Periodicity pitch

Musical pitch can be roughly divided in spectral pitch, as for a pure tone or a complex tone with resolved harmonics, and periodicity pitch for periodic modulated sounds as in complex sounds with unresolved harmonics. Because the peripheral auditory system represents tones with frequency below ~ 2 kHz both in temporal fashion (phase-locking) and spectral fashion (place of activation on the basilar membrane) the pitches of such tone are more salient than for higher frequencies. The temporal vs. place representation of pitch has been the topic of discussion for nearly 200 years, originally putting researcher firmly in one camp or the other. Strong evidence for the role of temporal mechanisms cam from the phenomena of central pitch constructed in the brain based on pitch-less components presented to each ear. However, recent psychoacoustic studies have demonstrated that tonotopic representation is crucial to pitch perception for complex sounds. As we have demonstrated in Chapter 5, representation of amplitude modulations decreases in upper limit from auditory nerve to auditory cortex. This suggests a change in representation of periodicity pitch from mostly temporal in the periphery to a place representation in auditory cortex. Evidence for specific areas in auditory cortex that represent pitch have been reported. Several imaging studies have suggested a periodotopic map in the cortex that is orthogonal to the tonotopic map, but others show that the maps are largely overlapping. The latter configuration may aid in allowing the crucial combination of tonotopy and periodotopy in complex pitch perception.