The Science of Human Nature: A Psychology for Beginners

by William Henry Pyle

Similarly, we hear only by means of the ears. If we are born deaf, or if injury destroys some important part of the hearing mechanism, then we cannot hear. In like manner, we taste only by means of the taste organs in the mouth, and smell only with the organs of smell in the nose. In a word, our primary knowledge of the world comes only through the sense organs. We shall see presently just how this sensing or perceiving is accomplished.

Dependence of Mind on Nerves and Brain. We have seen how in a general way the mind is dependent on the body. We have seen how in a more intimate way it is dependent on the special sense organs. But the part of the body to which the mind is most directly and intimately related is the nervous system. The sense organs themselves are merely modifications of the nerve ends together with certain mechanisms for enabling stimuli to act on the nerve ends. The eye is merely the optic nerve spread out to form the retina and modified in certain ways to make it sensitive to ether vibrations. In addition to this, there is, of course, the focusing mechanism of the eye. So for all the sense organs; they are, each of them, some sort of modification of nerve-endings which makes them sensitive to some particular force or substance.

Let us make the matter clear by an illustration. Suppose I see a picture on the wall. My eyes are directed toward the picture. Light from the picture is refracted within the eyes, forming an image on each retina. The retina is sensitive to the light. The light produces chemical changes on the retina. These changes set up an excitation in the optic nerves, which is conducted to a certain place in the brain, causing an excitation in the brain. Now the important point is that when this excitation is going on in the brain, we are conscious, we see the picture.

As far as science can determine, we do not see, nor hear, nor taste, nor smell, nor have any other sensation unless a sense organ is excited and produces the excitation in the brain. There can be no doubt about our primary, sensory experience. By primary, sensory experience is meant our immediate, direct knowledge of any aspect of the world. In this field of our conscious life, we are entirely dependent upon sense organs and nerves and brain. Injuries to the eyes destroying their power to perform their ordinary work, or injuries to the optic nerve or to the visual center in the brain, make it impossible for us to see.

These facts are so self-evident that it seems useless to state them. One has but to hold his hands before his eyes to convince himself that the mind sees by means of eyes, which are physical sense organs. One has but to hold his hands tight over his ears to find out that he hears by means of ears—again, physical sense organs.

But simple and self-evident as the facts are, their acceptance must have tremendous consequences to our thinking, and to our view of human nature. If the mind is dependent in every feature on the body with its sense organs, this must give to this body and its sense organs an importance in our thought and scheme of things that they did not have before. This close dependence of mind upon body must give to the body a place in our scheme of education that it would not have under any other view of the mind. We wish to emphasize here that this statement of the close relation of the mind and body is not a theory which one may accept or not. It is a simple statement of fact. It is a presupposition of psychology. By “presupposition” is meant a fundamental principle which the psychologist always has in mind. It is axiomatic, and has the same place in psychology that axioms have in mathematics. All explanations of the working of the mind must be stated in terms of nerve and brain action, and stimulation of sense organs.

Since the sense organs are the primary and fundamental organs through which we get experience, and since the sensations are the elementary experiences out of which all mental life is built, it is necessary for us to have a clear idea of the sense organs, their structure and functions, and of the nature of sensations.

Vision. The Visual Sense Organs. The details of the anatomy of the eye can be looked up in a physiological textbook. The essential principles are very simple. The eye is made on the principle of a photographer’s camera. The retina corresponds to the sensitive plate of the camera. The light coming from objects toward which the eyes are directed is focused on the retina, forming there an image of the object. The light thus focused on the retina sets up a chemical change in the delicate nerve tissue; this excitation is transmitted through the optic nerve to the occipital (back) part of the brain, and sets up brain action there. Then we have visual sensation; we see the object.

The different colors that we see are dependent upon the vibration frequency of the ether. The higher frequencies give us the colors blue and green, and the lower frequencies give us the colors yellow and red. The intermediate frequencies give us the intermediate colors blue-green and orange. By vibration frequencies is meant the rate at which the ether vibrates, the number of vibrations a second. If the reader wishes to know something about these frequencies, such information can be found in a textbook on physics.

It will be found that the vibration rates of the ether are very great. It is only within a certain range of vibration frequency that sunlight affects the retina. Slower rates of vibration than that producing red do not affect the eye, and faster than that producing violet do not affect the eye. The lightness and darkness of a color are dependent upon the intensity of the vibration. Red, for example, is produced by a certain vibration frequency. The more intense the vibration, the brighter the red; the less intense, the darker the red.