Re: Rationale for Critical Bands

[Martin Braun <nombraun@xxxxxxxxx>]

Richard F. Lyon asked:

"I'm open to the idea that ....... some kinds of psychophysical experiments
give a CB that doesn't vary with level, though I
haven't really seen the evidence for it yet.
Maybe you can point us toward some."

The best "experiments" for your answers are ordinary speech and music.

1) The quality of speech perception does not deteriorate when sound level 
increases from 50 to 80 dB.

2) The consonance vs. dissonance balance of a musical chord does not change 
when sound level increases from 50 to 80 dB.

These observations tell us that spectral filtering, including band 
filtering, in the auditory system is as good as unchanged in this level 
range.

We probably have lateral inhibition at all stages in the auditory pathway. 
This means that not only neural excitation is level dependent, but also 
lateral inhibition. Therefore it is no surprise that many experiments show 
level dependence in spectral filtering. Results vary with experimental 
design and say very little about real-life acoustical filtering such as in 
speech and music.

The central nucleus of the inferior colliculus (ICC) has a unique role in 
lateral inhibition, because here it is anatomically predetermined by the 
laminar structure of the nucleus. The mechanism of this nucleus enables the 
level independence of spectral filtering that we experience in speech and 
music.

The best descriptions of this mechanisms that I know of are in:

http://www.ncbi.nlm.nih.gov/pubmed/9237756

http://www.ncbi.nlm.nih.gov/pubmed/10190753

Martin


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Martin Braun
Neuroscience of Music
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Sweden
email: nombraun@xxxxxxxxx
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