On the Acoustical and Perceptual Features of Vowel Nasality by Will Styler B.A., University of Colorado, 2008 M.A., University of Colorado, 2008 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirement for the degree of Doctor of Philosophy Department of Linguistics 2015 This thesis, entitled: On the Acoustical and Perceptual Features of Vowel Nasality written by Will Styler has been approved for the Department of Linguistics Dr. Rebecca Scarborough, Committee Chair Dr. Kathy Arehart Dr. Mans Hulden Dr. Martha Palmer Dr. David Rood Dr. Wayne Ward Date: The final copy of this thesis has been examined by the signatories, and we find thatboththe content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. IRB Protocol #: 13-0668 Will Styler - Final Submitted Version Abstract Styler, Will (Ph.D., Linguistics, Department of Linguistics) On the Acoustical and Perceptual Features of Vowel Nasality Thesis directed by Assistant Professor Rebecca A. Scarborough Although much is known about the linguistic function of vowel nasality, either contrastive (as in French) or coarticulatory (as in English), less is known about its perception. This study uses careful examination of production patterns, along with data from both machine learning and human listeners to establish which acoustical features are useful (and used) for identifying vowel nasality. A corpus of 4,778 oral and nasal or nasalized vowels in English and French was collected, and feature data for 29 potential perceptual features was extracted. A series of Linear Mixed-Effects Regressions showed 7 promising features with large oral-to-nasal feature differences, and high- lighted some cross-linguistic differences in the relative importance of these features. Two machine learning algorithms, Support Vector Machines and RandomForests, were trained on this data to identify features or feature groupings that were most effective at predicting nasality token-by-token in each language. The list of promising features was thus narrowed to four: A1-P0, Vowel Duration, Spectral Tilt, and Formant Frequency/Bandwidth. These four features were manipulated in vowels in oral and nasal contexts in English, adding nasal features to oral vowels and reducing nasal features in nasalized vowels, in an attempt to influence oral/nasal classification. These stimuli were presented to native English listeners in a lexical choice task with phoneme masking, measuring oral/nasal classification accuracy and reaction time. Only modifications to vowel formant structure caused any perceptual change for listeners, resulting in increased reaction times, as well as increased oral/nasal confusion in the oral-to-nasal (feature addition) stimuli. Classification of already-nasal vowels was not affected by any modifications, suggesting a perceptual role for other acoustical characteristics alongside nasality-specific cues. A Support Vector Machine trained on the same stimuli showed asimilar pattern of sensitivity to the experimental modifications. Thus, based on both the machine learning and human perception results, formant structure, par- ticularly F1 bandwidth, appears to be the primary cue to the perception of nasality in English. This close relationship of nasal- and oral-cavity derived acoustical cues leads to a strong perceptual role for both the oral and nasal aspects of nasal vowels. iii Will Styler - Final Submitted Version Acknowledgements First and foremost, thanks to my primary Advisor, Rebecca, for her constant willingness to help, hone my work, and eliminate entire unnecessary paragraphs from my writing, as well as for her vigilant efforts to keep me from getting too ambitious, too mired in code, or too engineer-ish. In addition, I am and will forever be grateful for her unflagging personal support and mentorship, through good and bad times, and for the many meetings where I left her office feeling less stressed and overwhelmed than when I walked in. I realize now that this was an incredible gift, and hope to some day pass it along to students of my own. Thanks to my other advisor, Martha, who has helped Rebecca in supporting me, personally and financially, throughout graduate school. Martha has offered me incredible opportunities fortrain- ing, employment, publication and experience, all seemingly without ever questioning what a pho- netician was doing hanging around natural language processing projects. She has given me access to wonderful data, projects, and people, and has been a wonderful mentor, whose approach to complex problems and projects will likely always be reflected in my own. A warm thank you to Lise Menn, my other, other advisor, who, despite a sincere attempt at re- tirement, has nevertheless continued to talk with me, mentor me, write kind things about me, and offer me tea. She also deserves credit as the teacher whose innocuous, mid-lecture comment about widespread across-speaker vowel formant variability, many years ago, set my obsession with complexity and variability in speech perception in motion. Many students go through school never having a great advisor and mentor. I had three of them. I am a very lucky man. Of course, I would like to thank the rest of my committee as well, for their willingness to meet with me, connect me with audiometry gear, read the occasional chapter, and to sit through 170 pages of writing on nasality. Special thanks to Georgia Zellou for recording both Philadelphia-based speakers of French, to Story Kiser for assisting with data collection for Experiment 3, and to Luciana Marques for her help in recording and segmenting French files (as well as for her cheerful willingness to nerdout about nasality and share her insights). Thanks to Pam Beddor, Andries Coetzee, Rob Hagiwara, Jesse Stewart, Paul Boersma, Susan Lin, Kate Phelps, Daniel Peterson, Shumin Wu, and all those other people who have provided me with useful tips, ideas, references, advice, motivation, or generalized phonetic moral support during this process. I must also recognize the wonderful community in the CU Linguistics department: faculty, staff, students, and softball team. I will always fondly remember odd conversations in hallways, know- ing looks mid-lecture, and watching the sunset from the outfield of the Mapleton softball fields, wearing the beschwaed jersey of the Illocutionary Force. Of course, much love and gratitude to my family. To my parents, who have always supported my education and my passion for language, and who took my choice of fields rather well, all things considered. To my Godparents, who have always been there for me, and supported my education iv Will Styler - Final Submitted Version and sanity with a steady stream of unintentionally extravagant dinners. To Cindy and Donna, who kept me laughing, and whose fur-children, past, present, and future, graciously lent their names to my English speakers. Perhaps most of all, a loving thank you to my partner and fiancée, Jessica, for her constant support, her understanding when I arrived at the dinner table glazed over with a head full of nasality problems, and her willingness to both tear me away from writing my dissertation, and push me towards it, as she deemed healthy at the time. Nobody should ever be asked to share a partner with vowel perception, but somehow, she doesn’t seem to mind, and for that, I am deeply grateful. Finally, I’d like to thank vowels, for preventing the catastrophic nuclear implosion of syllables around the world, and for being both magical and fractally weird, thus ensuring that no matter what I accomplish in my career, I will never run out of questions to ask. v Will Styler - Final Submitted Version Contents 1 Introduction 1 1.1 On Vowel Nasality ..................................... 3 1.2 Analyzing Nasality in the Laboratory ........................... 3 1.3 Dealing with noise in nasality measurement ....................... 4 1.4 Building a better understanding .............................. 5 1.5 Proposed Course of Action ................................. 6 2 Background: On Vowel Nasality in English and French 9 2.1 Vowel Nasality in English ................................. 9 2.1.1 The nature of vowel nasality in English ..................... 9 2.1.2 Variation in vowel nasality in English ...................... 12 2.1.3 The usefulness of vowel nasality to English listeners .............. 13 2.2 Vowel Nasality in French ................................. 15 2.2.1 French coarticulatory nasality and the present work .............. 15 2.2.2 Contrastive nasality in French ........................... 16 2.2.3 Variation in French vowel nasality ........................ 19 2.3 The Acoustics of Nasality ................................. 20 2.3.1 The Source and the Filter ............................. 21 2.3.2 Nasal Resonances .................................. 23 2.3.3 Nasal Zeroes .................................... 25 2.3.4 Overall Reduction in Amplitude ......................... 27 2.3.5 Changes to vowel formants ............................ 27 2.3.6 Temporal Features ................................. 28 2.4 Can cues to vowel nasality differ across languages? ................... 29 2.5 The Perception of Vowel Nasality ............................. 31 2.5.1 The Perception of Vowel Nasality in English .................. 32 2.5.2 The Perception of Vowel Nasality in French ................... 33 2.5.3 Automated Detection of Nasality ......................... 35 3 Data Collection