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Re: mechanical cochlear model

Hello Martin,

Today I partially agree with you. The measured instantaneous-frequency-versus-
time curves of click-evoked BM responses [e.g., Recio and Rhode (2000),
JASA 108, 2281-2298, chinchilla] indeed imply that the low-frequency components 
of the click propagate through the basal part of the cochlear channel not via a 
slow travelling wave starting at the base but via a fast liquid-compression wave.

I still believe, however, that the slow travelling wave plays an important part
at high frequencies. The hydrops cases that are mentioned in the references
which you have given concern low frequencies. As you know, the liquid motion 
in a high-frequency (i.e., short-wavelength) cochlear travelling wave is
spatially restricted to two regions just "above" and "below" the (narrow) BM.
The round window, at the "floor" of the "lower" cochlear half-channel,
is not involved; its blockage does not prevent the travelling wave.

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 .

----Ursprüngliche Nachricht----
Von: nombraun@xxxxxxxxx
Datum: 06.03.2010 21:29
An: <AUDITORY@xxxxxxxxxxxxxxx>
Betreff: Re: mechanical cochlear model

While the cochlear traveling wave has appeared in numerous empirical reports 
on real physical models and real biological animals, it's function in 
hearing is not yet universally appreciated. Some people still think that it 
provides the well known frequency selectivity that we observe in the 
auditory nerve. This view, however, has been proved wrong by multiple direct 
experimental evidence. Just consider two bodies of evidence:

1) Hearing sensitivity is not affected, when endolymphatic hydrops presses 
the basilar membrane flat upon the bony cochlear wall of the scala timpani:



2) It is a well established observation for more than 50 years that closure 
of the round window does not affect hearing sensitivity. This means that a 
pressure difference across the basilar membrane and a resulting traveling 
wave cannot be a necessary condition of hair cell excitation. Recently, 
Perez et al. (2009) reported that closure of the round window not only 
leaves hearing sensitivity unchanged but increases cochlear vulnerability at 
high sound levels. This second new observation is a further compelling 
indication as to the real function of the cochlear traveling wave.


Martin Braun
Neuroscience of Music
S-671 95 Klässbol
email: nombraun@xxxxxxxxx
web site: http://www.neuroscience-of-music.se/index.htm