Re: Cochlea Amplifier models : a new list ("reinifrosch@xxxxxxxx" )


Subject: Re: Cochlea Amplifier models : a new list
From:    "reinifrosch@xxxxxxxx"  <reinifrosch@xxxxxxxx>
Date:    Sun, 21 Oct 2007 15:03:21 +0000
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

Hello Matt Flax and List, At first I thought that your newest posting ("Thank you Reinhart ...", see below) was meant ironically -- but a later private message from you convinced me that you earnestly, and probably in contradiction to me, consider a "compression amplifier". I would now like to discuss a "DPOAE" (distortion- product oto-acoustic emission) treated in T. Ren et al., "Backward propagation of otoacoustic emissions in the cochlea", in "Auditory Mechanisms" = Portland 2005 proceedings, World Scientific, 2006: 79-85, in order to show that these data are not in conflict with "my" cochlear model (involving the "HC-resonator"). Cochleae of young and healthy gerbils. Two simultaneous 70-db (SPL) sine-tones, f_2 = 17 kHz, f_1 = 14 kHz. The active peak of the f_2-wave is at about x_b(2) = 2.30 mm, and that of the f_ 1-wave is at about x_b(1) = 2.75 mm. The (-10dB)-width of these active peaks is about 0.4 mm. Because of the comparatively high level (70dB), the f_1-wave BM-displacement amplitude at x_b(2) = 2.30 mm is fairly large, so it is in the region ranging from about x_b = 2.1 mm to x_b = 2.5 mm where a soft "cubic combination tone" is generated, because the waveform (displacement versus time) of the two waves is slightly flat-topped rather than exactly sinusoidal. (See Appendix XII of Helmholtz's "On the sensations of tone"). This cubic combination tone is also called "distortion product" and has the frequency f(DP) = 2f_1 - f_2 = 11 kHz. An additional travelling wave (TW) with that frequency of 11 kHz is generated at and near x_b = 2.3 mm and travels, on the BM, apex-ward, gaining in amplitude, to the 11-kHz active-peak location, x_b(DP) = 3.3 mm, then dies at about x_b = 3.7 mm. That 11-kHz wave is passive from 2.3 to about 2.9 mm, where the 11-kHz active peak and the energy generation by the OHC's begin. A similar (i.e., slow) TW also travels from x_b = 2.3 mm base-ward; this wave can be predicted by time-reversal of an 11-kHz wave starting at the base and having the correct amplitude at x_b = 2.3 mm; thus the BM-displacement amplitude of that that base-ward 11-kHz wave will be small at 2.3 mm and even smaller on approaching the base. The strongest 11-kHz BM vibration (amplitude at least 10 times larger than at 2.3 mm) will occur at 3.3 mm. On the basal side of that active 11-kHz peak, from about 2.9 to 3.3 mm, the Hensen-Cell resonators vibrate strongly, i.e., the angle between RL and BM in that 4 mm long x_b-region oscillates at 11 kHz. I now conjecture that the part of the organ of Corti containing the IHC's, the IP-cells, the inner tunnel, the OP-cells, the OHC's, Deiters cells, the outer tunnel, and the Hensen cells has a fairly tight wall around it, so that in the mentioned 4-mm x_b-section with strong HC-resonator vibration the liquid pressure and the liquid volume oscillate at 11 kHz. That region is postulated to be the source of a liquid- compression wave (i.e., an ordinary sound wave) which spreads at c_s = 1500 m/s through the cochlear liquid and causes the round window and the oval window to vibrate. The wavelength is c_s / f(DP) = 1500 / 11000 = 0.136 m = 136 mm, so at any given moment in time, the liquid pressure is about equal at all points in the cochlear liquid. Thus that sound wave causes no across-BM pressure difference and thus (I believe) no significant signals from the IHC's to the brain, but it can, via the middle-ear ossicles and/or via air from the round window to the eardrum, generate a signal in a microphone in the ear canal. 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: flatmax@xxxxxxxx Datum: 20.10.2007 19:02 An: <AUDITORY@xxxxxxxx> Kopie: "reinifrosch@xxxxxxxx"<reinifrosch@xxxxxxxx> Betreff: Re: Cochlea Amplifier models : a new list Thank you Reinhart. On behalf of the list. You have finally walked a mind experiment which has led you to your version of the Compression amplifier. [...]


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Electrical Engineering Dept., Columbia University