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The Ear and Sound

THE HUMAN EAR
The Tomatis Method® is above all a pedagogy (education) of active listening; its goal is to give everyone the desire and the possibility to use his or her auditive function to its full potential and thus to enter into a real dynamic of communication.


However, in order to better understand the mechanisms, notably the psychological mechanisms, which can lead to dysfunction in communication, it is necessary to know how the human ear functions.

Ear


Physiology

  • The ear is formed of the outer part (auricle, outer auditory canal, tympanic membrane), the middle part (tympanic cavity, ossicles composed of the hammer, anvil and stirrup bone) and finally the inner ear (the labyrinth, composed of the vestibule and the cochlea).

  • The outer ear and the middle ear function in the air environment, whereas the inner ear functions in the liquid environment

  • Each part of the ear participates in the perception of sound. The purpose of this particular function is hearing, and its functioning can be impeded not only by mechanical causes, but also by psychological causes affecting the desire to listen to a greater or lesser degree.

  • The development of the listening function will condition a particular triad represented by verticality, laterality and language.

  • Correctly speaking, the sensorial organ is the membranous labyrinth, composed of the vestibule and the cochlea.

  • The vestibular part manages the balance of the body thanks to the utricle and the semicircular canals which also bring temporal and spatial awareness; thanks to the saccule, the vestibule also manages the awareness of body image. The two vestibules work in harmony.

  • The cochlear part assures both the differentiation of sounds and the cortical charge; this cerebral stimulation contributes to the constant evolution of the field of consciousness.

  • These two functions enable one to have a perception of the external and internal worlds which is constantly deepened, through sequential analysis on the one hand, and a quantitative analysis of frequency on the other.

  • The membranous labyrinth appears first in the development of the foetus; followed by the bone labyrinth, the middle ear, then the outer ear as protection, regulation and perfection of the system. The entirety of the auditory sensorial organ is constituted at four and a half months.

  • On a cellular level, the auditory cell is a aquatic ciliary cell, like the first sensorial cell; from the outset it plays the role of a stimulation sensor and both carries information and transforms these stimulations into electrical energy, thus participating in the activity of the brain and therefore in the vitality of the organism. Moreover, these cells give the first information on the surrounding space.

Sound

  • It circulates in an elastic environment in which the possibility of extension exists.

  • It results from vibratory movements represented in physics by a sinusoid (sinusoidal wavelength).

  • Its wavelength characterises the frequency in Hertz (Hz): the shorter it is, the higher the frequency.

  • Its intensity is expressed in decibels (dB): it is dependent on the amplitude of its wavelength and therefore on vibratory movement.

  • Its speed is all the greater in that the environment in which it develops becomes more dense, 330 m/s per sec in air, 1500 m/s in water and 5600 m/s in glass, respectively.

  • It is directly related to the phenomenon of acoustic resonance; in fact, through the emission of a particular note, any object which creates this note is itself set in movement (e.g., a singer can make a glass "sing" and if the sound intensity surpasses the resistance of the glass, the glass will break).

  • It is naturally complex: it contains a more or less basic low note which will contain and generate a whole range of more high-pitched harmonics.

  • To be pure, it must be created by a sophisticated technology; a classic audiogram in an anechoic room therefore does not really translate the usual auditory attitude.



Sound and the Ear

  • The human ear has an auditory spectrum ranging from 16 to 16,000 Hz; below this auditory spectrum lies infrasound and beyond, ultrasound.

  • The whispered voice is situated at 25 dB, the spoken voice at 60 dB, a rock band at 90 dB. The ear is in danger if it is exposed to 100 dB for a long period of time, the pain threshold is reached at 120 dB and a threshold of very serious danger is situated at 150 dB.

  • The discriminative ability of the ear allows for the fine analysis of sounds, this function going progressively from low-pitched to high-pitched sounds during childhood.

  • Solicited by several sounds, the ear can "choose", both voluntarily or non voluntarily, the sound which it wishes to focus on; in the case of automatic selection, it is not rare to see a psychological dimension appear, the subject blocking out the perception of certain frequencies over others.

  • The ear can focus on several sounds at once, provided that one of them is not clearly dominant, as a sound of strong intensity covers the totality of the sound environment through auditory saturation: this is the mask effect.

  • Bone conduction is favoured in relation to the air and aquatic environment; it is transmitted to the soft tissue and to liquids with a slight latency time. The transformation of sound from air to bone takes place through the tympanic membrane.

  • The ear has a complex system for the regulation of sound information: it is first of all pneumatic through the variation between the air pressures of the outer ear and the middle ear, neurological through the action of the glossopharyngeal nerve controlling the opening and closing of the Eustachian tube, mechanical through the mobilisation of the musculo-ligamental-ossicular apparatus of the outer ear and above all of the middle ear (the ossicles and the muscles of the hammer and the stirrup simultaneously playing on the tympanic membrane and on the oval window), liquid, finally, in the inner ear through the apparition of turbulence in the perilymph and the endolymph which shakes the basilar membrane where the sensorial cells are implanted.

  • It should be noted that three constant features are necessary for the correct functioning of the inner ear: regular temperature, good vascularisation, and normal physiological pressure.

  • The ear plays the role of a dynamo, participating very significantly in the charge of the cortex; in this function, high-pitch frequencies are very important, to the extent that they correspond to very dense iso-frequency zones in sensorial cells and are all the more stimulated when the sound is intense.

  • Listening, contrary to hearing, is a willed act expressing a real desire and making the whole body participate; as a result, one can easily appreciate the psychological dimension of The Tomatis Method® which is very much a pedagogy (education) of listening and the very particular attention paid to working on the listening posture.


The Propagation of Sound

  • Several theories on the propagation of sound exist, and notably that of Helmholtz, developed by Bekesy, and that of A. Tomatis corroborated by the results obtained thanks to his Method of listening education.

  • Bekesy's classic theory stipulates that sound passes through the ossicles, from the tympanum to the oval window, inducing the appearance of turbulence in the perilymph and the endolymph which shakes the basilar membrane where the sensorial cells are implanted; the cilia of these cells immobilised by the tectorial membrane are then activated in terms of a polarisation or a depolarisation which is expressed by a nervous stimulus. The round window is mobilised by the turbulence.

  • Tomatis's new theory stipulates that sound arrives to the tympanum, is transmitted to the sulcus tympanum, to the petrous pyramid, the bone labyrinth, the spiral ganglion and the membranous labyrinth. The tectorial membrane mobilises in relation to the basilar membrane, stimulating the cilia of the sensorial cells. The endolymph is set in movement: formation of endolymphatic, then perilymphatic turbulence occurs, the latter coming into collision with the round window and the oval window.

  • The outer ear has the same function in the two theories: the form of the auricle allows, through its specificity, on the one hand to apprehend certain pieces of information concerning the surrounding space and on the other, to give maximum focus to the sound wave which is then canalised by the external auditory meatus to be concentrated on the tympani. This action is increased by the tension of the auricular muscles, associated by a particular listening mimic of the muscles of the face and the cranium.

  • The middle ear plays the role of transmitter in the classic theory and of regulator-damper in the new theory.

  • The inner ear is not stimulated in the same way in the two theories: in the classic theory, there are propagation fibres in the basilar membrane which the sound wave stimulates through liquid propagation (this is Bekesy's turbulence). In the new theory, there is neither liquid propagation of the initial sound wave, nor propagation of the basilar membrane: in fact, on the one hand, air conduction becomes bone conduction as soon as it reaches the tympanum, and on the other hand, the existence of iso-frequency zones in the cochlea allows for a spontaneous analysis in relation to frequency and intensity.

 

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