Subject: AW: Cochlear nonlinearity & TTS From: "reinifrosch@xxxxxxxx" <reinifrosch@xxxxxxxx> Date: Wed, 17 Jan 2007 13:43:39 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>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@xxxxxxxx . ----Ursprüngliche Nachricht---- Von: nshahnaz@xxxxxxxx Datum: 16.01.2007 18:17 An: <AUDITORY@xxxxxxxx>, <reinifrosch@xxxxxxxx> 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. Cheers Navid