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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
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.
Dr. phil. nat.,
r. PSI and ETH Zurich,
Phone: 0041 56 441 77 72.
Mobile: 0041 79 754 30 32.
E-mail: reinifrosch@xxxxxxxxxx .
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.