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

[Martin Braun <nombraun@xxxxxxxxx>]

Peter Cariani wrote:

> Modulation-tuned units have been found in abundance, but there are some
> basic problems with these when it comes to pitch:
> 1) they cannot explain pitch equivalence between pure and complex tones
> (big, big problem)

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

> 2) they are not likely to represent multiple competing pitches in a
> robust fashion (e.g. two musical instruments playing notes a third
> apart --)

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.

> 3) they are not likely to yield a representation that does not degrade
> at high SPLs

Level stability is provided by lamina-based lateral inhibition in the
midbrain.

> 4) they are not likely to explain the pitch shifts of inharmonic
> complex tones

Period detectors register these pitch shifts, as calculated many years ago.

> 5) it's not clear if predicted pitches of low harmonics will be
> invariant with respect to phase spectrum (as they should be)

There are plenty of possibilities for phase resetting between cochlea and
midbrain.


In general: There is not one observation, either psychoacoustic or
physiological, that is not compatible with pitch extraction in the central
nucleus of the inferior colliculus by periodotopic arrays of tuned pitch
neurons.

The evidence for this mechanism has accumulated since 1987.

For reviews:
http://w1.570.telia.com/~u57011259/eng5.htm

For some recent evidence:
http://w1.570.telia.com/~u57011259/Galazyuk.htm

Martin

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