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pitch in primate auditory cortex
John Bates wrote:
..... I refer to "The neuronal representation of pitch in primate auditory
cortex." by Daniel Bendor and Xiaoqin Wang in the August 25 issue of
Nature. They demonstrate that the missing fundamental is a valid neural
Pitch neurons had previously been recorded in the auditory midbrain, i.e.
two synaptic levels below the primary auditory cortex, by Biebel and Langner
(1997 and 2002). The new findings of Bendor and Wang agree well with the
earlier ones, and they provide an important missing link for the hypothesis
of Langner (1992) that pitch is extracted by periodicity analysis in the
midbrain and then coded, and transmitted up to the cortex, as part of the
low-frequency section of the auditory neural pathway. While the exact
location of the now discovered pitch neurons in the cortex remains to be
determined by future anatomical studies, the new physiological data indicate
that they may not only be present in the low-frequency section of the
primary auditory cortex, but also in adjacent low-frequency sections of
secondary auditory fields. Such a distribution would agree with the
important role of pitch in the high-order processes that underlie sound
identification and acoustic communication.
An interesting detail of the new results is the following one: When partials
6 and 7 of the complex tone stimulus were the two lowest ones, pitch
salience, as measured in neuronal firing rate, was still optimum. But when
partials 7 and 8 were the two lowest ones, pitch salience was clearly
sub-optimum (Fig. 4c). This breakpoint in pitch salience above partial 7
agrees exactly with psychoacoustic data from humans for the pitch range of
the central octave of music (C4-C5). This finding adds to previous data
suggesting that the origin of the breakpoint lies in the laminar
architecture of the auditory midbrain (Braun, 1999). Because the cochlea is
smaller in marmosets than in humans, frequency resolution at this level is
likely to be better in humans. But frequency resolution at the midbrain
level, which apparently determines the contribution of partials in pitch
detection (Braun, 1999), may be very similar in both species.
Bendor, D., Wang, X. (2005). The neuronal representation of pitch in primate
auditory cortex. Nature, 436, 1161-1165.
Biebel, U.W., Langner, G. (1997). Evidence for "pitch neurons" in the
auditory midbrain of chinchillas. In: Syka, J. (Ed.), Acoustic Signal
Processing in the Central Auditory System. Plenum Press, New York, pp.
Biebel, U.W., Langner, G. (2002). Evidence for interactions across frequency
channels in the inferior colliculus of awake chinchilla. Hear. Res. 169,
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.
Braun, M., (2000). Inferior colliculus as candidate for pitch extraction:
multiple support from statistics of bilateral spontaneous otoacoustic
emissions. Hear. Res. 145, 130-140.
Langner, G., (1992). Periodicity coding in the auditory system. Hear. Res.
Langner, G., Schreiner, C.E., Biebel, U.W., (1998). Functional implications
of frequency and periodicity coding in auditory midbrain. In: Palmer, A.R.,
Rees, A., Summerfield, A.Q., Meddis, R. (Eds.), Psychophysical and
Physiological Advances in Hearing. Whurr, London, pp. 277-285.
Rees, A. and Sarbaz, A. (1997) The influence of intrinsic oscillations on
the encoding of amplitude modulation by neurons in the inferior colliculus.
In: J. Syka (Ed.), Acoustic Signal Processing in the Central Auditory
System, Plenum Press, New York, pp. 239-252.
Schreiner, C.E., Langner, G., (1997). Laminar fine structure of frequency
organization in auditory midbrain. Nature 388, 383-386.
Neuroscience of Music
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