Re: [AUDITORY] Gammatone filter bank in MATLABr2019a

[William Yost <William.Yost@xxxxxxx>]

I agree with your view. In fact, I often argue that one of the major things the success of the cochlear implant implies is that one does not need an "ear" to "hear," but one does need a "brain." And, the "brain" only needs a crude representation of what the "ear" provides to "hear."

William A. Yost, PhD
Research Professor
Spatial Hearing Laboratory
College of Health Solutions
ASU, P.O. Box 870102
Tempe, AZ 85287 USA
480-727-7148
Fax: 480-965-8516
William.Yost@xxxxxxx
https://isearch.asu.edu/profile/1099656


-----Original Message-----
From: AUDITORY - Research in Auditory Perception <AUDITORY@xxxxxxxxxxxxxxx> On Behalf Of Bastian Epp
Sent: Tuesday, April 16, 2019 12:04 AM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Gammatone filter bank in MATLABr2019a

Dear list,

This morning I read through the release notes of MATLAB R2019a and was happy to find that there was an implementation of a Gammatone filter bank included: 

"Gammatone Filter Bank: Mimic the human auditory system"

With the reference to (among others):

Glasberg, Brian R., and Brian CJ Moore. "Derivation of Auditory Filter Shapes from Notched-Noise Data." Hearing Research. Vol. 47. Issue 1-2, 1990, pp. 103 –138.

This made me quite happy because it is a proper description of what Gammatone filter banks most often are used for - to model the frequency selectivity of the auditory system (as measured using psychoacoustics).

However, in the DOC page, they show a picture of the Basilar membrane on top with the frequency response of the filter bank - suggesting that there exists a 1:1 correspondance.

Everybody needs a topic to grow old and grumpy on - mine is this: 

From my point of view, this is only correct under the (overly strong?) assumption that the cochlear is the only place in the auditory system underlying the perceptually observed frequency selectivity. Measuring "auditory filters" means to evaluate the auditory system as a whole (the concept of a "neuron" also only makes sense when being embedded in its network). "Cochlear filters" are measured on/in the cochlea . 

Besides the common critiques (linearity, coarse approximation of the actual "filter" shape, etc), the main problem in my point of view is that we teach students that we can "measure" the function of a "subsystem" (the cochlea) using a method that assesses the function of the "whole" system. There are some data sets that suggest a strong link, but the "tool" of psychoacoustics simply does not allow such a statement.

Even though I like the working hypothesis "The brain exists to keep the cochlea warm", I think equating cochlear frequency selectivity with auditory filters (without explicitly stating the assumption that no(!) element along the auditory pathway modifies this frequency selectivity) is a point where we could  be more careful to avoid misconceptions and overly strong conclusions. In most publications and books, this point is not explicitly wrong, but not as precise as it could be in my opinion.

I hope that someone from MATHWORKS follows this list and considers a more careful description in the DOCs. I would also be happy to compile all the constructive arguments that people might have for/against my point of view.

Have a great day everybody!

BAstian




--
Bastian Epp
Associate Professor

DTU Healthtech
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