From voicing to register: the evolution of a sound change in Southeast Asia

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While there is no doubt that language changes over time, the question of why particular changes happen when and where they do - the so-called 'actuation problem' - has proven extremely difficult to answer. This is especially true at the level of individual sounds: changes in pronunciation are, almost by definition, unnoticeable while they are happening. In order to gain a better understanding of sound change, however, we need to be studying languages at these early stages of change, in order to identify the properties which lead to change in some cases but not others.In this project, we address the actuation problem by focusing on the evolution so-called 'register languages'. In a register language, words are often distinguished from one another based on a 'bundle' of acoustic properties such as voice quality, vowel quality, and pitch. For example, in the Mon language as spoken in Thailand, the syllable /klan/ has two distinct pronunciations: a 'high register' version, with the meaning 'lick', produced with a clear voice, at a slightly higher pitch, and with a slightly lower-sounding vowel; and 'low register' version, with the meaning 'naughty', produced with a breathier voice, at a slightly lower pitch, and with a slightly more schwa-like vowel.We know that many, or perhaps all, register languages were once much like English in distinguishing such word pairs chiefly through presence or absence of vocal fold vibration, a property known as 'voicing'. Just like English distinguishes the word 'bin' from 'pin' on the basis of voicing, so too did Mon speakers once pronounce the word for 'naughty' as /glan/, with an initial /g/ sound, to distinguish it from /klan/. Our goal in this project is to understand how and why languages shift from being 'voicing languages' like English, to being 'register languages' like Mon.Part of the answer to this question involves the fact that vocal fold vibration is not the only cue to voicing. For example, we know that vowels following voiceless consonants, like /p t k/, start with a higher pitch than those following voiced consonants, like /b d g/. In languages like Chinese, this pitch difference was exaggerated and took on a primary role, turning a contrast once based on voicing into a contrast signaled by pitch - what linguists call a tone language. But pitch is not the only cue that accompanies voicing: there is evidence that both voice quality (breathiness or creakiness) and vowel quality (or timbre) are affected by voicing as well. However, no systematic acoustic study of these secondary cues to voicing has yet been conducted in real languages; nor do we understand why register systems often evolve into simple tone systems or languages with many vowel qualities. In order to better understand the conditions which lead to register systems, we will conduct acoustic and perceptual studies of a range of Southeast Asian languages, including those which retain a voicing contrasts as well languages at various stages along the path to developing register. We focus on Southeast Asia because of the rich diversity of voicing and register languages that are found in this part of the world. Our findings will be used to build computational models of the evolution of voicing designed to address questions such as: Why do some languages develop register, while others preserve the original voicing contrast? Why do different register systems seem to emphasize different secondary properties of voicing, like pitch or voice quality? Why are some paths of change more common, while others are more rarely attested? These models will allow us to test hypotheses about how factors such as perceptual salience, word shape, and contact impact the evolution of voicing and register. The results will contribute not only to our understanding of how register systems emerge, but will also give a unique insight into the life cycle of a sound change.