SENSATIONS AND OUR PERCEPTION OF THEM
[Sidenote: _Mind's Source of Supplies_]
Whatever you know or think you know, of the external world comes
to you through some one of your five primary senses, sight, hearing,
touch, taste and smell, or some one of the secondary senses, such
as the muscular sense and the sense of heat and cold.
The impressions you receive in this way may be true or they may be
false. They may constitute absolute knowledge or they may be merely
mistaken impressions. Yet, such as they are, they constitute all the
information you have or can have concerning the world about you.
[Sidenote: _Does Matter Exist?_]
Philosophers have been wrangling for some thousands of years as
to whether we have any real and absolute knowledge, as to whether
matter actually does or does not exist, as to the reliability or
unreliability of the impressions we receive through the senses.
But there is one thing that all scientific men are agreed upon,
and that is that such knowledge as we do possess comes to us by
way of perception through the organs of sense.
If you have never given much thought to this subject, you have
naturally assumed that you have direct knowledge of all the
material things that you _seem_ to perceive about you. It has
never occurred to you that there are intervening physical agencies
that you ought to take into account.
[Sidenote: _First-Hand Knowledge_]
When you look up at the clock, you instinctively feel that there is
nothing interposed between it and your mind that is conscious of it.
You seem to feel that your mind reaches out and envelops it.
As a matter of fact, your sense impression of that bit of furniture
must filter through a great number of intervening physical agencies
before you can become conscious of it.
Direct perception of an outside reality is impossible.
[Sidenote: _Second-Hand Knowledge_]
Before you can become aware of any object there must first arise
between it and your mind a chain of countless distinct physical
events.
Modern science tells us that light is due to undulations or
wave-like vibrations of the ether, sound to those of the air, etc.
These vibrations are transmitted from one particle of ether or air
to another, and so from the thing perceived to the body of man.
Think, then, what crisscross of air currents and confusion of ether
vibrations, what myriad of physical events, must intervene between
any distant object and your own body before sensations come and
bring a consciousness of that object's existence!
Nor can you be sure, even after any particular vibration has
reached the surface of your body, that it will reach your mind
unaltered and intact!
[Sidenote: _Etheric Vibrations as Causing Sensations_]
What goes on in the body itself is made clear by your knowledge
of the cellular structure of man.
You know that you have a system of nerves centering in the brain
and with countless ramifications throughout the structural tissues
of the body.
You know that part of these nerves are sensory nerves and part of
them are motor nerves. You know that the sensory nerves convey to
the brain the impressions received from the outer world and that
the motor nerves relay this information to the rest of the body
coupled with commands for appropriate muscular action.
[Illustration: DIAGRAM SHOWING THE FOUR CHIEF ASSOCIATION CENTERS
OF THE HUMAN BRAIN]
[Sidenote: _The Road to Perception_]
The outer end of every sensory nerve exposes a sensitive bit of
gray matter. These sensitive, impression-receiving ends constitute
together what is called the "sensorium" of the body.
When vibrations of light or sound impinge upon the sensorium, they
are relayed from nerve cell to nerve cell until they reach the
central brain. Then it is, and not until then, that sensations and
perceptions occur.
Consider, now, the infinitesimal size of a nerve cell and you will
have some conception of the number of hands through which the
message must pass before it is received by the central office.
Many of our sensations, especially those of touch, seem to occur
on the periphery of the body--that is to say, at that part of the
exposed surface of the body which is apparently affected. If your
finger is crushed in a door, the sensation of the blow and the pain
all seem to occur in the finger itself.
[Sidenote: _The Place Where Sensation Occurs_]
As a matter of fact, this is not the case, for if one of your arms
should be amputated, you would still feel a tingling in the fingers
of the amputated arm. Thus has arisen a superstition that leads many
people to bury any part of the body lost in this way, thinking that
they will never be entirely relieved of pain until the absent member
is finally at rest.
Of course, the fact is that you would only _seem_ to have feeling
in the amputated arm. The sensation would really occur in the central
brain tissue as the organ of the governing intelligence, the organ
of consciousness.
[Sidenote: _Laboratory Proof of Sense-Perceptive Process_]
And you may set it down as an established principle that _all states
of consciousness, whether seemingly localized on the surface of the
body or not, are connected with the brain as the dominant center_.
The facts we have been recounting have been established by the
experiments of physiological psychology. Thus, the work of the
laboratory has shown that between the moment when a sense vibration
reaches the body and the moment when sensation occurs a measurable
interval of time intervenes.
If your eyes were to be blindfolded and your hand unexpectedly
pricked with a white-hot needle, the time that would elapse before
you could jerk your hand away could be readily measured in fractions
of a second with appropriate instruments.
[Sidenote: _Reaction Time_]
This interval is known as _reaction-time_. It varies greatly with
different persons. During this reaction-time, the cell or cells
attacked upon the surface of the hand have conveyed news of the
assault through numberless intermediate sensory nerve cells to
the brain. The brain in turn has sent out its mandate through the
appropriate motor nerve cells to all the muscle and other cells
surrounding the injured cell, commanding them to remove it from
the point of danger.
The work of the nervous system in dealing with the ether vibrations
that are constantly impinging upon the surface of the body has been
likened to that of the transmitter, connecting wire and receiver
of a telephone. Air-waves striking against the transmitter of the
telephone awaken a similar vibratory movement in the transmitter
itself. This movement is passed along the wire to the receiver,
which vibrates responsively and imparts a corresponding wave-like
motion to the air.
[Sidenote: _The Human Telephone_]
These air-waves when heard are what we call _sound_.
In the same way, air-waves striking the ear are communicated by
the auditory nerve to the brain, where they awaken a corresponding
sensation of sound. But these waves must be vibrating at between
30 and 20,000 times a second. If they are vibrating so slowly or
so rapidly as not to come within this range, we cannot hear them.
[Sidenote: _The Living Telegraph_]
This process is by no means a mechanical affair. On the contrary,
it is a series of _mental_ acts. Every cell in the living telegraph
must receive the message and transmit it. _Every cell_ must
exercise a form of intelligence, from the auditory cell reporting
a sound-wave or the skin cell reporting an injury to the muscle
cells that ultimately receive and understand a message directing
them to remove the part from danger.
Reaction-time, so called, is thus occupied by cellular action in
the form of _mental_ processes intervening between the nerve-ends
and the brain center, in much the same way that light and sound
vibrations intervene between the object perceived and the surface
of the body.
[Sidenote: _The Six Steps to Reaction_]
For even the simplest of sense-perceptions we have, then, this
sequence of events: first, the object perceived; second, the series
of vibrations of ether particles intervening between the object
and the body; third, the impression upon the surface of the body;
fourth, the series of mental processes, cell after cell, in the
nerve filaments leading to the brain; fifth, when these impressions
or messages have reached the brain, a determination of what is to
be done; and, sixth, a transmission by cellular action of a new
message that will awaken some response in the muscular tissues.
[Sidenote: _Unopened Mental Mail_]
This process is completely carried out, however, in only
comparatively few instances. The vast majority of sense-impressions
awaken no reaction. They are registered in the mind, but they are
not perceived. We are not conscious of them. They form a part, not
of consciousness, but of subconsciousness. They are messages that
reach the mind but are laid aside like unopened mail because they
possess no present interest.
Wherever and however you may be placed, you are always and
everywhere immersed in a flood of etheric vibrations. Light, sound
and tactual vibrations press upon you from every side. At a busy
corner of a city street these vibrations rise to a tumultuous
fortissimo; in the hush of a night upon the plains they sink to
pianissimo. Yet at every moment of your day or night they are there
in greater or less degree, titillating the unsleeping nerve-ends of
the sensorium.
[Sidenote: _Selective Process that Determines Conduct_]
Your mind cannot take time to make all these sense-impressions the
subject of conscious thought. It can trouble itself only with those
that bear in some way upon your interests in life.
_Your mind is like the receiving apparatus of the wireless telegraph
which picks from the air those particular vibrations to which it is
attuned. Your mind is selective. It is discriminating. It seizes
upon those few sensory images that are related to your interests in
life and thrusts them forward to be consciously perceived and acted
upon. All others it diverts into a subconscious reservoir of
temporary oblivion._
[Sidenote: _In Tune with Life-Interest_]
You will have a clearer understanding of the sense-perceptive
processes and a more vital realization of the practical significance
of these facts when you consider how they affect your knowledge of
material things and your conception of the external world.
This subject possesses two distinct aspects.
One aspect has to do with the inability of the sense-organs to
record the facts of the outer world with perfect precision. These
organs are the result of untold ages of evolution, and, generally
speaking, have become wonderfully efficient, but they display
surprising inaccuracies. These inaccuracies are called Sensory
Illusions.
[Sidenote: _Practical Aspects of Perception Process_]
The other aspect of the Sense-Perceptive Process has to do with the
mental interpretation of environment.
Both these aspects are distinctly practical.
You should know something of the weaknesses and deficiencies of the
sense-perceptive organs, because all your efforts at influencing
other men are directed at their organs of sense.
You should understand the relationship between your mind and your
environment, since they are the two principal factors in your
working life.