This article throws light upon the three main types of tactual perception. The types are: 1. Solidity, Weight, Movement and Form of Tactual Perception 2. Space or Extension of Tactual Perception 3. Distance or Space of the Third Dimension of Tactual Perception.
Type # 1.
Solidity, Weight, Movement and Form of Tactual Perception:
We perceive solidity, magnitude, movement of objects directly by active touch or movement. Solidity or impenetrability is perceived directly by impeded or thwarted movement. Here there is intense muscular tension accompanied by intense sensation of pressure.
Weight is perceived through kinesthetic or motor sensation and pressure sensation when a body is lifted. Both sensations are necessary for the perception of weight.
But when the motor sensation is absent, the mere pressure sensation gives us some idea of weight, when, for example, a weight is placed on a palm which rests on a table. The correct weight of an object is always perceived the rough the combination of motor sensation with pressure sensations.
The movement of an object is perceived by passive and active touch. If a blind man touches a moving object without moving his own hand, he will have a succession of tactual sensations with different local signs. He knows that he is not the author of his change in tactual sensations.
Thus he knows that it is due to the movement of the object. Or he may follow the moving object with his moving hand. His tactual sensation will remain the same. But he will have a succession of changing muscular sensations. Though these motor sensations he knows the movement of the object.
The form, size, or magnitude of an object is directly perceived through active touch or movement. We explore the form of an object by movement and touch. The tactual and motor sensations give us the idea of its form directly.
The tactual sensations with different local signs combined with motor sensations yield the tactuo-muscular perception of form. For example, when we clasp a ball, we perceive its roundness from the quality of tactual sensations and kinesthetic sensations.
Coloured hearing is a typical example of synesthesia. Sounds are heard by some normal persons as if they possessed colours.
A deep tone is heard as dark blue, a trumpet as bright red, and so on. Different numbers are heard as possessing different colours. In synesthesia a sensation is experienced, when a different sense-organ is stimulated.
Acquired Auditory Perception of Space:
We cannot directly perceive distance and direction through hearing. We have only an indirect or acquired auditory perception of space.
(i) Auditory Perception of Distance:
A familiar sound e.g., whistle of a railway engine has been heard at different distances, its different degrees of intensity have been observed accurately. The greater is the distance, the fainter is the sound. The nearer is the distance, the louder is the sound. Different degrees of intensity of familiar sounds suggest different distances. But we cannot judge the distance of unfamiliar sounds accurately.
The other auditory cue to distance is complexity or frequency composition of sound. It can he used as a cue because high frequencies are more observed by the air and objects in the path of a sound than low frequencies are.
Hence a low-frequency sound can be heard from a greater distance than can a high-frequency sound low-pitched sounds of a log horn can be heard many miles away on the sea. When we hear the low notes better than the high notes, we judge the sound to be very distant.
Both intensity and frequency composition of sound are monaural cues (of one ear) we can judge distance with one ear.
(ii) Auditory Perception of Direction:
Auditory perception of direction depends upon three factors:
(i) A sound wave coming from the right side will reach the ear quickly arid the more time to reach the left car because it will go around the head. A sound wave coming from the left side will reach the car quickly and take more time to reach the right ear for the same reason.
When the sound wave is directly ahead, it will reach the two ears at the same time. Hence the time difference is a binaural cue to the perception of direction.
Young devised an instrument called a pseudophone which has two horns with two tubes. Two ears are fitted with two tubes. Sound from the left side is carried by the other horn to the left ear. A subject wearing this device is confused as to the source of sounds.
When a sound comes from the right, he turns to the left, and when a sound comes from the left, he turns to the right. His confusion persists until he adjusts himself to the new situation.
(ii) The phase of sound is another cue to the perception of direction. The sound wave striking, the nearer ear may be in a different pan of its cycle then when it strikes the farther ear.
(iii) The intensity of sound is another cue to the perception of direction. A sound striking the nearer ear is loud. A sound striking the farther ear is faint. Thus (1) time difference, (2) difference in intensity: and difference in phase are the cues to the perception of direction.
Generally auditory perception of distance and direction is aided by the movement. When we hear a sound come from the right side, we turn our heads towards this side and hear the sound distinctly. Normally we locate a sound by movement.
Different degrees and qualities of sounds are associated with movements repeatedly, through which we perceive distance and direction. So they suggest them later so that we have acquired auditory perception of distance and direction.
Type # 2.
Space or Extension of Tactual Perception:
Let us see how these three factors cooperate with one another in the blind man’s tactual perception of space. The blind man touches an extended object, e.g., a table with one or both hands simultaneously. But he does not move his hands.
This bare contact is called passive touch because it does not involve active movement from one part of an object to another. Stout calls it synthetic touch because it yields a total simultaneous impression of all or many parts of the object. Through the extensity of tactual sensations, the blind man perceives all or many parts of the objects simultaneously.
When his palms ate in bare contact with the table, the different parts of his palms are stimulated by different parts of the table, so that the tactual sensations produced by them have different local signs. Thus, through the local signs of the tactual sensations he perceives the different parts of the table as different from one another. Then he moves his fingertips from one part of the table to another in various ways.
Through the active movement of his finger-tips he perceives the distance, direction and position of the different parts of the table. This is called active touch because it essentially consists in active movement. Stout calls it analytic touch because it analyses and extended whole perceived by synthetic touch into a series of successive impressions.
Thus the perception of spatial order is due to the cooperation of synthetic and analytic touch with a unity and continuity of interest. Neither passive touch nor active touch alone suffices. Persons born blind acquire perception of space in this manner.
Type # 3.
Distance or Space of the Third Dimension of Tactual Perception:
By active touch or movement we can perceive distance directly. We can perceive a small distance by stretching out our hands or legs. We can perceive a long distance by walking or running. This is called active touch or movement. It contains two factors, viz.; (i) tactual sensations and (ii) muscular or motor sensations. Through active touch or tactuo-muscular sensations we can perceive distance directly.
Theories of the Perception of Space:
(i) Genetic Theory:
The English Associationists, Hume. J. S. Mill, Bain and Herbert and Spencer, hold that the idea of space is derived from the sensations by association. They are empiricists, and derive all ideas from experiences. They are advocates of the genetic theory of the perception of space.
(ii) Nativist Theory of Kant:
Kant, the great German philosopher, expounds an opposite view. The idea of space is a priori form of perception, which is supplied by the mind from within itself to the discrete sensations derived from external objects, which are not in space.
Sensibility supplies the a priori the idea of space to the manifold of sensations and arranges them in space. Thus it converts non-spatial sensations into spatial objects. Kant propounds the nativist theory of the perception of space. There is no space in the world. But the mind makes it a spatial order.
(iii) Theory of James:
William James advocates a sensationist form of nativist theory of the perception of space. All kinds of sensation, not only visual and tactual, have extensity or volume. The idea of extension is developed out of the extensity of sensations.
But we have already found that extension is not mere extensity. Simultaneous stimulation of an area of the skin or a part of retina gives an idea of extensity of tactual sensations or visual sensations but it cannot give the idea of extension which contains a formal factor, viz., order and arrangement of parts, which can be given by active touch, movement, or tactuo-muscular experience. So James’ view is not correct.
Kant’s view is repugnant to common experience of mankind. The world is perceived to be in space, in which external objects are perceived as exclusive of one another. So it is impossible to believe that the spatial order is a creation of the mind and that space is an a priori form of perception, a full-fledged subjective idea.
(iv) Wundt’s Theory:
Wundt maintains that the visual perception of space contains three elements, viz., qualities of optical sensations their local signs, and motor sensations of the eyes, which yield the idea of the space by creative synthesis. Creative synthesis is akin to chemical combination, in which certain components are combined into a new thing possessed of qualities which are not possessed by them.
We have explained the visual perception of extension in this manner. The tactual perception of space also similarly contains qualities of cutaneous sensations, their local signs, and motor sensations. The first two give an idea of a plurality of resisting objects, and the third gives an idea of order and arrangement among them. We have explained tactual perception of extension in this manner.
(v) McDougall’s Theory:
McDougall maintains that the mind has an innate capacity for moulding these physical elements into, the idea of space. It is a reaction of the mind to appropriate stimuli—a mental response. It combines the elements of truth in the nativist and genetic theories. It appears to be the correct view.