Some articles on ear mechanics of the past years:

http://www.ploscompbiol.org/article/info%3Adoi%2F10.1371%2Fjournal.pcbi.1003336

http://www.fasebj.org/content/early/2012/06/11/fj.11-200535.full.pdf+html

http://www.eurekalert.org/pub_releases/2007-03/acft-omm032707.php

http://www.eurekalert.org/pub_releases/2002-05/jhmi-hsr050202.php

http://physicsworld.com/cws/article/news/2006/mar/14/inner-ear-mystery-solved

http://phys.org/news128352212.html

http://www.eurekalert.org/pub_releases/2008-04/vu-sll042508.php

http://www.eurekalert.org/pub_releases/2006-05/vu-anm050806.php

http://newswire.rockefeller.edu/2005/11/18/new-report-bolsters-theory-on-ears-inner-amplifier/

http://www.scientificamerican.com/article.cfm?id=ear-motor-helps-play-soun

http://news.softpedia.com/news/Human-Ears-Also-Create-Sounds-of-Their-Own-109279.shtml

Regards,

Joachim

Thank you very much Joachim,

I'll see the articles if they deal with what I seek. The first one has something to offer probably.

Thanks a lot.

Regards

Rajat

Umm,

Sorry to add that so far I've not succeeded in getting the information desired. It seems no research has been done in this regard or there are not enough NEUROPHYSIOLOGISTS and other researchers on RG yet who are interested to reply.

Is it true that independent of loudness/intensity the entire basilar membrane is excited whenever sound is received by the ear?

Hope somebody gives the required information.

Regards and thanks in advance,

Rajat

Dear Ranjit Pradhan,

How much of Basilar membrane is stimulated is dependent on more than just intensity of the tone. if you keep the frequency of the tone constant, then undoubtedly the tone of higher intensity will lead to greater excitation of BM than the lower intensity tone. But if the frequencies are different for the two tones, then it is a difficult to answer. It can still be assumed that a low frequency tone, even with relatively lesser intensity as that of a high frequency tone will excite greater regions of BM than that by a high frequency tone. A high frequency tone needs to be significantly more intense than the low frequency tone to cause an equal amount of excitation for the two tones.

I hope you got the basic information from this,

Anoop

Thank you very much Anoop,

Could you please give me the references for articles/books that demonstrate the fact that for the same frequency greater intensity of sound leads to the stimulation of a greater span of the BM?

Best wishes and Regards

Rajat

You can find all the answers in a book by B. C. J. Moore, titled "cochlear hearing loss".

You can also find it in his other book "Perceptual consequences of cochlear hearing loss"

In general, any article related to spread of masking in the cochlea should give you the information. Just google Spread of masking and you will find many articles related to your need

Thank you both Shai and Anoop for your kind responses to the query.

I thought that a greater portion of the BM excited would lead to the excitation of a larger number of auditory nerves. What I came to know is that the entire basilar membrane responds to every sound frequency but the displacement/amplitude of BM vibrations depend on the loudness.

If the BM has a larger displacement at a position, will it lead to the firing of more auditory nerves at that position, or is it independent of the displacement ?

If there is larger displacement of BM will it lead to a larger population of neurons firing in the auditory cortex ?

Regards,

Rajat

One of the best references still regarding the mechanical responses of the cochlea is the review by Robbles and Ruggero, Physiol. rev. 81 n°3, 2001.

The answer I would give to your question is 'definitely yes', keeping in mind that the basilar membrane is an extended mechanical system that requires a continuum mechanics description. The reponse of the BM to a sound stimulus takes the form of a mechanical wave that travels along the membrane from the base to the apex of the cochlea. This so-called 'cochlear travelling wave' was discovered by von Bekesy, for which, among other things, he won the Nobel price. The BM is mechanically tuned, so that the peak amplitude of this wave occurs at a specific location along the cochlea depending on the frequency of the stimulus. Given two sounds of identical waveforms (say of the same frequency) but differing in loudness, the louder sound will excite a larger region of the BM, simply because the peak elicited gets larger: in a sense this is a trivial observation!

What makes the picture not so trivial is that for low stimulus levels the amplitude of the BM vibration is boosted by an amplification process, the so-called 'active process' or 'cochlear amplifier. The details of this process are not fully clarified, but evidence for its existence is overwhelming. Its effect can be measured by interferometric measurements of the BM vibrations, which show that the in vivo response of the BM is boosted by up to 60dB compared to the passive (post-morted) response. This is discussed at length in the above review. Two characteristics of the cochlear amplification process are 1) it is highly tuned, so that it gives rise to a peak of BM vibration that is much sharper and displaced by about 1/2 octave relative to the passive peak of Bekesy's travelling wave. 2) it gradually switches off as the stimulus level increases above hearing threshold, so that at very high levels the BM response becomes essentially passive.

The consequence is that the response of the BM is highly nonlinear and not simple to describe. But this also reinforces the above 'yes': at low sound levels the BM peak is sharp and highly tuned, extending over a small region of the BM, while at high levels the peak broadens and covers a more and more extended region of the BM. At least, this is the picture accepted by most researchers in the field.

take a look on this paper also: Basilar membrane nonlinearity and its influence on auditory nerve rate-intensity functions

GK Yates - Hearing research, 1990 - Elsevier

I know that every intensity stimulate a specific area of the basilar membrane either in the apical or the basal turns of the chochlea.

I have an old research demonstrating these data, but it is non beer reviewed.

I uploaded this research to Research Gate.

Trandil H. Elmehallawi and Magda A.El-demiaty. Protection From Gentamycin Ototoxicity By Deferoxamine As An Iron Chelator In Guinea Pig : Electrophysiological and Histopathological Study.Tanta Medical Journal Vol. (33 Supp.), 2005

Thank you Magda,Please send me a copy of your paper.

Regards

Rajat

Thanks

Hope that my work can help you

Dear All,

I'm very sorry to add that so far I have not gotten a direct answer to my well-posed query above. Is there any reference that directly addresses the question ?

What I learnt from all your suggested references is that

(1) the peak occurs at particular place on BM corresponding to a particular frequency.

(2) The peak becomes higher as the intensity grows keeping the frequency constant

But, my doubt is that --

(1) a higher peak may not be having a greater BM span, and

(2) even if it has a greater span, it may not be leading to excitation of larger no. of neurons, due to elastic properties of the BM.

Please help, if you have any ideas or experimental data or any explanation to clarify my understanding in this regard.

Regard

Rajat

Dear Rajat,

Sorry if previous answers were not clear enough. Unless I misunderstood them, the answers to both your questions are indeed 'yes':

(1) The larger span of the BM vibration for larger stimulus levels can be directly observed by interferometry at different points along the BM. This is clear and has been measured in vivo: See for example Fig. 1D in the paper by Russel and Nilsen, 1997, PNAS 94:2660-2664.

(2) The evidence that a larger span of BM vibration excites a larger population of auditory neurons is also strong. At least there is little doubt that this is the case for a "simple" (pure tone) stimulus. This is clear from the 'V' shape of the tuning curves measured on single auditory fibers in response of such tones (the TC is a plot of the sound level required to elicit a given rate of discharge as a function of stimulus frequency). See for example Taberner and Liberman 2005, J Neurophysiol 93: 557–569. Note that as the span of BM vibration increases, the peak of the vibration is shifted towards the basal cochlear regions, so that the neurons that respond most are not the same for low and high level stimuli.

Of course this does not answer the question of how loudness is perceived, or more specifically, which regions of the cochlea contribute most to the perception of a complex sound, and how these regions interact and change with loudness. These issues are far from resolved.

Thank you very much Jacques. I will see these references.

Thanks and Regards

Rajat