Observations on Man (6th edition)/Part I/Chapter II/Section V
Section V[edit]
THE SENSE OF HEARING.
The immediate organ of hearing appears to be the soft portion of the seventh pair of nerves, distributed in the cochlea, and semi-circular canals. What the particular uses of these cavities are, is not known. They bear some obscure likeness to the instruments commonly made use of for increasing either the loudness of sounds, or the effects of them upon the ear; just as the coats and humours of the eye resemble lenses. The auditory nerve is also like the optic in detaching no branches off to the neighbouring parts; and there are many other instances of resemblance between these two most refined and spiritual, if one may so say, of our senses; some of which I shall mention in the course of this Section.
The auricle and meatus auditorius are cartilaginous, and seem by this means to be peculiarly fitted for receiving and retaining the vibrations of the air, and for communicating them to the membrana tympani.
This membrane appears to be kept in a state of constant tension by muscles, that act upon the small bones in different ways, and thus to be fitted for vibrating synchronously to the several sounds which affect it. Agreeably to which, the degree of tension varies, so as to be less when the musculus externus and obliquus act, greater when these are relaxed, and the internus acts. The degree of sensibility both in the membrane itself, and in the whole organ, is probably greater when the tension is greater.
The vibrations of the air seem to shake off the mucus which lodges upon the membrana tympani in the new-born child, just as the action of light fits the cornea, and aqueous humour, for vision.
The eustachian tube serves to supply the cavity of the tympanum with air, to carry off the vapour which exhales into it, and perhaps to increase the effects of sounds by the tremors in its cartilaginous extremity, and particularly those of the person’s own voice.
The stapes, its muscle, and the foramen ovale, seem designed to convey the vibrations of the membrana tympani to the auditory nerve, in a precise manner. But the vibrations excited in its æther may be much more frequent than those of the membrana tympani, as has already been observed.
There does not appear to be any method for conveying air into the cavities of the vestibulum cochlea, and semi-circular canals, nor any necessity or use for it there. The great hardness of the bony part of the organ of hearing may make it more easily susceptible of vibrations. Agreeably to which, it may be observed, that we can hear imperfectly, though the ears, nose, and mouth, be all stopped, and consequently all access to the membrana tympani by the vibrations of the air denied. The vibrations are here excited probably in the cartilages of the auricle and meatus, and in the bones of the skull, and thus communicated to the cochlea, and semi-circular canals. It seems to agree with this, that some partially deaf persons can hear best, when driven in a coach over stones or gravel; i.e. when all the parts of their bodies, and particularly those of the bones, are put into a vibrating motion.
The bony part of the organ of hearing seems to come to its full size early in life. Is not the final cause of this, that one part may, on account of its size, be most disposed to vibrate with one tone, another with another? And does not this hold particularly in respect of the lamina spiralis? For thus the same tone would be affixed and associated to the same nerves, so as to affect them peculiarly, from childhood or youth to old age.
Here we may consider, first, the different strength of sounds. Now, as this arises from the different condensation of the air in the pulses, so the effect which it has upon the membrana tympani, the membrane of the foramen ovale, and the nerves of hearing, must be different likewise, and afford the mind a sufficient foundation for distinguishing sounds in respect of strength and feebleness.
Secondly, the gravity and acuteness of sounds arise from the slowness or frequency of the vibrations. Now, as the vibrating of the membrana tympani are synchronous to those of the air, they may either excite synchronous ones in the particles of the auditory nerves, and thus be distinguished from each other in respect of frequency by the mind; or if every pulse of the air, and oscillation of the membrana tympani, excite innumerable infinitesimal vibrations in the auditory nerves, the renewal of these at different intervals according to the different gravity or acuteness of the sound will, however, afford a like criterion.
It may be remarked, that grave sounds are in general strong, acute ones feeble. For the bodies which yield grave sounds are in general large, and consequently will make an impression upon the air by a large number of trembling particles.
Thirdly, all very loud noises are disagreeable. Now it is easy to conceive, that very violent agitations of the membrana tympani may produce the solution of continuity in the small medullary particles of the auditory nerve. An inflammation in the small vessels of the auditory nerve may render it so susceptible of violent vibrations, as to be hurt by gentle sounds, as sometimes happens in distempers; and to produce that acuteness in the sense of hearing, which answers to the nyctalopia in the eye.
Fourthly, Single musical, i.e. uniform sounds, whether vocal or instrumental, are pleasant in proportion to their loudness, provided this be not excessive. We must therefore suppose here, that the repeated impulses of the air, at equal distances, make the vibrations approach to the solution of continuity; yet still so as to fall short of it.
Fifthly, Two musical notes sounded together, suppose upon an organ or violin, afford a greater original pleasure than one, provided the ratios of their vibrations be sufficiently simple. Thus any note sounded with its eighth, fifth, fourth, third major or minor, sixth major or minor, affords pleasure, the ratios being here, respectively, those of 1 to 2, 2 to 3, 3 to 4, 4 to 5, 5 to 6, 3 to 5, and 5 to 8, which are all very simple ones. But a note with its flat or sharp, second, or seventh, or flat fifth, is originally disagreeable. It may be observed also, that concords seem to be originally pleasant in proportion to the simplicity of the ratios by which they are expressed, i.e. in the order above set down. Hence we may perhaps suspect, that even the concords were originally unpleasant to the ear of the child, from the irregularity of the vibrations which they impress upon the membrana tympani, and consequent solution of continuity; and that they fell at last within the limits of pleasure, as many other pains do, by repetition. For thus those concords in which the ratios are simplest would become pleasant first, and the others would continue to excite pain, or to border upon it. It is agreeable to this, that discords become at last pleasant to the ears of those that are much conversant in music, and that the too frequent recurrency of concords cloys.
Sixthly, Concords sounded in succession seem to have the same effect, in kind, upon the ear, as when sounded together, only less in degree. But discords in succession do not offend, unless the chromatic succession of half notes, or some such remarkable ones, and even these please at last. All this follows easily from the last paragraph; and the present paragraph, with the two last, taken together, contain the principal grounds of the natural and original pleasures of music. The pleasures which it derives from association will be considered hereafter.
Sounds ought to decrease in the reciprocal duplicate ratio of the distance, did they not receive some support from the reflection of the bodies over which they pass. This makes them decrease in a less ratio; however, they do decrease in general with the distance; and this decrease, being an associate of the increase of distance, ought to suggest it to the imagination. And, agreeably to this, we may observe, that, when the wind opposes the sound of bells, they appear farther off; when a person calls through a speaking trumpet, he appears nearer, than at the true distance.
As to the position of the sounding body we have no clear or certain criterion, unless it be very near us; so as that the pulses may strike one ear, or one part of the head, considerably stronger than another. Hence we judge of the position of the speaker, or sounding body, by the eye, or by some other method independent on the ear. And thus, if from some mistaken presumption a voice, or sound, shall be deemed to come from a quarter different from the true place of it, we shall continue in that error from the strength of that mistaken presumption.
By laying these things together, and also considering farther, that indistinctness in articulate sounds is an associated mark of distance, we may see how ventriloqui, or persons that speak in their throats, without moving their lips, impose upon the audience. Their voice is faint and indistinct, and therefore appears to come from a more distant quarter than the speaker. The hearers look about therefore, and, being surprised, their imagination fixes strongly upon that corner, or cavity, which appears most plausible; and afterwards they continue to impose upon themselves by the strength of this prejudice.
One may suppose the external and internal ear to be so formed, as that all the differences in the vibrations of the air, which arrive at the ear, may affect the auditory nerves with corresponding differences. Let us therefore first consider in what manner different sounds impress different vibrations upon the air.
First, then, Since not only the parts about the throat, but those of the mouth, cheeks, and even of the whole body, especially of the bones, vibrate in speaking, the figure of the vibrations impressed upon the air by the human voice will be different from that of the vibrations proceeding from a violin, flute, &c. provided the distance be not too great. This therefore may be considered as one help for distinguishing articulate sounds from all others.
Secondly, Articulation consists in breaking out from a whisper into sound, or closing the sound in different manners, the organs of speech being put also into different shapes, so as to join the differences mentioned in the last paragraph with various eruptions and interruptions, ascents and descents of sound. And thus each letter may be distinguished from every other by hearing.
Thirdly, It is agreeable to all this, that it is difficult at great distances to distinguish the tone of one musical instrument from another, or of any from the tone of a human voice, cæteris paribus; or to distinguish articulate sounds from one another. For at great distances the vibrations of the air are circular to sense, and all the ascents, descents, eruptions and interruptions of sound, which distinguish one compound sound from another, are confounded by numberless reflections from the intermediate bodies.
Fourthly, We may observe, that as the preserving the distinction of place is the chief end of the coats and humours in the organ of sight, so the distinction of time is of the greatest importance in hearing. It seems probable therefore, that the membrana tympani, small bones, and their muscles, are so contrived, as by their actions to preserve the distinction of time, i.e. to extinguish strong sounds, and to keep up weak ones, so as that the last may not be too much overpowered by the continuance of the first; just as the treble notes of a harpsichord would be by the bass ones, did not the bits of cloth affixed to the jacks check the vibration of the strings in due time.
Having now shown how articulate sounds may be distinguished from one another, and from all other sounds; I next observe, that, in fact, the speakers do not pronounce so articulately and distinctly in common conversation, as to furnish the hearers with the requisite criterions according to the foregoing theory; but that we arrive at a facility of understanding one another’s discourse, chiefly by the power of association.
And, first, It is needless to pronounce every letter so as to distinguish it from all others. For then words, which are composed of letters, would each have as many criterions as they have letters, and even more; for the order of the letters is a criterion, as well as the sound of each letter. In like manner, sentences would have as many compound criterions as they have words, besides the criterion arising from the particular order of the words.
Secondly, Since words are formed from combinations, not according to any rule, which brings up all the combinations of twos, threes, &c. in order, but by particular associations, agreeably to the nature of each language, since also sentences are formed in the same way, the several component parts of words and sentences suggest each other, and also the whole words and sentences, by the power of association. Thus the beginning is commonly observed to suggest the whole, both in words and sentences; and the same is true, in a less degree, of the middles and ends.
Thirdly, The subject matter of the discourse, the gestures used in speaking, a familiar acquaintance with the particular voice, pronunciation, gestures, &c. of the speaker, and other associated circumstances, contribute greatly also. And therefore, on the other hand, we find it difficult to distinguish proper names, and the words of an unknown language, and to understand a person that is a stranger, or that uses no action.
We may see also, that it is chiefly by the means of associated circumstances, that the sounds uttered by ventriloqui suggest to us the words which they are supposed to pronounce; for their articulation must be very incomplete, as they do not move their lips at all.
It is by a like set of associated circumstances that we are enabled to read with so much facility the irregular hand-writing of various persons, and of some more than others, in proportion as we are better acquainted with the subject, language, handwriting, &c.
For the theory of sounds deduced from the nature of an elastic fluid, and the tremors of the particles of sounding bodies, and afterwards verified, as it has been, by numerous experiments, becomes a guide to us in all inquiries into the vibrations of other elastic mediums, such as the æther, and into the effects, which such vibrations must impart to and receive from the small particles that are surrounded by the elastic medium. And the general tendency which is found in natural bodies, either to yield a sound upon percussion, or at least to support and convey sounds by receiving isochronous vibrations, and reflecting them, shews, that there are latent active powers in the small parts of bodies, which dispose them to vibrate. Now, if there be such powers in the biggest component particles, analogy inclines one to expect them in the several descending orders.
The doctrine of sounds does also furnish us with an answer to one of the principal and most obvious difficulties attending the supposition, that all sensation, thought, and motion, is performed by vibrations in the medullary substance. For it may be objected, that such a number of different vibrations as seems to be required in certain cases, can scarce exist together in the medullary substance. Thus it is not uncommon for a person to receive a series of sensations, carry on a train of thought, and perform a course of external actions, which have little connexion with each other, at the same time. Now to this we may answer, that vibrations as different from each other do, in fact, exist together in common air, in such a manner as to be perceived distinctly. Thus a person may listen to what part he pleases in a concert of music, and masters in the art can listen to more than one. They can also at the same time receive, attend to, and understand the vibrations of the air, arising from the discourse of other persons. But in whatever manner these different vibrations can exist together precisely at the same instant, or rather succeed each other at infinitesimal intervals, without confusion; in the same manner may vibrations and vibratiuncles exist together, or succeed each other, without confusion also, in the medullary substance. And by whatever power the soul is qualified to attend to, and distinguish from each other, these several vibrations of the air, by the same power may it correspond to the vibrations in the medullary substance, so that each shall have its peculiar effect of producing the appropriated sensation, thought, and motion. It is to be observed farther, that there is a difficulty in performing both the things here mentioned; that confusion does often arise; and that where any person is remarkable for doing more than one thing at once, it is in consequence of great practice, and also of exquisite mental powers, i.e. of an exquisite make of the medullary substance, according to the theory of these papers.
As all moderate and tolerably uniform sounds please young children, and the original pleasures from concords sounded together, from the succession of both concords and discords, and even from clear musical sounds, considered separately, remain with us through the whole progress of life, it is evident, that many of our intellectual pleasures must be illuminated and augmented by them. And on the contrary, harsh, irregular, and violently loud noises must add something to the disagreeableness of the objects and ideas with which they are often associated.
The pleasures of music are composed, as has been already observed, partly of the original, corporeal pleasures of sound, and partly of associated ones. When these pleasures are arrived at tolerable perfection, and the several compounding parts cemented sufficiently by association, they are transferred back again upon a great variety of objects and ideas, and diffuse joy, good-will, anger, compassion, sorrow, melancholy, &c. upon the various scenes and events of life; and so on reciprocally without perceptible limits.
The corporeal pleasures from articulate sounds are either evanescent from the first, or, however, become so very early in life. By this means we are much better qualified to receive information, with mental pleasure and improvement, from them; and the ear becomes, like the eye, a method of perception suited to the wants of a spiritual being. And indeed when we compare the imperfections of such as have never heard, with those of persons that have never seen, it appears, that the ear is of much more importance to us, considered as spiritual beings, than the eye. This is chiefly owing to the great use and necessity of words for the improvement of our knowledge, and enlargement of our affections; of which I shall have particular occasion to treat hereafter. An accurate inquiry into the mental progress of persons deprived of the advantages of language, by being born deaf, would be a still better test of the theory of these papers, than a like inquiry concerning persons born blind.
The ideas which audible impressions leave in the region of the brain, that corresponds to the auditory nerves, are, next to the ideas of sight, the most vivid and definite of any; and all the observations above made upon the ideas of sight may be applied to those of hearing, proper changes and allowances being made. Thus, after hearing music, conversing much with the same person, in general disorders of the brain, or particular ones of the nervous spasmodic kind in the stomach, after taking opium, in dreams, in madness, trains of audible ideas force themselves upon the fancy, in nearly the same manner, as trains of visible ideas do in like cases. And it may be, that in passing over words with our eye, in viewing objects, in thinking, and particularly in writing and speaking, faint miniatures of the sounds of words pass over the ear. I even suspect, that in speaking, these miniatures are the associated circumstances which excite the action, be it voluntary, or secondarily automatic. For children learn to speak chiefly by repeating the sounds which they hear, i.e. these sounds are the associated circumstances which excite to action. But if the sound does this, the idea of it must get the same power by degrees. I grant indeed, that the pictures of words in the eye, and their ideas, may be like associated circumstances, exciting to speak; and since it is necessary, according to the theory of these papers, that every semi-voluntary, voluntary, and secondarily automatic action should be excited by an associated circumstance, one may reckon words seen, and their visible ideas, amongst the number of such circumstances. But words heard, and their audible ideas, have a prior claim; and, in persons who cannot read or write, almost the only one. It confirms this, that in writing one is often apt to mis-spell in conformity with the pronunciation, as in writing hear for here; for this may proceed from the audible idea, which is the same in both cases; cannot from the visible one. Where a person mis-spells suitable to a mispronunciation, which sometimes happens, it can scarce be accounted for upon other principles. However, in writing, the associated circumstance, which excites the action of the hand, is most probably the visible idea of the word, not the audible one.
If it be objected to the supposition of these audible trains, that we ought to be conscious of them, I answer, that we are in some cases; which is an argument, that they take place in all, in a less degree; that the greater vividness of the visible trains makes us not attend to or recollect them, till the consciousness or memory be vanished; and that even visible trains do not appear as objects of consciousness and memory, till we begin to attend to them, and watch the evanescent perceptions of our minds.
The ideas of sight and hearing together are the principal storehouse of the fancy or imagination; and the imaginative arts of painting and music stand in the same relation to them respectively. Poetry comprehends both by taking in language, which is the general representative of all our ideas and affections.
As there is an artificial memory relative to the eye, by which trains of visible ideas, laid up in the memory in a certain order, are made to suggest both things themselves, and the order in which we desire to remember them; so compendious trains of technical words formed into verses may be made to suggest other words, also the numeral figures in a certain order; and by this means, to bring to view, at pleasure, the principles and materials of knowledge for meditation, inquiry, and more perfect digestion by the mind, as appears from Dr. Grey’s Memoria Technica. The visible loci make a stronger impression on the fancy, and therefore excel the audible ones in that view; but the audible ones have a much more ready and definite connexion with the things to be remembered; and therefore seem most proper, upon the whole, in most branches of literature. And as Dr. Grey’s method is highly useful in general, so it is particularly excellent in respect of all memorables that are represented by numeral figures. For, when the numeral figures are denoted by letters, collections of them, such as dates, and quantities of all kinds, make short and definite impressions upon the ear; which are not only easy to be remembered, but also preserve the order of the figures without danger of error: whereas neither the impressions which collections of figures make upon the eye, nor those which their enunciations in words at length make upon the ear, can be remembered with facility or precision; because neither figures, nor their names, cohere together, so as that the precedent shall suggest the subsequent; as the letters do in collections of them, capable of being pronounced. When the technical word coincides with, or approaches to, a familiar one, it is remembered with greater facility. Association is every where conspicuous in these things.
It does not appear at all improbable, that the vibrations, which are excited by sounds in the cartilages of the auricle and meatus auditorius, should pass into the small muscles of the auricle, and there occasion automatic motions. And I guess in particular, that in very loud sounds, the cartilages would be made to lie closer to the head. But the smallness of these muscles, and the practice of binding down the ears of new-born children close to the head, which restrains the natural action of these muscles, whatever it might be, prevent our making any certain judgment.
As to the four muscles which belong to the small bones, it appears to me, that since the externus and obliquus lie out of the tympanum, exposed to the common air, and are also so situated, that the externus may receive vibrations from the cartilage of the meatus auditorius, the obliquus from the cartilage of the processus ravianus, into which it is inserted, they must be much more affected by loud sounds, than the internus or musculus stapedis. It follows therefore, that the membrana tympani will be relaxed automatically by loud sounds. Here therefore is another remarkable coincidence between efficient and final causes.
For what reasons the musculus internus, and musculus stapedis, may act peculiarly in weak sounds, is difficult to say. They may perhaps, as was above conjectured of the radiated fibres of the iris, depend chiefly on the influences which descend from the brain, and therefore act always, when the other two will give them leave. It is most probable, that the four muscles act in various proportions and combinations, so as to answer a variety of purposes. But there is very little, that is satisfactory, to be met with in books of anatomy and physiology hitherto, concerning the peculiar minute uses and functions of the several parts of the organ of hearing.
Since grave sounds are in general loud, acute ones weak, the relaxation of the membrana tympani, which first attends upon loud sounds automatically, will afterwards, by association, be made to attend upon grave ones, even though they are not loud; and, in like manner, the membrane will be tense, from acute sounds, though they should be strong; i.e. the membrane will, by association, be fitted to vibrate isochronously with the several tones; just as the convexity of the cornea is made by association to suit itself to the several distances. The accommodation is at first gross in both cases; but is perfected afterwards from the view of pleasure and convenience, by means of the frequent recurrency of the actions. See Prop. XXII. Cor. I.
We seem also to have a voluntary power of preparing the ear previously for very strong, or very weak sounds, which we expect to hear, just as it was before observed of the eye, that we can suit it previously to see at an expected distance. The generation of these powers is the same as that of the other voluntary ones.