Acoustic and perceptual bases of functional pitch perception

Psychophysical studies on pitch perception revealed that the auditory system uses both spectral and temporal cues to encode pitch of relatively simple stimuli such as pure tones and harmonics. After a century of investigation, the manner in which pitch is actually perceived is still under debate and the underlying mechanism for pitch encoding remains unresolved. Unlike the traditional psychophysical approach, the primary focus of this dissertation was to evaluate the relative contributions of envelope and fine structure cues to functional pitch perception. Three groups of experiments were designed. The first group of experiments examined the contributions of temporal envelope cues to rhythmic and musical pitch perception in acoustic and electric hearing. Both normal-hearing and cochlear-implant listeners can rely on rhythmic cues to identify melodies, but finer spectral resolution or additional fine structure information is needed to recognize melodies in the absence of rhythmic cues. The second group of experiments examined the contribution of the temporal envelope and fine structure cues as well as the spectral envelope and fine structure cues to Mandarin tone recognition in both quiet and in noise in normal-hearing listeners. Results show that while listeners can achieve nearly perfect tone recognition performance with either the spectral or temporal fine structure in quiet and from -5 to +10 dB signal-to-noise ratios, envelope cues produce significantly poorer tone recognition in both quiet and noise. The third group of experiments explored the benefits of additional low-frequency fine structure cues for speech recognition in noise and musical pitch perception in bilaterally combined acoustic and electric hearing. For speech recognition in noise, the low-frequency fine structure cue alone produces no recognition, but significantly enhances speech recognition in competing noise when combined with the envelope cue. Melody recognition, on the other hand, is dominated by the low-frequency fine structure in the acoustic ear.;Data from these experiments suggest that while both spectral and temporal cues contribute significantly to pitch perception, unlike speech recognition in quiet, the fine structure is more important than the envelope for musical and voice pitch perception. Providing the fine structure can improve voice pitch perception and in turn enhance speech recognition in noise. These findings also imply that better encoding of the fine structure is needed to improve music appreciation and speech recognition in auditory prostheses.