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Re: Traveling waves or resonance?


I think your efforts at clarification actually muddy the waters, as I can't
agree with your attempts to dispel two "popular misconceptions".

1. Of course Gold predicted spontaneous otoacoustic emissions as well as the
cochlear amplifier. The reason is that the former depend on the latter. As
he explained it, positive feedback could easily be excessive and lead to
continuous oscillation. Following the logic through, he placed a microphone
in an ear canal and tried to detect the oscillation. A wonderful experiment
that had to wait until Kemp's efforts a quarter of a century later for

You criticise Gold's experiment because he caused the ear to ring beforehand
by imposing a loud sound, so you say he was really trying to detect tonal
tinnitus. Yes, there is a leap in logic in linking tonal tinnitus with
spontaneous mechanical activity produced by positive feedback in the
cochlea, but the leap is reasonable - both phenomena have similar
characteristics (continuous narrow-band oscillation) and relate to the ear.

It turns out that usually the frequencies of the two phenomena are
different, but there are cases in which the objective SOAE frequencies match
the subjective ones (as you allow with your qualifier "vast majority of
cases"). I can subjectively hear the 1440 Hz SOAE in my left ear, for
example. But then you say tinnitus can "never" be picked up with a
microphone, which, in the light of the foregoing, is clearly not the case.
Even if you meant that tinnitus originating as neural activity can never
drive the cochlea in reverse and be detected with a microphone, that is just
a preconceived notion, as we just don't know. It's a leap of logic which is
exactly the opposite of Gold's conjecture that tinnitus _always_ has a
counterpart in the cochlea and ear canal.

I remain open-minded on the possible connection between the subjective
(tinnitus) and objective (SOAEs) aspects of the auditory system. It's an
exciting one that is best not prejudged. As the saying goes, if it looks
like a duck, sounds like a duck, and walks like a duck, then it's very
likely that it is a duck.

2. I would not dismiss as "silly" Gold's argument that amplification before
detection is a sound strategy in signal detection. It means that
signal-to-noise ratio is preserved, and that is a fundamental physical
principle which has to be obeyed in order to detect signals down at the
theoretical limits. 


Andrew Bell
Research School of Biological Sciences
The Australian National University
Canberra, ACT 0200, Australia
T: +61 2 6125 9634
F: +61 2 6125 3808

-----Original Message-----
From: AUDITORY Research in Auditory Perception
[mailto:AUDITORY@LISTS.MCGILL.CA] On Behalf Of Martin Braun
Sent: Monday, 18 October 2004 4:42 AM
Subject: Re: [AUDITORY] Traveling waves or resonance?

On Friday, October 15, Andrew Bell wrote:

> .... Happily,
> progress has been made in my endeavours to revive a resonance theory of
> hearing

Current knowledge on resonance, traveling waves, and amplifiers in the inner
ear goes well beyond that what Andrew Bell now reviews. Also, the main parts
of this information is easily accessible on the web.

I would like to comment, however, on two popular misconceptions, which were
now repeated again, and for which no, or very little, information is
available on the web.

1) Thomas Gold predicted the cochlear amplifier, but not otoacoustic
emissions (OAEs). The "ringing in the ear" which he tried to measure, was
tonal tinnitus, which, in the vast majority of cases, has nothing to do with
OAEs. Such tinnitus is nearly always neurally based and can never be picked
up with any microphone.

2) Gold's argument that the inner ear "needed" a mechanical amplifier before
the stage of neural transmission is actually quite silly. Other sensory
organs have their amplification cascades on a biochemical level within the
sensory cells. The same also works in hearing. Only birds and mammals have
specialized mechanical pre-amp cells, as an additional mechanism. This
"design" provides several advantages, but it is by no means a precondition
of hyper-sensitive hearing.


Martin Braun
Neuroscience of Music
S-671 95 Klässbol
web site: http://w1.570.telia.com/~u57011259/index.htm