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

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.

The minority languages and cultures of Southeast Asia form a vital part of their local cultural ecosystems, yet a multitude of forces, in particular the cultural and economic dominance of the region's national languages, are converging to threaten their continued existence. This project will help to enhance the prestige of local minority languages, encouraging both additional documentation and preservation projects by demonstrating their cultural and scientific importance, but also providing the communities themselves with an opportunity to reflect on the immense cultural value of their own linguistic heritage. In the end, outsiders can do very little to stop a language from disappearing; only members of the speech community are truly in a position to ensure the survival of their language. However, we hope that by demonstrating and communicating the importance of minority languages, we may increase support for the preservation and documentation of minority languages and cultures. As part of this effort, we will pursue three avenues with the potential for substantial impact:

1. To the extent permitted by the rights holders, any materials obtained over the course of the project are made available to the public through easily accessible online archives. As most of the languages we plan to study are endangered, some of them critically, making sure that our materials are made widely accessible and available is crucial to supporting language documentation and preservation efforts. The longevity of these materials will be ensured by placing them in the digital archives of the Edinburgh DataShare Repository (http://datashare.is.ed.ac.uk/). However, the findings and materials will be offered to stakeholders in Southeast Asia, such as the National Archives of Thailand and the Vietnamese Museum of Ethnography, with a view to enhancing existing exhibitions on minority languages and cultures through incorporation of our recorded materials.

2. In addition to local impact, outreach opportunities will also be seized when appropriate. In particular, we will seek out the publication of non-technical articles and chapters aimed at NGOs and organizations engaged in language documentation and revitalization efforts (see "Pathways to Impact"), with the goal of impacting language planning and education at local and national levels. This will be facilitated through our existing network of contacts at universities, embassies, and NGOs throughout the region.

3. The outputs of this project can also serve to improve the naturalness and accuracy of automatic speech recognition systems for under-resourced languages. While systems of this sort for widely spoken languages such as English and Mandarin now are relatively accurate, they are not under development for most of the world's languages, as the necessary lexical resources are usually not available. However, advances in modern speech technology mean that it is increasingly possible to modify existing systems to work with new languages on the basis of comparatively little training data. We will work together with colleagues in the School of Informatics at the University of Edinburgh to incorporate our findings into their state-of-the-art speech recognition and synthesis systems, thereby helping to extend the advantages of speech technology to minority language communities.

Internationally, our project will serve as a demonstration of the commitment of both the UK and Canada to documenting and supporting endangered languages and cultures in developing economies, as well as to supporting and strengthening ties between Western and Southeast Asian cultural institutions.