Re: pitch neurons

[Martin Braun <nombraun@xxxxxxxxxxxxxxx>]

Hi Peter and List,

you wrote (Peter Cariani, Oct 9, 2nd mail):

> We all agree that there are neurons in the IC that have bandpass MTF
> functions. This is possibly the best theory that we have at the moment
> for some complex tone pitches,

It is not only "the best that we have", it is also the only one for which we
have physiological data. Terhardt's pitch theory, for example, is now 30
years old, and as yet not one piece of physiological data has been found to
support it.

> but it is a very weak explanation, with many problems:

Here I disagree strongly.

> 1) IC MTF functions generallyhave broad tunings to begin with when
> compared with pitch discriminations,

Pitch discrimination is based on large populations of MTF neurons that work
in parallel. The broad tuning we see in the data is from single unit or
small population recordings.

> 2) they flatten out at higher SPLs when pitch percepts remain highly
> salient,

Also this effect is likely to disappear in population coding.

> 3) Bandpass MTFs cannot explain pitch equivalence between pure and
> complex tones
>     (why would it be that all auditory systems down to goldfish do this?)

The paper by Biebel and Langner (2002), which I referenced in the first
message of this thread, confirms the "pitch equivalence between pure and
complex tones" that they had already reported at the Prague conference 1996
and in Syka's book 1997.

> 4) they cannot explain the pitch shifts of inharmonic AM tones (first
> effect
> of pitch shift, resolved harmonics, de Boer's rule),

This "pitch shift" only occurs with lab sound. It is likely that in this
case a non-pitch mechanism accidentally interferes with the pitch
mechanism.

> nor can they explain how it
> is that we can hear the pitches associated with both of 2 concurrent
> notes on the piano
> that are a few semitones apart (these interact destructively in an
> MTF-based representation)

Such a "destructive interaction" has never been shown, nor can it be
expected from the MTF data that we have.

Martin

-------------------------------------------
Martin Braun
Neuroscience of Music
S-671 95 Klässbol
Sweden
e-mail: nombraun@post.netlink.se
web site: http://hem.netlink.se/~sbe29751/home.htm
-------------------------------------------

On the evolution of a fact in science:
Stage 1 .......................... "Totally absurd stuff."
Stage 2 .......................... "Interesting, but queer."
Stage 3 .......................... "Correct, but unimportant."
Stage 4 .......................... "I have always said this."
[John BS Haldane (1892 - 1964), biologist]