SENSATION AND PERCEPTION.
As there is no distinction between sensation and perception except in
the fact that one is attended with the belief of a cause and the other
is not, they will be treated of together.
The mind of man is an immaterial existence, confined in its operations
by the body it inhabits, and depending upon the construction and
modifications of this envelope for much of its happiness or suffering.
The exercise of the imagination, when the eyes are closed and the body
at rest, will probably give us the best idea of what is the nature of
spiritual existence when disconnected with matter. It is one of the
offices of our bodily system to retain the spirit in its operations in
one particular place, so that ordinarily it can have direct communion
with no other mind which is not in the same place. Whether this is the
case with mere spiritual existence is a question for conjecture, and not
for any rational decision.
While the spirit of man is resident in its material frame, it is
furnished with facilities of communication with other minds, and with
organs which fit it to receive suffering or enjoyment from the material
objects by which it is surrounded. These organs of communication are the
several senses. They consist of expansions of the substance of which the
brain is formed, which, descending to the body through the spinal bone
of the back, are thence sent out in thousands of ramifications over the
whole system. Those branches which enter the eyes, and are spread over
the interior back part of this organ, are called the _optic nerve_.
Whenever the particles of light enter the eye, they strike the optic
nerve, and produce the sensation which is called _sight_. Those branches
which are spread over the tongue are the organ of _taste_. Those that
are extended through the cavities of the nostrils are called the
_olfactory_ nerves. When the small particles of matter that escape from
odoriferous bodies come in contact with these nerves, they produce the
sensation of _smell_.
The nerves that constitute the organ of _hearing_ are extended over the
cavity of the ear behind the _tympanum_, or _ear-drum_. This cavity is
filled with a liquid, and when the drum of the ear is caused to vibrate
by the air which is set in motion by sonorous bodies, it produces
undulations of this liquid upon these nerves, and thus the sensation of
_sound_ is produced. By the expansion of other nerves, the sense of
_feeling_ is extended all over the body, excepting the nails and the
hair. It is by the action of matter, in its different forms, on these
several senses, that the mind obtains ideas, and that ideas are imparted
from one mind to another.
_Perception_ never takes place unless some material object makes an
impression upon one of the senses. In the case of the eye, the ear, and
the nostrils, the object which is regarded as the cause of the sensation
does not come immediately in contact with the organs of sense. When we
see a body, we consider it as the cause of that perception; but it is
not the body that comes in contact with the organ of sight, but merely
the particles of light reflected from that body. In the case of smell,
the fragrant body is regarded as the cause of the sensation; but that
which acts on the sense is the material particles of perfume which flow
from that body.
Thus, also, with hearing. We consider the sonorous body as the cause;
but the sensation is produced through the medium of the air, which
affects the drum of the ear. But in the case of taste and touch, the
body which is regarded by the mind as the cause must come in contact
with the nerves of the tongue or the body to produce the sensation.
_Smell._
The sense of smell is one which greatly conduces to the preservation,
the comfort, and the happiness of man. It is a continual aid to him in
detecting polluted atmosphere or unhealthy food. The direct enjoyment it
affords is probably less in amount than that derived from any of the
other senses; yet, were we deprived of all the enjoyment gained through
this source, we should probably find the privation much greater than we
at first might imagine. When we walk forth among the beauties of nature,
the fresh perfumes that send forth their incense are sources both of
immediate and succeeding gratification. The beautiful images of nature
which rise to the mind in our imaginative hours, would lose many of
their obscure but charming associations were the fields stripped of the
fragrance of their greens and the flowers of their sweet perfumes.
Nature would appear to have lost that moving spirit of life which now
ever rides upon the evening zephyrs and the summer breeze. As it is, as
we walk abroad, all nature seems to send forth its welcome, while to its
Maker's praise
"Each odorous leaf,
Each opening blossom, freely breathes abroad
Its gratitude, and thanks Him with its sweets."
_Taste._
When a sapid body is applied to the organ of taste, two sensations are
produced, one of _touch_ and one of _taste_. We are conscious of the
difference of these sensations when we apply a body to the tongue which
has taste, and then immediately one which has not. It is probable,
however, that the same set of nerves serve both purposes.
It is one of the numberless evidences of the benevolence of our Creator
that the process which is necessary for the preservation of life, and
which depends upon the voluntary activity of every human being, should
be connected with a sense which affords such gratification that the duty
is sought as a pleasure. Were mankind led to seek food merely in the
exercise of reason for the purpose of preserving life, multitudes,
through carelessness and forgetfulness, would be perpetually neglecting
that regular supply without which the animal system would become
deranged and enfeebled. By the present constitution of the body, the
gratification of this sense is an object of desire, and thus we are
continually reminded of our duty, and led to it as a source of
enjoyment.
Nor is it the gratification of this sense which is the only source of
enjoyment connected with it. The regular periods for repast bring around
the social board those united to each other by the tenderest ties of
kindred and affection. These become seasons of cheerful hilarity and
relaxation, seasons of cessation from daily cares, seasons for the
interchange of kind feelings and intellectual stores; and while the mere
gratification of sense is one source of pleasure, to this is often added
the "feast of reason and the flow of soul."
The effect on the best feelings in thus assembling to participate in
common blessings is scarcely ever appreciated. Did every individual of
our race retire to secrecy and solitude to satisfy the cravings of
nature, how much would the sum of human happiness be diminished! But
thus has our benevolent Creator contrived that one source of enjoyment
should serve as an occasion for introducing many more.
_Hearing._
The sense of hearing is one more connected with the intellectual and
moral powers of man than either taste or smell, as it is through the
medium of this organ that both music and speech operate on the human
mind. We can form some imperfect estimate of the amount of happiness
derived from this sense by imagining the condition of mankind were they
at once and forever deprived of this source of improvement and
enjoyment. The voice of sympathy, friendship, and love would be hushed.
The eloquence of the forum, the debates of the Legislature, the
instructions of the pulpit, would cease. The music of nature--its
sighing winds and dashing waters--would be stilled, and the warbling of
the groves would charm no more. The sound of pipe, and harp, and solemn
harmonies of voice would never again waken the soul to thrilling and
nameless emotions. Where now ten thousand sounds of active life, or
cheerful hum of business, or music of language and song charm and
animate the soul, man would walk forth in silence and solitude.
The operation of mere sound, disconnected with the ideas which are often
conveyed by it, is a subject of curious speculation. Sounds differ from
each other in _quality_, _pitch_, _force_, and in _length_. The
difference in _tone_ may be illustrated by the sounds of a clarionet
compared with the sound of a bell or of the human voice. Every
instrument and every human voice has each a peculiar tone by which it is
distinguished from all others. The difference in _pitch_ is shown by
sounding a low and a high note in succession on an instrument. The
difference in _force_ is exhibited by singing or speaking loud or soft.
There are certain sounds that in themselves are either agreeable or
disagreeable from their tone alone. Thus the sound of a flute is
agreeable, and that of the filing of a saw is disagreeable. Sounds also
are agreeable according as they succeed each other.
_Melody_ is a succession of agreeable tones arranged in some regular
order as it respects their duration and succession. Some melodies are
much more agreeable to the ear than others. Some melodies produce a
plaintive state of mind, others exhilarate, and this without regard to
any thing except the nature of the sounds and their succession. Thus a
very young infant, by a certain succession of musical tones, can be made
either to weep in sorrow or smile with joy.
_Harmony_ is a certain _combination_ of sounds which are agreeable to
the ear; and it is found that the mind can be much more powerfully
affected by a combination of harmonious sounds than by any melody. The
effect of music on certain minds is very powerful, often awakening
strange and indescribable emotions. It has been, therefore, much
employed both to heighten social, patriotic, and devotional feeling.
There is probably nothing which produces stronger and more abiding
associations in the mind than musical sounds. As an example of this may
be mentioned the national air which is sung by the Swiss in their native
valleys. It is said that when they become wanderers in foreign lands, so
strongly will this wild music recall the scenes of their childhood and
youth, their native skies, their towering mountains and romantic glens,
with all the strong local attachments that gather around such objects,
that their heart sickens with longing desires to return. And so much was
this the case with the Swiss of the French armies, that Bonaparte
forbade this air being played among his troops. The Marseilles Hymn,
which was chanted in the scenes of the French Revolution, was said to
have been perfectly electrifying, and to have produced more effect than
all the eloquence of orators or machinations of statesmen.
The mind seems to acquire by experience only the power of determining
the place whence sounds originate. It is probable that, at first, sounds
seem to originate within the ear of the person who hears; and, even
after long experience, cases have been known, when a person suddenly
waked from sleep imagined the throbbing of his own heart was a knocking
at the door. But observation and experience soon teach us the direction
and the distance of sounds. The art of the ventriloquist consists in
nothing but the power which a nice and accurate ear gives him of
distinguishing the difference between sounds when near or far off, and
of imitating them.
_Touch._
The sense of touch is not confined to one particular organ, but is
extended over the whole system, both externally and internally. It is in
the hands, however, especially at the ends of the fingers, that this
sense is most acute and most employed. We acquire many more ideas by the
aid of this sense than by either hearing, smell, or taste. By these last
we become acquainted with only one particular quality in a body, either
of taste, smell, or sound; but by means of the touch we learn such
qualities as heat and cold, roughness and smoothness, hardness and
softness, figure, solidity, and extension.
It is supposed that it is by this sense that we gain the idea of
something _external_, or without ourselves. The sensation of smell would
seem to be within, as an act or emotion of the soul itself. Thus also
with hearing, which, being produced within the ear by the undulating
air, would seem to originate within. Thus also with sensations within
the eye. But when the limbs begin to move and to come in contact with
outward objects, and also in contact with various parts of the body, the
mind gains an idea of the existence of some outward object. This is
probably the first sense by which any idea of existence is wakened in
the mind. As one sense after another is called into action, the mind
continually gains new ideas, and then begins its operations of
comparing, abstracting, reasoning, and willing.
It is by the sense of touch that we gain our ideas of _resistance_ and
_extension_. In the class of ideas included under the head of ideas of
resistance may be placed those of solidity, liquidity, hardness,
softness, viscidity, roughness, and smoothness; these all being
different names for different modes of resistance to the muscles of the
hands, arms, or fingers, when applied to the bodies which have these
qualities. These ideas are not gained by simple contact; their existence
depends upon the contraction or expansion of the muscles, which are the
organs of motion and resistance in the human body.
We may suppose the infant to gain these ideas by a process somewhat
similar to this: He first moves his arms by instinct, without any
knowledge of the effects to follow. By this movement he gains certain
ideas of the simple contractions and extension of his muscles, and
learns also that by his own will he can exercise his muscles in this
manner. At length he attempts to move his arm in a manner to which he
has become familiar, and some object intervenes, and motion is
prevented, while all his wonted muscular efforts are vain. Thus arises
in his mind a new idea, of resistance, in addition to the sensations of
touch and of motion, which had before been experienced.
The ideas of _different degrees_ of this resistance are gained by
repeated experience, and when age furnishes the ability to understand
language, the names of hardness, softness, roughness, and the like, are
given to these ideas. In the use of his muscles, also, the infant must
first acquire its ideas of _extension_ and _figure_; for it must be
where resistance to muscular effort ceases that he must feel that the
cause ceases to exist. The little being extends his hand--an object
intervenes which interrupts his muscular motions; he grasps this object,
and wherever this feeling of resistance exists, there he feels that the
cause of it exists, and that after he has passed certain limits it does
not exist.
_Figure_ is defined as the _limits of extension_, and, of course, it can
be seen that ideas of figure can only be gained by thus finding the
limits of extension. It has formerly been supposed that ideas of
_extension_ and _figure_ were gained by the eye, but later experiments
and discussions show that the sense of feeling, including muscular
motion, is the medium by which these ideas are first gained, and that
afterward the eye, by the principle of association, acquires the power
of distinguishing figure and distance.
There is much enjoyment resulting from the sense of touch in many ways,
a large portion of which is almost unnoticed. Much also included under
the term _comfort_ results from this sense. Much of that which is
agreeable in clothing and in objects around us is of this nature.
Besides this, there are many endearments of friendship and affection
that gain expression only through this medium.
_Vision._
The organ of vision is the eye, which is one of the most curious and
wonderful parts of the human frame, and displays in astonishing variety
the wisdom and skill of its Designer.
The eye consists of a round ball, formed externally of various
coverings, and within of humors of different degrees of consistency. The
front part of the eye, which is exposed to view, has a small opening in
it, which admits the rays of light within this ball, while it is by the
operation of light on the nerves, which are spread in fine net-work over
the interior, that _sight_ is produced.
In examining the mechanism of the eye, a great variety of contrivances
appear, all aiding in accomplishing the object of vision. In the first
place, we may observe its modes of protection and defense. The lid is a
soft, moist wiper, which, with a motion quick as lightning, protects the
eye from outward violence, cleanses it from dust, veils it from
overpowering radiance, and in hours of repose entirely excludes the
light. On its edge is the fringing lash, which intercepts floating
matter that might otherwise intrude, while above is spread the eyebrow,
which, like a thatch, obstructs the drops that heat or toil accumulate
on the brow.
We next observe the organs of motion with which the eye is furnished,
and which, with complicated strings and pulleys, can turn it every way
at the will of the intelligent agent. The _pupil_ or _opening_ of the
eye, also, is so constructed, with its minute and multiplied circular
and crossing muscles, that it can contract or expand in size just in
proportion as the light varies in intensity.
The ball of the eye is filled with three substances of different degrees
of density. One is a watery humor, near the front of the eye; back of
this, and suspended by two muscles, is the solid lens of the eye, or the
_crystalline humor_; and the remainder of the eye, in which this lens is
imbedded, consists of the _vitreous humor_, which is of the consistence
of jelly. These all have different degrees of transparency, and are so
nicely adjusted that the rays of light, which start from every point in
all bodies in _diverging_ lines, are by these humors made to _converge_
and meet in points on the _retina_, or the nerve of the eye, forming
there a small picture, exactly of the same proportions, though not the
same size, as the scene which is spread before the eye.
When the outer covering of the back part of the eye is removed, the
objects which are in front of the eye may be discerned, delicately
portrayed in all their perfect colors and proportions, on the retina
which lines the interior. It is this impression of light on the optic
nerve which gives our ideas of light and colors.
The eye is also formed in such a way that it can alter its shape and
become somewhat oblong, while at the same time its lens is projected
forward or drawn back. The object of this contrivance is to obtain an
equally perfect picture of distant and of near objects.
Our ideas of _shape_ and _size_ at first are not gained by the eye, but
by the sense of touch. After considerable experience we learn to
determine shape and size by the eye. Experiments made upon persons born
blind and restored to sight furnish many curious facts to support this
assertion.
When the eye first admits the light, all objects appear to _touch_ the
eye, and are all a confused mass of different colors. But by continual
observation, and by the aid of the sense of touch, objects gradually are
separated from each other, and are then regarded as separate and
distinct existences.
The eye is so formed that the picture of any object on the retina varies
in size according to its _distance_. Two objects of equal size will make
a different picture on the back of the eye, according to the distance at
which they are held. The ideas of size at first are regulated by the
proportions of this picture in the eye, until by experience it is found
that this is an incorrect mode, and that it is necessary to judge of the
_distance_ of a body before we can determine its _size_. This accounts
for the fact that objects appear to us so different according as we
conceive of their distance, and that we are often deceived in the size
of bodies because we have no mode of determining their distance.
But it appears also that our ideas of distance are gained, not by the
eye alone, but by the eye and the sense of feeling united. A child by
the sense of feeling learns the size of his cup or his playthings. He
sees them removed, and that their apparent size diminishes. They are
returned to him, and he finds them unaltered in size. When attempting to
recover them, he finds that when they look very small he is obliged to
pass over a much greater distance to gain them than when they appear
large, and that the distance is always in exact proportion to their
apparent size. In this way, by oft-repeated experiments, the infant
reasoner learns to judge both of the size and distance of objects. From
this it appears that, in determining the size of an object, we
previously form some judgment of its distance, and likewise that, in
finding the distance, we first determine the size.
The _shape_ of objects is learned altogether by the sense of _feeling_.
It has before been stated that at the first exercise of vision every
thing is a confused mass of different colors, and all appearing to touch
the eye. By the aid of the hands the separate existence of different
bodies is detected, and the feeling of touch, which once was the sole
mode of determining shape, is now associated with a certain form or
picture on the eye, so that, in process of time, the eye becomes the
principal judge of shape.
But, in determining the shape of a thing, an act of judgment is
necessary. This may be illustrated by the example of a hoop, which in
one position will make a picture in the eye which is circular, in
another position the picture of it will be oval, and in another only a
straight line. If a person will observe a hoop in these different
positions, and then attempt to draw a picture of it, he will be
conscious of this varying picture in the eye. Of course, in order to
decide the shape of a thing, we must decide its distance, its relative
position, and various circumstances which would alter the form of the
picture in the eye. It is only by long experience that the infant child
gradually acquires the power of determining the shape, size, and
distance of objects.
The painter's art consists in laying on to canvas an enlarged picture of
the scene which is painted in the interior of his own eye. In this
minute picture of the eye, the more distant an object the smaller its
size, the more indistinct its outline, and the fainter its colors. These
same are transferred to canvas in an enlarged form; the distant objects
are made small in size, faint in colors, and indistinct in outline, just
in proportion to their distance.
The organ of vision is the inlet of more enjoyment to the mind than any
of the other senses. Through this small loop-hole the spirit looks forth
on the rich landscape of nature, and the charms both of the natural and
moral world. The fresh colors, the beauty of motion, the grace of
figures, the fitness of proportion, and all the charms of taste, are
discovered through this medium. By the eye, also, we learn to read the
speaking face of man, we greet the smile of friendship and love, and all
those varying charms that glance across the human face divine. By the
aid of this little organ, too, we climb not only the summits of earth's
domains, but wander forth to planets, stars, and suns, traverse the vast
ethereal expanse, and gather faint images and flitting visions of the
spirit's future home.