"pure place code" and "pure phase-locking code" (Martin Braun )

Subject: "pure place code" and "pure phase-locking code"
From:    Martin Braun  <nombraun(at)POST.NETLINK.SE>
Date:    Sat, 21 Oct 2000 13:32:13 +0200

Annemarie wrote: "I had in mind the study by Steinschneider et al., JASA, 104 (5), 1998, 2935 ff. who found that at the level of the primary auditory cortex phase locked responses occurred only at sites with high best frequencies up to about 200 Hz (stimuli: alternating polarity click trains), ............ Does that mean that the temporal code might not play a role at all in the low frequency channels or is it more likely that phase locking had been transformed into a rate-place code before the A1 (perhaps in the midbrain)?..........." Answers: 1) As soon as a harmonic is resolved in the cochlea, spectral coding take= s place and then runs along the complete auditory pathway. 2) If the spectral information is poor in the cochlea, as with click stimuli, it is also poor anywhere else in the auditory system. 3) Current evidence indicates that f0 in the main speech and music range = is transcoded from a temporal to a place code in the central nucleus of the inferior colliculus (ICC). In other words, time-locking in this f0 range disappears above the ICC, and the extracted f0-pitch is coded at its frequency place by discharge rate, as most other information that is transported into and around the cortex. (See references below) 4) Phase-locking to acoustic frequencies recorded in the cortex possibly = is not related to pitch extraction at all. It may be a by-product of other functions of the auditory system, e.g. orientation in space. In conclusion: A) In the cortex, f0-pitch in the main speech and music range is coded purely spectrally. (No phase-locking in pitch coding) B) Up to the ICC, f0-pitch in the main speech and music range can be code= d purely temporally, but for all natural, i.e. non-laboratory, complex tone= s it is coded spectrally and temporally. (Phase-locking necessary for pitch coding) Langner, G., 1992. Periodicity coding in the auditory system. Hear. Res. = 60, 115-142. Schreiner, C.E., Langner, G., 1997. Laminar fine structure of frequency organization in auditory midbrain. Nature 388, 383-386. 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. Braun, M., 1999. Auditory midbrain laminar structure appears adapted to f= 0 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. Martin Martin Braun Neuroscience of Music Gansbyn 14 S-671 95 Kl=E4ssbol Sweden nombraun(at)post.netlink.se

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