CHAPTER III.

ACQUIRED PERCEPTIONS.

borrower from the

It must be understood that in the preceding chapter we have given but a bare outline of the philosophy of Sensation and Perception, and that their relations are not quite so simple as this representation might seem to indicate. Each one of the senses furnishes its very large, diverse, and yet peculiar group of sensations which stand as signs of external facts, the interpretation of which constitutes perception. But these become curiously and wondrously complicated from the fact that each sense bor- Each sense a rows from the others. One seems to convey to us knowledge which must have been gained only others. by another. Thus I find by touch that a certain object is hard, and that another is soft. The one may be a piece of iron, the other a lump of dough. I observe that there is a difference in their appearance. It is probable that we may need a series of experiments in this line We learn by before we come to recognize the fact that in a large proportion of soft things there is a certain common appearance to the eye, and that in a large proportion of hard things there is a certain other appearance. We soon learn to distinguish these different appearances, and to associate one with the quality of hardness, and the other with that of softness. Henceforth we distinguish by the eye objects as hard and soft, not always so accurately as

experience.

Sight bor

touch.

by the touch, and yet for the most part accurately enough for practical purposes. So we say of a certain rowing from appearance that it has a warm look, and of another that it has a cold look. Now warm and cold are not qualities that appeal at all to the eye, but we have noticed many times that this appearance of the sky or clouds is accompanied by the one temperature, and that, by the other; hence we use these terms, and are seldom wrong in the qualities they symbolize.

Sound bor

touch and

sight.

A barrel has another sound if rapped upon when it is empty than when it is full. Hence it is not necessary to ascertain the fact either by sight or by rowing from touch, as the sound will give the information sought. So a mason, if he wishes to find whether a wall is solid, can tell by striking here and there with a hammer, and a carpenter will determine where to drive a nail in a plastered wall which has a perfectly uniform appearance to the eye, by rapping with his hammer along the surface till he finds a place which gives a deadened sound. He knows by this that there is a joist behind the lath. In this way, also, do we recognize roughness and smoothness, flexibility and rigidity, solid and fluid substances, and many others by the eye, where the primary means of distinguishing them is by the touch.

Sight borrowing from

Not unfrequently vision has the same effect as physical taste. One is made sick sometimes by the sight of some object which is associated with a nauseous odor or flavor. So the sight appropriates as its own what is a matter of judgment, in which, perhaps, several sources of cognition are involved. We learn to estimate distance by the eye. This is gained by a varied process and by considerable experience. We

taste.

some

We easily

Distance de

termined by rowing from

the eye bor

the other

senses and

see an object with which we are familiar. determine whether it is near by or far off by its visible appearance. If its outline be clear and distinct, and if it make a certain angle on the eye, we know it is near by. If the outline be what dim and indistinct, and if the visual angle faculties. be much smaller than in the other case, we at once decide that it is far off, and we learn to estimate these comparative distances and their measurements by these signs. A butcher or drover who is in the practice of buying cattle Weight estiby weight, will learn to estimate with marvel- mated by lous approximation to correctness how much an animal will weigh by simply looking at him.

sight.

mind cog

Not only do we learn by the eye what is primarily the product of the other senses, but we very readily apprehend what is directly the product of no sense. States of We see a blushing cheek, a smiling or frowning nized by the face, a downcast expression; all these tell of eye. certain emotions as plainly as we can learn them through any means whatever. Yet certainly emotions are not matters of sensual observation. It is by this mental cooperation, as we might say, of the senses, this service of one to another, of all to each, that we add immeasurably to the number, variety, and wealth of our perceptions. It is probable that our knowledge is many hundred-fold greater than it would be if we were dependent on what each sense, operating by itself and limited to its own natural powers, would give us. This very reasoning suggests to us a certain caution respecting the use of our senses, which may also show us a reason why certain indications that our perceptions are not always valid, are not themselves

Manifold in

crease of our

knowledge by

this co-op

eration of the

senses.

trustworthy.

The testimony of our senses valid when origi

nal and not borrowed.

In general, we may say that the natural and primary perceptions are always valid. It is only the acquired perceptions that sometimes mislead us. Dr. Wayland relates the story of a person who, on coming to a certain house where he had an appointment, found the door locked; but looking up, he saw what appeared to him to be the key of the door, which he proceeded to take down. On reaching for the key he found there was none there. It was only the painted figure of the key, so shaded as to make the same impression on the eye as a real key would have done. The question arises: Did not his senses deceive him? Is not this an instance of invalid perception? It might appear so. But the latter appearance is no less fallacious than the former. The appearance of the key was false; the appearance of deceit in the sense and perception was also false. Instead of his senses deceiving him, they removed the deception. Instead of his perception apprehending what was not in existence, it was a perception of the real character of the object that set him right and corrected his error. The truth about the matter is, that it was not the primal sense of sight, and the accompanying perception, by which he was misled, but the borrowed or acquired perception, the transfer from touch to sight, which did the mischief. The man had associated the particular shades mary percep- of color then and there appealing to the sense tion correct. of sight, with a certain form which can only be primarily known through the sense of touch. soon as the proper sense was brought into requisition, the error vanished.

The acquired perception deceptive,

but the pri

As

It is thus also that we are deceived by the appearance

of objects seen in a fog. By our acquired perceptions, as we have seen, we estimate size by distance, and Objects seen distance by the greater or less distinctness of in a fog. outline. In a fog, the objects seem farther off than they really are, and we therefore, from our experience in a clear atmosphere, estimate the size accordingly; that is, we estimate the size to be greater than it really is. But this is not from the invalidity of natural and primary perceptions, but from trusting too implicitly to acquired perceptions. Hence it is evident that when our perceptions seem to mislead us, it will generally be found that the error arises, not from our original perceptions, but from those which are acquired.

In the destruction of remaining senses beacute.

one sense the

come more

The facility with which, when one sense is destroyed, the other senses acquire means to make up a portion of the deficiency, and the extent to which this can be carried, is worthy of our consideration. We all know how sight supplies the place of hearing in the deaf. Sight, gestures, movements, and facial expressions, instead of sounds, now become symbols of conceptions and thoughts. Not only, thus, does conversation become comparatively easy and rapid between two individuals in the presence of each other, but through the same means, written language is learned, and thus the unfortunate subjects of this deprivation are brought into communication with the intelligent and wise in all ages and places.

So the blind acquire a vastly quicker and larger range of perceptions by means of hearing and touch. It is wonderful how easily a blind man will distin- Hearing and guish pieces of money on which the impressions are only slightly different; how easily he learns

touch substiin the blind.

tuting sight