In preceding chapters we have seen that in the phase of mental activity in which the Intellect is concerned, the processes of which are known as “Thought” in the narrower sense of the term, there are several stages or steps involving the use of several faculties of the mind. The first of these steps or stages is called _Perception_.
Many persons confuse the idea of Sensation and Perception, but there is a clear distinction between them. Sensations arise from nerve action–from the stimulation of nerve substance–which gives rise to a peculiar effect upon the brain, which results in an elementary form of consciousness. An authority says: “Sensation is the peculiar property of the nervous system in a state of activity, by which impressions are conveyed to the brain or sensorium. When an impression is made upon any portion of the bodily surface by contact, heat, electricity, light, or any other agent, the mind is rendered conscious of this by sensation. In the process there are three stages–reception of the impression at the end of the sensory nerve, the conduction of it along the nerve trunk to the sensorium, and _the change it excites in the sensorium itself, through which is produced sensation_.”
Just why and how this nerve action is translated into consciousness of an elementary kind, science is unable to explain. Our knowledge is based in a great part, or entirely, upon impressions which have been received over the channel of the senses–sensations of sight, hearing, tasting, smelling and touch. Many authorities hold that all of the five senses are modifications of the sense of touch, or feeling; as for instance, the impression upon the organs of sight is really in the nature of a delicate touch or feeling of the light-waves as they come in contact with the nerves of vision, etc. But, although sensations give us the raw materials of thought, so to speak, they are not _knowledge_ in themselves. Knowledge arises from the operation of Perception upon this raw material of Sensation.
But yet, Sensation plays a most active part in the presentation of the raw material for the Perceptive faculties, and must not be regarded as merely a physiological process. It may be said to be the connecting link between the physical and the mental activities. As Ziehen says: “It follows that the constitution of the nervous system is an essential factor in determining the quality of sensation. This fact reveals the obvious error of former centuries, first refuted by Locke, though still shared by naive thought today, that the objects about us themselves are colored, warm, cold, etc. As external to our consciousness, we can only assume matter, vibrating with molecular motion and permeated by vibrating particles of ether. The nervous apparatus selects only certain motions of matter or of ether, which they transform into that form of nerve excitation with which they are familiar. It is only this nerve excitation that we perceive as red, warm or hard.”
Passing from Sensation to Perception, we see that the latter interprets the reports of the former. Perception translates into consciousness the impressions of Sensation. Perception, acting through one or more of the mental faculties, gives us _our first bit of real knowledge_. Sensation may give us the impression of a small moving thing–Perception translates this into the thought of _a cat_. Sensation is a mere _feeling_–Perception is the _thought_ arising from that feeling. A Percept is the product of Perception, or in other words, our _idea_ gained through Perception. The majority of our percepts are complex, being built up from a number of minor percepts; as for instance, our percept of _a peach_ is built up from our minor percepts of the form, shape, color, weight, degree of hardness, smell, taste, etc., of the peach, each sense employed giving minor percepts, the whole being combined in the conscious as the whole percept of that particular peach.
Brooks says: “All knowledge does not come directly from perception through the senses, however. We have a knowledge of external objects, and we have a knowledge that transcends this knowledge of external objects. Perception is the _immediate_ source of the first kind of knowledge, and the _indirect_ source of the second kind of knowledge. This distinction is often expressed by the terms _cause_ and _occasion_. Thus perception is said to be the _cause_ of our knowledge of objects, since it is the immediate source of such knowledge. Perception is also said to be the _occasion_ of the ideas and truths of intuition; for, though in a sense necessary to these ideas, it is not the source of them. Perception also furnishes the understanding with materials out of which it derives ideas and truths beyond the field of sense. As thus attaining a knowledge of external objects, affording material for the operations of the understanding, and furnishing the occasion for the activity of the intuitive power, _perception may be said to lie at the basis of all knowledge_.”
Perception is of course manifest in all persons. But it varies greatly in degree and power. Moreover, it may be developed and cultivated to a great degree. As Perception is an interpretation of the impression of the senses, we often confuse the cultivation of Perception with the development of the senses themselves. Two persons of equally perfect sense of sight may vary greatly in their degree of Perception of sight impressions. One may be a most careless observer, while the other may be a very close observer and able to distinguish many points of interest and importance in the object viewed which are not apparent to the first observer. Cultivation of Perception is cultivation of the _mental background of the senses_, rather than of the sense organs themselves. The Perception accompanying each sense may be developed and cultivated separately from that accompanying the others.