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AW: Cochlear nonlinearity & TTS

Dear Navid and List,

As pointed out by Dick Lyon in his answer of January 17, the 
cochlear amplifier works everywhere. An important role is played by 
the "second degree of freedom", i.e., by a resonator the spring of 
which is not a part of the basilar membrane, but rather a part of  
other structures (outer hair cells, Hensen cells, tectorial 
membrane). At a given place in the cochlea, the resonance frequency 
of that second resonator is lower, by about one octave, than the 
resonance frequency of the first resonator, constituted by the 
springs in the basilar membrane and the mass of the connected cells. 
A travelling wave of given frequency approaches the second resonator 
having that resonance frequency before it has a chance of approaching 
the corresponding first resonator, because that first resonator is 
further apexward.

The active vibration of the outer hair cells causes a strong 
amplification if the frequency of that vibration is close to the 
resonance frequency of the second resonator. If the tone is loud, 
however, the amplification factor is not large, because the outer 
hair cells cannot supply a high power. 

In my posting of January 16, I have briefly discussed "high-side 
suppression": Suppressor at 10 kHz, suppressed tone at 8 kHz. There 
is also "low-side suppression", e.g., suppressor at 5 kHz, suppressed 
tone at 8 kHz. In that case, the suppressor must have a fairly high 
level in order to significantly suppress the response of the 8-kHz-
neuron. The amplification of the 8-kHz travelling wave in the one-mm 
region just basal of the 8-kHz characteristic place is hindered by 
the broad passive peak of the 5-kHz wave.

Reinhart Frosch.

Reinhart Frosch,
Dr. phil. nat.,
r. PSI and ETH Zurich,
Sommerhaldenstr. 5B,
CH-5200 Brugg.
Phone: 0041 56 441 77 72.
Mobile: 0041 79 754 30 32.
E-mail: reinifrosch@xxxxxxxxxx .

----UrsprÃngliche Nachricht----
Von: nshahnaz@xxxxxxxxxxxxxxxxxx
Datum: 16.01.2007 18:17
An: <AUDITORY@xxxxxxxxxxxxxxx>, <reinifrosch@xxxxxxxxxx>
Betreff: Re: AW: Cochlear nonlinearity & TTS

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.