Re: pitch neurons (Eckard Blumschein )

Subject: Re: pitch neurons
From:    Eckard Blumschein  <Eckard.Blumschein(at)E-TECHNIK.UNI-MAGDEBURG.DE>
Date:    Mon, 7 Oct 2002 10:37:27 +0200

Dear Martin and List,

Israel Nelken referred to the following poster by Dave McAlpine:
"Are Pitch Neurones the Result of Difference Tones on the Basilar Membrane?"

At 14:33 02.10.2002 +0200, Martin Braun wrote:
>Israel Nelken wrote:
>
>> All in all, I think that the cautious position at the moment is still
>> that there is no unequivocal evidence for pitch sensitivity up to and
>> including the level of primary auditory cortex in animals, independent
>> of the spectral content of the sounds.

Eli supports the traditional notion of purely spectral coding inside cochlea.
However a while ago, Viemeister wrote:

"Physiological and some psychophysical data have indicated that this
distortion hypothesis is incorrect. It occasionally re-emerges as
an explanation..."

he added

"The generally-accepted explanation of the beats of mistuned consonances
stems from the classic study of Plomp (1967) and invokes the periodic
changes in the fine structure of the waveform that are produced by
mistuned consonances. This "waveform" hypothesis requires preservation
of fine structure in the auditory nerve and thus relies on phase locking."

and he reported

"The beats of a mistuned octave (and fifth) are highly detectable at
frequencies above those for which fine structure information is
well-preserved (e.g. 4000 Hz and  8003 Hz)".

Perhaps, we don't understand how phase locking works at 4kHz and above.
In a private reply to David Pressnitzer, I already tried to explain
what I grasped from Delgutte. I will try it again in other words and hope
for David's support if I don't manage to express myself here convincingly:

Peter Dallos mentioned an estimated 10,000 papers dealing with the auditory
nerve. Nonetheless, some essentials have obviously been overlooked.
On average, ten auditory nerve fibers cooperate statistically with just
one inner hair cell. Each fiber is bound to refractory time. So roughly
speaking, all ten together cannot continuously phase lock with intervals
smaller than a tenth of refractory time. Merely below about 1kHz,
synchrony can be very high.
This limitation due to statistic time sharing does, however, not exist
immediately after nearly all fibers reached a state of readiness for firing.
Given frequency of modulation or rate of clicks is low enough for that,
then the stationary upper frequency limitation is much less relevant
for the whole temporal structure, including interaural envelope delay (IED),
during a split millisecond of adaptation.

So I consider Israel Nelken and Dave McAlpine possibly close to the truth
in that they imagine a peripheral mechanism involved. Saturation of OHCs
is close to but different from stochastics of auditory nerve fibers.
Martin, I feel you are correct.

Regards,
Eckard