Editing Pitch (music) (section)

===Theories of pitch perception===

[[Scientific theory|Theories]] of pitch perception try to explain how the physical sound and specific physiology of the auditory system work together to yield the experience of pitch. In general, pitch perception theories can be divided into [[Place theory (hearing)|place coding]] and [[Temporal theory (hearing)|temporal coding]]. Place theory holds that the perception of pitch is determined by the place of maximum excitation on the [[basilar membrane]].

A place code, taking advantage of the [[tonotopy]] in the auditory system, must be in effect for the perception of high frequencies, since neurons have an upper limit on how fast they can [[Volley_theory#Phase-locking|phase-lock]] their [[action potential]]s.<ref name=plack /> However, a purely place-based theory cannot account for the accuracy of pitch perception in the low and middle frequency ranges. Moreover, there is some evidence that some non-human primates lack auditory cortex responses to pitch despite having clear tonotopic maps in auditory cortex, showing that tonotopic place codes are not sufficient for pitch responses.<ref>{{cite journal|last=Norman-Haignere|first=S.V.|author2=Kanwisher, N.G.|author3=McDermott, J. |author4=Conway, B.R. |title=Divergence in the functional organization of human and macaque auditory cortex revealed by fMRI responses to harmonic tones|journal=Nature Neuroscience|volume=22|issue=7|pages=1057–1060|issn=1097-6256|date=10 June 2019|doi=10.1038/s41593-019-0410-7|pmid=31182868|pmc=6592717}}</ref>

Temporal theories offer an alternative that appeals to the temporal structure of action potentials, mostly the [[Volley_theory#Phase-locking|phase-lock]] of action potentials to frequencies in a stimulus. The precise way this temporal structure helps code for pitch at higher levels is still debated, but the processing seems to be based on an [[autocorrelation]] of action potentials in the auditory nerve.<ref>{{cite journal|last=Cariani|first=P.A.|author2=Delgutte, B. |title=Neural Correlates of the Pitch of Complex Tones. I. Pitch and Pitch Salience|journal=Journal of Neurophysiology|date=September 1996|volume=76|issue=3|pages=1698–1716|pmid=8890286|url=http://www.brainmusic.org/MBB91%20Webpage/Pitch_II_Cariani.pdf|access-date=13 November 2012|doi=10.1152/jn.1996.76.3.1698}}</ref> However, it has long been noted that a neural mechanism that may accomplish a delay—a necessary operation of a true autocorrelation—has not been found.<ref name=plack /> At least one model shows that a temporal delay is unnecessary to produce an autocorrelation model of pitch perception, appealing to [[Phase shift#Phase shift|phase shifts]] between cochlear filters;<ref>{{cite journal|last=Cheveigné|first=A. de|author2=Pressnitzer, D.|title=The Case of the Missing Delay Lines: Synthetic Delays Obtained by Cross-channel Phase Interaction|journal=Journal of the Acoustical Society of America|date=June 2006|volume=119|issue=6|pages=3908–3918|pmid=16838534|url=http://audition.ens.fr/dp/pdfs/cheveigne-2006-synthetic_delay.pdf|access-date=13 November 2012|bibcode = 2006ASAJ..119.3908D |doi = 10.1121/1.2195291 }}</ref> however, earlier work has shown that certain sounds with a prominent peak in their autocorrelation function do not elicit a corresponding pitch percept,<ref>{{cite journal|last=Kaernbach|first=C.|author2=Demany, L. |title=Psychophysical Evidence Against the Autocorrelation Theory of Auditory Temporal Processing|journal=Journal of the Acoustical Society of America|date=October 1998|volume=104|issue=4|pages=2298–2306|pmid=10491694|bibcode = 1998ASAJ..104.2298K |doi = 10.1121/1.423742 }}</ref><ref name=pressnitzer2012>{{cite journal|last=Pressnitzer|first=D.|author2=Cheveigné, A. de|author3=Winter, I.M.|title=Perceptual Pitch Shift for Sounds with Similar Waveform Autocorrelation|journal=Acoustics Research Letters Online|date=January 2002|volume=3|issue=1|pages=1–6|doi=10.1121/1.1416671|doi-access=free}}</ref> and that certain sounds without a peak in their autocorrelation function nevertheless elicit a pitch.<ref>{{cite journal|last=Burns|first=E.M.|author2=Viemeister, N. F. |title=Nonspectral Pitch|journal=Journal of the Acoustical Society of America|date=October 1976|volume=60|issue=4|pages=863–69|bibcode = 1976ASAJ...60..863B |doi = 10.1121/1.381166 }}</ref><ref>{{cite journal|last=Fitzgerald|first=M. B.|author2=Wright, B. |title=A Perceptual Learning Investigation of the Pitch Elicited by Amplitude-Modulated Noise|journal=Journal of the Acoustical Society of America|date=December 2005|volume=118|issue=6|pages=3794–3803|pmid=16419824|bibcode = 2005ASAJ..118.3794F |doi = 10.1121/1.2074687 }}</ref> To be a more complete model, autocorrelation must therefore apply to signals that represent the output of the [[cochlea]], as via auditory-nerve interspike-interval histograms.<ref name=pressnitzer2012/> Some theories of pitch perception hold that pitch has inherent [[octave]] ambiguities, and therefore is best decomposed into a pitch ''chroma'', a periodic value around the octave, like the note names in Western music—and a pitch ''height'', which may be ambiguous, that indicates the octave the pitch is in.<ref name=hartmann/>