Doctoral Dissertation Research: Articulatory Dynamics of Sibilant Convergence & Change

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The goal of this dissertation research is to contribute to the scientific understanding of sound change, focusing on the way in which some sound changes are asymmetrically distributed. That is, given that the phonetic motivations for a sound change may be present in multiple phonological environments (the adjacent sounds), why is the change observed in one environment and not the others? This project will address this question through an examination of /s/-retraction, an ongoing sound change in American English in which /s/ is pronounced as /sh/ in /str/ words (such that 'street' is pronounced as 'shtreet') but rarely in /spr/ and /skr/ words ('scream' is not pronounced as 'shcream' and 'spree' is not pronounced as 'shpree'). The results of this project will most directly influence the scientific understanding of /s/-retraction narrowly and sound change and its initiation and propagation more broadly, but can potentially contribute to developments in related fields and industries. By examining individual variation, these findings may offer insights into first and/or second language acquisition and may aid in the development of speech recognition systems that are faster and more accurate for a greater number of users, especially those with non-standard accents.This project will examine participants' production and perception of /s/ in these environments in order to better understand the observed asymmetries in /s/-retraction. For this project, participants will listen to auditory prompts containing /s/ in different phonological environments corresponding to visually presented images, and in turn give oral instructions for the computer to select the correct image. This design has two important components: firstly, it is a lexical decision task, meaning that the participant has to select the best meaning (represented by the images) given the possibly ambiguous or unexpected acoustic signal (auditory instructions). Secondly, the task encourages phonetic accommodation, the process by which a speaker begins to sound more like their interlocutor (the model talker giving instructions), which can provide insight into how sound changes propagate across a speech community. Throughout the experiment, three simultaneous measurements will be collected: audio recording, ultrasound imaging of the tongue, and eye gaze tracking. Ultrasound imaging will elucidate the varying articulations of /s/ in different phonological environments and will also provide novel evidence for the articulatory reality of phonetic accommodation. Eye gaze measurements will provide information about listeners' use of /s/ variation in real time. These measurements will be collected simultaneously in order to examine the relationship between participants' production and perception of /s/ in these environments.