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Re: mechanical cochlear model

Hello Dick,

I was present at the 2008 Mechanics-of-Hearing workshop
at Keele University; in my opinion you have not lost touch.

Nevertheless, up to now I do not agree with your statement
"[...] the fluid has to have some place to go" (see below).
The fluid is compressible, it can and does change its local density 
and thus it propagates "ordinary" (compression) sound waves. 
As mentioned before, I think that at low frequency the oscillation 
propagates through the basal part of the cochlear channel 
mainly via such a sound wave. The low-frequency slow travelling wave is 
suppressed near the base, because it is "tsunami-like", i.e., it represents
a "long-wave" case, with liquid-particle motion down to the floor and
up to the roof of the cochlear channel. At the floor near the base,
however, the soft round window prevents the build-up of a
significant liquid sound-pressure. 

Experimental evidence: e.g., Fig. 2 of Shera (2001), "Frequency glides in 
click responses ...", JASA 109, 2023-2034, based on data of Recio and 
Rhode (2000; see below); for the low-frequency components of the click, 
the delay is found to be shorter than that expected for a "slow" cochlear  
travelling wave starting at the base.

In Fig. 3 of Recio and Rhode (2000), "Basilar membrane responses to broadband
stimuli", JASA 108, 2281-2295, one sees that a click with 30-nm first-peak umbo 
displacement towards the inside of the cochlea causes, at the 5.5-kHz best 
place of the chinchilla cochlea, an initial BM displacement (towards scala tympani)
which on the diagram looks small but is easily calculated to 
amount to as much as 100 nm. The delay from umbo to BM onset is only 
48 microseconds, too short for a "slow" cochlear travelling wave starting at the 
base. That initial BM displacement could however be caused by a sound wave 
from the stapes to the considered place of the BM. 

Very preliminary conjecture: If one blocks the round window, then tsunami-
like slow waves are possible, leading to increased hearing loss after high-level


----Ursprüngliche Nachricht----
Von: DickLyon@xxxxxxx
Datum: 08.03.2010 22:08
An: <AUDITORY@xxxxxxxxxxxxxxx>
Betreff: Re: mechanical cochlear model



I'm not convinced that Reinhart's explanation solves the problem.  If 
the stapes moves and initiates a traveling wave, the fluid has to 
have some place to go; that is, the basal region is in the long-wave 
region, not just a wave confined to the around the membrane.


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 .