Re: mechanical cochlear model (Mitchell Cotter )

Subject: Re: mechanical cochlear model From: Mitchell Cotter <mcotter7@xxxxxxxx> Date: Fri, 12 Mar 2010 13:19:53 -0500 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY> --00504502d33bf1a2f704819e936b Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Version:1.0 StartHTML:0000000200 EndHTML:0000008743 StartFragment:0000002936 EndFragment:0000008707 SourceURL:file://localhost/Users/user/Desktop/DwnloadSink/MAC_comments%20to= AUDITORY100312.doc Dear AUDITORY List people: I have been reading with respect the many extended comments on Mechanical Cochlear Model. I have been delighted to see the intense interest that the discussion has stimulated. I have a few points to make for consideration by the list. 1) So much of the discussion is naturally focused on the cochlear peripheral system as though it existed as an analyzer in itself. This reductionist perspective separates the peripheral from the whole animal, thereby often missing the functional value of sensor parts as components of a complete working system (animal). I have in mind the title of the 1967 Zwicker & Feldtkeller book =93Das Ohr Als Nachrichtenemphanger=94. For me the big ide= a of their approach was considering the sensory system as-a-whole-process, neural as well as peripheral. The extraordinary sensitivity (as in receiver terms = =96 =93noise figure=94) for auditory performance implies some very special syst= em properties that require some internal form of parametric amplification to achieve what seems to be better than 3 dB noise figure considering animal body temperature. How this is accomplished by animal auditory means is a tale not yet fully told. 2) There is an important signal-processing concept with respect to *time domain behavior* of =93receiver systems=94. A signal path can be constructed from a chain of very highly resonant sections so that for extremely slowly varying signals it would appear to be flat in frequency response. The behavior of such resonant element network with *transient signals* is an altogether different matter =96 transients j= ust don=92t pass through such a network. The exceptional time domain abilities= in auditory perception require something more like a transversal process than resonant ones. Nature is known to be an Ocam=92s Razor devotee and it would seem to be heavily weighted towards transversal processing whether peripheral or combined with CNS resources. This may well include some resonant elements however of limited Q. From this perspective, - what might be the transducer parts of such systems? Bregman=92s Auditory Scene Analysis sets the stage for more integrated perspective on the auditory perceptual apparatus. A recent study has shown the ability of humans to resolve acoustic rise time differences of 5 microseconds or less. (Kunshar 2008) 3) The development of the telephone has greatly altered concepts of auditory communication. People tend to neglect the extent to which such marginal and disturbed sound tools *depend upon aural skills and memory *rather than the accuracy of reproduction. Even more neglected is the effects of sound of wavelengths greater than one meter in providing recognizable and comfortable sonic sense of place. Such spectrum is received more via whole body sense than by the diminished long wavelength sensitivity of human ears. There have been few efforts to examine human long-wavelength sound perception. Mitchell Cotter, CTO AIR ISOSYS TECHNOLOGIES Mcotter7@xxxxxxxx On Fri, Mar 12, 2010 at 9:07 AM, Peter van Hengel <pwj.vanhengel@xxxxxxxx>wrote: > Dear list, > > With a background in fluid mechanics perhaps my perspective on the > traveling wave helps the discussion. > > I don't think there is a question whether or not there is a traveling wave > in the cochlea. Fluid mechanics dictates that there has to be one. > > The confusion comes - I think - from comparing the basilar memebrane with= a > string where the energy is passed on through the string and it is that sa= me > string which is showing the movement. In this respect the comparison with > surface waves on water is much appropriate. The fluid-air interface is > showing the movement, but it is the underlying fluid which passes > on the motion. Imagine a pond surface covered with ducks. Imagine it to be > covered so densely you cannot see the water surface. When the water is set > in motion (not neccessarily at its > surface), the ducks will move. This motion will look like a wave and I > guess everyone would agree with the use of the term travelling wave in th= is > case. The energy causing the > ducks to move is not passed on from one duck to the other, but stems from > the motion of > the fluid. > > Likewise in the cochlea the BM motion is caused by motion of the fluid. T= he > fact that we > have fluid on both sides of the BM, whereas in the example we have fluid > below and air on > top can be shown (mathematically) to be of no consequence for the > principle. Also the > fact that in the example the restoring force acting on the ducks is > gravity, whereas in > the cochlea it is the BM stiffness does not affect this story. > > The main problem with the resonator/resonance theory (at least in the > versions I know) is > that the motion of neighbouring resonators is independent. In the example > neighouring ducks can not move independently because their motion is link= ed > through the motion of the underlying (continous) water. > > Complicating factor in the discussion is perhaps that in the cochlea, the > restoring force being stiffness combined inevitably with mass, we > automatically get resonators. So in my view it > is not a question of resonance OR travelling wave. It has to be a bit of > both. > > Fluid mechanics dictates that there is a travelling wave on the basilar > membrane unless cochlear fluid is unlike any other fluid I know. The > question that may remain is whether this wave motion is what causes the > effective stimulation of haircells. But there should not be a question > whether or not there is a traveling wave, even if it has not been shown > definitively in measurements. > > The problem I see with a compression wave being the stimulus and the > haircells acting as pressure sensors is that. This assumes that the > haircells will be compressed by a pressure acting on them form the outsid= e. > However, the haircells are filled with fluid themselves and there will be= no > pressure difference between the inside and outside of the cell. This impl= ies > that the cell wil not deform and I do not quite see how the sensor would > then operate. (But the fact that I don't see it does not mean it impossib= le, > of course...). > > The references to texts already given by dr Frosch and others are excelle= nt > and I don't have much else to add. > > All the best, > Peter van Hengel > --00504502d33bf1a2f704819e936b Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Version:1.0 StartHTML:0000000200 EndHTML:0000008743 StartFragment:0000002936 EndFragment:0000008707 SourceURL:file://localhost/Users/user/Desktop/DwnloadSink/MAC_comments%20to= AUDITORY100312.doc <meta name=3D"Title" content=3D""> <meta name=3D"Keywords" content=3D""> <meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3Dutf-8"> <meta name=3D"ProgId" content=3D"Word.Document"> <meta name=3D"Generator" content=3D"Microsoft Word 11"> <meta name=3D"Originator" content=3D"Microsoft Word 11">  <style>  </style> Dear AUDITORY List people: =A0 I have been reading with respect the many extended comments on Mechanical Cochlear Model.=A0 I have been delighted to see the intense interest that the discussion has stimulated.=A0 </spa= n>I have a few points to make for consideration by the list. =A0 1) So much of the discussion is naturally focused on the cochlear peripheral system as though it existed as an analyzer in itself.=A0 This reductioni= st perspective separates the peripheral from the whole animal, thereby often missing the functional value of sensor part= s as components of a complete working system (animal).=A0 I have in= mind the title of the 1967 Zwicker & Feldtkeller book =93Das Ohr Als Nachrichtenemphanger=94. For me the big ide= a of their approach was considering the sensory system as-a-whole-process, neura= l as well as peripheral. The extraordinary sensitivity (as in receiver terms =96 =93noise figure=94) for auditory performance implies some very special syst= em properties that require some internal form of parametric amplification to achieve what seems to be better than 3 dB noise figure considering animal b= ody temperature.=A0 How this is accomplished by animal auditory means is a tale not yet fully told.<= /font> =A0 2) There is an important signal-processing concept with respect to time domain behav= ior of =93receiver systems= =94. A signal path can be constructed from a chain of very highly resonant sections so th= at for extremely slowly varying signals it would appear to be flat in frequency response.=A0 The behavior of such resonant element network with transient signals is an altogether different matter =96 transients just don=92t pass through such a network.=A0 The ex= ceptional time domain abilities in auditory perception require something more like a transversal process than resonant ones. Natur= e is known to be an Ocam=92s Razor devotee and it would seem to be heavily weigh= ted towards transversal processing whether peripheral or combined with CNS resources. This may well include some resonant elements however of limited Q.=A0 From this perspective, -=A0 what might be t= he transducer parts of such systems?=A0=A0 Bregman=92s Auditory Scene Analysis sets the stage for more integrated perspective on t= he auditory perceptual apparatus.=A0 A recent study has shown the ability of humans to resolve acoustic rise time differences of 5 microseconds or less.=A0 (Kunshar 2008)=A0 =A0 3) The development of the telephone has greatly altered concepts of auditory communication.=A0 People tend to neglect the extent to which such marginal and disturbed sound tools depe= nd upon aural skills and memory rather than the accuracy of reproduction.=A0 Even more neglec= ted is the effects of sound of wavelengths greater than one meter in providing recognizable and comfortable sonic sense of place.=A0 Such spectrum is received more via whole body sense than by the diminished long wavelength sensitivity of human ears.=A0 There= have been few efforts to examine human long-wavelength sound perception. =A0 Mitchell Cotter,=A0 CTO =A0 AIR ISOSYS TECHNOLOGIES <a href=3D"mailto:Mcotter7@xxxxxxxx">Mcotter7@xxxxxxxx</a>= =A0 <div class=3D"gmail_quote">On Fri, Mar 12, 2010 at 9:07 AM, Peter v= an Hengel <<a href=3D"mailto:pwj.vanhengel@xxxxxxxx">= pwj.vanhengel@xxxxxxxx</a>> wrote: <blockquote class=3D"gmail= _quote" style=3D"margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204,= 204, 204); padding-left: 1ex;"> Dear list, =A0 With a background in fluid mechanics perhaps my per= spective on the traveling wave helps the discussion. =A0 I don't = think there is a question whether or not there is a traveling wave in the c= ochlea. Fluid mechanics dictates that there has to be one. The confusion comes - I think - from comparing the basilar memebrane wit= h a string where the energy is passed on through the string and it is that = same string which is showing the movement. In this respect the comparison w= ith surface waves on water is much appropriate. The fluid-air interface is = showing the movement, but it is the underlying fluid which passes on the motion. Imagine a pond surface covered with ducks. Imagine it to be = covered so densely you cannot see the water surface. When the water is set = in motion (not neccessarily at its surface), the ducks will move. This m= otion will look like a wave and I guess everyone would agree with the use o= f the term travelling wave in this case. The energy causing the ducks to move is not passed on from one duck to the other, but stems from t= he motion of the fluid. =A0 Likewise in the cochlea the BM motion = is caused by motion of the fluid. The fact that we have fluid on both si= des of the BM, whereas in the example we have fluid below and air on top can be shown (mathematically) to be of no consequence for the principle= . Also the fact that in the example the restoring force acting on the du= cks is gravity, whereas in the cochlea it is the BM stiffness does not a= ffect this story. =A0 The main problem with the resonator/resonance theory (at least in th= e versions I know) is that the motion of neighbouring resonators is inde= pendent. In the example neighouring ducks can not move independently becaus= e their motion is linked through the motion of the underlying (continous) w= ater. =A0 Complicating factor in the discussion is perhaps that in the cochlea= , the restoring force being stiffness combined inevitably with mass, we aut= omatically get resonators. So in my view it is not a question of resonan= ce OR travelling wave. It has to be a bit of both. Fluid mechanics dictates that there is a travelling wave on the basilar = membrane unless cochlear fluid is unlike any other fluid I know. The questi= on that may remain is whether this wave motion is what causes the effective= stimulation of haircells. But there should not be a question whether or no= t there is a traveling wave, even if it has not been shown definitively in measurements. =A0 The problem I see with a compressio= n wave being the stimulus and the haircells acting as pressure sensors is t= hat. This assumes that the haircells will be compressed by a pressure actin= g on them form the outside. However, the haircells are filled with fluid th= emselves and there will be no pressure difference between the inside and ou= tside of the cell. This implies that the cell wil not deform and I do not q= uite see how the sensor would then operate. (But the fact that I don't = see it does not mean it impossible, of course...). =A0 The references to texts already given by dr Frosch and others are ex= cellent and I don't have much else to add. All the best, Peter van Hengel </blockquote></div> --00504502d33bf1a2f704819e936b--

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