Subject: Re: active travelling waves, DPOAEs and the Cochlea Amp. From: Erik Larsen <elarsen@xxxxxxxx> Date: Thu, 4 Oct 2007 13:09:36 -0400 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>I'm not sure there is a fundamental problem with a 2f2-f1 in the traveling wave model. If you'll allow me to think out loud: All that is required is an interaction between f1 and f2 in the hair bundle, such that the receptor potential contains a 2f2-f1 component (just as for the 2f1-f2). If this occurs in a region where 2f2-f1 would be amplified, that DP will grow. For the 2f2-f1 this necessarily occurs in a region where f1 and f2 are still quite small, hence there is presumably less distortion and the 2f2-f1 component in the receptor potential is small, which would explain why you measure a smaller amplitude in the ear canal. Once f1 and f2 are large, you are too far apical for the 2f2-f1 component in the receptor potential to propagate. Nonetheless, where this component is generated in more basal locations it could be amplified (because it would be near its own CF place) and thus lead to a measurable DPOAE. Erik Matt Flax wrote: > Hello all, > > I can easily see the stapes driven passive travelling wave. I am still > at a loss for the second travelling wave ... > > Current theory for explaining the generation of DPOAEs requires the > Cochlea Amplifier. > > I am writing this summary to set the scene ... it is the current active > travelling wave point of view ... > > Those models which rely on Travelling Wave activity propose the following > [1] : > The distributed travelling wave amp. amplifies a signal which is > generated and this signal travels in two directions. One apical going > wave reflects off the lower frequency (2f1-f2) DP resonant location on > the BM. The other wave reflects off the oval window. This oval window > reflection generates the DPOAE in the middle ear. > > In the above treatment, the two frequencies f1 and f2 reside between the > oval window and the 2f1-f2 DP frequency. > > Now please consider the 2f2-f1 DPOAE. > > Interestingly, the 2f1-f2 and 2f2-f1 DPs have similar nature - although > the 2f2-f1 DP is of a lower level. They both have a band pass nature > with respect to f2 frequency glide [2] ... and so on .... > > 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 ??? > > thanks > Matt > > [1] @xxxxxxxx{shera:2005, > author = {Shera, C.A. and Tubis, A. and Talmadge, C.L.}, > title = {{Coherent reflection in a two-dimensional cochlea: Short-wave > versus > long-wave scattering in the generation of reflection-source > otoacoustic > emissions}}, > journal = {The Journal of the Acoustical Society of America}, > year = {2005}, > volume = {118}, > pages = {287}, > publisher = {ASA} > } > > [2] @xxxxxxxx{fahey:2006, > author = {Fahey, PF and Stagner, BB and Martin, GK}, > title = {{Mechanism for bandpass frequency characteristic in > distortion product > otoacoustic emission generation}}, > journal = {The Journal of the Acoustical Society of America}, > year = {2006}, > volume = {119}, > pages = {991}, > publisher = {ASA} > } > > > thanks > Matt > -- Erik Larsen PhD candidate Speech and Hearing Bioscience and Technology http://web.mit.edu/shbt Whenever anyone says, "theoretically," they really mean, "not really." -- Dave Parnas