Subject: Re: Rationale for Critical Bands From: Martin Braun <nombraun@xxxxxxxx> Date: Tue, 15 Jun 2010 15:10:10 +0200 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>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 --------------------------------------------------------------------- Martin Braun Neuroscience of Music S-671 95 Klässbol Sweden email: nombraun@xxxxxxxx web site: http://www.neuroscience-of-music.se/index.htm