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.

Perception in Adult Life.—In our study of general method, sense perception was referred to as the most common mode of acquiring particular knowledge. A description of the development of this power to perceive objects through the senses should, therefore, prove of pedagogical value. But to understand how an individual acquires the ability to perceive objects, it is well to notice first what takes place in an ordinary adult act of perception, as for instance, when a man receives and interprets a colour stimulus and says that he perceives an orange. If we analyse the person's idea of an orange we find that it is made up of a number of different quality images—colour, taste, smell, touch, etc., organized into a single experience, or idea, and accepted as a mental representation of an object existing in space. When, therefore, the person referred to above says that he perceives an orange, what really happens is that he accepts the immediate colour and light sensation as a sign of the whole group of qualities which make up his notion of the external object, orange, the other qualities essential to the notion coming back from past experience to unite with the presented qualities. Owing to this fact, any ordinary act of perception is said to contain both presentative and representative elements. In the above example, for instance, the colour would be spoken of as a presentative element, because it is immediately presented to the mind in sensuous terms, or through the senses. Anything beyond this which goes to make up the individual's notion orange, and is revived from past experience, is spoken of as representative. For the same reason, the sensuous elements involved in an ordinary act of perception are often spoken of as immediate, and the others as mediate elements of knowledge.

Genesis of Perception.—To trace the development of this ability to mingle both presentative and representative elements of knowledge into a mental representation, or idea, of an external object, it is necessary to recall what has been noted regarding the relation of the nervous system to our conscious acts. When the young child first comes in contact with the world of strange objects with which he is surrounded, the impressions he receives therefrom will not at first have either the definite quality or the relation to an external thing which they later secure. As a being, however, whose first tendencies are those of movement, he grasps, bites, strokes, smells, etc., and thus goes out to meet whatever his surroundings thrust upon him. Gradually he finds himself expand to take in the existence of a something external to himself, and is finally able, as the necessary paths are laid down in his nervous system, to differentiate various quality images one from the other; as, touch, weight, temperature, light, sound, etc. This will at once involve, however, a corresponding relating, or synthetic, attitude of mind, in which different quality images, when experienced together as qualities of some vaguely felt thing, will be organized into a more or less definite knowledge, or idea, of that object, as illustrated in the figure below. As the child in time gains the ability to attend to the sensuous presentations which come to him, and to discriminate one sensation from another, he discovers in the vaguely known thing the images of touch, colour, taste, smell, etc., and finally associates them into the idea of a better known object, orange.

figure

A. Unknown thing. B. Sensory stimuli. C. Sensory images. D. Idea of object.

Control of Sensory Image as Sign.—Since the various sense impressions are carried to the higher centres of the brain, they will not only be interpreted as sensory images and organized into a knowledge of external objects, but, owing to the retentive power of the nervous tissue, will also be subject to recall. As the child thus gains more and more the ability to organize and relate various sensory images into mental representations, or ideas, of external objects, he soon acquires such control over these organized groups, that when any particular sensation image out of a group is presented to the mind, it will be sufficient to call up the other qualities, or will be accepted as a sign of the presence of the object. When this stage of perceptual power is reached, an odour coming from the oven enables a person to perceive that a certain kind of meat is within, or a noise proceeding from the tower is sufficient to make known the presence of a bell. To possess the ability thus to refer one's sensations to an external object is to be able to perceive objects.

Fulness of Perception Based on Sensation.—From the foregoing account of the development of our perception of the external world, it becomes evident that our immediate knowledge, or idea, of an individual object will consist only of the images our senses have been able to discover either in that or other similar objects. To the person born without the sense of sight, for instance, the flower-bed can never be known as an object of tints and colours. To the person born deaf, the violin cannot really be known as a musical instrument. Moreover, only the person whose senses distinguish adequately variations in colour, sound, form, etc., is able to perceive fully the objects which present themselves to his senses. Even when the physical senses seem equally perfect, one man, through greater power of discrimination, perceives in the world of objects much that totally escapes the observation of another. The result is that few of us enter as fully as we might into the rich world of sights, sounds, etc., with which we are surrounded, because we fail to gain the abundant images that we might through certain of our senses.

Passing to a consideration of the senses as organs through which the mind is made aware of the concrete world, it is to be noted that a number of factors precede the image, or mental interpretation, of the impression. When, for instance, the mind becomes cognizant of a musical note, an analysis of the whole process reveals the following factors:

1. The concrete object, as the vibrating string of a violin.

2. Sound waves proceeding from the vibrating object to the sense organ.

3. The organ of sense—the ear.

figure

4. The nerves—cells and fibres involved in receiving and conveying the sense stimulus.

5. The interpreting cells.

6. The reacting mind, which interprets the impression as an image of sound.

The different factors are somewhat arbitrarily illustrated in the accompanying diagram, the arrows indicating the physical stimulation and the conscious response:

Of the six factors involved in the sensation, 1 and 2 are purely physical and belong to the science of acoustics; 3, 4, and 5 are physiological; 6 is conscious, or psychological. It is because they always involve the immediate presence of some physical object, that the sensation elements involved in ordinary perception are spoken of as immediate, or presentative, elements of knowledge.

CLASSIFICATION OF SENSATIONS

Our various sensations are usually divided into three classes as follows:

1. Sensations of the special senses, including: sight, sound, touch (including temperature), taste, and smell.

2. Motor, or muscular, sensations.

3. Organic sensations.

Sensations of the Special Senses.—As a study of the five special senses has been made by the student-teacher under the heading of physiology, no attempt will be made to explain the structure of these organs. It must be noted, however, that not all senses are equally capable of distinguishing differences in quality. For example, it seems quite beyond our power to recall the tastes and odours of the various dishes of which we may have partaken at a banquet, while on the other hand we may recall distinctly the visual appearance of the room and the table. It is worthy of note, also, that in the case of smell, animals are usually much more discriminative than man. Certain of our senses are, therefore, much more intellectual than others. By this is meant that for purposes of distinguishing the objects themselves, and for providing the mind with available images as materials for further thought, our senses are by no means equally effective. Under this heading the special senses are classified as follows:

Higher Intellectual Senses: sight, hearing, touch.

Lower Intellectual Senses: taste and smell.

Muscular Sensations.—Under motor, or muscular, sensations are included the feelings which accompany consciousness of muscular exertion, or movement. In distinction from the other sense organs, the muscles are stimulated by having nervous energy pass outward over the motor nerves to the muscles. As the muscles are thus stimulated to movement, sensory nerves in turn convey inward from the muscles sensory impressions resulting from these movements. The important sensations connected with muscular action are those of strain, force, and resistance, as in lifting or pushing. By means of these motor sensations, joined with the sense of touch, the individual is able to distinguish especially weight, position, and change of position. In connection with the muscular sense, may be recalled that portion of the Montessori apparatus known as the weight tablets. These wooden tablets, it will be noted, are designed to educate the muscular sense to distinguish slight differences in weight. The muscular sense is chiefly important, however, in that delicate distinctions of pressure, movement, and resistance must be made in many forms of manual expression. The interrelation between sensory impression and motor impulse within the nervous system, as illustrated in the figures on page 200, is already understood by the reader. For an adequate conscious control of movements, especially when one is engaged in delicate handwork, as painting, modelling, wood-work, etc., there must be an ability to perceive slight differences in strain, pressure, and movement. Moreover, the most effective means for developing the muscular sense is through the expressive exercises referred to above.

Organic Sensations.—The organic sensations are those states of consciousness that arise in connection with the processes going on within the organism, as circulation of the blood, digestion; breathing, or respiration; hunger; thirst; etc. The significance of these sensations lies in the fact that they reveal to consciousness any disturbances in connection with the vital processes, and thus enable the individual to provide for the preservation of the organism.

EDUCATION OF THE SENSES

Importance.—When it is considered that our general knowledge must be based on a knowledge of individuals, it becomes apparent that children should, through sense observation, learn as fully as possible the various qualities of the concrete world. Only on this basis can they build their more general and abstract forms of knowledge. For this reason the child in his study of objects should, so far as safety permits, bring all of his senses to bear upon them and distinguish as clearly as possible all their properties. By this means only can he really know the attributes of the objects constituting his environment. Moreover, without such a full knowledge of the various properties and qualities of concrete objects, he is not in a position to turn them fully to his own service. It is by distinguishing the feeling of the flour, that the cook discovers whether it is suited for bread-making or pastry. It is by noting the texture of the wood, that the artisan can decide its suitability for the work in hand. In fine, it was only by noting the properties of various natural objects that man discovered their social uses.

How to be Effected.—One of the chief defects of primary education in the past has been a tendency to overlook the importance of giving the child an opportunity to exercise his senses in discovering the properties of the objects constituting his environment. The introduction of the kindergarten, objective methods of teaching, nature study, school gardening, and constructive occupations have done much, however, to remedy this defect. One of the chief claims in favour of the so-called Montessori Method is that it provides especially for an education of the senses. In doing this, however, it makes use of arbitrarily prepared materials instead of the ordinary objects constituting the child's natural environment. The one advantage in this is that it enables the teacher to grade the stimulations and thus exercise the child in making series of discriminations, for instance, a series of colours, sounds, weights, sizes, etc. Notwithstanding this advantage, however, it seems more pedagogical that the child should receive this needful exercise of the senses by being brought into contact with the actual objects constituting his environment, as is done in nature study, constructive exercises, art, etc.

Dangers of Neglecting the Senses.—The former neglect of an adequate exercise of the senses during the early education of the child was evidently unpedagogical for various reasons. As already noted, other forms of acquiring knowledge, such as constructive imagination, induction, and deduction, must rest primarily upon the acquisitions of sense perception. Moreover, it is during the early years of life that the plasticity and retentive power of the nervous system will enable the various sense impressions to be recorded for the future use of the mind. Further, the senses themselves during these early years show what may be termed a hunger for contact with the world of concrete objects, and a corresponding distaste for more abstract types of experience.

Learning Through all the Senses.—In recognizing that the process of sense perception constitutes a learning process, or is one of the modes by which man enters into new experience, the teacher should further understand that the same object may be interpreted through different senses. For example, when a child studies a new bird, he may note its form and colour through the eye, he may recognize the feeling and the outline through muscular and touch sensations, he may discover its song through the ear, and may give muscular expression to its form in painting or modelling. In the same way, in learning a figure or letter, he may see its form through the eye, hear its sound through the ear, make the sound and trace the form by calling various muscles into play, and thus secure a number of muscular sensations relative to the figure or letter. Since all these various experiences will be co-ordinated and retained within the nervous system, the child will not only know the object better, but will also be able to recall more easily any items of knowledge concerning it, on account of the larger number of connections established within the nervous system. One chief fact to be kept in mind by the teacher, therefore, in using the method of sense perception, is to have the pupil study the object through as many different senses as possible, and especially through those senses in which his power of discrimination and recall seems greatest.

Use of Different Images in Teaching.—The importance to the teacher of an intimate knowledge of different types of imagery and of a further acquaintance with the more prevailing images of particular pupils, is evident in various ways. In the first place, different school subjects may appeal more especially to different types of imagery. Thus a study of plants especially involves visual, or sight, images; a study of birds, visual and auditory images; oral reading and music, auditory images; physical training, motor images; constructive work, visual, tactile, and motor images; a knowledge of weights and measures, tactile and motor images. On account of a native difference in forming images, also, one pupil may best learn through the eye, another through the ear, a third through the muscles, etc. In learning the spelling of words, for example, one pupil may require especially to visualize the word, another to hear the letters repeated in their order, and a third to articulate the letters by the movement of the organs of speech, or to trace them in writing. In choosing illustrations, also, the teacher will find that one pupil best appreciates a visual illustration, a second an auditory illustration, etc. Some young pupils, for instance, might best appreciate a pathetic situation through an appeal to such sensory images as hunger and thirst.

An Illustration.—The wide difference in people's ability to interpret sensuous impressions is well exemplified in the case of sound stimuli. Every one whose ear is physically perfect seems able to interpret a sound so far as its mere quality and quantity are concerned. In the case of musical notes, however, the very greatest difference is found in the ability of different individuals to distinguish pitch. So also the distinguishing of distance and direction in relation to sound is an acquired ability, in which different people will greatly differ. Finally, to interpret the external relations involved in the sound, that is, whether the cry is that of an insect or a bird, or, if it is the former, from what kind of bird the sound is proceeding, this evidently is a phase of sense interpretation in which individuals differ very greatly. Yet an adequate development of the sense of hearing might be supposed to give the individual an ability to interpret his surroundings in all these ways.

Power of Sense Perception Limited: A. By Interest.—It should be noted, however, that so far as our actual life needs are concerned, there is no large demand for an all-round ability to interpret sensuous impressions. For practical purposes, men are interested in different objects in quite different ways. One is interested in the colour of a certain wood, another in its smoothness, a third in its ability to withstand strain, while a fourth may even be interested in more hidden relations, not visible to the ordinary sense. This will justify one in ignoring entirely qualities in the object which are of the utmost importance to others. From such a practical standpoint, it is evidently a decided gain that a person is not compelled to see everything in an object which its sensuous attributes might permit one to discover in it. In the case of the man with the so-called untrained sense, therefore, it is questionable whether the failure to see, hear, etc., is in many cases so much a lack of ability to use the particular sense, as it is a lack of practical interest in this phase of the objective world. In such processes as induction and deduction, also, it is often the external relations of objects rather than their sensory qualities that chiefly interest us. Indeed, it is sometimes claimed that an excessive amount of mere training in sense discrimination might interfere with a proper development of the higher mental processes.

B. By Knowledge.—From what has been discovered regarding the learning process, it is evident that the development of any sense, as sight, sound, touch, etc., is not brought about merely by exercising the particular organ. It has been learned, for instance, that the person who is able to observe readily the plant and animal life as he walks through the forest, possesses this skill, not because his physical eye, but because his mind, has been prepared to see these objects. In other words, it is because his knowledge is active along such lines that his eye beholds these particular things. The chief reason, therefore, why the exercise of any sense organ develops a power to perceive through that sense, is that the exercise tends to develop in the individual the knowledge and interest which will cause the mind to react easily and effectively on that particular class of impressions. A sense may be considered trained, therefore, to the extent to which the mind acquires knowledge of, and interest in, the objective elements.