Thesis (Ph.D.) OGI School of Science & Engineering at OHSU, March 2008. / Includes bibliographical references (leaves 99 - 108).

Ph.D. / Computer Science and Electrical Engineering / Nasalization refers to the process of speech production in which significant amounts of airfow and sound energy are transmitted through the nasal tract. In phonetics, nasalization is necessary for certain phonemes to be produced in normal speech; and it can also be a normal consequence of coarticulation. In disordered speech, however, inappropriate nasalization can be one of the causes that reduces the intelligibility of speech. Instrumental measurement and analysis techniques are needed for better understanding the relationship between the physiological status and the aerodynamic and acoustic effects of nasalization during speech. The main aim of the research work presented in this dissertation is to investigate the aerodynamic and acoustic effects of nasalization, and to develop objective approaches to measure, analyze, and detect the nasalized segments in speech. Based on an extensive survey of existing literature on the measurements of velopharyngeal function, the acoustic production models of speech, the analysis methods and results of normal nasalization, and the analysis methods of resonance disorders, it is understood that the final acoustic representation of nasalization is a complex outcome that is affected by the degree of velopharyngeal opening, the variation of vocal tract configurations, the mixture of multiple acoustic channels and speaker differences. It is proposed to incorporate more available information besides single channel acoustic signals during the analysis of nasalization. In our research work, a parallel study of acoustic and aerodynamic signals reveals the complimentary information within the signals. In addition, dual-channel acoustic studies help to understand the acoustic relationship between the oral and nasal cavities, and show inherent advantages over the single-channel analysis. Based on the derivation and analysis of the dual-channel acoustic properties, automatic detectors of nasalization are developed and successfully tested. The techniques developed in these explorations provide novel instrumental and analysis approaches to possible applications such as phonetic studies of the normal nasalization process, clinical assessment of disordered nasal resonance, and special feature extraction for speech recognition.