My Blog On Importance Of Stimulus And Response
Posted By Admin on September 2, 2010
IMPORTANCE OF STIMULUS AND RESPONSE.–Like all other tissues of the
body, the nerve cells and fibers are developed by judicious use. The
sensory and association centers require the constant stimulus of nerve
currents running in from the various end-organs, and the motor centers
require the constant stimulus of currents running from them out to the
muscles. In other words, the conditions upon which both motor and
sensory development depend are: (1) A rich environment of sights and
sounds and tastes and smells, and everything else which serves as proper
stimulus to the sense organs, and to every form of intellectual and
social interest; and (2) no less important, an opportunity for the
freest and most complete forms of response and motor activity.
An illustration of the effects of the lack of sensory stimuli on the
cortex is well shown in the case of Laura Bridgman, whose brain was
studied by Professor Donaldson after her death. Laura Bridgman was born
a normal child, and developed as other children do up to the age of
nearly three years. At this time, through an attack of scarlet fever,
she lost her hearing completely and also the sight of her left eye. Her
right eye was so badly affected that she could see but little; and it,
too, became entirely blind when she was eight. She lived in this
condition until she was sixty years old, when she died. Professor
Donaldson submitted the cortex of her brain to a most careful
examination, also comparing the corresponding areas on the two
hemispheres with each other. He found that as a whole the cortex was
thinner than in the case of normal individuals. He found also that the
cortical area connected with the left eye–namely, the right occipital
region–was much thinner than that for the right eye, which had retained
its sight longer than the other. He says: “It is interesting to notice
that those parts of the cortex which, according to the current view,
were associated with the defective sense organs were also particularly
thin. The cause of this thinness was found to be due, at least in part,
to the small size of the nerve cells there present. Not only were the
large and medium-sized cells smaller, but the impression made on the
observer was that they were also less numerous than in the normal
cortex.”
EFFECT OF SENSORY STIMULI.–No doubt if we could examine the brain of a
person who has grown up in an environment rich in stimuli to the eye,
where nature, earth, and sky have presented a changing panorama of color
and form to attract the eye; where all the sounds of nature, from the
chirp of the insect to the roar of the waves and the murmur of the
breeze, and from the softest tones of the voice to the mightiest sweep
of the great orchestra, have challenged the ear; where many and varied
odors and perfumes have assailed the nostrils; where a great range of
tastes have tempted the palate; where many varieties of touch and
temperature sensations have been experienced–no doubt if we could
examine such a brain we should find the sensory areas of the cortex
excelling in thickness because its cells were well developed and full
sized from the currents which had been pouring into them from the
outside world. On the other hand, if we could examine a cortex which had
lacked any one of these stimuli, we should find some area in it
undeveloped because of this deficiency. Its owner therefore possesses
but the fraction of a brain, and would in a corresponding degree find
his mind incomplete.
NECESSITY FOR MOTOR ACTIVITY.–Likewise in the case of the motor areas.
Pity the boy or girl who has been deprived of the opportunity to use
every muscle to the fullest extent in the unrestricted plays and games
of childhood. For where such activities are not wide in their scope,
there some areas of the cortex will remain undeveloped, because unused,
and the person will be handicapped later in his life from lack of skill
in the activities depending on these centers. Halleck says in this
connection: “If we could examine the developing motor region with a
microscope of sufficient magnifying power, it is conceivable that we
might learn wherein the modification due to exercise consists. We might
also, under such conditions, be able to say, ‘This is the motor region
of a piano player; the modifications here correspond precisely to those
necessary for controlling such movements of the hand.’ Or, ‘This is the
motor tract of a blacksmith; this, of an engraver; and these must be the
cells which govern the vocal organs of an orator.’” Whether or not the
microscope will ever reveal such things to us, there is no doubt that
the conditions suggested exist, and that back of every inefficient and
awkward attempt at physical control lies a motor area with its cells
undeveloped by use. No wonder that our processes of learning physical
adjustment and control are slow, for they are a growth in the brain
rather than a simple “learning how.”
The training of the nervous system consists finally, then, in the
development and coördination of the neurones of which it is composed. We
have seen that the sensory cells are to be developed by the sensory
stimuli pouring in upon them, and the motor cells by the motor impulses
which they send out to the muscles. The sensory and the motor fibers
likewise, being an outgrowth of their respective cells, find their
development in carrying the impulses which result in sensation and
movement. Thus it is seen that the neurone is, in its development as in
its work, a unit.
DEVELOPMENT OF THE ASSOCIATION CENTERS.–To this simpler type of sensory
and motor development which we have been considering, we must add that
which comes from the more complex mental processes, such as memory,
thought, and imagination. For it is in connection with these that the
association fibers are developed, and the brain areas so connected that
they can work together as a unit. A simple illustration will enable us
to see more clearly how the nervous mechanism acts to bring this about.
Suppose that I am walking along a country road deeply engaged in
meditation, and that I come to a puddle of water in my pathway. I may
turn aside and avoid the obstruction of discipline child without my attention being called
to it, and without interruption of my train of thought. The act has been
automatic. In this case the nerve current has passed from the eye (_S_)
over an afferent fiber to a sensory center (_s_) in the nervous system
below the cortex; from there it has been forwarded to a motor center
(_m_) in the same region, and on out over a motor fiber to the proper
muscles (_M_), which are to execute the required act. The act having
been completed, the sensory nerves connected with the muscles employed
report the fact back that the work is done, thus completing the circuit.
This event may be taken as an illustration of literally thousands of
acts which we perform daily without the intervention of consciousness,
and hence without involving the hemispheres.
If, however, instead of avoiding the puddle unconsciously, I do so from
consideration of the danger of wet feet and the disagreeableness of
soiled shoes and the ridiculous appearance I shall make, then the
current cannot take the short circuit, but must pass on up to the
cortex. Here it awakens consciousness to take notice of the obstruction,
and calls forth the images which aid in directing the necessary
movements. This simple illustration may be greatly complicated,
substituting for it one of the more complex problems which are
continually presenting themselves to us for solution, or the associated
trains of thought that are constantly occupying our minds. But the truth
of the illustration still holds. Whether in the simple or the discipline child complex
act, there is always a forward passing of the nerve current through the
sensory and thought centers, and on out through the motor centers to the
organs which are to be concerned in the motor response.
THE FACTORS INVOLVED IN A SIMPLE ACTION.–Thus it will be seen that in
the simplest act which can be considered there are the following
factors: (1) The stimulus which acts on the end-organ; (2) the ingoing
current over an afferent nerve; (3) the sensory or interpreting cells;
(4) the fibers connecting the sensory with a motor center; (5) the motor
cells; (6) the efferent nerve to carry the direction for the movement
outward to the muscle; (7) the motor response; and, finally, (8) the
report back that the act has been performed. With this in mind it fairly
bewilders one to think of the marvelous complexity of the work that is
going on in our nervous mechanism every moment of our life, even without
considering the higher thought processes at all. How, with these added,
the resulting complexity all works out into beautiful harmony is indeed
beyond comprehension.
3. EDUCATION AND THE TRAINING OF THE NERVOUS SYSTEM
Fortunately, many of the best opportunities for sensory and motor
training do not depend on schools or courses of study. The world is full
of stimuli to our senses and to our social natures; and our common lives
are made up of the responses we make to these stimuli,–the movements,
acts and deeds by which we fit ourselves into our world of environment.
Undoubtedly the most rapid and vital progress we make in our development
is accomplished in the years before we have reached the age to go to
school. Yet it is the business of education to see that we do not lack
any essential opportunity, to make sure that necessary lines of stimuli
or of motor training have not been omitted from our development.
EDUCATION TO SUPPLY OPPORTUNITIES FOR STIMULUS AND RESPONSE.–The great
problem of education is, on the physical side, it would seem, then, to
provide for ourselves and those we seek to educate as rich an
environment of sensory and social stimuli as possible; one whose
impressions will be full of suggestions to response in motor activity
and the higher thought processes; and then to give opportunity for
thought and for expression in acts and deeds in the largest possible
number of lines. And added to this must be frequent and clear sensory
and motor recall, a living over again of the sights and sounds and odors
and the motor activities we have once experienced. There must also be
the opportunity for the forming of worthy plans and ideals. For in this
way the brain centers which were concerned in the original sensation or
thought or movement are again brought into exercise, and their
development continued. Through recall and imagination we are able not
only greatly to multiply the effects of the immediate sensory and motor
stimuli which come to us, but also to improve our power of thinking by
getting a fund of material upon which the mind can draw.
ORDER OF DEVELOPMENT IN THE NERVOUS SYSTEM.–Nature has set the order in
which the powers of the nervous system shall develop. And we must follow
this order if we would obtain the best results. Stated in technical
terms, the order is _from fundamental to accessory_. This is to say that
the nerve centers controlling the larger and more general movements of
the body ripen first, and those governing the finer motor adjustments
later. For example, the larger body muscles of the child which are
concerned with sitting up come under control earlier than those
connected with walking. The arm muscles develop control earlier than the
finger muscles, and the head and neck muscles earlier than the eye
muscles. So also the more general and less highly specialized powers of
the mind ripen sooner than the more highly specialized. Perception and
observation precede powers of critical judgment and association. Memory
and imagination ripen earlier than reasoning and the logical ability.
This all means that our educational system must be planned to follow the
order of nature. Children of the primary grades should not be required
to write with fine pencils or pens which demand delicate finger
adjustments, since the brain centers for these finer coördinations are
not yet developed. Young children should not be set at work
necessitating difficult eye control, such as stitching through
perforated cardboard, reading fine print and the like, as their eyes
are not yet ready for such tasks. The more difficult analytical problems
of arithmetic and relations of grammar should not be required of pupils
at a time when the association areas of the brain are not yet ready for
this type of thinking. For such methods violate the law of nature, andthe child is sure to suffer the penalty.Habit is our “best friend or worst enemy.” We are “walking bundles ofhabits.” Habit is the “fly-wheel of society,” keeping men patient and
docile in the hard or disagreeable lot which some must fill. Habit is a
“cable which we cannot break.” So say the wise men. Let me know your
habits of life and you have revealed your moral standards and conduct.
Let me discover your intellectual habits, and I understand your type of
mind and methods of thought. In short, our lives are largely a daily
round of activities dictated by our habits in this line or that. Most of
our movements and acts are habitual; we think as we have formed the
habit of thinking; we decide as we are in the habit of deciding; we
sleep, or eat, or speak as we have grown into the habit of doing these
things; we may even say our prayers or perform other religious exercises
as matters of habit. But while habit is the veriest tyrant, yet its good
offices far exceed the bad even in the most fruitless or depraved life.
Many people when they speak or think of habit give the term a very
narrow or limited meaning. They have in mind only certain moral or
personal tendencies usually spoken of as one’s “habits.” But in order to
understand habit in any thorough and complete way we must, as suggested
by the preceding paragraph, broaden our concept to include every
possible line of physical and mental activity. Habit may be defined as
_the tendency of the nervous system to repeat any act that has been
performed once or many times_.
THE PHYSICAL BASIS OF HABIT.–Habit is to be explained from the
standpoint of its physical basis. Habits are formed because the tissues
of our brains are capable of being modified by use, and of so retaining
the effects of this modification that the same act is easier of
performance each succeeding time. This results in the old act being
repeated instead of a new one being selected, and hence the old act is
perpetuated.
Even dead and inert matter obeys the same principles in this regard as
does living matter. Says M. Leon Dumont: “Everyone knows how a garment,
having been worn a certain time, clings to the shape of the body better
than when it was new; there has been a change in the tissue, and this
change is a new habit of cohesion; a lock works better after having been
used some time; at the outset more force was required to overcome
certain roughness in the mechanism. The overcoming of this resistance is
a phenomenon of habituation. It costs less trouble to fold a paper when
it has been folded already. This saving of trouble is due to the
essential nature of habit, which brings it about that, to reproduce the
effect, a less amount of the outward cause is required. The sounds of a
violin improve by use in the hands of an able artist, because the fibers
of the wood at last contract habits of vibration conformed to harmonic
relations. This is what gives such inestimable value to instruments that
have belonged to great masters. Water, in flowing, hollows out for
itself a channel, which grows broader and deeper; and, after having
ceased to flow, it resumes when it flows again the path traced for
itself before. Just so, the impressions of outer objects fashion for
themselves in the nervous system more and more appropriate paths, and
these vital phenomena recur under similar excitements from without, when
they have been interrupted for a certain time.”[2]
ALL LIVING TISSUE PLASTIC.–What is true of inanimate matter is doubly
true of living tissue. The tissues of the human body can be molded into
almost any form you choose if taken in time. A child may be placed on
his feet at too early an age, and the bones of his legs form the habit
of remaining bent. The Flathead Indian binds a board on the skull of his
child, and its head forms the habit of remaining flat on the top. Wrong
bodily postures produce curvature of the spine, and pernicious modes of
dress deform the bones of the chest. The muscles may be trained into the
habit of keeping the shoulders straight or letting them droop; those of
the back, to keep the body well up on the hips, or to let it sag; those
of locomotion, to give us a light, springy step, or to allow a shuffling
carriage; those of speech, to give us a clear-cut, accurate
articulation, or a careless, halting one; and those of the face, to give
us a cheerful cast of countenance, or a glum and morose expression.
HABIT A MODIFICATION OF BRAIN TISSUE.–But the nervous tissue is the
most sensitive and easily molded of all bodily tissues. In fact, it is
probable that the real _habit_ of our characteristic walk, gesture, or
speech resides in the brain, rather than in the muscles which it
controls. So delicate is the organization of the brain structure and so
unstable its molecules, that even the perfume of the flower, which
assails the nose of a child, the song of a bird, which strikes his ear,
or the fleeting dream, which lingers but for a second in his sleep, has
so modified his brain that it will never again be as if these things had
not been experienced. Every sensory current which runs in from the
outside world; every motor current which runs out to command a muscle;
every thought that we think, has so modified the nerve structure through
which it acts, that a tendency remains for a like act to be repeated.
Our brain and nervous system is daily being molded into fixed habits of
acting by our thoughts and deeds, and thus becomes the automatic
register of all we do.