Knowledge of the External Senses

a) the external senses Everyone agrees that there are at least five external senses, and some psychologists insist that there are more. It will be best for us to accept the minimum division of these senses, and to leave to scientists the discussion of the question whether any of the five is itself divided into two or more distinct senses.

The five external senses are Sight or Vision; Hearing or Audition; Smell of Olfaction; Taste or Gustation; Touch or Feeling.

Sight and hearing are sometimes called the superior senses, and the other, three are called inferior.

The reason for this classification lies in the fact that sight and hearing grasp their proper object in a manner that is entirely objective, while the other three senses perceive the subject as affected by objects.

Thus I see a flower and hear a melody without being directly aware of myself as experiencing the sensations; my attention is taken up with the objective flower and the objective sounds. But when I smell an agreeable odor, taste a pleasing flavor, or touch a hard surface, I am aware of myself as experiencing the odor, the flavor, the resistance. Of course, the subject makes its own contribution to every sense-act, but the point is that the place and function of the subject is less insistently obvious in seeing and hearing than in other sense acts. One does not know without scientific investigation that colors act causally upon sight and sounds upon hearing; one simply sees colored objects and hears sounds. This is what we mean by saying that sight and hearing grasp their proper objects in a manner that is wholly objective. One does know, however, without scientific investigation, that an odorous object is the cause of the sensation of smell; that flavored or sapid body is the cause of the sensation of taste; that a bodily object is the cause of the resistance sensed by touch. One senses oneself as causally affected by the objects of the inferior senses. It is no argument against this fact to say that a blinding light makes one aware of pain or distress as caused by the light, or that a piercing shriek makes one advert to the unpleasant act of hearing as caused by the sound. Inasmuch as light pains the eye, it is sensed by touch, not by vision. Inasmuch as noise distresses the ear, it is sensed by touch, not by hearing. The organ of touch is diffused throughout the body, and even through the organs of the other senses. When over-stimulation of an organ occurs, it is touch that perceives the excessive impression as painful.

We must now comment briefly on the several external senses and their sensories or organs:

1. Sight or vision.—The organ of sight is the eye.

More accurately, the organ of sight is made up of the terminals of the optic or seeing nerve. These terminals are called the rods and cones of the eye.

Sensations of seeing are aroused by waves or vibrations of ether which stimulate these rods and cones.

The number of vibrations or waves of ether varies for the different colors. 2. Hearing or audition.—The organ of hearing is the ear. More precisely, this organ is the terminals of the acoustic or hearing nerve in the basilar membrane of the inner ear. Other parts of the outer and inner ear assist in receiving and transmitting the vibrations which affect this organ. Sensations of hearing are effected by the sound-vibrations of the air, which are carried through the channels of the ear to stimulate the terminals of the acoustic nerve. 3. Smell or olfaction.—The organ of smell is the nose, or, more exactly, the terminals of the olfactory or smelling nerve, which appear as cells in the membrane that lines the upper nose. The sensation of smelling is aroused when tiny particles of an odorous body are drawn into the nostrils by breathing and are so brought into contact with the olfactory cells. 4. Taste or gustation.—The organ of taste is made up of the papillae or “buds” which are distributed over the tongue and palate. These buds are the terSENSE-KNOWLEDGE 55 minals of the gustatory or tasting nerve. The sensation of tasting is aroused when a suitable bodily substance (called sapid) comes into contact, while in solution, with the taste-buds.

Z. Touch or feeling.—The organ of touch is a system of papillae in the dermis or under-skin, and is distributed, but not evenly, over the whole body. The papillae of the tactual or touching system are the terminals of the touching nerve. When suitable objects come in contact with these terminals, the sensation of touching results. Touch is a complex sense, and it reports several sensations, such as pressure, weight, temperature (that is, hot and cold, not precise degrees of temperature), pain, muscular sensations of movements, strain, friction.

Object of the External Senses

I. Sight.—The object of sight is light. In light we distinguish intensity and color. It is the latter, viz., color, that is the proper object of sight. Color must be extended to have real bodily character, and it takes this extension in or on the surface of bodies.

Hence we may say at once that the proper object of sight is colored surface. For an object to be visible, it must have color. The color must be neither too vivid and overwhelming (as is the sun at noonday in summer), nor too dim, nor extended over too small a surface. In a word, for sight to function properly, its object must be proportioned to the sense. Further, the sense itself must be organically normal, and it must be employed in a suitable medium of adequate clear light. 2. Hearing.—The proper object of the sense of hearing is sound. Sound may be loosely classified as noise and tone, and it varies in volume and in pitch.

Sound is emitted by bodily vibrations which are carried by the air to the organ of hearing. For hearing to function properly, sound must be proportioned to the organ, and therefore must be neither too intense nor too faint; the organ itself must be normal, and the medium must be suitable and unobstructed. 3. Smell.—The proper object of the sense of smell is odorous bodily substance. To function properly, the sense must be organically normal, and the object must be neither too strong nor too faint for the proper stimulation of the olfactory cells in the membrane of the upper nose. The sense of smell tires very quickly, and if the stimulation be unvaried and long continued, the object will be no longer perceived as odorous at all, or, at least, its precise quality of odor will not be accurately sensed. 4. Taste.—The proper object of the sense of taste is sapid substance, that is, bodily substance capable of solution in saliva, and suitable, when in solution, to stimulate the taste-buds of tongue and palate. For proper functioning, the structure and condition of the taste-organ must be normal, and the sapid substance must be suitably flavored for stimulating the taste-buds, that is, the object must be neither too strong nor too faint. Taste becomes ill-conditioned, and ceases to function normally, when stimulation is unvaried and long continued. Further, stimulation by one flavor renders taste temporarily ill-conditioned for accurately perceiving another. Even a sweet orange tastes sour after one has been eating candy. 5. Touch.—It is difficult to name the proper object of touch in a simple word or phrase, for this is a very complex sense. The proper object of this sense may, however, be loosely indicated as resistance and temperature. For proper functioning, the object of this sense must come in sufficiently forceful contact with the papillae of touch in the dermis or underskin, and the contact must be effected where the papillae are sufficiently numerous to enable the sense to grasp its object adequately. The papillae are most numerous in the finger-tips.

This is not the place to discuss the validity of sense-knowledge, but it is well to indicate here the conditions that must be verified in external senseknowledge before there can be any question of validity or any criticism of the value of such knowledge.

These conditions are the four that follow: (a) The sense must be normal in organic structure and condition. (b) The sense must be employed upon its proper object, (c) The proper object must be proportioned to the sense, its impression being neither too strong nor too faint. (4) The medium in which the sense operates must be suitable for its normal functioning. We shall find in a later chapter that, when these conditions are met, the senses give us knowledge that is infallibly true.

Summary Of The Article

In this article we have enumerated the five external senses, and have classified them as superior (sight, hearing) and inferior (smell, taste, touch).

We have studied the five external senses in some detail, indicating the organ of each, the stimulus that arouses it to function, and the proper object. Finally, we mentioned the conditions under which the senses must function to give us reliable knowledge.