Re: A new paradigm?(On pitch and periodicity (was "correction to post")) ("Richard F. Lyon" )


Subject: Re: A new paradigm?(On pitch and periodicity (was "correction to post"))
From:    "Richard F. Lyon"  <DickLyon@xxxxxxxx>
Date:    Thu, 15 Sep 2011 18:28:30 -0700
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

Pim, Sometimes it's hard to get a reaction when you are trying to replace a paradigm, as the silence here illustrates. I didn't really get into the new ideas of your book much, but I have some comments on the introductory material about why you reject the current paradigm. You discuss and reject two wave concepts: first, the pressure sound wave that travels so fast that wavelengths will always be long compared to the size of the cochlea, and second, "capillary" or "interfacial" waves, presumably meaning those water surface waves where gravity provides the restoring force. Of course, neither of these can be the explanation for how the cochlea works. But they are not invoked that way, normally. The traveling wave in the cochlea is sort of like water surface gravity waves, but the restoring force can't be gravity, as you note, since there are not different fluid densities. Rather, the restoring force is due to the compliance of the basilar membrane. If you go back to Airy's and Lamb's analysis of the physics of gravity waves using 2D inviscid incompressible irrotational approximations, and substitute the compliance of the BM for the surface restoring force of gravity, you can derive the wave equations that describe the (approximate) physics of waves in the cochlea, in the 2D case (which is much better than the 1D long-wave and short-wave approximations, and not quite as comprehensive as a 3D model, which is harder). Right at the BM, you also can't completely get away with the inviscid assumption, since there must be a viscous boundary layer providing a drag force where the fluid velocity is discontinuous from the zero longitudinal velocity of the BM; but that can be lumped into BM impedance. You also attribute to Lighthill some strange wrong ideas about transmission lines only being able to transmit energy near their resonance. Actually, he showed the opposite: that a sinusoidal wave will propagate until the point where the transmission line resonance gets low enough to match the wave frequency, and at that point it will slow down to zero velocity and die out. This is not exactly how the cochlea works (the BM is not very resonant), but not a bad concept from base to near the best place. You conclude that "the existence of two sound energy transport phenomena with different transfer velocities within this tiny cochlear volume of perilymph fluid as suggested by Lighthill is impossible." Yet all observations do see a slow wave, much slower than the speed of sound, and basic mathematical physics of the same sort that has been working well for over 100 years to describe waves in fluids predicts exactly that behavior. Some may quibble that it has not been conclusively proved that the observed slow wave carries energy; but no workable alternative has been put forward, and no experiment convincingly contradicts this main hypothesis of the current paradigm, as far as I know. I know some on this list will probably say I'm wrong, now that I've opened the door. I was intrigued by your pointing out that the thin Reissner's membrane, even though very flexible, will disrupt some aspects of the assumed physics of the fluid behavior, since the longitudinal velocity will not be continuous across it and it will introduce viscous drag to longitudinal flow. It's a good point that I hadn't thought of before, and it's not clear exactly what the effect is. Near "resonance" however, in the short-wave region, the fluid movement is all very close to the BM, well inside scala media and away from RM; so the normal 2D wave equations should work well there at least. It sounds like you're trying to get away from a Helmholtz-like conception of resonators or places responding to frequencies, and replace it with a more time-domain approach that works for a lot of pitch phenomena. But it will work better to put that time-domain mechnanisms AFTER the what the cochlea does. Each hair cell is a "tap" on the BM, reporting a time-domain waveform as filtered by the traveling-wave mechanism; that's where the pitch-processing nonlinear time-domain operations start... Dick At 6:39 PM -0400 9/9/11, Willem Christiaan Heerens wrote: >Dear List, > > >In this thread: ³A new paradigm?(On pitch and periodicity ..)² the >original start of all this was the question of Nedra Floyd-Pautler about >auditory illusions in relation to hearing aids. >But it was the comment of Randy Randhawa addressed to her with the >following content: > >In my opinion the most enduring (over 200 years) of all >auditory "illusions" is what has been called the "missing fundamental". The >fact that this has not been satisfactorily resolved by the tortured use of >existing signal processing techniques leads some, including yours truly, to >believe that the auditory system has figured out a unique way to do >frequency analysis and to meet the dictum in biology that "form follows >function". Taking into account where we are and the discussions that take >place, e.g. this forum, it is interesting that there has been no discussion >as to why the cochlear has the shape it does. Therefore some experimental >phenomenon that we may call as an illusion, could have a very natural >consequence of how frequency analysis is done. One is lead to believe that >we are truly very far from understanding how the auditory system works and >therefore hearing aid designs are a bit of a hoax foisted on >the "proletariat". Sorry if I sound a bit harsh, but I think it is time >people recognized that the emperor has not clothes. > >And sorry for those who have other ideas, I completely agree with Randy¹s >remarks here above. And I have reasons for this opinion. > >Although not being an auditory expert, but having an academic applied >physics background I have studied already for more than ten years the >functionality of the mammalian hearing sense. >Together with ENT MD J. Alexander de Ru I have recently published a booklet >with the following title: > >Applying Physics Makes Auditory Sense > >With subtitle: >A new paradigm in hearing > >This booklet describes in the first chapter ­ Introduction ­ the objections >we have against a number of existing hypotheses, simply because they are at >variance with general laws of physics. > >In the second chapter ­ The new hypothesis ­ we describe how based on our >findings the mammalian hearing sense can function in such a way that it is >on the one hand in full agreement with the rules and laws of general >physics and mechanics and that on the other hand it explains clearly all >the salient mysteries and anomalies, has the potential to explain even much >more yet unclear details in our auditory system and predicts other >verifiable hearing phenomena. > >The third chapter ­ Methods and experiments for verification ­ deals with >perception experiments in which the Œmissing fundamental¹ and the Œstrike >note of bells¹ are found to be normal hearing phenomena, so no illusions, >while the Œshift in pitch¹, described in literature as result of a uniform >frequency shift in higher Œincomplete harmonic¹ sound complexes, is found >as an illusion, based on subjective perception of musically trained >experimenters. > >The other four chapters describe details about the functioning of the >cochlea. > >If you combine this with the formulation of Richard Lyon in his comment to >Ita Katz: > >It would be much more robust to say that "The pitch is determined based on >an approximately common periodicity of outputs of the cochlea," which I >believe is consistent with your intent. > >Why is this better?  > >First, it doesn't say the periodicity is determined; what is determined is >the pitch (even that is a bit of stretch, but let's go with it).  >Second, it doesn't depend on whether the signal is periodic, that is, >whether harmonics exist. >Third, it doesn't depend on being able to isolate and separately >characterize components, harmonic or otherwise.  >Fourth, it doesn't need "multiples" (or divisors), but relies on the >property of periodicity that a signal with a given period is also periodic >at multiples of that period, so it only needs to look for "common" >periodicities--which doesn't require any arithmetic, just simple neural >circuits. Fifth, it admits approximation, so that things like "the strike >note of a chime" and noise-based pitch can be accommodated.  >Sixth, it recognizes that the cochlea has a role in pitch perception. It's >still not complete or perfect, but I think presents a better picture of how >it actually works, in a form that can be realistically modeled. > >You will observe that all these six aspects are forming parts of the >concept we have named a new paradigm in hearing. > >You can download the e-book version of our booklet from the website of the >University of Utrecht: > >http://igitur-archive.library.uu.nl/med/2011-0204-200555/UUindex.html > >But for your convenience I have attached the PDF version of the booklet to >this message > > > >Regards > >Pim Heerens > > > >Attachment converted: MacintoshHD:Book Heerens >de Ru EN.pdf (PDF /«IC») (00AF4693)


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