Subject: Re: AW: Cochlear nonlinearity & TTS From: =?ISO-8859-2?Q?Harczos_Tam=E1s?= <harczos@xxxxxxxx> Date: Thu, 18 Jan 2007 20:12:59 +0100 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>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 > >