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Re: AUDITORY Digest - 29 Sep 2007 to 30 Sep 2007 (#2007-223)
I have a rather naive question, but please, if you have a second, indulge me?
When you model hair cell sensitivity to frequency, how do you take
into account active feedback via the outer hair cells' ability to
change the response characteristics of the membrane? Wouldn't that
upset any kind of predictibility?
R
eOn 10/1/07, AUDITORY automatic digest system <LISTSERV@xxxxxxxxxxxxxxx> wrote:
> There is 1 message totalling 108 lines in this issue.
>
> Topics of the day:
>
> 1. HC selectivity ... was Re: Physiological models of cochlea activity -
> alternatives to the travelling wave
>
> ----------------------------------------------------------------------
>
> Date: Mon, 1 Oct 2007 13:25:39 +1000
> From: Matt Flax <flatmax@xxxxxxxx>
> Subject: Re: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave
>
> Hi Reggie, Bob and the group,
>
> In the linear case I agree with you Reggie.
>
> But hair cell physiology is not linear. The closest they get is with the
> Goldman-Hodgkin-Katz [1] equation. The furthest they get is with kinetic
> algorithms [references not listed].
>
> For this reason I would write .. actually BEGIN to write the membrane
> frequency dependence with respect to other signals like this
>
> 1
> wc(t) = =========================================
> ___ _
> |__ \ (_)
> ) | _ __ _
> / / | '_ \| |
> / /_ | |_) | | r(t)c(t)
> |____| | .__/|_|
> | |
> |_|
>
>
> A nonlinear impedance. The time factor being the important change ...
>
> I don't believe that it is valid to give hair cell selectivity a first
> order electrical model.... Sorry ... as simple as that...
>
> For this reason, previous assumptions on the frequency selectivity of
> the cochlea hair cell is - in terms of frequency distributed power -
> incorrect.
>
> A lot of mind or mathematical models may have incorrect assumptions to
> date.
>
> The time dependent model should be able to explain frequency dispersion
> and a certain amount of hair cell adaptation.
>
> sincerely
> Matt
>
> [1] @BOOK{Hille:2001,
> title = {Ion Channels of Excitable Membranes (3rd Edition)},
> publisher = {Sinauer Associates},
> year = {2001},
> author = {Hille, B.},
> month = {July},
> url =
> {http://www.amazon.fr/exec/obidos/ASIN/0878933212/citeulike04-21}
> }
>
>
>
> On Sat, Sep 29, 2007 at 11:23:03AM -0500, Reggie Weece wrote:
> > Bob and Matt -
> >
> > The difference between your two values for the cut off frequency
> > appears to be the 2pi factor. From
> > http://en.wikipedia.org/wiki/RC_circuit,
> > wc = 1/(RC) rad/s
> > fc = 1/(2piRC) Hz
> >
> > Thus wc = 25000 rad/s (not 25 kHz, as Matt suggested!)
> > Bob's calculation of fc = ~4kHz is correct.
> >
> > - Reggie
> >
> > > Date: Fri, 28 Sep 2007 08:24:35 -0400
> > > From: Bob Masta <audio@xxxxxxxxxxx>
> > > Subject: Re: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave
> > >
> > > On 28 Sep 2007 at 12:55, Matt Flax wrote:
> > >
> > > <snip>
> > >
> > > > With respect to a hair cell at rest ... take the following general
> > > > values for membrane resistance and capacitance :
> > > > R= 40 Meg Ohms ... taken from [4] for example
> > > > C= 1 pF ... taken from [5] for example
> > > > The first order cut-off frequency would be about 25 kHz.
> > > > fc=25 kHz.
> > >
> > > How do you obtain this 25 kHz value? Using
> > > f = 1 / (2 * pi * R * C)
> > > I come up with about 4 kHz.
> > >
> > > Best regards,
> > >
> > >
> > >
> > > Bob Masta
>
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> ------------------------------
>
> End of AUDITORY Digest - 29 Sep 2007 to 30 Sep 2007 (#2007-223)
> ***************************************************************
>
--
======================
Dr. Rick Nance
Composer at Large
PlasticMusic.Net