When to Develop Interests.—It is to be noted further concerning many of these forms of interest, that youth is the special period for their development. The child who does not, during his early years, have an opportunity to develop his social tendencies, is not likely later in life to acquire an interest in his fellow-men. In the same manner, if youth is spent in surroundings void of æsthetic elements, manhood will be lacking in artistic interests. It is in youth also that our intellectual interests, such as love of reading, of the study of nature, of mathematics, must be laid.
Interests Must be Limited.—While emphasizing the importance of establishing a wide range of interests when educating a child, the teacher must remember that there is danger in a child acquiring too wide a range. This can result only in a dissipation of effort over many fields. While this prevents narrowness of vision and gives versatility of disposition, it may prevent the attainment of efficiency in any department, and make of the youth the proverbial "Jack-of-all-trades."
A study of the feeling of interest has been made at this stage on account of its close connection with the problem of attention, and in fact with the whole learning process. An examination of the other classes of feeling will be made at a later stage in the course.
CHAPTER XXV
SENSE PERCEPTION
Sensation and Perception Distinguished.—Sensation and perception are two terms applied usually without much distinction of meaning to our recognition of the world of objects. When, for instance, a man draws near to a stove, he may say that it gives him a sensation of heat, or perhaps that he perceives it to be hot. In psychology, however, the term sensation has been used in two somewhat different meanings. By some the term is used to signify a state of consciousness conditioned merely upon the stimulation of a sense organ, as the eye, ear, etc., by its appropriate stimulus. To others, however, sensation signifies rather a mental image experienced by the mind as it reacts upon and interprets any sensory impression. Perception, on the other hand, signifies the recognition of an external object as presented to the mind here and now.
Sensation Implies Externality.—When, however, a sensory image, such as smooth, yellow, cold, etc., arises in consciousness as a result of the mind reacting when an external stimulus is applied to some sense organ, it is evident that, at least after very early infancy, one never has the image without at once referring it to some external cause. If, for instance, a person is but half awake and receives a sound sensation, he does not ask himself, "What mental state is this?" but rather, "What is that?" This shows an evident tendency to refer our sensations at once to an external cause, or indicates that our sensations always carry with them an implicit reference to an external object. Leaving, therefore, to the scientific psychologist to consider whether it is possible to have a pure sensation, we shall treat sensation as the recognition of a quality which is at least vaguely referred to an external object. In other words, sensation is a medium by which we are brought into relation with real things existing independently of our sensations.
Perception Involves Sensation Element.—Moreover, an object is perceived as present here and now only because it is revealed to us through one or more of the senses. When, for instance, I reach out my hand in the dark room and receive a sensation of touch, I perceive the table as present before me. When I receive a sensation of sound as I pass by the church, I perceive that the organ is being played. When I receive a colour sensation from the store window, I say that I perceive oranges. Perception, therefore, involves the referring of the sensuous state, or image, to an external thing, while in adult life sensation is never accepted by our attention as satisfactory unless it is referred to something we regard as immediately presenting itself to us by means of the sensation. It is on account of this evident interrelation of the two that we speak of a process of sense perception.
Perception an Acquired Power.—On the other hand, however, investigation will show that this power to recognize explicitly the existence of an external object through the presentation of a sensation, was not at first possessed by the mind. The ability thus to perceive objects represents, therefore, an acquirement on the part of the individual. If a person, although receiving merely sensations of colour and light, is able to say, "Yonder is an orange," he is evidently interpreting, or giving meaning to, the present sensations largely through past experience; for the images of colour and light are accepted by the mind as an indication of the presence of an external thing from which could be derived other images of taste, smell, etc., all of which go to make up the idea "orange." An ordinary act of perception, therefore, must involve not merely sensation, but also an interpretation of sensation through past experience. It is, in fact, because the recognition of an external object involves this conscious interpretation of the sensuous impressions, that people often suffer delusion. When the traveller passing by a lone graveyard interprets the tall and slender shrub laden with white blossoms as a swaying ghost, the misconception does not arise from any fault of mere vision, but from the type of former knowledge which the other surroundings of the moment call up, these evidently giving the mind a certain bias in its interpretation of the sensuous, or colour, impressions.