Subject: pitch in primate auditory cortex From: Martin Braun <nombraun(at)TELIA.COM> Date: Tue, 20 Sep 2005 15:29:17 +0200John 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 > percept ......... 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. 263-269. Biebel, U.W., Langner, G. (2002). Evidence for interactions across frequency channels in the inferior colliculus of awake chinchilla. Hear. Res. 169, 151-168. 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. 60, 115-142. 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. Martin ---------------------------- Martin Braun Neuroscience of Music S-671 95 Klässbol Sweden web site: http://w1.570.telia.com/~u57011259/index.htm