Re: Wasn't v. Helmholtz right? (BM/neural tuning) (Andrew Bell )

Subject: Re: Wasn't v. Helmholtz right? (BM/neural tuning)
From:    Andrew Bell  <bellring(at)SMARTCHAT.NET.AU>
Date:    Tue, 27 Jun 2000 11:39:04 +1000

Dear Enrique and List: It is clear that this data (like similar data over previous years) demonstrates that the BM and neural curves are equally sharply tuned. The puzzling question then naturally arises - and it is a question that has been vexing hearing science for quite some time (a century or more) - how could the BM (or any passive cochlea structure) be so sharply tuned when it is essentially a slack membrane, or conjoined fibres, immersed in fluid? Such a structure would have a very low Q. So if we assume that 'intermediate' structures merely amplify the BM response, we end up with something with a similarly low Q. As Gold suggested, some positive feedback is needed to sharpen the response. I have suggested a mechanism involving the OHC and tectorial membrane that provides high Q in a fluid environment. Incidentally, the BM picks up this vibration. However, the BM is not the primary tuned element of the ear; it is an accessory structure designed to absorb excess energy. Andrew. -----Original Message----- From: AUDITORY Research in Auditory Perception [mailto:AUDITORY(at)LISTS.MCGILL.CA]On Behalf Of Enrique A. Lopez-Poveda Sent: Tuesday, 27 June 2000 12:38 To: AUDITORY(at)LISTS.MCGILL.CA Subject: Re: Wasn't v. Helmholtz right? (BM/neural tuning) Andrew, I take your point and I agree with your comment that Narayan et al. could have made the curves to match at their base. In that case, neural thresholds would be lower than the BM threshold. However, even if you did that, their data show that BM response is as sharply tuned as AN response. The bandwidths of their tuning curves are comparable at the tip, even though their thresholds may be different. Assuming that the BM and AN tuning curves are made to match at their tails, one could then argue that the role of intermediate structures (e.g., OHC, IHC, etc) could be only to "amplify" the BM response, but NOT to sharpen the tuning of the system. Any comments on this? -- Enrique

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