words, adding numbers, and a large share of simple
mental performances, are essentially associative reactions. In most
cases from ordinary life, the _preparation_ is less complete than in
the laboratory experiments, and the reaction time is accordingly
longer.
Reflex Action
The simple reaction has some points of resemblance with the "reflex",
which, also, is a prompt motor response to a sensory stimulus. A
familiar example is the reflex wink of the eyes in response to
anything touching the eyeball, or in response to an object suddenly
approaching the eye. This "lid reflex" is quicker than the quickest
simple reaction, taking about .05 second. The knee jerk or "patellar
reflex", aroused by a blow on the patellar tendon just below the knee
when the knee is bent and the lower leg hanging freely, is quicker
still, taking about .03 second. The reason for this extreme quickness
of the reflex will appear as we proceed. However, not every reflex is
as quick as those mentioned, and some are slower than the quickest of
the simple reactions.
A few other examples of reflexes may be given. The "pupillary reflex"
is the narrowing of the pupil of the eye {25} in response to a bright
light suddenly shining into the eye. The "flexion reflex" is the
pulling up of the leg in response to a pinch, prick or burn on the
foot. Coughing and sneezing are like this in being protective
reflexes, and the scratching of the dog belongs here also.
There are many internal reflexes: movements of the stomach and
intestines, swallowing and hiccoughing, widening and narrowing of the
arteries resulting in flushing and paling of the skin. These are
muscular responses; and there are also glandular reflexes, such as the
discharge of saliva from the salivary glands into the mouth, in
response to a tasting substance, the flow of the gastric juice when
food reaches the stomach, the flow of tears when a cinder gets into
the eye. There are also inhibitory reflexes, such as the momentary
stoppage of breathing in response to a dash of cold water. All in all,
a large number of reflexes are to be found.
Most reflexes can be seen to be _useful_ to the organism. A large
proportion of them are protective in one way or another, while others
might be called regulative, in that they adjust the organism to the
conditions affecting it.
Now comparing the reflex with the simple reaction, we see first that
the reflex is more deep-seated in the organism, and more essential to
its welfare. The reflex is typically quicker than the simple reaction.
The reflex machinery does not need a "Ready" signal, nor any
preparation, but is always ready for business. (The subject in a
simple reaction experiment would not make the particular finger
movement that he makes unless he had made ready for that movement.)
The attachment of a certain response to a certain stimulus, rather
arbitrary and temporary in the simple reaction, is inherent and
permanent in the reflex. Reflex action is involuntary and often
entirely unconscious.
Reflexes, we said, are permanent. That is because they {26} are native
or inherent in the organism. You can observe them in the new-born
child. The reflex connection between stimulus and response is
something the child brings with him into the world, as distinguished
from what he has to acquire through training and experience. He does
acquire, as he grows up, a tremendous number of habitual responds that
become automatic and almost unconscious, and these "secondary
automatic" reactions resemble reflexes pretty closely. Grasping for
your hat when you feel the wind taking it from your head is an
example. These acquired reactions never reach the extreme speed of the
quickest reflexes, but at best may have about the speed of the simple
reaction. Though often useful enough, they are not so fundamentally
necessary as the reflexes. The reflex connection of stimulus and
response is something essential, native, closely knit, and always
ready for action.
The Nerves in Reflex Action
Seeing that the response, in reflex action, is usually made by a
muscle or gland lying at some distance from the sense organ that
receives the stimulus--as, in the case of the flexion reflex, the
stimulus is applied to the skin of the hand (or foot), while the
response is made by muscles of the limb generally--we have to ask what
sort of connection exists between the stimulated organ and the
responding organ, and we turn to physiology and anatomy for our
answer. The answer is that the _nerves_ provide the connection. Strands
of nerve extend from the sense organ to the muscle.
But the surprising fact is that the nerves do not run directly from
the one to the other. There is no instance in the human body of a
direct connection between any sense organ and any muscle or gland. The
nerve path from sense organ to muscle always leads through a _nerve
center_. One {27} nerve, called the sensory nerve, runs from the sense
organ to the nerve center, and another, the motor nerve, runs from the
center to the muscle; and the only connection between the sense organ
and the muscle is this roundabout path through the nerve center. The
path consists of three parts, sensory nerve, center, and motor nerve,
but, taken as a whole, it is called the _reflex arc_, both the words,
"reflex" and "arc", being suggested by the indirectness of the
connection.
[Illustration: Fig. 1.--The connection from the back of the hand,
which is receiving a stimulus, and the arm muscle which makes the
response. The nerve center is indicated by the dotted lines.]
The _nervous system_ resembles a city telephone system. What passes
along the nerve is akin to the electricity that {28} passes along the
telephone wire; it is called the "nerve current", and is electrical
and chemical in nature.
[Illustration: Fig. 2.--(From Martin's "Human Body.") General view of
the nervous system, showing brain, cord, and nerves.]
All nerve connections, like the great majority of telephone
connections, are effected through the centers, called "centrals" in
{29} the case of the telephone. Telephone A is connected directly with
the central, telephone B likewise, and A and B are indirectly
connected, through the central switchboard. That is the way it is in
the nervous system, with "nerve center" substituted for "central", and
"sense organ" and "muscle or gland" for "telephones A and B."
[Illustration: Fig. 3.--Location of the cord, cerebrum and cerebellum.
The brain stem continues the cord upward into the skull cavity.
(Figure text: cerebrum, cerebellum, cord, tongue)]
The advantage of the centralized system is that it is a _system_,
affording connections between any part and any other, and unifying the
whole complex organism.
The _nerve centers_ are located in the brain and spinal cord. The
brain lies in the skull and the cord extends from the brain down
through a tube in the middle of the {30} backbone. Of the brain many
parts can be named, but for the present it is enough to divide it into
the "brain stem", a continuation of the spinal cord up along the base
of the skull cavity, and the two great outgrowths of the brain stem,
called "cerebrum" and "cerebellum". The spinal cord and brain stem
contain the lower or reflex centers, while the cerebellum, and
especially the cerebrum, contain the "higher centers". The lower
centers are directly connected by nerves with the sense organs, glands
and muscles, while the higher centers have direct connections with the
lower and only through them with the sense organs, glands and muscles.
In other words, the sensory nerves run into the cord or brain stem,
and the motor nerves run out of these same, while interconnecting
nerve strands extend between the lower centers in the cord and brain
stem and the higher centers in the cerebrum and cerebellum.
The spinal cord contains the reflex centers for the limbs and part of
the trunk, and is connected by sensory and motor nerves with the limbs
and trunk. The brain stem contains the reflex centers for the head and
also for part of the interior of the trunk, including the heart and
lungs, and is connected with them by sensory and motor nerves. The
nerve center that takes part in the flexion reflex of the foot is
situated in the lower part of the cord, that for the similar reflex of
the hand lies in the upper part of the cord, that for breathing lies
in the lower or rear part of the brain stem, and that for winking lies
further forward in the brain stem.
Big movements, such as the combined action of all four legs of an
animal in walking, require cord and brain stem to work together, and
throw into relief what is really true even of simpler reflexes, namely
that a reflex is a _coordinated_ movement, in the sense that different
muscles cooperate in its execution.
{31}
Internal Construction of the Nerves and Nerve Centers
We shall understand nerve action better if we know something of the
way in which the nervous system is built. A nerve is not to be thought
of as a unit, nor are the brain and cord to be thought of as mere
masses of some peculiar substance.
[Illustration: Fig. 4.--A motor nerve cell from the spinal cord,
highly magnified. (Figure text: dendrites, cell body, axon,
termination of axon in muscle)]
A nerve is a bundle of many slender insulated threads, just as a
telephone cable, running along the street, {32} is a bundle of many
separate wires which are the real units of telephonic communication. A
nerve center, like the switchboard in a telephone central, consists of
many parts and connections.
The whole nervous system is essentially composed of _neurones_. A
neurone is a nerve cell with its branches. Most nerve cells have two
kinds of branches, called the _axon_ and the _dendrites_.
The nerve cell is a microscopic speck of living matter. Its dendrites
are short tree-like branches, while its axon is often several inches
or even feet in length. The axon is the "slender thread", just spoken
of as analogous to the single telephone wire. A nerve is composed of
axons. [Footnote: The axon is always protected or insulated by a
sheath, and axon and sheath, taken together, are often called a "nerve
fiber".] The "white matter" of the brain and cord is composed of
axons. Axons afford the means of communication between the nerve
centers and the muscles and sense organs, and between one nerve center
and another.
The axons which make up the motor nerves are branches of nerve cells
situated in the cord and brain stem; they extend from the reflex
center for any muscle out to and into that muscle and make very close
connection with the muscle substance. A nerve current, starting from
the nerve cells in the reflex center, runs rapidly along the axons to
the muscle and arouses it to activity.
The axons which make up the optic nerve, or nerve of sight, are
branches of nerve cells in the eye, and extend into the brain stem.
Light striking the eye starts nerve currents, which run along these
axons into the brain stem. Similarly, the axons of the nerve of smell
are branches of cells in the nose.
The remainder of the sensory axons are branches of nerve cells that
lie in little bunches close alongside the cord or {33} brain stem.
These cells have no dendrites, but their axon, dividing, reaches in
one direction out to a sense organ and in the other direction into the
cord or brain stem, and thus connects the sense organ with its "lower
center".
[Illustration: Fig. 5.--Sensory and motor axons, and their nerve
cells. The arrows indicate the direction of conduction. (Figure text:
eye, brain stem, skin, cord, muscle)]
Where an axon terminates, it broadens out into a thin plate, or breaks
up into a tuft of very fine branches ( the "end-brush"), and by this
means makes close contact with the muscle, the sense organ, or the
neurone with which it connects.
{34}
The Synapse
Now let us consider the mode of connection between one neurone and
another in a nerve center. The axon of one neurone, through its
end-brush, is in close contact with the dendrites of another neurone.
There is contact, but no actual growing-together; the two neurones
remain distinct, and this contact or junction of two neurones is
called a "synapse". The synapse, then, is not a thing, but simply a
junction between two neurones.
[Illustration: Fig. 6.--The synapse between the two neurones lies just
above the arrow.]
The junction is good enough so that one of the two neurones, if itself
active, can arouse the other to activity. The end-brush, when a nerve
current reaches it from its own nerve cell, arouses the dendrites of
the other neurone, and thus starts a nerve current running along those
dendrites to their nerve cell and thence out along its axon.
Now here is a curious and significant fact: the dendrites are
receiving organs, not transmitting; they pick up messages from the
end-brushes across the synapse, but send out no messages to those
end-brushes. Communication across a synapse is always in one
direction, from end-brush to dendrites.
This, then, is the way in which a reflex is carried out, the pupillary
reflex, for example. Light entering the eye starts a nerve current in
the axons of the optic nerve; these axons terminate in the brain stem,
where their end-brushes arouse the dendrites of motor nerve cells, and
the axons of these {35} cells, extending out to the muscle of the
pupil, cause it to contract, and narrow the pupil.
Or again, this is the way in which one nerve center arouses another to
activity. The axons of the cells in the first center (or some of them)
extend out of this center and through the white matter to the second
center, where they terminate, their end-brushes forming synapses with
the cells of the second center. Let the first center be thrown into
activity, and immediately, through this connection, it arouses the
second.
[Illustration: Fig. 7.--Different forms of synapse found in the
cerebellum, "a" is one of the large motor cells of the cerebellum (a
"Purkinje cell"), with its dendrites above and its axon below; and
"b," "c" and "d" show three forms of synapse made by other neurones
with this Purkinje cell. In "b," the arrow indicates a "climbing
axon," winding about the main limbs of the Purkinje cell. In "c," the
arrow points to a "basket"--an end-brush enveloping the cell body;
while "d" shows what might be called a "telegraph-wire synapse."
Imagine "d" superimposed upon "a": the axon of "d" rises among the
fine dendrites of "a," and then runs horizontally through them; and
there are many, many such axons strung among the dendrites. Thus the
Purkinje cell is stimulated at three points: cell body, trunks of the
dendrites, and twigs of the dendrites.]
The "gray matter" comprises the nerve centers, lower and higher. It is
made up of nerve cells and their dendrites, of the beginnings of axons
issuing from these cells and of the terminations of incoming axons.
The white matter, as was said before, consists of axons. An axon
issues from the {36} gray matter at one point, traverses the white
matter for a longer or shorter distance, and finally turns into the
gray matter at another point, and thus nerve connection is maintained
between these two points.
There are lots of nerve cells, billions of them. That ought to be
plenty, and yet--well, perhaps sometimes they are not well developed,
or their synapses are not close enough to make good connections.
[Illustration: Fig. 8.--A two-neurone reflex arc. (Figure text:
stimulus, skin, sensory axon, bit of the spinal cord, motor axon,
muscle)]
Examined under the microscope, the nerve cell is seen to contain,
besides the "nucleus" which is present in every living cell and is
essential for maintaining its vitality and special characteristics,
certain peculiar granules which appear to be stores of fuel to be
consumed in the activity of the cell, and numerous very fine fibrils
coursing through the cell and out into the axon and dendrites.
The _reflex arc can now be described_ more precisely than before.
Beginning in a sense organ, it extends along a sensory axon (really
along a team of axons acting side by side) to its end-brush in a lower
center, where it crosses a synapse and enters the dendrites of a motor
neurone and so {37} reaches the cell body and axon of this neurone,
which last extends out to the muscle (or gland). The simplest reflex
arc consists then of a sensory neurone and a motor neurone, meeting at
a synapse in a lower or reflex center. This would be a two-neurone
arc.
[Illustration: Fig. 9.--A three-neurone arc, concerned in respiration.
This also illustrates how one nerve center influences another.
(Figure text: white matter, gray matter, lung, respiratory center in
the brain stem, diaphragm, motor center in cord for the diaphragm)]
Very often, and possibly always, the reflex arc really consists of
three neurones, a "central" neurone intervening between the sensory
and motor neurones and being connected through synapses with each. The
central neurone plays an important rôle in coördination.
COÖRDINATION
The internal structure of nerve centers helps us see how coördinated
movement is produced. The question is, how {38} several muscles are
made to work together harmoniously, and also how it is possible that a
pin prick, directly affecting just a few sensory axons, causes a big
movement of many muscles. Well, we find the sensory axon, as it enters
the cord, sending off a number of side branches, each of which
terminates in an end-brush in synaptic connection with the dendrites
of a motor nerve cell.
[Illustration: Fig. 10.--Coördination brought about by the branching
of a sensory axon. (Figure text: cord, sensory neurone, motor neurone)]
Thus the nerve current from a single sensory neurone is distributed to
quite a number of motor neurones. Where there are central neurones in
the arc, their branching axons aid in distributing the excitation; and
so we get a big movement in response to a minute, though intense
stimulus.
But the response is not simply big; it is definite, coordinated,
representing team work on the part of the muscles as distinguished
from indiscriminate mass action. That means selective distribution of
the nerve current. The axons of the sensory and central neurones do
not connect with any and every motor neurone indiscriminately, but
link up with selected groups of motor neurones, and thus harness
together teams that will work in definite ways, producing {39} flexion
of a limb in the case of one such team, and extension in the case of
another. Every reflex has its own team of motor neurones, harnessed
together by its outfit of sensory and central neurones. The same motor
neurone may however be harnessed into two or more such teams, as is
seen from the fact that the same muscle may participate in different
reflex movements; and for a similar reason we believe that the same
sensory neurone may be utilized in more than one reflex arc.
[Illustration: Fig. 11.--Coördination brought about by the branching
of the axon of a central neurone. (Figure text: sensory, central,
motor)]
The most distinctive part of any reflex arc is likely to be its
central neurones, which are believed to play the chief part in
coördination, and in determining the peculiarities of any given
reflex, such as its speed and rhythm of action.
Reactions in General
Though the reflex is simple by comparison with voluntary movements, it
is not the simplest animal reaction, for it is coördinated and depends
on the nervous system, while the simplest animals, one-celled animals,
have no nervous system, any more than they have muscles or organs of
any {40} kind. Without possessing separate organs for the different
vital functions, these little creatures do nevertheless take in and
digest food, reproduce their kind, and move. Every animal shows at
least two different motor reactions, a positive or approaching
reaction, and a negative or avoiding reaction.
The general notion of a reaction is that of a _response_ to a
_stimulus_. The stimulus acts on the organism and the organism acts
back. If I am struck by a wave and rolled over on the beach, that is
passive motion and not my reaction; but if the wave stimulates me to
maintain my footing, then I am active, I respond or react.
Now there is no such thing as wholly passive motion. Did not Newton
teach that "action and reaction are equal"?--and he was thinking of
stones and other inanimate objects. The motion of a stone or ball
depends on its own weight and shape and elasticity as much as on the
blow it receives. Even the stone counts for something in determining
its own behavior.
A loaded gun counts for more than a stone, because of the stored
energy of the powder that is set free by the blow of the hammer. The
"reaction" of the gun is greater than the force acting on it, because
of this stored energy that is discharged.
An animal reaction resembles the discharge of the gun, since there is
stored energy in the animal, consisting in the chemical attraction
between food absorbed and oxygen inspired, and some of this energy is
utilized and converted into motion when the animal reacts. The
stimulus, like the trigger of the gun, simply releases this stored
energy.
The organism, animal or human, fully obeys the law of conservation of
energy, all the energy it puts out being accounted for by stored
energy it has taken in in food and oxygen. But at any one time, when
the organism receives {41} a stimulus, the energy that it puts forth
in reaction comes from inside itself.
There is another way in which the organism counts in determining its
reaction. Not only does it supply the energy of the response, but its
own internal arrangements determine how that energy shall be directed.
That is to say, the organism does not blow up indiscriminately, like a
charge of dynamite, but makes some definite movement. This is true
even of the simplest animals, and the more elaborate the internal
mechanism of the animal, the more the animal itself has to do with the
kind of response it shall make to a stimulus. The nervous system of
the higher animals, by the connections it provides between the
stimulus and the stores of energy in the muscles, is of especial
importance in determining the nature of the response.
Stimuli are necessary to arouse the activity of the organism. Without
any stimulus whatever, it seems likely that the animal would relapse
into total inactivity. It should be said, however, that stimuli, such
as that of hunger, may arise within the organism itself. The stimulus
may be external or internal, but some stimulus is necessary in order
to release the stored energy.
In general, then, a reaction consists in the release by a stimulus of
some of the stored energy of an animal, and the direction of that
energy by the animal's own internal mechanism of nerves and muscles
(and, we may add, bones and sinews) into the form of some definite
response.
{42}
EXERCISES
1. Outline of the chapter, being at the same time a "completion
test". Complete the following outline by filling in the blank
spaces (usually a single word will fill the blank, but sometimes two
words will be better):
A. Definition: A reaction is a response to a ___________.
The stimulus energy stored in the organism, and the __________
has a definite form determined by the organism's own machinery
of ________ and ______.
B. Among very prompt reactions are the reflex and the "simple
reaction". The reflex differs from the "simple reaction" in that:
(1) It usually takes less________.
(2) It requires no___________,
(3) The machinery for it is ________in the organism.
C. The machinery for a reflex consists of:
(1) a________ organ.
(2) a ________nerve.
(3) a nerve ________,
(4) a _________nerve.
(5) a muscle or _________.
D. The sensory and motor nerves consist of ________ which are
branches of ______. The cells for the motor nerves lie in the
________, and those for the sensory nerves lie in two cases in
the _________, and in all other cases in bunches located close
beside the _________or ________,
E. The neurone is the _______ of which the nervous ______ is
composed. It consists of a ________ and of two sorts of
branches, the ________ and the ________. Internally, the neurone
shows a peculiar structure of ________ and ________.
F. Communication from one neurone to another occurs across
a _____ called the synapse. The _________of an axon here comes
into close contact with the ______or with the _________of
another neurone. The communication takes place from the
________of the first neurone to the ___________ of the second.
G. The "nerve current" in a reflex therefore runs the following
course: from the sense organ into a ________ axon, along this to
its _________ in a nerve, and across a _________ there into the
_________ of a neurone, and thence {43} out along the _______of
this neurone to the ________or _________ that executes the
reflex. This is a two-neurone _________, but often there is a
third, ________neurone between the _________ and the
_____________.
H. Coördination is effected by the ________ of the axons of the
sensory and ________ neurones, by which means the nerve current
is ______ to a team of ________ and so to a team of _________.
2. Is the reaction time experiment, as described in the text, an
introspective or an objective experiment?
3. Mention two cases from common life that belong under the
"simple reaction", two that belong under "choice reaction", and two
that belong under the "associative reaction".
4. Arrange the reflexes mentioned in the text under the two heads
of "protective" and "regulative".
5. Draw diagrams of (a) the neurone, (b) a synapse, (c) a reflex
arc, and (d) a coördinated movement. Reduce each drawing to the
simplest possible form, and still retain everything that is
essential.
6. What part of the nervous system lies (a) in the forehead and
top of the head, (b) in the very back of the head, (c) along the
base of the skull, (d) within the backbone, (e) in the arm?
7. Using a watch to take the time, see how long it takes you to
name the letters in a line of print, reading them in reverse order
from the end of the line to the beginning. Compare with this time
the time required to respond to each letter by the letter following
it in the alphabet (saying "n" when you see m, and "t" when you see
s, etc.). Which of these two "stunts" is more like reflex action,
and how, nevertheless, does it differ from true reflex action?
8. The pupillary reflex. Describe the reaction of the pupil of the
eye to light suddenly shining into the eye. This response can best
be observed in another person, but you can observe it in yourself
by aid of a hand mirror. On another person you can also observe the
"crossed" pupillary reflex, by throwing the light into one eye only
while you watch the other eye. What sort of connection do you
suppose to exist between the two eyes, making this crossed reflex
possible?
9. The lid reflex, or wink reflex, (a) Bring your hand suddenly
close to another person's eye, and notice the response of the
eyelid, (b) See whether you can get a crossed reflex here, (c) See
whether your subject can voluntarily prevent (inhibit) the lid
reflex, (d) See whether the reflex occurs when he gives the
stimulus himself, by moving his own hand suddenly up to his eye.
(e) What other stimulus, besides the visual one that you have been
using, will arouse the same response?
{44}
REFERENCES
C. Judson Herrick, in his _Introduction to Neurology_, 2nd edition,
1918, gives a fuller and yet not too detailed account of the neurone
in Chapter III, and of reflex action in Chapter IV.
Percy G. Stiles, in his _Nervous System and Its Conservation_, 1915,
discusses these matters in Chapters II, III and IV.
Ladd and Woodworth's _Elements of Physiological Psychology_, 1911, has
chapters on these topics.
{45}
CHAPTER III
REACTIONS OF DIFFERENT LEVELS
HOW SENSATIONS, PERCEPTIONS AND THOUGHTS MAY BE CONSIDERED AS FORMS OF
INNER RESPONSE, AND HOW THESE HIGHER REACTIONS ARE RELATED IN THE
NERVOUS SYSTEM TO THE SIMPLER RESPONSES OF THE REFLEX LEVEL.
Having defined a reaction as an act of the individual aroused by a
stimulus, there is no reason why we should not include a great variety
of mental processes under the general head of reactions. Any mental
process is an activity of the organism, and it is aroused by some
stimulus, external or internal; therefore, it is a reaction.
I hear a noise--now, while the noise, as a physical stimulus, comes to
me, my hearing it is my own act, my sensory reaction to the stimulus.
I recognize the noise as the whistle of a steamboat--this recognition
is clearly my own doing, dependent on my own past experience, and may
be called a perception or perceptive response. The boat's whistle
reminds me of a vacation spent on an island--clearly a memory
response. The memory arouses an agreeable feeling--an affective
response, this may be called. In its turn, this may lead me to imagine
how pleasant it would be to spend another vacation on that island, and
to cast about for ways and means to accomplish this result--here we
have imagination and reasoning, aroused by what preceded just as the
sensation was aroused by the physical stimulus.
In speaking of any mental process as an act of the individual, we do
not mean to imply that he is always _conscious_ {46} of his activity.
Sometimes he feels active, sometimes passive. He feels active in hard
muscular work or hard thinking, while he feels passive in reflex
action, in sensation, and in simply "being reminded" of anything
without any effort on his own part. But he is active in everything he
does, and he does everything that depends on his being alive. Life is
activity, and every manifestation of life, such as reflex action or
sensation, is a form of vital activity. The only way to be inactive is
to be dead.
But vital activity is not "self-activity" in any absolute sense, for
it is _aroused_ by some stimulus. It does not issue from the
individual as an isolated unit, but is his _response_ to a stimulus.
That is the sense of calling any mental process a reaction; it is
something the individual does in response to a stimulus.
To call a sensation a form of reaction means, then, that the sensation
is not something done to the person, nor passively received by him
from outside, but something that he himself does when aroused to this
particular form of activity. What comes from outside and is received
by the individual is the stimulus, and the sensation is what he does
in response to the stimulus. It represents the discharge of internal
stored energy in a direction determined by his own inner mechanism.
The sensation depends on his own make-up as well as on the nature of
the stimulus, as is especially obvious when the sensation is abnormal
or peculiar. Take the case of color blindness. The same stimulus that
arouses in most people the sensation of red arouses in the color-blind
individual the sensation of brown. Now what the color-blind individual
_receives_, the light stimulus, is the same as what others receive,
but he responds differently, _i.e._, with a different sensation,
because his own sensory apparatus is peculiar.
The main point of this discussion is that all mental {47} phenomena,
whether movements, sensations, emotions, impulses or thoughts, are a
person's acts, but that every act is a response to some present
stimulus. This rather obvious truth has not always seemed obvious.
Some theorists, in emphasizing the spontaneity and "self-activity" of
the individual, have pushed the stimulus away into the background;
while others, fixing their attention on the stimulus, have treated the
individual as the passive recipient of sensation and "experience"
generally. Experience, however, is not received; it is lived, and that
means done; only, it is done in response to stimuli. The concept of
reaction covers the ground.
While speaking of sensations and thoughts as belonging under the
general head of reactions, it is well, however, to bear in mind that
all mental action tends to arouse and terminate in muscular and
glandular activity. A thought or a feeling tends to "express itself"
in words or (other) deeds. The motor response may be delayed, or
inhibited altogether, but the tendency is always in that direction.
Different Sorts of Stimuli
To call all mental processes reactions means that it is always in
order to ask for the stimulus. Typically, the stimulus is an external
force or motion, such as light or sound, striking on a sense organ.
There are also the internal stimuli, consisting of changes occurring
within the body and acting on the sensory nerves that are distributed
to the muscles, bones, lungs, stomach and most of the organs. The
sensations of muscular strain and fatigue, and of hunger and thirst,
are aroused by internal stimuli, and many reflexes are aroused in the
same way.
Such internal stimuli as these are like the better known external
stimuli in that they act upon sense organs; but it {48} seems
necessary to recognize another sort of stimuli which act directly on
the nerve centers in the brain. These may be called "central stimuli"
and so contrasted with the "peripheral stimuli" that act on any sense
organ, external or internal. To do this is to take considerable
liberty with the plain meaning of "stimulus", and calls for
justification. What is the excuse for thus expanding the notion of a
stimulus?
The excuse is found in the frequent occurrence of mental processes
that are not directly aroused by any peripheral stimulus, though they
are plainly aroused by something else. Anything that arouses a thought
or feeling can properly be called its stimulus. Now it often happens
that a thought is aroused by another, just preceding thought; and it
seems quite in order to call the first thought the stimulus and the
second the response. A thought may arouse an emotion, as when the
thought of my enemy, suddenly occurring to mind, makes me angry; the
thought is then the stimulus arousing this emotional response.
If hearing you speak of Calcutta makes me think of India, your words
are the stimulus and my thought the response. Well, then, if I _think_
of Calcutta in the course of a train of thought, and next think of
India, what else can we say than that the thought of Calcutta acts as
a stimulus to arouse the thought of India as the response? In a long
train of thought, where A reminds you of B and B of C and C of D, each
of these items is, first, a response to the preceding, and, second, a
stimulus to the one following.
There is no special difficulty with the notion of "central stimuli"
from the physiological side. We have simply to think of one nerve
center arousing another by means of the tract of axons connecting the
two. Say the auditory center is aroused by hearing some one mention
your friend's name, {49} and this promptly calls up a mental picture
of your friend; here the auditory center has aroused the visual. What
happens in a train of thought is that first one group of neurones is
aroused to activity, and then this activity, spreading along the axons
that extend from this group of neurones to another, arouses the second
group to activity; and so on. The brain process may often be
exceedingly complex, but this simple scheme gives the gist of it.
The way nerve currents must go shooting around the brain from one
center or group of neurones to another, keeping it up for a long time
without requiring any fresh peripheral stimulus, is remarkable. We
have evidence of this sort of thing in a dream or fit of abstraction.
Likely enough, the series of brain responses would peter out after
awhile, in the absence of any fresh peripheral stimulus, and total
inactivity ensue. But response of one brain center to nerve currents
coming from another brain center, and not directly from any sense
organ, must be the rule rather than the exception, since most of the
brain neurones are not directly connected with any sense organ, but
only with other parts of the brain itself. All the evidence we have
would indicate that the brain is not "self-active", but only
responsive; but, once thrown into activity at one point, it may
successively become active at many other points, so that a long series
of mental operations may follow upon a single sensory stimulus.
The Motor Centers, Lower and Higher
A "center" is a collection of nerve cells, located somewhere in the
brain or cord, which gives off axons running to some other center or
out to muscles or glands, while it also receives axons coming from
other centers, or from sense organs. These incoming axons terminate in
end-brushes and so form synapses with the dendrites of the local {50}
nerve cells. The axons entering any center and terminating there
arouse that center to activity, and this activity, when aroused, is
transmitted out along the axons issuing from that center, and produces
results where those axons terminate in their turn.
[Illustration: Fig. 12.--Side view of the left hemisphere of the
brain, showing the motor and sensory areas (for the olfactory area,
see Fig. 18). The visual area proper, or "visuo-sensory area," lies
just around the corner from the spot marked "Visual," on the middle
surface of the hemisphere, where it adjoins the other hemisphere.
(Figure text: frontal lobe, parietal lobe, central fissure, occipital
lobe, motor area, somesthetic area, auditory area, fissure of Sylvius,
temporal lobe, brain stem, cerebellum)]
The _lower_ motor centers, called also reflex centers, are located in
the cord or brain stem, and their nerve cells give rise to the axons
that form the motor nerves and connect with the muscles and glands. A
muscle is thrown into action by nerve currents from its lower motor
center.
The principal _higher_ motor center is the "motor area" of the brain,
located in the cortex or external layer of gray matter, in the
cerebrum. More precisely, the motor area is a long, narrow strip of
cortex, lying just forward of what is called the "central fissure" or
"fissure of Rolando".
{51}
If you run your finger over the top of the head from one side to the
other, about halfway back from the forehead, the motor areas of the
two cerebral hemispheres will lie close under the path traced by your
finger.
[Illustration: Fig. 13.--(After Cajal.) Type of the brain cells that
most directly control muscular movement. (Figure text: Axon. Giant
pyramid cell from the motor area of the cerebral cortex, magnified 35
diameters. Cell body of same farther magnified)]
The motor area in the right hemisphere is connected with the left half
of the cord and so with the muscles of the left half of the body; the
motor area of the left hemisphere similarly affects {52} the right
half of the body. Within the motor area are centers for the several
limbs and other motor organs. Thus, at the top, near the middle line
of the head (and just about where the phrenologists located their
"bump of veneration"!), is the center for the legs; next below and to
the side is the center for the trunk, next that for the arm, next that
for head movements, and at the bottom, not far from the ears, is the
center for tongue and mouth.
[Illustration: Fig. 14.--The nerve path by which the motor area of the
cortex influences the muscles. The upper part of this path, consisting
of axons issuing from the giant pyramids of the motor area and
extending down into the spinal cord, is the pyramidal tract. The lower
part of the path consists of axons issuing from the motor cells of the
cord and extending out to the muscles. The top of the figure
represents a vertical cross-section of the brain, such as is given, on
a larger scale, in Fig. 18. (Figure text: cortex, cord, muscles)]
The largest nerve cells of all are found in the motor area, and are
called, from their shape, the "giant pyramids". They have large
dendrites and very long axons, which latter, {53} running in a thick
bundle down from the cortex through the brain stem and cord,
constitute the "pyramidal tract", the principal path of communication
from the cerebrum to the lower centers. The motor area of the brain
has no direct connection with any muscle, but acts through the
pyramidal tract on the lower centers, which in turn act on the
muscles.
How The Brain Produces Muscular Movements
The motor area is itself aroused to action by nerve currents entering
it through axons coming from other parts of the cortex; and it is by
way of the motor area that any other part of the cortex produces
bodily movement. There are a few exceptions, as, for example, the
movements of the eyes are produced generally by the "visual area"
acting directly on the lower motor centers for the eye in the brain
stem; but, in the main, any motor effect of brain action is exerted
through the motor area. The motor area, as already mentioned, acts on
the lower motor centers in the cord and brain stem, and these in turn
on the muscles; but we must look into this matter a little more
closely.
A lower motor center is a group of motor and central neurones, lying
anywhere in the cord or brain stem, and capable of directly arousing a
certain coördinated muscular movement. One such unit gives flexion of
the leg, another gives extension of the leg, a third gives the rapid
alternation of flexion and extension that we see in the scratching
movement of the dog. Such a motor center can be aroused to activity by
a sensory stimulus, and the resulting movement is then called a
reflex.
The lower center can be aroused in quite another way, and that is by
nerve currents coming from the brain, by way of the motor area and the
pyramidal tract. Thus flexion of the leg can occur voluntarily as well
as reflexly. The same {54} muscles, and the same motor neurones, do
the job in either case. In the reflex, the lower center is aroused by
a sensory nerve, and in the voluntary movement by the pyramidal tract.
The story is told of a stranger who was once dangling his legs over
the edge of the station platform at a small backwoods town, when a
native called out to him "Hist!" (hoist), pointing to the ground under
the stranger's feet. He "histed" obediently, which is to say that he
voluntarily threw into play the spinal center for leg flexion; and
then, looking down, saw a rattler coiled just beneath where his feet
had been hanging. Now even if he had spied the rattler first, the
resulting flexion, though impulsive and involuntary, would still have
been aroused by way of the motor area and the pyramidal tract, since
the movement would have been a response to _knowledge_ of what that
object was and signified, and knowledge means action by the cerebral
cortex, which we have seen to affect movement through the medium of
the motor area. But if the snake had made the first move, the same leg
movement on the man's part, made now in response to the painful
sensory stimulus, would have been the flexion reflex.
Facilitation and Inhibition
Not only can the motor area call out essentially the same movements
that are also produced reflexly, but it can prevent or _inhibit_ the
execution of a reflex in spite of the sensory stimulus for the reflex
being present, and it can reinforce or _facilitate_ the action of the
sensory stimulus so as to assist in the production of the reflex. We
see excellent examples of cerebral facilitation and inhibition in the
case of the knee jerk. This sharp forward kick of the foot and lower
leg is aroused by a tap on the tendon running in front {55} of the
knee. Cross the knee to be stimulated over the other leg, and tap the
tendon just below the knee cap, and the knee jerk appears. So purely
reflex is this movement that it cannot be duplicated voluntarily; for,
though the foot can of course be voluntarily kicked forward, this
voluntary movement does not have the suddenness and quickness of the
true reflex. For all that, the cerebrum can exert an influence on the
knee jerk. Anxious attention to the knee jerk inhibits it; gritting
the teeth or clenching the fist reinforces it. These are cerebral
influences acting by way of the pyramidal tract upon the spinal center
for the reflex.
Thus the cortex controls the reflexes. Other examples of such control
are seen when you prevent for a time the natural regular winking of
the eyes by voluntarily holding them wide open, or when, carrying a
hot dish which you know you must not drop, you check the flexion
reflex which would naturally pull the hand away from the painful
stimulus. The young child learns to control the reflexes of
evacuation, and gradually comes to have control over the breathing
movements, so as to hold his breath or breathe rapidly or deeply at
will, and to expire vigorously in order to blow out a match.
The coughing, sneezing and swallowing reflexes likewise come under
voluntary control. In all such cases, the motor area facilitates or
inhibits the action of the lower centers.
Super-motor Centers in the Cortex
Another important effect of the motor area upon the lower centers
consists in combining their action so as to produce what we know as
skilled movements. It will be remembered that the lower centers
themselves give coördinated movements, such as flexion or extension of
the whole limb; but still higher coördinations result from cerebral
control. {56} When the two hands, though executing different
movements, work together to produce a definite result, we have
coördination controlled by the cortex. Examples of this are seen in
handling an ax or bat, or in playing the piano or violin. A movement
of a single hand, as in writing or buttoning a coat, may also
represent a higher or cortical coördination.
[Illustration: Fig. 15.--(From Starr.) Axons connecting one part of
the cortex with another. The brain is seen from the side, as if in
section. At "A" are shown bundles of comparatively short axons,
connecting near-by portions of the cortex; while "B," "C," and "D"
show bundles of longer axons, connecting distant parts of the cortex
with one another. The "Corpus Callosum" is a great mass of axons
extending across from each cerebral hemisphere to the other, and
enabling both hemispheres to work together. "O. T." and "C. N." are
interior masses of gray matter, which can be seen also in Fig. 18. "O.
T." is the thalamus, about which more later.]
Now it appears that the essential work in producing these higher
coördinations of skilled movement is performed not by the motor area,
but by neighboring parts of the cortex, which act on the motor area in
much the same way as the motor area acts on the lower centers. Some of
these {57} skilled-movement centers, or super-motor centers, are
located in the cortex just forward of the motor area, in the adjacent
parts of the frontal lobe. Destruction of the cortex there, through
injury or disease, deprives the individual of some of his skilled
movements, though not really paralyzing him. He can still make simple
movements, but not the complex movements of writing or handling an
instrument.
It is a curious fact that the left hemisphere, which exerts control
over the movements of the right hand and right side of the body
generally, also plays the leading part in skilled movements of either
hand. This is true, at least, of right-handed persons; probably in the
left-handed the right hemisphere dominates.
Motor power may be lost through injury at various points in the
nervous system. Injury to the spinal cord, destroying the lower motor
center for the legs, brings complete paralysis. Injury to the motor
area or to the pyramidal tract does not destroy reflex movement, but
cuts off all voluntary movement and cerebral control. Injury to the
"super-motor centers" causes loss of skilled movement, and produces the
condition of "apraxia", in which the subject, though knowing what he
wants to do, and though still able to move his limbs, simply cannot
get the combination for the skilled act that he has in mind.
Speech Centers
Similar to apraxia is "aphasia" or loss of ability to speak. It bears
the same relation to true paralysis of the speech organs that hand
apraxia bears to paralysis of the hand. Through brain injury it
sometimes happens that a person loses his ability to speak words,
though he can still make vocal sounds. The cases differ in severity,
some retaining the ability to speak only one or two words which {58}
from frequent use have become almost reflex (swear words, sometimes,
or "yes" and "no"), while others are able to pronounce single words,
but can no longer put them together fluently into the customary form
of phrases and sentences, and still others can utter simple sentences,
but not any connected speech.
[Illustration: Fig. 16.--Side view of the left hemisphere, showing the
location of the "speech centers." The region marked "Motor" is the
motor speech center, that marked "Auditory" the auditory speech
center, and that marked "Visual" the visual speech center. (Figure text:
central fissure, motor area, auditory area, visual area, fissure of
Sylvius, brain stem, cerebellum)]
In pure cases of _motor aphasia_, the subject knows the words he
wishes to say, but cannot get them out. The brain injury here lies in
the frontal lobe in the left hemisphere, in right-handed people, just
forward of the motor area for the mouth, tongue and larynx. This
"motor speech center" is the best-known instance of a super-motor
center. It coördinates the elementary speech movements into the
combinations called words; and perhaps there is no other motor
performance so highly skilled as this of speaking. It is acquired so
early in life, and practised so constantly, that {59} we take it quite
as a matter of course, and think of a word as a simple and single
movement, while in fact even a short word, as spoken, is a complex
movement requiring great motor skill.
There is some evidence that the motor speech center extends well
forward into the frontal lobe, and that the front part of it is
related to the part further back as this is to the motor area back of
it. That is to say, the back of the speech center combines the motor
units of the motor area into the skilled movements of speaking a word,
while the more forward part of the speech center combines the word
movements into the still more complex movement of speaking a sentence.
It is even possible that the very front part of the speech center has
to do with those still higher combinations of speech movements that
give fluency and real excellence of speaking.
The Auditory Centers
Besides the motor aphasia, just mentioned, there is another type,
called _sensory aphasia_, or, more precisely, auditory aphasia. In
pure auditory aphasia there is no inability to pronounce words or even
to speak fluently, but there is, first, an inability to "hear words",
sometimes called word deafness, and there is often also an inability
to find the right words to speak, so that the individual so afflicted,
while speaking fluently enough and having sense in mind, misuses his
words and utters a perfect jargon. One old gentleman mystified his
friends one morning by declaring that he must go and "have his
umbrella washed", till it was finally discovered that what he wanted
was to have his hair cut.
The cortical area affected in this form of aphasia is located a little
further back on the surface of the brain than {60} the motor speech
center, being close to the auditory area proper. The latter is a small
cortical region in the temporal lobe, connected (through lower
centers) with the ear, and is the only part of the cortex to receive
nerve currents from the organ of hearing. The auditory area is,
indeed, the organ of hearing, or an organ of hearing, for without it
the individual is deaf. He may make a few reflex responses to loud
noises, but, consciously, he does not hear at all; he has no auditory
sensations.
In the immediate neighborhood of the auditory area proper (or of the
"auditory-sensory area", as it may well be called), are portions of
the cortex intimately connected by axons with it, and concerned in
what may be called auditory perceptions, i.e., with recognizing and
understanding sounds. Probably different portions of the cortex near
the auditory-sensory center have to do with different sorts of
auditory perception. At least, we sometimes find individuals who, as a
result of injury or disease affecting this general region, are unable
any longer to follow and appreciate music. They cannot "catch the
tune" any longer, though they may have been fine musicians before this
portion of their cortex was destroyed. In other cases, we find,
instead of this music deafness, the word deafness mentioned just
above.
The jargon talk that so often accompanies word deafness reminds us of
the fact that speech is first of all auditory to the child. He
understands what is said to him before he talks himself, and his
vocabulary for purposes of understanding always remains ahead of his
speaking vocabulary. It appears that this precedence of auditory
speech over motor remains the fact throughout life, in most persons,
and that the auditory speech center is the most fundamental of all the
speech centers, of which there is one more not yet mentioned, used in
reading.
{61}
[Illustration: Fig. 17.--(From Cajal.) Magnified sections through the
cortex, to show the complexity of its inner structure. One view shows
nerve cells and their dendrites, with only a few axons, while the
other shows axons, outgoing and incoming, and some of their fine
branches. Imagine one view superimposed upon the other, and you get
some idea of the intricate interweaving of axons and dendrites that
occurs in the cortex.]
{62}
The Visual Centers
There is a visual-sensory area in the occipital lobe, at the back of
the brain, that is connected with the eye in the same way as the
auditory center is connected with the ear. Without it, the individual
still shows the pupillary reflex to light, but has no sensations of
sight. He is blind.
[Illustration: Fig. 18.--Vertical cross-section through the brain,
showing the cortex on the outside, the thalamus and other interior
masses of gray matter, some of the paths to and from the cortex, and
the callosum or bridge of axons connecting the two cerebral
hemispheres. The "Motor path" is the pyramidal tract, only the
beginning of which is shown here, its further course being indicated
in Fig. 14. (Figure text: tactile path, motor path, auditory path,
callosum, thalamus, olfactory area)]
This visual-sensory area occupies only a small portion of the
occipital lobe, and yet practically the whole lobe is concerned with
vision. Some portions of the lobe are concerned in perceiving words in
reading, and without them the individual is "word blind". Other
portions are concerned in perceiving (recognizing, understanding) seen
objects, and without them the individual is "object blind". Other {63}
portions are concerned in perceiving color relations, and still other
portions in perceiving spatial relations through the sense of sight
and so knowing where seen objects are and being able to guide one's
movements by sight.
Cortical Centers for the Other Senses
There is an olfactory area in a rather secluded part of the cortex,
and this is related to the sense of smell in the same general way.
Probably there is a similar taste center, but it has not been
definitely located. Then there is a large and important area called
the "somesthetic", connected with the body senses generally, i.e.,
chiefly with the skin and muscle senses. This area is located in a
narrow strip just back of the central fissure, extending parallel to
the motor area which lies just in front of the fissure, and
corresponding part for part with it, so that the sensory area for the
legs lies just behind the motor area for the legs, and so on.
Destruction of any part of this somesthetic area brings loss of the
sensations from the corresponding part of the body.
Just behind this direct sensory center for the body, in the parietal
lobe, are portions of the cortex concerned in perceiving facts by aid
of the body senses. Perception of size and shape by the sense of
touch, perception of weight by the muscle sense, perception of degrees
of warmth and cold by the temperature sense, are dependent on the
parietal lobe and disappear when the cortex of this region is
destroyed. It appears that there is a sort of hierarchy of centers
here, as in the motor region and probably also in the visual and
auditory regions. Skill in handling objects is partly dependent on the
"feel" of the objects and so is impaired by injuries to the parietal
lobe, as well as by injury to the frontal lobe; and knowing how to
manage a fairly complex situation, as in lighting a fire when you have
the various {64} materials assembled before you, seems also to depend
largely on this part of the cortex.
Lower Sensory Centers
[Illustration: Fig. 19.--Sensory path from the skin of any portion of
the trunk or limbs. The path consists of three neurones, the cell body
of the first lying just outside the spinal cord, that of the second
lying in the cord, and that of the third lying in the thalamus. The
last part of this path is the "Tactile path," shown in Fig. 18.
(Figure text: cortex, thalamus, cord, skin)]
As already indicated, no portion of the cortex, not even the sensory
areas, is directly connected with any sense organ. The sensory axons
from the skin, for example, terminate in the spinal cord, in what may
be called the lowest sensory centers. Here are nerve cells whose axons
pass up through the cord and brain stem to the thalamus or interbrain,
where they terminate in a second sensory center. And cells here send
their axons up to the somesthetic area of the cortex.
{65}
The thalamus is remarkable as an intermediate center for all the
senses, except smell; but exactly what is accomplished by this big
intermediate sensory center remains rather a mystery, though it
certainly appears that the thalamus has something to do with feeling
and emotion.
The Cerebellum
Regarding the cerebellum, there is much knowledge at hand, but it is
difficult to give the gist of it in a few words. On the one hand, the
cerebellum receives a vast number of axons from the lower sensory
centers; while, on the other hand, it certainly has nothing to do with
conscious sensation or perception. Its use seems to be motor. It has
much to do with maintaining the equilibrium of the body, and probably
also with maintaining the steadiness and general efficiency of
muscular contraction. Though it has no known sensory or intellectual
functions, it is very closely connected with the cerebrum, receiving a
tremendous bundle of axons from different parts of the cerebrum, by
way of the brain stem. Possibly these are related to motor activity.
The phrenologists taught that the cerebellum was the center for the
sexual instinct, but there is no evidence in favor of this guess.
Different Levels of Reaction
Let a noise strike the ear and start nerve currents in along the
auditory nerve, passing through the lowest and intermediate centers
and reaching the auditory-sensory area of the cortex. When this last
is aroused to activity, we have a sensation of sound, which is the
first conscious reaction to the external stimulus. Axons running from
the auditory-sensory to the near-by cortex give a perception of some
fact indicated by the external stimulus, and this perception is a {66}
second and higher conscious reaction, which, to be sure, ordinarily
occurs so quickly after the first that introspection cannot
distinguish one as first and the other as second; but the facts of
brain injury, already mentioned, enable us to draw the distinction.
The perceived fact may call up a mental image, or a recognition of
some further fact less directly signified by the noise; these would be
reactions of still higher order. Much of the cortex is apparently not
very directly connected with either the sensory or the motor areas,
and probably is concerned somehow in the recognition of facts that are
only very indirectly indicated by any single sensory stimulus, or with
the planning of actions that only indirectly issue in muscular
movement.
On the sensory and intellectual side, the higher reactions follow the
lower: sensation arouses perception and perception thought. On the
motor side, the lower reactions are aroused by the higher. Thus the
speech center arouses the motor centers for the speech organs,
combining the action of these into the speaking of a word; and in a
similar way, it seems, the intention to speak a sentence expressing a
certain meaning acts as a stimulus to call up in order the separate
words that make the sentence. A general plan of action precedes and
arouses the particular acts and muscular movements that execute the
plan.
{67}
EXERCISES
1. Outline of the chapter. Fill in sub-topics under each of the
following heads:
A. Mental processes of all kinds are reactions.
B. The stimulus that directly arouses a mental process is often
"central".
C. Brain activities of all sorts influence the muscles by way
of the motor area and the lower motor centers.
D. Brain action in skilled movement.
E. Brain action in speech.
F. Brain action in sensation.
G. Brain action in recognizing seen or heard objects.
H. Relations of reactions of different levels.
2. Define and illustrate these classes of stimuli:
A. Peripheral:
(1) External.
(2) Internal.
B. Central.
3. Show by a diagram how one cortical center arouses another.
Compare the diagram in Fig. 9, p. 37.
4. Facilitation of the patellar reflex or "knee jerk". Let your
subject sit with one leg hanging freely from the knee down. With
the edge of your hand strike the patellar tendon just below the
knee cap. (a) Compare the reflex movement so obtained with a
voluntary imitation by the subject. Which is the quicker and
briefer? (b) Apply a fairly strong auditory stimulus (a sudden
noise) a fraction of a second before the tap on the tendon, and see
whether the reflex response is reinforced, (c) Ask the subject to
clench his fists or grit his teeth, and tap the tendon as he does
so. Reinforcement? (d) Where is the reflex center for the patellar
reflex, and whence comes the reinforcing influence?
5. Construct a diagram showing the different centers and connections
involved in making the skilled movement of writing; and consider
what loss of function would result from destruction of each of the
centers.
REFERENCES
Herrick's _Introduction to Neurology_, 1918, Chapter XX, on the
"Functions of the Cerebrum".
Stile's _Nervous System and Its Conservation_, Chapters X, XI
and XII.
{68}
CHAPTER IV
TENDENCIES TO REACTION
HOW MOTIVES INFLUENCE BEHAVIOR, AND HOW THEY FIT INTO A PSYCHOLOGY
WHICH SEEKS TO ANALYZE BEHAVIOR INTO REACTIONS.
One advantage of basing our psychology on _reactions_ is that it keeps
us "close to the ground", and prevents our discussions from sailing
off into the clouds of picturesque but fanciful interpretation.
Psychology is very apt to degenerate into a game of blowing bubbles,
unless we pin ourselves down to hard-headed ways of thinking. The
notion of a reaction is of great value here, just because it is so
hard-headed and concrete. Whenever we have any human action before us
for explanation, we have to ask what the stimulus is that arouses the
individual to activity, and how he responds. Stimulus-response
psychology is solid, and practical as well; for if it can establish
the laws of reaction, so as to predict what response will be made to a
given stimulus, and what stimulus can be depended on to arouse a
desired response, it furnishes the "knowledge that is power". Perhaps
no more suitable motto could be inscribed over the door of a
psychological laboratory than these two words, "Stimulus-Response."
Such a motto would not frighten away the modern introspectionists, for
they, no less than the behaviorists, could find a congenial home in a
stimulus-response laboratory. They would begin by studying sensations,
and, advancing to more complex responses, would observe the conscious
processes entering into the response.
{69}
But, however useful the reaction may be as affording a sound basis for
psychological study, we must not allow it to blind our eyes to any of
the real facts of mental life; and, at first thought, it seems as if
_motives, interests_ and _purposes_ did not fit into the
stimulus-response program. Many hard-headed psychologists have fought
shy of such matters, and some have flatly denied them any place in
scientific psychology. But let us see.
_S ---> R_
[Illustration: Fig. 20.--The symbol of stimulus-response psychology.
_S_ means the stimulus, and _R_ the response. The line between is the
connection from stimulus to response.]
Suppose we are looking out on a city street during the noon hour. We
see numbers of people who--lunch over, nothing to do till one
o'clock!--are standing or walking about, looking at anything that
chances to catch their eye, waving their hands to friends across the
street, whistling to a stray dog that comes past, or congregating
about an automobile that has broken down in the crowded thoroughfare.
These people are responding to stimuli, obviously enough, and there is
no difficulty in fitting their behavior into the stimulus-response
scheme.
But here comes some one who pays little attention to the sights and
sounds of the street, simply keeping his eyes open enough to avoid
colliding with any one else. He seems in a hurry, and we say of him,
"He must have business on hand; he has to keep an appointment or catch
a train". He is not simply responding to the stimuli that come to him,
but has some purpose of his own that directs his movements.
Here is another who, while not in such a hurry, is not idling by any
means, since he peers closely at the faces of the men, neglecting the
women, and seems to be looking for some one in particular; or,
perhaps, he neglects men and {70} women alike, and looks anxiously at
the ground, as if he had lost something. Some inner motive shuts him
off from most of the stimuli of the street, while making him extra
responsive to certain sorts of stimuli.
Purposive Behavior
Now it would be a great mistake to rule these purposeful individuals
out of our psychology. We wish to understand busy people as well as
idlers. What makes a man busy is some inner purpose or motive. He
still responds to present stimuli--otherwise he would be in a dream or
trance and out of all touch with what was going on about him--but his
actions are in part controlled by an inner motive.
To complete the foundations of our psychology, then, we need to fit
purpose into the general plan of stimulus and response. At first
thought, purpose seems a misfit here, since--
First, a purpose is an inner force, whereas what arouses a response
should be a stimulus, and typically an external stimulus. We do not
wish to drop back into the old "self-activity" psychology, which
thought of the individual as originating his acts from within himself.
But if we could show that a purpose is itself an inner response to
some external stimulus, and acts in its turn as a "central stimulus"
to further reactions, this difficulty would disappear.
Second, while a typical reaction, like the reflex or the simple
reaction of the experiment, is prompt and over with at once, a purpose
persists. It keeps the busy man, in our illustration, hurrying all the
way down the street and around the corner and how much farther we
cannot say. It is very different from a momentary response, or from a
stimulus that arouses a momentary response and nothing more.
Third, what persists, in purposive behavior, is the tendency {71}
towards some end or goal. The purposeful person wants something he has
not yet got, and is striving towards some future result. Whereas a
stimulus pushes him from behind, a goal beckons to him from ahead.
This element of action directed towards some end is absent from the
simple response to a stimulus.
In short, we have to find room in our stimulus-response psychology for
action persistently steered in a certain direction by some cause
acting from within the individual. We must find room for _internal_
states that _last_ for a time and _direct_ action. In addition, we
sometimes, though not always, need to find room for conscious
foreknowledge of the goal towards which the action is directed.
[Illustration: Fig. 21.--The stimulus-response scheme complicated to
allow for the existence of T, an inner motive or tendency, which,
aroused by an external stimulus, itself arouses a motor response. If
the reaction-tendency were linked so firmly to a single response as to
arouse that response with infallible certainty and promptness, then it
would be superfluous for psychology to speak of a tendency at all. But
often quite a series of responses, R1, R2, etc., follows upon a single
stimulus, all tending towards the same end-result, such as escape; and
then the notion of a "tendency" is by no means superfluous.]