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Re: AW: Cochlear nonlinearity & TTS

Dear Ramdas,

can you please point onto sources regarding "Egbert deBoer's reconstruction
method" that you mentioned?

Thanks in advance,
Tamas H.

On Thu, 18 Jan 2007 11:25:01 -0500, Ramdas Kumaresan wrote
> Navid, Richard and the listees,
> I have heard a lot of speculation about the cochlear amplifier for 
> many years. One of the questions that  I have wondered about as a 
> signal processing engineer for many years, is with all the 
> sophisticated  nonlinearities, delays, amplifiers, filters etc that 
> are present in the auditory periphery, how does it "represent" an 
> acoustic signal in the neural spike patterns that emanate from the 
> auditory periphery? (I guess everyone  wonders about it.) Is it 
> possible to reconstruct the acoustic signal if you were able to 
> measure/monitor   the spike patterns  that are put out by all the 
> auditory nerve fibers?  What is the reconstruction 'algorithm"?
> (I know about   Egbert deBoer's reconstruction method  for a single 
> nerve fiber.) Is'n't the information about the signal distributed 
> across many, many  nerve fibers? Should'nt the reconstruction take 
> information from all nerve fibers and fuse them to reconstruct the 
> signal? Just wondering aloud. RK
> Richard F. Lyon wrote:
> > At 9:17 AM -0800 1/16/07, Navid Shahnaz wrote:
> >
> >> Thank you Reinhart for your clarification. Does the cochlear 
> >> amplifier works on both sides of the excitation pattern peak on the 
> >> BM? or the amplifier operates  wore efficiently at a place that is 
> >> just above or toward the apex from the point of disturbance created 
> >> by travelling wave? Operationally this point may be an ideal point as 
> >> it is less likely saturates the amplifier due to sharp slope of the 
> >> travelling wave on the apical side.
> >> Cheers
> >> Navid
> >
> >
> > Navid,
> >
> > Both Monita and Reinhart have given good explanations, but let me add 
> > a bit.
> >
> > The way I think of it, the active amplification is active everywhere, 
> > but it competes with the passive loss mechanisms, and is only 
> > significant at low enough levels.  The active loss mechanism (damping) 
> > increases rapidly apically when a sine wave travels past a 
> > characteristic place.  Because of the active gain, the response to a 
> > sine wave can travel further before it damps out; from the "passive 
> > peak" that Reinhart mentions, the peak response location can be 
> > further apical, up to about a half octave worth of place further, when 
> > the active amplification is significant, to the "active peak". The 
> > "net" amplification is positive (in dB per mm or whatever) before the 
> > response peak, and negative after the response peak, pretty much by 
> > definition of peak.  That net includes the active gain, which 
> > saturates, and the passive loss, which doesn't, so it's level dependent.
> >
> > In addition to the saturation that reduces the active gain at high 
> > level, there is also efferent control that turns down the gain in 
> > response to afferent response level and possibly other central control 
> > signals.  This effect of efferent control of mechanical gain has been 
> > directly demonstrated, but I don't recall exactly who/when/where to 
> > cite right now.
> >
> > Dick
> >