Re: active travelling waves, DPOAEs and the Cochlea Amp. ("Richard F. Lyon" )

Subject: Re: active travelling waves, DPOAEs and the Cochlea Amp.
From:    "Richard F. Lyon"  <DickLyon@xxxxxxxx>
Date:    Thu, 4 Oct 2007 11:08:29 -0700

At 12:20 AM +1000 10/5/07, Matt Flax wrote: >My question to the list is : > >Can anyone please explain how this travelling wave point of view can >generate a DPOAE when the DP is the 2f2-f1 DP ? >In this case, the DP sits between the oval window and the probe >frequencies f1 and f2. > >If you can explain that, then please also explain what happens to the >apical going travelling wave ??? Distortion-product oto-acoustic emissions originate where the distortion is, which is the region where both f1 and f2 have strong responses. Odd-order nonlinearities (OHC approximating saturation) will generate 2f1-f2 and 2f2-f1 about equally, and they will propagate in both directions, probably preferentially toward the apex. To me the question is not why we get 2f2-f1, but why it is as much weaker than it is. As you point out, this may involve reflection of some 2f1-f2 from the place where it is localized more apically. Or as Erik Larsen points out, it may be that most of the distortion is happening at place where 2f2-f1 doesn't propagate very well. But the fact that you get some 2f2-f1 is in no way surprising. The apical-going part of 2f2-f1 is quickly attentuated, since it's past its best place. The part going toward the base, if not attentuated too much, will quickly arrive at a region where it will be amplifies on the way out. I do not have a computational model that will reproduce such bidirectional nonlinear effects, but I suspect it's not hard. Does anyone have one? Maybe I'll give it a try some time. Dick

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