Production and Perception of Native and Non-native Speech Enhancements
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Date
2020-12-08
Authors
Kato, Misaki
Journal Title
Journal ISSN
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Publisher
University of Oregon
Abstract
One important factor that contributes to successful speech communication is an individual’s ability to speak more clearly when their listeners do not understand their speech. Though native talkers are able to implement various acoustic-phonetic speech enhancements to make their speech more understandable to their listeners (e.g., by speaking more slowly, loudly, or by articulating sounds more clearly), such goal-oriented adaptations employed by non-native talkers are much less well-understood. This dissertation investigates how talkers’ ability to implement speech enhancements is shaped by their target language experience and how these enhancements impact listeners’ perception. Specifically, we examine acoustic characteristics of speech enhancements produced by native English talkers and non-native English talkers of higher- and lower-proficiency in different contexts: in a reading task where talkers are explicitly asked to read materials clearly, as well as in a simulated communication task where listeners’ communicative needs for enhanced intelligibility are signaled implicitly in the context. We further examine perceptual consequences of speech enhancements in terms of intelligibility (whether listeners understand the speech) and other subjective evaluations of the speech, including perceived degree of comprehensibility (how easy the listeners perceive the speech is to understand).
The results show that native talkers and higher-proficiency non-native talkers generally make larger acoustic modifications than lower-proficiency talkers. However, such effects of talkers' target language experience differ depending on the type of acoustic manipulations involved in the productions. Furthermore, an improvement in intelligibility does not necessarily correspond to an improvement in other subjective evaluations of the speech, suggesting that perceptual benefits resulting from speech enhancements could vary depending on how listeners are asked to evaluate the speech.
The results of this dissertation highlight that talkers have the flexibility to accommodate listeners’ communicative needs in a native and non-native language, and suggest that this flexibility is shaped by the combination of talkers’ linguistic backgrounds and the focus of adaptation. Furthermore, the current work provides evidence that perceptual consequences of speech enhancements are multi-faceted, and suggest that acoustic features of speech enhancements responsible for an improvement in intelligibility may differ from those influence other types of subjective evaluations.
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Keywords
Phonetics, Second language acquisition, Speech perception, Speech production