Neural coding and perception of pitch in the normal and impaired human auditory system

Pitch is an important attribute of hearing that allows us to perceive the musical quality of sounds. Besides music perception, pitch contributes to speech communication, auditory grouping, and perceptual segregation of sound sources. In this work, several aspects of pitch perception in humans were investigated using psychophysical methods. First, hearing loss was found to affect the perception of binaural pitch, a pitch sensation created by the binaural interaction of noise stimuli. Specifically, listeners without binaural pitch sensation showed signs of retrocochlear disorders. Despite adverse effects of reduced frequency selectivity on binaural pitch perception, the ability to accurately process the temporal fine structure (TFS) of sounds at the output of the cochlear filters was found to be essential for perceiving binaural pitch. Monaural TFS processing also played a major and independent role for a variety of basic auditory tasks, indicating that it may be a crucial measure to consider for hearing-loss characterization. In contrast to hearing-impaired listeners, adults with dyslexia showed no deficits in binaural pitch perception, suggesting intact low-level auditory mechanisms. The second part of this work investigated the role of temporal and spectral information for complex pitch perception. In particular, it was shown that the low pitch evoked by high-frequency complex tones was not conveyed by temporalenvelope cues as such. Moreover, the fact that the individual frequency components could not be heard out separately by the listeners suggested that the low pitch relied on TFS information, even in high-frequency regions where phase-locking in auditorynerve cells is believed to be weak. A second set of experiments could however not validate the assumption of a temporally-coded pitch and indicated that the use of spectral cues remained plausible. Simulations of auditory-nerve representations of the complex tones further suggested that a spectrotemporal mechanism combining precise timing information across auditory channels might best account for the behavioral data. Overall, this work provides insights into the fundamental auditory mechanisms underlying pitch perception, and may have implications for future pitch-perception models, as well as strategies for auditory-profile characterization and restoration of accurate pitch perception in impaired hearing.