Re: comparing cochlear models ?

[Michael RAPSON <MICHAEL.RAPSON@xxxxxxxxx>]

Hi all,

I have also been thinking about comparing cochlear models and came to the conclusion that having the models implemented in the same software 'framework' has major advantages when it comes to drawing comparisons. 

By framework I mean a set of methods that can implement all the models of interest fairly and provide identical conditions for both models aside from the differences investigated. For example, if two different approaches of incorporating outer hair feedback are studied, it seems reasonable to compare them on the same cochlear geometry with a similar model of the stapes and middle ear. If code that can do this is used a range of mathematical norms can be used to quantify the differences in their response numerically. Even if this level of comparison is not useful, a number of uncertainties about the causes of differences in response are immediately eliminated. 

A framework of this kind need not provide every solution technique used in cochlear modeling so far. The same basic model (say the finite difference model used by Neely in 1981) can be implemented in a range of different ways (the finite element method or Green's functions for example) and all of these can be treated as the same model with different implementations. 

Given the range of cochlear models that have been proposed, a framework of this type has to provide a very broad set of options for users who want to implement a specific model. I have been putting together a library that can do this, with the aim to be able to support models that require two scalae as required for models like Andrew Bell and others propose, communication between radial segments as required for feed-forward models and nonlinear behavior in the time domain. 

Something that I would like to see is a framework like this that provides a passive cochlear model widely agreed to be accurate. People building active models would then add their proposed mechanisms into the passive environment in order to modify its behavior. However there are a number of difficulties associated with designing something of this sort.

Regards,
Michael

>>> Bastian Epp  05/21/10 1:39 PM >>>
Dear list!

As the comparison and evaluation of cochlear models is exactly what 
bothered my during the last year (or so), I think I want to share my points:

In general, it is very interesting to compare and to evaluate models of 
the cochlea...even though that is sometimes quite hard due to different 
approaches.

I agree with the view, that one way to evaluate cochlear models is to 
look at their performance to account for many different datasets 
(physical (OAE), physiological(I/O) and even psychoacoustical) 
simultaneously with a "decent" amount of fixed parameters....but 
especially for the psychoacoustic paradigms, the potential for arguing 
starts at the metric which is evaluated to account for the data. So 
maybe one should start with physiological data and/or use very simple 
(and still feasable) approaches for psychoacoustics. Some ideas as a 
starter:

Excitation patterns:
Evaluation of the shape of the excitation pattern (slopes basal/apical, 
Q-factor, ...) in a panoramic view (whole cochlea) and at a single place 
for different frequencies (place-fixed view).

I/O-functions:
Evaluation of the response of the model at a fixed place for different 
levels of the same frequency

OAE:
Propagation of the cochlear activity through a simple model of the 
middle ear (which should be comparable as long as the used middle ear is 
linear).
Phase-issues with evoked (e.g. CEOAE) emissions?

Two-tone suppression:
Here it's getting neccessary to define the metric which is evaluated, 
but there should be the phenomenon of a nonlinear interaction of two 
tones...independently of the analysis which is applied.

...

All these measures should be relatively robust against absolute scaling 
and hence be comparable and (if the model is supposed to be "realistic" 
in one sense or the other) in line with data.

I see a big chance in that, since different models account (and are 
developped for) different aspects of cochlear functioning, and all 
reflect a special case of THE cochlea which was implemented by nature.

We did the things mentioned above (and some more) using the 
Duifhuis-Transmission line in a modifed form. I would be happy to share 
ideas with anybody who is also interested. We are also preparing a 
manuscript and I am also happy to share that as soon as it is in a 
readable form. (BTW: Thx Jon for sharing the manuscript, nice collection 
of data and a good start for discussions....)

If anybody read the message until here: Sorry for the length.

Best from Oldenburg

BAstian


 

###
UNIVERSITY OF CAPE TOWN 

This e-mail is subject to the UCT ICT policies and e-mail disclaimer published on our website at http://www.uct.ac.za/about/policies/emaildisclaimer/ or obtainable from +27 21 650 4500. This e-mail is intended only for the person(s) to whom it is addressed. If the e-mail has reached you in error, please notify the author. If you are not the intended recipient of the e-mail you may not use, disclose, copy, redirect or print the content. If this e-mail is not related to the business of UCT it is sent by the sender in the sender's individual capacity.

###