Temporal articulatory stability, phonological variation, and lexical contrast preservation in diaspora Tibetan

This dissertation examines how lexical tone can be represented with articulatory gestures, and the ways a gestural perspective can inform synchronic and diachronic analysis of the phonology and phonetics of a language. Tibetan is chosen an example of a language with interacting laryngeal and tonal phonology, a history of tonogenesis and dialect diversification, and recent contact-induced realignment of the tonal and consonantal systems. Despite variation in voice onset time (VOT) and presence/absence of the lexical tone contrast, speakers retain a consistent relative timing of consonant and vowel gestures. Recent research has attempted to integrate tone into the framework of Articulatory Phonology through the addition of tone gestures. Unlike other theories of phonetics-phonology, Articulatory Phonology uniquely incorporates relative timing as a key parameter. This allows the system to represent contrasts instantiated not just in the presence or absence of gestures, but also in how gestures are timed with each other. Building on the different predictions of various timing relations, along with the historical developments in the language, hypotheses are generated and tested with acoustic and articulatory experiments. Following an overview of relevant theory, the second chapter surveys past literature on the history of sound change and present phonological diversity of Tibetic dialects. Whereas Old Tibetan lacked lexical tone, contrasted voiced and voiceless obstruents, and exhibited complex clusters, a series of overlapping sound changes have led to some modern varieties that are tone, lack clusters, and vary in the expression of voicing and aspiration. Furthermore, speakers in the Tibetan diaspora use a variety that has grown out of the contact between diverse Tibetic dialects. The state of the language and the dynamics of diaspora have created a situation ripe for sound change, including the recombination of elements from different dialects and, potentially, the loss of tone contrasts. The nature of the diaspora Tibetan is investigated through an acoustic corpus study. Recordings made in Kathmandu, Nepal, are being transcribed and forced-aligned into a useful audio corpus. Speakers in the corpus come from diverse backgrounds across and outside traditional Tibetan-speaking regions, but the analysis presented here focuses on speakers who grew up in diaspora, with a mixed input of Standard Tibetan (spyi skad) and other Tibetan varieties. Especially notable among these speakers is the high variability of voice onset time (VOT) and its interaction with tone. An analysis of this data in terms of the relative timing of oral, laryngeal, and tone gestures leads to the generation of hypotheses for testing using articulatory data. The articulatory study is conducted using electromagnetic articulography (EMA), and six Tibetan-speaking participants. The key finding is that the relative timing of consonant and vowel gestures is consistent across phonological categories and across speakers who do and do not contrast tone. This result leads to the conclusion that the relative timing of speech gestures is conserved and acquired independently. Speakers acquire and generalize a limited inventory of timing patterns, and can use timing patterns even when the conditioning environment for the development of those patterns, namely tone, has been lost

Recognizing Speech in a Novel Accent: The Motor Theory of Speech Perception Reframed

The motor theory of speech perception holds that we perceive the speech of another in terms of a motor representation of that speech. However, when we have learned to recognize a foreign accent, it seems plausible that recognition of a word rarely involves reconstruction of the speech gestures of the speaker rather than the listener. To better assess the motor theory and this observation, we proceed in three stages. Part 1 places the motor theory of speech perception in a larger framework based on our earlier models of the adaptive formation of mirror neurons for grasping, and for viewing extensions of that mirror system as part of a larger system for neuro-linguistic processing, augmented by the present consideration of recognizing speech in a novel accent. Part 2 then offers a novel computational model of how a listener comes to understand the speech of someone speaking the listener's native language with a foreign accent. The core tenet of the model is that the listener uses hypotheses about the word the speaker is currently uttering to update probabilities linking the sound produced by the speaker to phonemes in the native language repertoire of the listener. This, on average, improves the recognition of later words. This model is neutral regarding the nature of the representations it uses (motor vs. auditory). It serve as a reference point for the discussion in Part 3, which proposes a dual-stream neuro-linguistic architecture to revisits claims for and against the motor theory of speech perception and the relevance of mirror neurons, and extracts some implications for the reframing of the motor theory

Cortical Dynamics of Language

The human capability for fluent speech profoundly directs inter-personal communication and, by extension, self-expression. Language is lost in millions of people each year due to trauma, stroke, neurodegeneration, and neoplasms with devastating impact to social interaction and quality of life. The following investigations were designed to elucidate the neurobiological foundation of speech production, building towards a universal cognitive model of language in the brain. Understanding the dynamical mechanisms supporting cortical network behavior will significantly advance the understanding of how both focal and disconnection injuries yield neurological deficits, informing the development of therapeutic approaches

An exploration of the rhythm of Malay

In recent years there has been a surge of interest in speech rhythm. However we still lack a clear understanding of the nature of rhythm and rhythmic differences across languages. Various metrics have been proposed as means for measuring rhythm on the phonetic level and making typological comparisons between languages (Ramus et al, 1999; Grabe & Low, 2002; Dellwo, 2006) but the debate is ongoing on the extent to which these metrics capture the rhythmic basis of speech (Arvaniti, 2009; Fletcher, in press). Furthermore, cross linguistic studies of rhythm have covered a relatively small number of languages and research on previously unclassified languages is necessary to fully develop the typology of rhythm. This study examines the rhythmic features of Malay, for which, to date, relatively little work has been carried out on aspects rhythm and timing. The material for the analysis comprised 10 sentences produced by 20 speakers of standard Malay (10 males and 10 females). The recordings were first analysed using rhythm metrics proposed by Ramus et. al (1999) and Grabe & Low (2002). These metrics (∆C, %V, rPVI, nPVI) are based on durational measurements of vocalic and consonantal intervals. The results indicated that Malay clustered with other so-called syllable-timed languages like French and Spanish on the basis of all metrics. However, underlying the overall findings for these metrics there was a large degree of variability in values across speakers and sentences, with some speakers having values in the range typical of stressed-timed languages like English. Further analysis has been carried out in light of Fletcher’s (in press) argument that measurements based on duration do not wholly reflect speech rhythm as there are many other factors that can influence values of consonantal and vocalic intervals, and Arvaniti’s (2009) suggestion that other features of speech should also be considered in description of rhythm to discover what contributes to listeners’ perception of regularity. Spectrographic analysis of the Malay recordings brought to light two parameters that displayed consistency and regularity for all speakers and sentences: the duration of individual vowels and the duration of intervals between intensity minima. This poster presents the results of these investigations and points to connections between the features which seem to be consistently regulated in the timing of Malay connected speech and aspects of Malay phonology. The results are discussed in light of current debate on the descriptions of rhythm

Gesture-speech coupling in L2 lexical stress production: A pre-registration of a speech acoustic and gesture kinematic study

The prosody of a second language (L2) is notoriously difficult to acquire. It requires the mastery of a range of nested multimodal systems, including articulatory but also gestural signals, as hand gestures are produced in close synchrony with spoken prosody. It remains unclear how easily the articulatory and gestural systems acquire new prosodic patterns in the L2 and how the two systems interact, especially when L1 patterns interfere. This interdisciplinary pre-registered study investigates how Dutch learners of Spanish produce multimodal lexical stress in Spanish-Dutch cognates (e.g., Spanish profeSOR vs. Dutch proFESsor). Acoustic analyses assess whether gesturing helps L2 speakers to place stress on the correct syllable; and whether gesturing boosts the acoustic correlates of stress through biomechanic coupling. Moreover, motion-tracking and time-series analyses test whether gesture-prosody synchrony is enhanced for stress-matching vs. stress-mismatching cognate pairs, perhaps revealing that gestural timing is biased in the L1 (or L2) direction (e.g., Spanish profeSOR with the gesture biased towards Dutch stressed syllable -fes). Thus, we will uncover how speakers deal with manual, articulatory, and cognitive constraints that need to be brought in harmony for efficient speech production, bearing implications for theories on gesture-speech interaction and multimodal L2 acquisition

A syllable-based investigation of coarticulation

Coarticulation has been long investigated in Speech Sciences and Linguistics (Kühnert & Nolan, 1999). This thesis explores coarticulation through a syllable based model (Y. Xu, 2020). First, it is hypothesised that consonant and vowel are synchronised at the syllable onset for the sake of reducing temporal degrees of freedom, and such synchronisation is the essence of coarticulation. Previous efforts in the examination of CV alignment mainly report onset asynchrony (Gao, 2009; Shaw & Chen, 2019). The first study of this thesis tested the synchrony hypothesis using articulatory and acoustic data in Mandarin. Departing from conventional approaches, a minimal triplet paradigm was applied, in which the CV onsets were determined through the consonant and vowel minimal pairs, respectively. Both articulatory and acoustical results showed that CV articulation started in close temporal proximity, supporting the synchrony hypothesis. The second study extended the research to English and syllables with cluster onsets. By using acoustic data in conjunction with Deep Learning, supporting evidence was found for co-onset, which is in contrast to the widely reported c-center effect (Byrd, 1995). Secondly, the thesis investigated the mechanism that can maximise synchrony – Dimension Specific Sequential Target Approximation (DSSTA), which is highly relevant to what is commonly known as coarticulation resistance (Recasens & Espinosa, 2009). Evidence from the first two studies show that, when conflicts arise due to articulation requirements between CV, the CV gestures can be fulfilled by the same articulator on separate dimensions simultaneously. Last but not least, the final study tested the hypothesis that resyllabification is the result of coarticulation asymmetry between onset and coda consonants. It was found that neural network based models could infer syllable affiliation of consonants, and those inferred resyllabified codas had similar coarticulatory structure with canonical onset consonants. In conclusion, this thesis found that many coarticulation related phenomena, including local vowel to vowel anticipatory coarticulation, coarticulation resistance, and resyllabification, stem from the articulatory mechanism of the syllable

A split-gesture, competitive, coupled oscillator model of syllable structure predicts the emergence of edge gemination and degemination

The phonological mechanisms responsible for the emergence of edge geminates in phonological processes like the Italian Raddoppiamento (Fono-)Sintattico (RS) are an open issue. Previous analyses of Italian treat gemination of (i) word initial consonants, (ii) morpheme-final consonants, and (iii) word final consonants as separate processes brought about by dedicated rule/constraints. We argue that these edge gemination processes result from the same, independently established principles. Through computational simulation of the split-gesture, competitive, coupled oscillator model of syllable structure of Articulatory Phonology, we show that increases in closure duration typical of geminates arise from changes to consonant/vowel couplings. Word initial gemination follows from coupling of a closure gesture to a preceding vowel across a word boundary. Word final gemination follows from coupling of a release gesture to a following vowel. In both cases, the posited structures reflect changes in syllabification hypothesized in previous work. The model simulation also predict different durations for resyllabified edge geminates and medial lexical geminates, in line with experimental findings on the topic. Changes to consonant/vowel couplings also account for the opposite effect: word initial degemination. Thus, the coupled oscillator model of Articulatory Phonology, originally developed to model intergestural timing, predicts the emergence of edge gemination/degemination

Compression Effects in English

This paper reports the results of an English experiment on vowel-shortening in different contexts. The data concern compression effects, whereby, in syllables with a greater number of segments, each one of the segments is shorter than in syllables with fewer segments. The experiment demonstrates that the amount of vowel compression found in English monosyllabic words depends in part on which consonants occur adjacent to the vowel in that word, how many consonants occur, and in which position they occur. Consonant clusters drive more vowel shortening than singletons when they involve liquids, but not when they involve only obstruents. Clusters involving nasals drive shortening relative to singletons only in onset position. We suggest that the results cannot be reduced to general principles of gestural overlap and coordination between consonants and vowels, but instead require a theory with overt representation of auditory duration