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Re: Rationale for Critical Bands

I'm still unclear on Ehret's point of view on this critical band in ICC and its level dependence or not. The 1988 quotes don't clarify a lot.

I still haven't been able to find the basis for this statements that the critical band he finds in ICC is level independent. His own 1985 figure with Merzenich seems to contradict the idea that CB is level independent. See http://dicklyon.com/tech/Scans/Ehret_data.png where I fitted the high-level and low-level points separately, and got lines spaced apart by a half octave and more between them, sort of like CB in the periphery. There's too much noise in the data to draw any strong conclusion, but certainly the data doesn't support the idea that this measure of bandwidth of level independent.

I have no quibble with Ehret's statement that "The regression line gives a good approximation of average neuronal critical bandwidths valid for the whole tested intensity range." That is, it's an OK level-independent approximation; such approximations are commonly done, and not unique to ICC.

As to "the critical band analysis must arise in higher auditory brain centers," that may be true for what he's describing here as "the critical band analysis". I'm not convinced it has a lot to do with what's usually called critcal bands, which are on the order of 1/4 to 1/3 octave over most of the auditory range. Nearly half of Ehret's data are over 1 full octave, and there's huge scatter. It really seems like a different beast.

The other p.140 quote also sounds sensible, but not clearly relevant to the discussion.

I'd still like to see what he published in 1995 and referenced for the conclusion of constancy with level.


At 9:34 PM +0200 6/23/10, Martin Braun wrote:
Dear Dick and other,

You need not find the proceedings of the 1994 Irsee conference. Ehret's (and Merzenich's) work on CB related observations in the ICC of the cat is completely documented in a comprehensive review from 1988:


Here you find many neuronal tuning curves which show you a level independence over large level ranges. Further, as to the authors' opinion on your question, you might like to read the following three quotes from this review:

"It is suggested that the critical band analysis must arise in
higher auditory brain centers." (p. 140)

"This convergence of input on a single map of frequency representation in
the ICC can be expected to give rise  to coding of critical band
characteristics which lack an explanation by neuronal responses at
lower levels." (p. 140)

"The critical bandwidth, of which in 1970 J.V. Tobias said in the foreword
to Scharf's chapter on critical bands
'..... the other senses lack the mysteriousness of this unseen - perhaps nonexistent - but pervasive auditory filter', would exist in the functional anatomy of the central nucleus of the IC." (p. 160)

Why it is the anatomy of the ICC, which is unique in the brain concerning its CB relatedness, is described in the work of Langner, Schreiner, and Braun, which I have already referenced twice in this thread.


Martin Braun
Neuroscience of Music
S-671 95 Klässbol
email: nombraun@xxxxxxxxx
web site: http://www.neuroscience-of-music.se/index.htm

----- Original Message ----- From: "Richard F. Lyon" <DickLyon@xxxxxxx>
To: <AUDITORY@xxxxxxxxxxxxxxx>
Sent: Wednesday, June 23, 2010 7:34 PM
Subject: Re: Rationale for Critical Bands

A follow-up, in case anyone still cares...