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Re: Pitch neurons (was "Autocorrelation-like ...")

Peter Cariani wrote:

> Martin: "No problem. F0 periods that arise in the frequency laminae of
> the partials are forwarded to the frequency laminae of F0."

> if this were the case then there should be true pitch detectors that
> respond both to a pure tone and a complex with a missing F0 at the same
> frequency. Schwarz & Tomlinson (1990) looked hard in the awake monkey
> cortex without success.

F0 pitch and pure-tone pitch are detected by the same neurons in the
low-frequency laminae of the midbrain. After that they are not represented
by the same neurons in the cortex. This is no surprise at all. An F0 comes
together with spectral information (timbre), a pure-tone doesn't. We have
completely different inhibitory response chains for the two stimuli.
Remember that pure-tones do not occur in nature, and that our hearing is in
no way adapted to them.

> Martin: "We only hear two pitches, if there are strong timbre labels
> attached to them. These are decoded in the cortex, which then feeds
> back to the pitch neurons in the midbrain."

> Simultaneously play two notes a whole step (or more) apart on the
> piano. Do you hear one or two notes?

No note at all. Only a chord.

> On what basis can you say that the notes MUST be separated in the
> cortex? How "anatomically and physiologically realistic" is this
> assertion?

Timbre detection is based on memory reference. This is not possible below
the cortex.

> But it still seems to me that even at the level of the IC,
> interval representations for low pitches still have more plausibility
> than those based on modulation-tuned pitch detectors

Interval representations are the matter that must be detected by SOMETHING.
This something are tuned pitch neurons.

> Martin: "Level stability is provided by lamina-based lateral inhibition
> in the midbrain."

> Show me the neural data. I want to see MTFs and pitch representations
> that are every bit as good at 90 dB SPL as they are at 40 or 50 dB.

MTFs [modulation transfer functions] do not occur with a piano tone. With a
piano tone you have beats between the partials in the middle-frequency
laminae of the midbrain, which are then detected by tuned pitch neurons.
Sound level does not affect either the partial frequencies or the beat
frequencies. It only affects the mutual inhibition of partial frequencies,
and thus strength of pitch, but not pitch height.

> Martin: "Period detectors register these pitch shifts, as calculated
> many years ago."

> Only if they are based on autocorrelation or something roughly
> equivalent. Modulation detectors won't work ...

See last answer. Also see what I wrote on beats in the midbrain (Braun,
1999). You will then see that pitch neurons that function as tuned
resonators can do all what autocorrelators can. Subcellular time constants
are solutions of biology, whereas autocorrelation circuits are solutions of
man-made electronics.

Braun, M., 1999. Auditory midbrain laminar structure appears adapted to f0
extraction: further evidence and implications of the double critical
bandwidth. Hear. Res. 129, 71-82.


Martin Braun
Neuroscience of Music
S-671 95 Klassbol
e-mail: nombraun@telia.com
web site: http://w1.570.telia.com/~u57011259/index.htm