How The Ear Works Popular

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Published on July 8, 2009

Author: beterhoren

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plus Slechthorend - .nl A different look at HEARING Do we hear perhaps different from what hearing experts assume? Willem Chr. Heerens

plus Slechthorend - .nl YES WE DO ! I say frankly According to physics our hearing sense can function completely different.

plus Slechthorend - .nl May I introduce myself  Willem Chr. Heerens [1940]  Masters degree in physics [1967]  Doctors degree in technical sciences [1979]  Earlier retirement as associate professor TU-Delft [1999]  Papers about hearing: http://www.een-andere-kijk-op-horen.nl/ [2003] 3

plus Slechthorend - .nl Relevant for my contributions in “hearing issues”: Technical expertise particularly in:  Mechanics : Membrane & plate displacements.  Vacuum technology & pressure measurement.  Physics transport phenomena & hydrodynamics.  Electricity & magnetism.  Sensor technology & electrical measurement techniques.  Fourier analysis & special function theory.  Differential & integral mathematics.  Complex function theory. 4

plus Slechthorend - .nl Hearing expertise:  Since 1985 as Ménière patient: “Expert in the field”.  During quite a couple of years “direct” observations of several hearing phenomena and effects.  Since 2001 Autodidact and theoretic hearing researcher.  Meanwhile designer of a revolutionary and alternative COCHLEAR MODEL Based on stringent application of laws and rules of physics.  What perhaps can lead to a paradigm shift 5

plus Slechthorend - .nl Therefore the intriguing title: According to physics our hearing sense can function completely different. 6

plus Slechthorend - .nl Points of criticism on the existing models:  Mostly they offer only solutions for parts of the total subject.  Too many phenomena remain unexplained.  Mostly unexplained phenomena are ascribed to functioning of the brain without clear evidence.  New refined investigations offer a growing number of anomalies that undermine the existing hearing sense models.  Respectable research quite often fails plausible logic explanation. But above all:  Several hypotheses declared as basic theory are in conflict with fundamental physics laws and rules. 7

plus Slechthorend - .nl Our hearing sense schematically :  Concha  Eardrum muscle  Outer ear channel  Cochlea  Eardrum  Hearing nerve  Ossicular chain. 8

plus Slechthorend - .nl The cochlea in detail: stirrup helicotrema oval window scala vestibuli organ of Corti scala media round window scala tympani 9

plus Slechthorend - .nl Scala media in detail: scala vestibuli tectoriaal Reissner membrane membrane inner hair cell outer hair cells scala media common connection to the brain basilar membrane hearing nerve scala tympani 10

plus Slechthorend - .nl A remarkable experiment from 1950: Ernest Glen Wever and Merle Lawrence: The acoustic pathways to the cochlea JASA 1950 July, 22: 460-467 Experiment:  In a cat’s ear they eliminated eardrum + ossicular chain.  They fabricated a tube around the round window to isolate it acoustically from the oval window area.  They stimulated with pure tones as follows: Stimulus only on the oval window. Stimulus only on the round window. Stimulus on both windows with different phases, varying in phase between 0o and 180o  They recorded the “cochlear microphonics”, the signal that is widely and directly brought into connection with the signal via the auditory nerve. 11

plus Slechthorend - .nl Results:  Independent stimulation of each window with the same signal resulted in equal changes in “cochlear microphonics” [CM].  Combined stimulation of both windows in the same direction [0o] resulted in: CM = 0  Stimulation of both windows in opposite directions [180o phase shift] resulted in: CM = maximal  That maximum was 6 dB higher than each of the two stimuli alone performed.  In-between phase settings evoked vectorial increase of CM from 0 to a maximum at phase differences of the stimuli from 0o to 180o. 12

plus Slechthorend - .nl Quite recently verified by: S.E. Voss, J.J. Rosowski, W.T Peake: Is the pressure difference between the oval and round windows the stimulus for cochlear responses? JASA(1996) Sep.,100(3): 1602-16. which resulted in:  Affirmation of the results of Wever & Lawrence. 13

plus Slechthorend - .nl Conclusions: Wever & Lawrence:  It is proven that the stimulation of the same sensory cells takes place via each of the two ways with the same intensity pattern.  Over almost the total frequency range a minimum in response is obtained if both waves stimulate in phase the oval respectively the round window. Voss, Rosowski, Peake:  The pressure differences between the oval and round window are in good approximation the effective acoustic stimulus for the cochlea. 14

plus Slechthorend - .nl My conclusions:  An electrical response [CM or CP] is only evoked in case of an evoked perilymph movement in the combined ducts of scala vestibuli [SV] and scala tympani [ST].  In case of maximal cooperation between the two in size equal stimuli [180o phase shift] the total movement stimulus is two times larger.  But then the changes in electrical response are not two but four times as large. Just because: 10 × 10log 4 = 6 dB  The electrical response in the inner ear is proportional to the square of the de perilymph velocity. 15

plus Slechthorend - .nl Our hearing sense is differentiating and squaring But then the question rises: Does there exist in physics such a relationship? And the answer is yes already known for a long time: Bernoulli’s law published in 1738. 16

plus Slechthorend - .nl And that law of Bernoulli is formulated as: In a floating liquid the sum of the static and dynamic pressure is constant. Static pressure = pressure on the walls of the duct. Dynamic pressure = pressure that the particles are evoking on each other due to their floating. Dynamic pressure is proportional to the square of the liquid velocity v and the density ρ of the liquid. 17

plus Slechthorend - .nl Bernoulli’s law expressed in a formula and applied on the cochlear duct: Pressure evoked on the wall of scala tympani, so also on the basilar membrane: ∆p = - ½ ρ v 2 ∆p : change in pressure [Pa] ρ : density perilymph [kg/m3] v : velocity perilymph [m/s] 18

plus Slechthorend - .nl To what result leads this for a single tone with frequency f ?  The sound wave evokes in front of the eardrum subsequent increases and decreases of pressure: ∆P = ∆P0 sin[2πf t]  The deflection of the eardrum is proportional to that: U = U0 sin[2πf t]  Via a reduction [by the ossicular chain] this also counts for the stirrup and the perilymph movement: A = A0 sin[2πf t] 19

plus Slechthorend - .nl  Deflection or displacement of the perilymph: A = A0 sin[2πf t]  Results into a velocity: v = A0 2πf cos[2πf t] Velocity = time derivative of deflection or displacement. 20

plus Slechthorend - .nl From perilymph velocity to membrane pressure presented in a figure: 21

plus Slechthorend - .nl  That pressure stimulus on the basilar membrane given by: ∆p = - ½ ∆p0 - ½ ∆p0 cos[4πf t] exists of: Not hearable static pressure stimulus: - ½ ∆p0 Proportional to the average sound intensity/energy. Hearable dynamic pressure stimulus: - ½ ∆p0 cos[4πf t] Proportional to the instantaneous sound intensity/energy. 22

plus Slechthorend - .nl And what happens in case of two tones with frequencies f1 and f2 ?  Sound wave  time dependent pressure increase and decrease according to: ∆P = ∆P1 sin[2πf1t] + ∆P2 sin[2πf2t]  And all the following mathematical steps are almost similar to those of one frequency, until the perilymph velocity  But then the squaring of the perilymph velocity must be carried out according to the following algebraic rule: (a + b)2 = a2 + 2ab + b2 23

plus Slechthorend - .nl The “mixed” term can be handled as follows:  Using goniometric rules for multiplied sinus and cosine functions: 2 cos a cos b = cos (a - b) + cos (a + b) finally for the contributions to the stimuli on the basilar membrane can be written:  The difference frequency contribution: - ½ ∆p0m cos[2π(f1 - f2) t]  The sum frequency contribution: - ½ ∆p0m cos[2π (f1 + f2) t] 24

plus Slechthorend - .nl The final result? Each two evoked pure tones f1 and f2 together result in five distinguishable signals on the basilar membrane, given as:  A frequency independent contribution proportional to the average sound intensity.  For each tone a one octave higher than the offered frequency signal: 2f1 respectively 2f2  A sum frequency f1 + f2  A difference frequency f1 - f2 = pitch or basal tone. 25

plus Slechthorend - .nl In the form of a figure: 26

plus Slechthorend - .nl But now you must realize the following:  At least according to physics not in our brain but in our hearing sense the missing fundamental or pitch is generated. And for the total nerve signal counts:  1 tone  1 frequency + 1 static signal 2 tones  4 frequencies + 1 static signal 100 tones  10.000 frequencies + 1 static signal Which is a real “ENIGMATIC CODE”. 27

plus Slechthorend - .nl The consequences:  Georg Von Békésy’s “mystery of the missing pitch” is no mystery anymore.  Therefore violin virtuoso Tartini could let his soprano violin sound as a cello.  On smaller church organs the 32 – feet pipe is missing. But if the organist let sound in the proper amplitude ratio simultaneously the 16 – feet and 10 2/3 – feet pipes, his audience will nevertheless hear that very low bass tone of that huge pipe. But their stomach does not vibrate as well. That only happens when that bass pipe really sounds.  The theoretical textbooks about “virtual pitch” in sound perception can be added to the historic archive. 28

plus Slechthorend - But there is more: .nl  Is a very young child be gifted with musical talent?  All those extra frequencies are unbearable to hear in a squaring hearing sense. Just construction not musicality. 29

plus Slechthorend - .nl What about the “Cochlear Amplifier”  The stressing of the tensor tympani gives a change in signal transfer of about 30 times.  The musculus stapedius also counts for a factor of approximately 30 times, maybe somewhat more.  Together an effect of 1.000 times on the stimulus of the oval window.  Due to the squaring this becomes 1.000.000 or 60 dB.  And the commanding signal for that? The static pressure signal on the basilar membrane can serve as such. 30

plus Slechthorend - .nl Consequences of that hypothesis? A static under pressure effect on the basilar membrane by any cause in the hearing sense result in hearing loss symptoms. Accompanied by pressure sensations in the ear.  The unpleasant hearing sensations during takeoff or landing of an airplane.  Increasing, sometimes temporarily, hearing impairment in case of increasing endolymfatic hydrops in Ménière patients.  Sudden deafness, which sometimes can heal also spontaneously.  Hearing impairment for airborne sound in case of the PET syndrome by pressure fluctuations in the middle ear cavity on the rhythm of the own breathing. 31

plus Slechthorend - .nl And the other extremes?  Due to degeneration of large areas in the organ of Corti, also resulting in reduced transfer of the static pressure signal, a loss of dynamic range, known as: Recruitment  By a trauma or other phenomenon caused reduction or even total loss of functioning of the tensor tympani and/or musculus stapedius: An extraordinary loud hearing of the somewhat louder sounds. A form of: Hyperacusis But for this last phenomenon there are more causes to give. 32

plus Slechthorend - .nl How does the phenomenon OAE fits in this model? Thesis:  If a Spontaneous Oto Acoustic Emission [SOAE] is a reaction on earlier heard signals and is generated by tensor tympani / musculus stapedius, than that SOAE must have clearly traces of tone combinations evoked by the squaring process in the inner ear.  That tone combinations must exist of: Two frequencies with in the middle of them a third frequency. The so-called “triplet” A singular frequency equal to the frequency differences in the triplet. The “pitch” belonging to the triplet. 33

plus Slechthorend - .nl Analysis of such an arbitrary SOAE spectrum: From the Nederlands Tijdschrift voor Natuurkunde September 2001 Emile de Kleine: “Ear sounds on a “wall-bed” [Title translated] 34

plus Slechthorend - .nl Determined spectrum: Table 1. Measured frequency peaks in OAE - spectrum Nr Freq. Peak Nr Freq. Peak Nr Freq. Peak 1 816 W 14 1741 W 27 3532 VW 2 870 M 15 1947 M 28 3668 VW VW very weak 3 966 M 16 2033 W 29 3795 W 4 1000 VW 17 2097 S 30 3847 W W weak 5 1056 S 18 2160 VW 31 3987 S M moderate 6 1172 M 19 2297 S 32 4180 M S strong 7 1240 VW 20 2564 VW 33 4288 VW 8 1286 S 21 2650 W 34 4452 W 9 1300 VW 22 2746 W 35 4572 W 10 1310 VW 23 2830 S 36 4660 S 11 1368 S 24 3138 W 37 4750 VW 12 1608 VW 25 3202 S 38 4840 VW 13 1674 S 26 3374 M 39 4898 W 35

plus Slechthorend - .nl Results:  3 triplets with accompanying pitch.  6 triplets without a pitch. But pitch frequency was lower than the lower boundary of 800 Hz. Example triplet + pitch:  Pitch Peak: 6 f : 1172 Hz  Triplet Peaks: 13 - 23 - 31 f : 1674 - 2830 - 3987 Hz. Triplet distances: 1156 respectively 1157 Hz. Accuracy generally within 1 % of the pitch distance. This cannot be an accident anymore ! 36

plus Slechthorend - .nl The valid hypothesis for OAE’s at this moment ? That sounds completely different:  Those tones are evoked by a simultaneous effort of the outer hair cells, that evoke a backwards traveling wave in the cochlea into the direction of the oval window, and that finally via the ossicular chain brings the eardrum in motion.  Which is in agreement with the common hypothesis of traveling waves in the cochlea. According to Georg von Békésy’s “Traveling wave theory” 37

plus Slechthorend - .nl But in 2004 the following paper was presented: Tianying Ren: Reverse propagation of sound in the gerbil cochlea Nature Neuroscience 7, pp 333 - 334 (2004) Brief Communications Subject of many discussions Pro and Contra. Experiment:  Laser interferometrical measurement of basilar membrane movements.  Simultaneous registration of stirrup movements.  With stimuli, normally evoking DPOAE’s [Distorsion Product OAE’s]. Measurement results:  There aren't found backwards traveling waves.  Only a wavy movement, which equal to the normally incoming sound runs from the round window into the direction of the helicotrema.  The stirrup moves a fraction earlier than the basilar membrane. 38

plus Slechthorend - .nl Ren’s unintentional attacks on Von Békésy’s “Traveling Wave Theory” An earlier paper of Ren was also a hot item: Longitudinal pattern of basilar membrane vibration in the sensitive cochlea Proceedings of the National Academy of Sciences - pnas.org PNAS | December 24, 2002 | vol. 99 | no. 26 | 17101-17106. Experiment:  Laser interferometrical measurements of the basilar membrane movement.  In the 13,3 – 19 kHz area of the basilar membrane of a gerbil. Results:  The movement of the basilar membrane, from the higher frequency side towards the lower side, is restricted to 300 µm on both sides of the point of maximum activity.  The shape of the movement was exactly symmetrical around this point. 39

plus Slechthorend - .nl How do we have to interpret that “wavy” movement of the basilar membrane ? In this we have to observe the following facts in physics: In a medium [gas, liquid , solid material] there exists a uniform relation between the propagation velocity v of sound or vibration, the frequency f and the wavelength λ of the sound or vibration wave: v=f×λ  v is lowest in gasses In air 330 m/s  v in water but also in perilymph 1500 m/s  v is highest in solid material to ca. 8000 m/s Together with the lowest [20 Hz] and highest [20.000 Hz] sound frequencies that we are able to hear, the wavelength varies in the perilymph from 75 meter to 7,5 cm. Always significantly larger than the size of the cochlea. 40

plus Slechthorend - .nl Consequences:  In the much shorter perilymph duct there cannot run a “sound wave”.  The perilymph between oval and round windows is just able to move forwards and backwards as a whole.  Tissue around the perilymph channel behaves more like a solid material than like a liquid.  That tissue needs a larger size for a traveling wave. Conclusion: There cannot propagate a traveling wave inside the cochlea. 41

plus Slechthorend - .nl But what kind of movement is observed then ? Therefore we must observe at first the way of movement of a singular resonator.  A resonator exist of a body connected to a spring, and is possessing in practice also damping.  If the body is given a deflection in opposite direction to the spring influence and that body is released, it will move harmonically with descending amplitude around the equilibrium point. The frequency in that case is known as resonance frequency fr  If the resonator is brought into a vibrating movement, then three different situations can exist, dependent on the relationship between stimulus frequency f and resonance frequency fr : with phase angle: f < fr reduced in phase movement 0 f = fr increase due to resonance but also a phase retardation ½π f > fr strongly reduced movement in opposite direction π 42

plus Slechthorend - .nl Followed by the remarkable mechanical setup of the basilar membrane: This basilar membrane [BM] exists of an array of small resonators, that have gradually decreasing resonance frequencies from the round window up to the helicotrema. And then in case of an everywhere equal in phase stimulus on the entire BM, the following is happening:  fr > f move in phase with the stimulus. All parts of the BM having  That movement becomes larger if fr approaches f closer and will retard gradually in phase. In case of resonance a large movement is and there exist a phase retardation of ½ π.  All parts of the BM with fr < f are more and more moving in opposite phase with the stimulus and with a growing decreasing in deflection. 43

plus Slechthorend - .nl And what phenomenon is comparable to this? The “wave” in the stadium! And dependent on the quality factor in resonance, strongly coupled to the rate of damping, the moving area becomes smaller, while the maximum deflection becomes larger.  On theoretical grounds it is no mystery that this “wavy movement” of the BM is always running from the round window [base] towards the helicotrema [apex] of the cochlea.  It is a locally bound reaction behavior on a universally existing stimulus.  Using the material specifications this behavior can be calculated in a 44 perfect way.

plus Slechthorend - .nl And if you calculate this and you make an animation movie of it, it looks as follows:  Round window Helicotrema  Basilar membrane f / fr = 0,1 Resonance point f = fr f / fr = 10  High frequencies low frequencies  45

plus Slechthorend - .nl But then the cochlear model still wasn’t complete. The fenomenon “Bone conduction” was still missing Based on my own experiences I observed that:  Bone conduction in principle does not differ that much from airborne hearing signals. So that stimulus should also undergo squaring.  The bone conduction signal is in my case extremely strong if it is evoking vibrations on places on the skull where the skull bones are relatively thin.  The construction of the cochlea inside the hardest bone in our body makes vibration transfer by means of deformation almost completely impossible. 46

plus Slechthorend - .nl And after a further study of the anatomy I found:  Next to the by me already known endolymphatic channel, between the cerebrospinal cavity and the cochlea there exists another direct connecting channel, the cochlear aqueduct.  The cochlear aqueduct connection is relatively close situated in the vicinity of the round window in the scala tympani and exchanges perilymph between cerebrospinal cavity and the cochlea. 47

plus Slechthorend - .nl And that brought me to the following hypothesis:  Contrarily to what is generally assumed, bone conduction signals aren’t generated by vibrations of the petrosal bone, the bone structure that surrounds the cochlea.  The “bone conduction” signal will be evoked by the push pull of perilymph via the cochlear aqueduct. And this happens on the rhythm of the vibration stimulus which is evoked elsewhere.  In that case every area forming a part of the surroundings of the cerebrospinal volume with a greater elasticity and flexibility can be a candidate for the introduction of the bone conduction stimuli. 48

plus Slechthorend - .nl Consequences of this hypothesis are:  Similar as airborne sound stimuli, bone conduction stimuli evoke movements of perilymph in the perilymph duct.  Due to the place where they are inserted in the cochlear duct, the movements evoked by bone conduction stimuli have opposite directions to those of the airborne stimuli.  The push pull movement via the cochlear aqueduct is divided between flow directly towards the round window and flow along the basilar membrane via helicotrema towards the oval window.  But due to the squaring effect according to Bernoulli’s law the bone conduction stimuli are transferred into the sound intensity signal, that will be sent to the brain. 49

plus Slechthorend - .nl What does this mean for the ENT- practice ?  In case a child has an otitis media the middle ear cavity will be filled by fluid and due to its incompressibility this fluid will hinder the deflection possibilities of the round window. So the movement will follow the easiest way. Along the basilar membrane via helicotrema, oval window, the ossicular chain and the eardrum to the external environment. The bone conduction signal evokes a higher velocity of perilymph in front of the basilar membrane in the affected ear. So there is also evoked a stronger signal.  The ENT-doctor puts a tune fork right in the middle of the child’s forehead, and ask the child: “In which ear you hear the tone the best?”  The child will indicate its infected ear. The ENT-doctor will say: Weber’s lateralisation is directed towards the affected ear. 50

plus Slechthorend - .nl Or in case of a more complex case:  If the Eustachian tube remains permanently open, like f.i. in case of the PET syndrome, the voice of the patient creates also a varying pressure in the middle ear. Under that pressure variations the eardrum will start to move and will not only transfer that motion to the ossicular chain, but will also put the perilymph in the cochlea into motion. But now with the same phase as the bone conduction sound signal, so this PET sound stimulus contribution and the also existing normal “bone conduction signal” are added up and create a higher total signal.  Together with the impaired hearing mentioned before, the patient will hear his own voice louder and starts to speak at a lower level. 51

plus Slechthorend - .nl An utmost tragic hearing history:  End 1993 a woman got an enormous slam on her left ear. She developed not only in that ear, but in a somewhat moderate way also in her right ear an intense strong hyper sensitivity for all sounds above the minimum. Nobody believed her, so she was treated for almost 6 years as a psychiatric patient. Until she read in a tabloid that her hearing problems have a name: Hyperacusis. Now again after visiting a number of hearing experts during years she is still confronted with much skepticism and there is no adequate aid for her. Actually experts still doesn’t believe her, because they don’t see reasons why a left side acoustic trauma can also create hyperacusis on the right side. And they observe her more as a neurotic person than as someone with a serious hearing problem.  But with the perilymph push pull according to my cochlear model, hyperacusis is no longer something extravagant, but can be the result of overstretching the membranes on both sides. A completely normal phenomenon. Perilymph movements can be strongly enlarged, and after the squaring an utmost strong signal inside the cochlea can be evoked. 52

plus Slechthorend - .nl Meanwhile on the website: http://www.een-andere-kijk-op-horen.nl/ like the cases explained here, you can find a number of hearing phenomena that are explained in a logic and plausible way by using my proposed cochlear model. And this list is still growing. 53

plus Slechthorend - .nl Final conclusion: In case my cochlear model can be proven by reliable experiments as being correct, I am convinced that I have offered you here a view on The holy grail of our auditory sense If not, than I can start to enjoy my pension. Thank you for your attention. 54

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