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Re: Laws of physics and old history (A new paradigm?(On pitch and periodicity (was "correction to post")))

Dear List,
As the mathematics of the proposed models get hairier one has to look back in history to some results of auditory patterns published by Dr. Harvey Fletcher, which showed that for pure tones the maximum peak of activity occurs at the CF location and decreasing peaks of activity at harmonic locations. The extant of such a pattern increases with stimulus strength, that is towards the basal end. I am not sure whether these results have been universally accepted, I for one have not seen any criticisms, but I find support in that, ISI's have been reported to reliably exist at integer fractions of the fundamental period of the stimulus, thereby indicating some sustained activity at the harmonics. It has also been reported, again I have no reason to dispute this, that the range of stiffness of the BM only varies by a factor of 6 or so, while our frequency range would demand a much larger number. If any model appeals to resonance as the basis of BM movement, then such resonance elements would have to be shown to have the required range of our hearing. With these observations, proposals using linear or non-linear models using only passive elements, then compressing a stimulus wavelength measured in meters to a length which is a fraction of 32 mm are hard to accept, irrespective of what the associated mathematics used by the models may show. I have my own doubts of how these equations are being interpreted, but I shall leave it to the rest of the auditory community to come to their own conclusions. 

Thanks, cheers,
Randy Randhawa


On 10/31/2011 10:39 PM, Steve beet wrote:

I'd just like to add my vote to Dick Lyon's interpretation of the laws of
physics: in the cochlea the "free-space" speed of propagation in the
perilymph / endolymph would be very high but the transverse dimensions of
the structures within the cochlea are small. Consequently there should be
only one mode of propagation in the normal audio frequency range - although
I'm not sure how well the concept of "modes of propagation" fits with
non-uniform partially-elastic structures such as those found in the cochlea.

> From the evidence I've seen, the speed of propagation within the cochlea is
almost entirely determined by the elasticity and dimensions of the basilar
membrane, and the density and viscosity of the fluids in the cochlea. The
other structures within the cochlea (notably the tectorial membrane and the
active effects of the OHCs) also need to be accounted for if you want a
truly accurate model, but I can see no reason to suppose that they are even
linear, let alone quantifiable in terms of a simple transmission-line model.

Steve Beet



-----Original Message-----
From: AUDITORY - Research in Auditory Perception
[mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Richard F. Lyon
Sent: 31 October 2011 21:47
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Re: A new paradigm?(On pitch and periodicity (was "correction to
post"))

In the ear, the stapes doesn't couple much energy into this fast
pressure-wave mode.  A much slower propagating vibration mode is involved in
the cochlear traveling waves that use the compliance of the basilar
membrane, as opposed to compression of the fluid, as the displacement-based
restoring force that leads to the wave equations.