Perceptual Learning of Systemic Cross-Category Vowel Variation Dissertation Presented in Partial Fulfillment of the Requirements

Perceptual Learning of Systemic Cross-Category Vowel Variation Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Kodi Weatherholtz ∼6 6 Graduate Program in Linguistics The Ohio State University 2015 Dissertation Committee: Professor Cynthia G. Clopper, Advisor Professor Shari R. Speer Professor Mark A. Pitt c Kodi Weatherholtz, 2015 Abstract Phonological processes such as vowel chain shifting result in complex systems of cross- category vowel variation across spoken varieties of a language (Labov, 1994). The experiments comprising this dissertation aimed to understand how listeners cope with such systemic pronunciation variation to recognize spoken words. Recent research has shown that the ability of listeners to cope with pronunciation variation is due, in large part, to perceptual learning mechanisms that adjust speech perception and recognition processes based on distributional properties of the speech input (see Samuel & Kraljic, 2009). Per- ceptual learning is not a singular phenomenon: learning outcomes differ depending on the nature of the variability in the speech input and the nature of exposure conditions. To date, however, despite the ubiquity of vowel variation across dialects and accents, few stud- ies have investigated perceptual learning of systemic vowel variation (though see, e.g., Maye, Aslin, & Tanenhaus, 2008; Sidaras, Alexander, & Nygaard, 2009). The experiments comprising this dissertation aimed to address this gap in the literature by investigating (i) the level of representational specificity at which exposure-driven perceptual adjustments occur when adapting to systemic vowel variation (i.e., the locus of learning) ; (ii) the nature of the perceptual adjustments that occur at that level of representational specificity; and (iii) the manner in which learning and generalization are constrained by properties of the environment. The empirical approach of the current experiments centered on a between-subjects exposure-test perceptual learning paradigm. During the initial exposure phase, one group of listeners was familiarized to a talker with a novel vowel chain shift, such as a \back vowel lowered" chain shift involving a clockwise rotation of English back vowels (e.g., the vowel /u/ shifted to sound like [U] and hence goose as \g[U]s"; /U/ shifted to sound like [o] and hence ii wooden as \w[o]den"; /o/ shifted to sound like [A] and hence nose as \n[A]se"). Listeners in control conditions were familiarized to a talker with a standard-sounding American English accent. Following exposure, listeners performed multiple word recognition tasks, which were designed to assess generalization of learning to new words, new talkers, and untrained vowel shifts. Perceptual learning and generalization were assessed by exposure-driven differences in word recognition at test. Across six experiments, passive familiarization to a talker with a novel vowel chain shift markedly improved recognition of accent-consistent pronunciations that were otherwise per- ceived as nonwords (e.g., \w[o]den" for wooden, given the lowering of /U/ to sound like [o]). This exposure-driven word recognition benefit consistently generalized to new words produced by the trained talker (i.e., words presented only during the post-familiarization word recognition tasks), which indicates that listeners learned to cope with the unfamiliar vowel variants by remapping their perceptual vowel space (a sublexical locus of learning), as op- posed to relying on memory of specific word forms from the familiarization phase. Further, perceptual learning generalized to new talkers with the same chain shift (Experiments 1- 3), despite the fact that listeners were only familiarized to a single talker, indicating that listeners remapped their perceptual vowel space talker-independently. The finding of si- multaneous generalization across words and talkers was robust across exposure and test conditions (Experiments 1-3). That is, varying the exposure phase to involve between 20 minutes and only 2 minutes of accent exposure|and hence manipulating listeners' experience with the trained talker's chain shift to involve several hundred words containing the target vowel shifts or only a few dozen words|had minimal influence on the strength of generalization. Further, listeners' ability to generalize learning across talkers under single talker exposure conditions was not determined (and only minimally influenced) by acoustic similarity between the trained and new talkers in terms of their vowel productions (Exper- iments 1-3; cf. Reinisch & Holt, 2014). iii Experiments 4-6 investigated generalization to untrained vowel variants. When listeners experienced only a subset of the vowel shifts that defined an unfamiliar vowel shift system, listeners were able to generalize learning to fill in incidental gaps in their experience (Exper- iment 4), indicating that listeners learned a pattern of co-variation among vowel categories, rather than adapting to an unfamiliar vowel chain shift by learning each constituent shift independently. In some cases, listeners were also able to leverage experience with a trained chain shift to facilitate recognition of words produced (by a different talker) with an untrained but structurally-related chain shift. Listeners who were familiarized to a novel system of back vowel lowering were able to generalize learning to an untrained system of back vowel raising (a system of shifts among the same vowels, but in the opposite direction from training; Experiments 4 and 5) and to an untrained system of front vowel lowering (a structurally parallel system of shifts in a different region of the vowel space; Experiment 6). These findings indicate that learning involved a general broadening of perceptual vowel categories, resulting in a greater tolerance for mismatch. However, when listeners were familiarized to a system of back vowel raising, they appeared to learn a direction-specific system of variation (i.e., they did not generalize to back vowel lowered variants; Experiment 4). Taken together, these findings demonstrate tremendous exposure-driven flexibility in vowel perception. Listeners adapt to unfamiliar vowel chain shifts by dynamically and sys- temically adjusting talker-independent perceptual vowel representations, and these adjustments can involve a general broadening of perceptual vowel categories or targeted perceptual shifts that reflect the direction of the vowel shifts in the speech input. An important direction for future research is to investigate why exposure to unfamiliar pronunciation variation affecting the same vowels but in different directions (i.e., back vowel lowering vs. back vowel raising) results in different patterns of adjustment to perceptual vowel representations. iv Acknowledgements I am grateful to many people for helping make this dissertation a reality. Foremost, I would like to express my deepest gratitude to Cynthia G. Clopper, my advisor and mentor, for immeasurable guidance, encouragement, patience, and support throughout my graduate career. She continually pushed me to think more deeply about language and cognition. She allowed me great freedom to explore my research interests, and she was unfailing in helping me identify meaningful and practical steps forward in my research when I got lost in the weeds. It is no exaggeration that Cynthia read and thoughtfully reviewed every word of every document I ever sent to her|and the clarity of my thinking and writing improved markedly because of her careful attention to the fine details of my work. I also extend my sincerest appreciation to Shari Speer, not least for her support and pragmatism. She encouraged my research vision from the outset, and she was always quick to put pen to paper in order to flesh out experimental designs and map out predictions. And I am grateful to Mark Pitt for keeping an eye on the big picture and challenging me to do the same by asking deceptively simple questions at every turn, like Why does this matter? and What do we learn if your predictions are correct? I owe a great deal more than gratitude to Kathryn Campbell-Kibler. When I applied to graduate school in linguistics, I had essentially no formal education in the field|only a stack of linguistics books and articles that I'd read and some vague but impassioned ideas about the psycholinguistics-sociolinguistics interface. Kathryn saw promise in my ideas. She took a chance on potential over credentials and, in doing so, changed my life. I am continually inspired by the breadth and depth of her thinking. I am grateful to many others for their persistent investment in my intellectual and personal growth. Kiwako Ito and Becca Morely were especially generous with their time v and energy, and I benefitted greatly from their hands-on approach. On many occasions, they permitted a one-hour meeting to last much longer (sometimes all afternoon) so we could really wrap our heads around a set of data together and discuss it deeply. T. Florian Jaeger sparked my early interest in statistics and data visualization|and he always answered my lengthy emails with equally-detailed replies full of insightful answers, poignant questions and snippets of R code that guided me forwarded. I am gratefully indebted to Laurie Maynell, Elizabeth A. McCullough, Mike Phelan, and Sara Philips-Bourass|both for their friendship and for recording speech stimuli for my dissertation experiments. These experiments would not have

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