Auditory cortex

“ But we do know that each sense has its special cortical area, and that adjacent to these sensory areas are portions of the cortex intimately concerned in response to different classes of complex stimuli. Near the auditory center the cortex is concerned in recognizing spoken words, and in following music; near the visual center it is concerned in recognizing printed words, in recognizing seen objects, in finding one's way by the sense of sight, etc. These special aptitudes thus have a fairly definite cortical localization, and possibly others have also. ”

“ It is owing to them and to their mechanism that we ought to feel, from the same excitant, a sensation of sound or one of colour, that is to say, impressions which appear, when compared, as the most different in the world. Now, so far as we can make out, the histological structure of our auditory centre is the same as that of our visual centre. ”

“ The function of the organs of hearing, therefore, is to impart faithfully to the auditory nerve, every condensation and rarefaction occurring in the surrounding medium. The function of the auditory nerve is to bring to our consciousness the vibrations of matter resulting at the given time, both according to their number and their magnitude. Here, first, certain combinations acquire a distinct name: here, first the vibrations become musical tones or discords (Misstöne) . ”

“ The auditory center, A, receives the nervous impulses started by sound. When it is aroused by impulses coming from the ears, the sensation of sound occurs; but when it is aroused by nerve-currents, not from the ears, but from other parts of the brain, we have only the memory of sound. For a word to be understood, the auditory center alone is not sufficient. The sound must awaken the memories of other sensations. ”

“ The auditory center of the brain often spoken of is not simply theoretical, but is defined with fair certainty. If, in a dog or an ape, a particular spot in the temporal fold of the cerebrum is destroyed on both sides, the animal will be made deaf, although his ear-organs have not been disturbed. ”

“ And though, in the case of hearing, we cannot so clearly trace the connexion of cause and effect, yet as we see that the auditory apparatus is one fitted to intensify those vibrations constituting sound, and to convey them to a receptacle containing liquid in which nerves are immersed, it can scarcely be doubted that the sensation of sound proximately results from molecular re-arrangements caused in these nerves by the vibrations of the liquid: knowing, as we do, that the re-arrangement of molecules is in all cases aided by agitation. ”

“ This end-organ in the cochlea may be compared very fitly to the telephone which receives the message, and that portion of the brain where the auditory tract ends, to the telephone at the distant end of the path, the listener there representing consciousness. The auditory path within the brain is long and complicated, there being, in fact, many way-stations through which the message passes before it reaches the final one. ”

“ In highly differentiated cells, however, it is not only the quantity, or intensity of the stimulus that is to be considered, but also the quality. The visual sense organ is not affected by auditory stimuli nor can the auditory sense organ be affected by visual stimulations. Similarly, in the functioning of the higher psycho-physiological systems the quality of the stimulus should not be overlooked. Systems that remain inactive under one set of stimuli, however intense, will respond to another set of a different quality. ”

“ Auditory phenomena may be divided into two categories: provoked automatisms, and spontaneous automatisms or clairaudience. The first may be considered as hallucinations induced by diverse methods. The [182] simplest method consists in the use of certain shells, horns, trumpets, or, in a word, any object capable of augmenting and allowing the perception of those external or internal sounds, which are not usually perceptible to the hearing. This is what is observed particularly with some sea-shells. When we apply them to the ear, we hear a murmur or a slight rumbling sound. ”

“ The internal ear is formed by an involution of the integument, and not by an outgrowth of the brain. But tissue, in connexion with it, becomes in part changed, thus forming the auditory nerve, which places the tegumentary sac in direct communication with the brain itself. ”

“ There is every reason then to believe that auditory tonal images are the sole primary and essential guides to the minute alterations of tension in the muscles of the larynx necessary for the production of corresponding vocal sounds. By humming a tune we concentrate our attention and thereby limit the activity of neural processes to systems and communities of neurones employed for the perception of tonal images and their activation in motor processes ”

“ Then 800 pulses of air will reach the ear each second, and the ear drum, being flexible, will respond and will vibrate at the same rate. The vibration of the ear drum will be transmitted by the three bones and the fluid to the fibers of the auditory nerves. The impulses imparted to the auditory nerve reach the brain and in some unknown way are translated into sound. ”

“ The parts which intervene between the optic and auditory nerves, being proportionably less, for instance, in brutes, will not admit of so great a variety of associations between the several ideas of these senses, because the optic and auditory nerves cannot have so great a variety of connexions and communications with each other. ”

“ And even though he be a physiologist, and knows that the force of sensation in this case is due to the propagation of vibrations to the auditory centre by other channels than the usual one of the ear, the deeply organized impulse to measure the strength of an external stimulus by the intensity of the sensation asserts its force. ”

“ If in other nervous arcs the structure is merely automatic, and can display no phenomena of itself, but requires the influence of an external agent—the optical apparatus inert save under the influence of light, the auditory save under the impression of sound—the cerebrum, being precisely analogous in its elementary structure, presupposes the existence of some agent to act through it. ”

“ Communication exists externally with the middle ear by the round and oval windows and internally with the internal auditory canal, through which passes the eighth cranial or auditory nerve, the special nerve of hearing, which is distributed to the inner ear only. ”

“ Acuteness of hearing requires the healthy action of the brain, and particularly of that portion of it from which the auditory nerve proceeds, combined with perfection in the structure and functions of the different parts of the ear. The best method, then, of retaining and improving the hearing, is to observe well the general laws of health, and particularly to avoid every thing that will in the least impair the structure or healthy action of the parts immediately concerned in the exercise of this function. ”

“ The pulses created in the air by a sounding body are received by the ear and the impulses which they impart to the auditory nerve pass to the brain and we become conscious of a sound. The ear is capable of marvelous discrimination and accuracy. "In order to form an idea of the extent of this power imagine an auditor in a large music hall where a full band and chorus are performing. Here, there are sounds mingled together of all varieties of pitch, loudness, and quality ”

“ Of those persons to whom music is but a confused mass of sounds, we may remark that almost all sing false. We are forced to think that they have the auditory apparatus so made, as to receive but brief and short undulation, or that the two ears not being on the same diapason, the difference in length and sensibility of these constituent parts, causes them to transmit to the brain only an obscure and undetermined sensation, like two instruments played in neither the same key nor the same measure, and which can produce no continuous melody. ”

“ Like the sense of sight and the sense of smell, that of hearing, even in its simplest grades, serves to bring the organism into relation with more or less distant bodies, so long as they are sufficiently sonorous to transmit the so-called "sound" vibrations through water or air to the sensitive organs which become attuned to receive such impressions.
An auditory organ does not seem to be present at all—certainly none has as yet been detected or inferred to exist—in many of the lower forms of life; while in other animals, though inferred to exist, it remains as yet unrecognized. ”

“ 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. ”

“ Here is a pigmentary spot to which we assign the dignity of the eye; there, a hair, an otocyst, which we call the auditory organ; and at the same time we assume that the spot is for seeing and the hair for hearing. As sight and hearing are known to us only as we have them, there results a deplorable misinterpretation of the sensorial function in animals. ”

“ Disease of the ear may obviously act in the same way, but, even apart from actual disease, various nervous disturbances favour the production of auditory hallucinations during sleep, and, in marked cases, even awake.
We may dream of listening to music in the absence of all external sounds having any musical character. In such cases, no doubt, the actual conditions [78] within the auditory mechanism are suggesting music to the brain, but the resulting music seems usually to be less definite, less rememberable, than when it forms around the nucleus of an external series of sounds. ”

“ It is obvious on this scheme that the cell which we have marked K may stand for the seat of either a resident or a remote sensation occasioned by the motor discharge. It may indifferently be a tactile, a visual, or an auditory cell. The idea of how the arm feels when raised may cause it to rise; but no less may the idea of some sound which it makes in rising, or of some optical impression which it produces. Thus we see that the 'mental cue' may belong to either of various senses; and that what our diagrams lead us to infer is what really happens ”

“ The vocal movement of saying the name is made in response to the auditory stimulus of hearing the name, but when the neurone in the "speech center" is thus made active, it takes up current also from the axon that reaches it from the visual center, even though the synapse between this axon and the speech neurone is far from close. This particular synapse between the visual and the speech centers, being thus exercised, is left in an improved condition. Each neurone in the diagram represents hundreds in the brain, for brain activities are carried on by companies and regiments of neurones. ”

“ The sonorous figures are formed in the auditory organ, and even in the auditory nerves, just as they have been represented upon an infinitely small scale in the air. The nerve becomes in hearing a sonorous figure. ”

“ In the middle of the parterre.' It is clear that the pure audile, seeking to develop only a single one of his faculties, may, like the pure visualizer, perform astounding feats of memory—Mozart, for example, noting from memory the Miserere of the Sistine Chapel after two hearings; the deaf Beethoven, composing and inwardly repeating his enormous symphonies. On the other hand, the man of auditory type, like the visual, is exposed to serious dangers; for if he lose his auditory images, he is without resource and breaks down completely. ”

“ In these cases the damaged or un practiced auditory center recognizes but a part of what is heard, but this is enough to suggest to the well-practiced visual center the complete memory of the visual words, which then calls up their usual, possibly incorrect, sound and utterance, with the associated meaning.
As time passes, the strange sounds, through constant repetition and efforts to imitate them, grow familiar and become strongly associated with every-day experiences, so that as soon as a word is heard the idea is vividly present in consciousness. ”

“ In the commonest case, that of coloured hearing, any auditory stimulus arouses, along with the appropriate sensation of hearing, whether tone or noise, a visual image of light or colour. The sound of the word Tuesday, for instance, may be seen as a light grey-green followed by a yellow! We might suppose, at first thought, that coloured hearing is due to association, to a connection between sight and hearing set up in childhood and continued into adult life; but the evidence points to some inborn connection in the nervous system; coloured hearing tends strongly to run in families. ”

“ From the membrane vibrations pass along the chain of bones, (3, 4, 5.) The bone 5 communicates with the internal ear, (7, 8, 9, 10, 11, 11, 11, 12, 12, 12.) From the internal ear the impression is transmitted to the brain by the nerve, (13.)
971. The auditory nerve, like the optic, has but one function, that of special sensibility. The nerves which furnish the ear with ordinary sensibility, proceed from the fifth pair.
HYGIENE OF THE ORGANS OF HEARING.
972. Hearing, like the other senses, is capable of very great improvement. ”