source file: m1410.txt
Date: Fri, 8 May 1998 19:07:45 -0700 (PDT)

Subject: ear architecture

From: Jesse Bagshaw Gay <jgay@reed.edu>

re: several things about the ear from several recent posts...

one of my texts(Sensation and Perception, by Coren et al)  says:

1. Individual neurons can fire up to 1000 time/sec.
The volley theory says that groups of neurons cooperate in response to
higher frequencies( for example, to
represent 2000 Hz, 2 neurons could fire at 1000 Hz each, 180 degrees out
of phase with each other) Such cooperation has been shown up to about 4000
Hz.

2. In general, there are two ways in which sounds are differentiated by
the ear.

a. Place theory:  The basilar membrane is shaped like a very long
triangle.  Each region resonates at a different frequency.  Consequently,
the place on the basilar membrane that gets most excited in response to
any incoming sound wave provides information about the frequency.

b.Frequency theory:  Individual neurons fire at the rate of the incoming
sound.(Or groups, as per the volley theory.)

The place theory does not hold below about 500 Hz, and the frequency
theory does not hold above about 4000Hz.  Between 500 and 4000 hz, both
mechanisms play a role.

3.  Some kind of higher processing occurs which enables the brain to infer
a fundamental from a set of sufficiently defined harmonics.