MIT researchers make new discovery in the anatomy of hearing

http://www.sciencedaily.com/releases/2007/10/071011140215.htm

keywords: Freeman Ghaffari Aranyosi "tectorial membrane"

-Carl

Very interesting Carl.

Did you find any other links?

"But the team has now found that a different kind of wave, a traveling wave that moves from side to side, can also carry sound energy.

This wave moves along the tectorial membrane, which is situated directly above the sensory hair cells that transmit sounds to the brain.

This second wave mechanism is poised to play a crucial role in delivering sound signals to these hair cells."

This is the part of the article which particularly interests me, as it may support my long-held suspicion that the traditional 2 dimensional model of sound waves and

perception is over-simplistic, and missing one or more further dimensions.

If this is found to be true, and we can devise a way to mathematically model it, it may provide a whole new way of visualising musical "harmonics", (and tuning?)

Charles Lucy lucy@lucytune.com

----- Promoting global harmony through LucyTuning -----

For information on LucyTuning go to: http://www.lucytune.com

LucyTuned Lullabies (from around the world):
http://www.lullabies.co.uk

Skype user = lucytune

http://www.myspace.com/lucytuning

On 13 Oct 2007, at 00:54, Carl Lumma wrote:

> http://www.sciencedaily.com/releases/2007/10/071011140215.htm
>
> keywords: Freeman Ghaffari Aranyosi "tectorial membrane"
>
> -Carl
>
>
>

--- In tuning@yahoogroups.com, Charles Lucy <lucy@...> wrote:
>
> Very interesting Carl.
>
> Did you find any other links?

I will be digger more this weekend, time permitting. -C.

The paper is an open-access PNAS affair.

http://www.pnas.org/cgi/reprint/0703665104v1.pdf

-Carl

I'll try to summarize the paper now:

http://www.pnas.org/cgi/reprint/0703665104v1.pdf

When sound enters your ear it drives the ear drum, which
drives some lever-action bones, which push and pull on
the "oval window" on the cochlea, which creates
*transverse waves* along the basilar membrane inside the
cochlea, which stimulate hair cells attached to the
basilar membrane, which create nerve impulses that go to
your brain.

That's the standard model of hearing. But above the
hair cells, running parallel to the basilar membrane (BM)
is this thing called the tectorial membrane (TM), which
is basically a very thin strip of Jell-O. Because it's
so soft and thin, nobody thought it was good for much.

Well these researchers believe otherwise. They've gone
and cut TMs out of mice, and mounted them on a jig where
they are strung between two supports. The scientists
jiggle one of the supports and watch what happens to the
TM with a strobe light.

What they found is that the TM can conduct *longitudinal
waves* when driven at audio frequencies. Moreover,
these waves travel through the TM at the same speed as
transverse waves do through the BM. Actually the BM
varies in stiffness along its length, so waves will change
speed as they go along it. Different frequencies hit
their maximum amplitude on the BM at different spots,
called "best frequencies" (this is how the ear extracts
the partials of a sound). It's the speed of waves *at
these spots* on the BM that matches the speed of waves
at any spot on the TM. According to the authors, this
means that the waves on the TM could selectively amplify
waves on the BM at their best frequencies, thus improving
the sensitivity of the ear.
Well, the width of the best frequencies is the critical
band (about a whole tone through the center of the piano)
while the selective amplification would cover an octave
according to this paper. So it's not entirely specific.

So that's kinda cool, but the problem of course is that
this was all done with tiny pieces of tissue on a jig,
not in a real cochlea where they are meant to fit. The
authors use a computer simulation to see if being inside
a real cochlea would change the results, and conclude
that it wouldn't. But this isn't terribly convincing.

So nifty research, but still pretty speculative.

-Carl

Does this in any way change our understanding of harmonics? Are we required
to modify partials of a single sound wave significatively in order to make
the physical world conform to our ears?

Oz.

----- Original Message -----
From: "Carl Lumma" <carl@lumma.org>
To: <tuning@yahoogroups.com>
Sent: 15 Ekim 2007 Pazartesi 1:42
Subject: [tuning] Re: MIT researchers make new discovery in the anatomy of
hearing

> I'll try to summarize the paper now:
>
> http://www.pnas.org/cgi/reprint/0703665104v1.pdf
>
> When sound enters your ear it drives the ear drum, which
> drives some lever-action bones, which push and pull on
> the "oval window" on the cochlea, which creates
> *transverse waves* along the basilar membrane inside the
> cochlea, which stimulate hair cells attached to the
> basilar membrane, which create nerve impulses that go to
> your brain.
>
> That's the standard model of hearing. But above the
> hair cells, running parallel to the basilar membrane (BM)
> is this thing called the tectorial membrane (TM), which
> is basically a very thin strip of Jell-O. Because it's
> so soft and thin, nobody thought it was good for much.
>
> Well these researchers believe otherwise. They've gone
> and cut TMs out of mice, and mounted them on a jig where
> they are strung between two supports. The scientists
> jiggle one of the supports and watch what happens to the
> TM with a strobe light.
>
> What they found is that the TM can conduct *longitudinal
> waves* when driven at audio frequencies. Moreover,
> these waves travel through the TM at the same speed as
> transverse waves do through the BM. Actually the BM
> varies in stiffness along its length, so waves will change
> speed as they go along it. Different frequencies hit
> their maximum amplitude on the BM at different spots,
> called "best frequencies" (this is how the ear extracts
> the partials of a sound). It's the speed of waves *at
> these spots* on the BM that matches the speed of waves
> at any spot on the TM. According to the authors, this
> means that the waves on the TM could selectively amplify
> waves on the BM at their best frequencies, thus improving
> the sensitivity of the ear.
> Well, the width of the best frequencies is the critical
> band (about a whole tone through the center of the piano)
> while the selective amplification would cover an octave
> according to this paper. So it's not entirely specific.
>
> So that's kinda cool, but the problem of course is that
> this was all done with tiny pieces of tissue on a jig,
> not in a real cochlea where they are meant to fit. The
> authors use a computer simulation to see if being inside
> a real cochlea would change the results, and conclude
> that it wouldn't. But this isn't terribly convincing.
>
> So nifty research, but still pretty speculative.
>
> -Carl
>
>
>
> You can configure your subscription by sending an empty email to one
> of these addresses (from the address at which you receive the list):
> tuning-subscribe@yahoogroups.com - join the tuning group.
> tuning-unsubscribe@yahoogroups.com - leave the group.
> tuning-nomail@yahoogroups.com - turn off mail from the group.
> tuning-digest@yahoogroups.com - set group to send daily digests.
> tuning-normal@yahoogroups.com - set group to send individual emails.
> tuning-help@yahoogroups.com - receive general help information.
>
> Yahoo! Groups Links
>
>
>

Oz wrote...

> Does this in any way change our understanding of harmonics?

Not that I can think of at this point, but it isn't out
of the question. There may be psychoacoustic phenomena
related to the octave boost thing.

-Carl

> ----- Original Message -----
> From: "Carl Lumma" <carl@...>
> To: <tuning@yahoogroups.com>
> Sent: 15 Ekim 2007 Pazartesi 1:42
> Subject: [tuning] Re: MIT researchers make new discovery in
> the anatomy of hearing
>
> > I'll try to summarize the paper now:
> >
> > http://www.pnas.org/cgi/reprint/0703665104v1.pdf
> >
> > When sound enters your ear it drives the ear drum, which
> > drives some lever-action bones, which push and pull on
> > the "oval window" on the cochlea, which creates
> > *transverse waves* along the basilar membrane inside the
> > cochlea, which stimulate hair cells attached to the
> > basilar membrane, which create nerve impulses that go to
> > your brain.
> >
> > That's the standard model of hearing. But above the
> > hair cells, running parallel to the basilar membrane (BM)
> > is this thing called the tectorial membrane (TM), which
> > is basically a very thin strip of Jell-O. Because it's
> > so soft and thin, nobody thought it was good for much.
> >
> > Well these researchers believe otherwise. They've gone
> > and cut TMs out of mice, and mounted them on a jig where
> > they are strung between two supports. The scientists
> > jiggle one of the supports and watch what happens to the
> > TM with a strobe light.
> >
> > What they found is that the TM can conduct *longitudinal
> > waves* when driven at audio frequencies. Moreover,
> > these waves travel through the TM at the same speed as
> > transverse waves do through the BM. Actually the BM
> > varies in stiffness along its length, so waves will change
> > speed as they go along it. Different frequencies hit
> > their maximum amplitude on the BM at different spots,
> > called "best frequencies" (this is how the ear extracts
> > the partials of a sound). It's the speed of waves *at
> > these spots* on the BM that matches the speed of waves
> > at any spot on the TM. According to the authors, this
> > means that the waves on the TM could selectively amplify
> > waves on the BM at their best frequencies, thus improving
> > the sensitivity of the ear.
> > Well, the width of the best frequencies is the critical
> > band (about a whole tone through the center of the piano)
> > while the selective amplification would cover an octave
> > according to this paper. So it's not entirely specific.
> >
> > So that's kinda cool, but the problem of course is that
> > this was all done with tiny pieces of tissue on a jig,
> > not in a real cochlea where they are meant to fit. The
> > authors use a computer simulation to see if being inside
> > a real cochlea would change the results, and conclude
> > that it wouldn't. But this isn't terribly convincing.
> >
> > So nifty research, but still pretty speculative.
> >
> > -Carl