IMPORTANCE OF TOUCH.

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of degrees of pressure, and then on its clear separation of local characters. Finally, it may be observed that owing to the sharp definition of tactual sensation with respect to commencement and termination we may compare them in rapid succession, as we are unable to do in the case of sensations of taste and smell. This knowledge-giving value of touch is further increased by the constant co-operation with tactual sensations proper of the muscular sensations to be spoken of presently. There is little wonder, then, that from the time of Aristotle downwards touch has been regarded as a sense of the first importance. More than one writer has attributed man's intellectual superiority over the lower animals in no small measure to his possession of a pair of hands capable of deriving such a variety of distinct sensations from the objects with which they are brought into contact.

HEARING.

§ 21. Characteristics of Auditory Sensations. Hearing and sight are universally recognised as the highest senses. Here we see for the first time a perfectly differentiated complex organ. The peculiar form of the stimulus (air or ether vibrations) allows of the action of bodies on each of these organs at considerable distances. And just as they stand alone in respect of the delicacy and complexity of the physical apparatus involved, so they are marked off from the other senses by the rich and delicately-graduated variety of their sensations.

The peripheral organ, the ear, consists of the end-organ proper, that is, the special structures in which the nervefilaments terminate, and a mechanical apparatus for collecting and bringing to bear on these the air-vibrations which form the stimulus.

The structure of the ear is too complex for one to attempt a brief description of it here. The auditory fibres are distributed in a somewhat intricate way over the internal ear or labyrinth, and their terminal structures differ in different regions of this labyrinth. It is still very doubtful what the precise functions of these several nervous structures may be.'

1 For an account of the ear and its known functions, see Ladd, op. cit., p. 185 and following.

Sensations of sound exhibit numerous and definite differences of intensity. In the case of sounds of moderate intensity we can recognise fine distinctions of loudness or strength according as the stimulus increases in force or amplitude of movement.

A number of experiments have been carried out by Volkmann, Vierordt and others with a view to determine the threshold of intensity in the case of sounds, as well as the least noticeable difference of intensity. The results are not very definite. It may, however, be said with some probability that, with respect to the least noticeable difference of intensity, this corresponds roughly (according to Weber's Law) to the ratio 3:4 in the objective stimulus. That is to say, an objective sound must be strengthened in the proportion of about one-third in order that an increase of intensity in the resulting sensation may ensue.1

The superiority of hearing to the senses already considered is most plainly evident in respect of the qualitative differences of the sensations. The ear presents to us a rich variety of sensuous quality. All ordinary sounds yield complex sensations; and the ear, unlike the senses of taste and smell, is capable of easily distinguishing (within certain limits) the several constituent parts of its complex impressions. This power of analysis, aided by objective research, enables us to classify the sensations of sound with something like completeness.

The first division of sounds is into musical sounds or tones and non-musical sounds or noises. This distinction is known to be connected with a clearly-marked difference in the mode of stimulation. Musical sounds depend on regular or periodic vibrations, noises on irregular or non-periodic vibrations.

Physiologists have attempted to connect sensations of noise and those of tone with different parts of the auditory structure. There is some plausibility in the hypothesis that sensations of tone are brought about by the stimulation of the rods of Corti or the membrane on which these rest in the cochlea. But the precise physiological process involved in the case both of noises and of tones is a matter of uncertainty.

1 On the measurement of the intensity of auditory sensations, see Ladd, op. cit., p. 370 ft.; Wundt, op. cit., i. cap. viii. § 2; Stumpf has shown in a curious way that the discrimination of intensity is modified by the quality of the sound. Thus sounds of a high pitch are judged as louder than those of low pitch. See Stumpf, Tonpsychologie, i. § 15, p. 354 ff.

See Ladd, op. cit., pp. 195, 196; cf. Stumpf, Tonpsychologie, ii. p. 87 ff.

§ 22. Musical Sensations: (a) Pitch. The most important characteristic of a tone is what we call pitch or height. Every musical sound or tone has its particular pitch, without which it would cease to be musical. Differences of pitch constitute the most important qualitative differences among musical sensations. There are as many distinct varieties of musical sensation or tones as there are distinguishable pitches or heights. These differences are known to depend on the rate of vibration of the medium (the atmosphere). A tone of high pitch corresponds to a rapid series of vibrations, one of low pitch to a slow series.

Although for good reasons our modern scale recognises only discrete tones separated by at least a semitone, the ear can distinguish much finer differences of pitch. If the rate of vibration be gradually increased or decreased, we experience a continuous change of sensation in respect of height or pitch. Hence the scale of pitch is spoken of as a continuum of one dimension, represented by a straight line.

This scale of pitch is closely analogous to that of intensity. Thus there is a lower threshold below which the slow atmospheric vibrations no longer produce a continuous sensation of sound, but rather a succession of non-musical sensations. At the upper extremity of the scale there is a point of maximum. pitch above which any further acceleration of the vibrations is followed by a non-musical effect of grating sound. Once more, within these extremes the least noticeable change of pitchquality corresponds roughly with one and the same proportionate increase or decrease of the stimulus in respect of rapidity. The discrimination of pitch, it may be added, is much finer in the median region of the scale than towards the extremes.1

Individuals are known to vary greatly in their discrimination of pitch, and it is this which determines the musical capacity of the individual. Some persons are called 'note-deaf' because they do not distinguish tones even when separated by a semitone interval and more.2

1 On the nature of the scale of pitch the student should consult Ladd, op. cit., p. 317 ff.; and Stumpf, Tonpsychologie, ii. § 10.

These variations come out in the results of experimental inquiry into the scale of pitch. Thus one person's discrimination of pitch is represented by the ratio 440: 439 636; another person's by the ratio 1000'5: 1000. According to the experiments of Stumpf unmusical people are less certain than musical in their discrimina.

(b) Timbre. In addition to this scale of pitch-quality, there are the differences known as timbre or 'clang tint'.

These are the qualitative differences in sensations of tone answering to differences in the instrument, as the piano, the violin, the human voice. These differences have been explained by Helmholtz as due to differences in the mode of composition of the several kinds of tone. Musical clangs, such as those produced by the human voice, the violin, etc., though appearing to subjective observation simple sensations, have been shown by objective (physical and physiological) analysis to be compounded of a number of more elementary sensations. These correspond to a fundamental or ground tone and subordinate upper tones. The pitch, the number, and the relative intensity of these last determine the particular timbre of the clang.1

(c) Musical Harmony and Dissonance. Lastly, in considering musical sensations reference must be made to the important fact of harmony or consonance and dissonance among tones. This is mainly a difference of feeling, that is, of an agreeable and disagreeable effect. Yet there is a difference of presentative

character involved. In the case of consonant and dissonant tone-groups alike the ear is able to distinguish the constituent tones. Hence the effect is subjectively recognised as a complex sensation. In the case of consonance, however, there seems a partial blending of the constituent tones, whereas in that of dissonance the constituent tones remain more distinct. In addition to this, dissonance involves a rough grating character in the total sensation. This has been attributed by Helmholtz to the substitution for a smooth uniform mode of stimulation of an intermittent series of violent shocks or pulsations of sound.

tion of pitch; but he sets down their differences to want of judgment rather than to want of discriminative sensibility (op. cit., i. § 14). Grant Allen gives an account of a remarkable example of note-deafness, where a person failed to distinguish the pitch of a tone from that of another tone a third and even a sixth above it. (See Mind, iii. p. 157 ff.)

1 For a fuller account of the sensations of clang the reader should consult Helmholtz's great work, The Sensations of Tone, translated by A. J. Ellis. The recent investigations of Stumpf have brought to light the fact that clang-tint is not an ultimate difference of quality in sound, but is constituted by differences in the pitch and intensity of the constituent partial tones. See his elaborate examination of the subject, op. cit., ii. p. 539 ff.

MUSICAL SENSATIONS.

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It is not certain wherein consist exactly the physical and physiological sub. strata of sensations of musical harmony. According to the older theory it was supposed that since in the case of tones which accord well, as those constituting an octave or a fifth, the vibrations stand in a simple numerical ratio one to another, the sense of harmony involves a sort of unconscious reckoning. Translated into physiological language, this might mean that the periodic coincidence of the vibrations would be favourable to the nervous elements involved. According to the researches of Helmholtz, musical harmony depends on a purely negative condition, viz., the absence of 'beats,' or those alternating augmentations and diminutions of tone-intensity which, in place of uniform strength of stimulation, accompany dissonant combinations, and produce the characteristic effect of roughness. Such beats may occur by the interference of the partial tones (upper-tones) of any two compound tones or clangs. According to this view, these beats produce a disagreeable effect by acting unfavourably upon and fatiguing the nerve. More recently attempts have been made by Lipps, Wundt and others to re-discover a positive condition of musical harmony.1

8 23. Noises. In addition to this wide range of musical § sensation the ear distinguishes a vast number of non-musical sounds, the characteristic 'noises' of different substances, such as the roar of the sea, the rustling of leaves, and the crack of a whip. Although the precise nature of noises is not fully understood, it seems probable that they involve a rapid and irregular variation of sensations of sound. The peculiar character of a noise, as grating, crashing, seems to depend on the number, relative intensity, and mode of variation of these constituent sensations. At the same time just as ordinary tones, say those of a violin, have an accompaniment of noise, so most noises involve elements of tone, and owe a part of their character to this circumstance (e.g., the roar of the sea or of a crowd). This remark applies, among others, to articulate sounds. The researches of Helmholtz go to show that different vowel sounds are characterised by peculiarities of timbre and thus approximate to true musical sounds.2

§ 24. Value of Sense of Hearing. Enough has been said to show the high degree of refinement characterising the sense of hearing. The delicate and far-reaching discrimination of

1 See Helmholtz, Sensations of Tone, pt. ii. especially chap. x.; Th. Lipps, Psychologische Studien, p. 92 ff.; and Wundt, op. cit., ii., p. 63.

The relation of noises to musical tones, that is, sounds of even or unchanging pitch, is well brought out by Stumpf, op. cit., ii. p. 498 ff. Stumpf's reasoning goes to show that noises are only partially distinguishable from tones. At the same time this partial difference favours the view that noises implicate another set of nervestructures, peripheral and central, than those engaged in the production of tones.