Covert contrast in the acquisition of English /ɹ/: a case study

In this thesis I examine the potential role of covert contrast (the phenomenon by which a phonological contrast produced by a language learner falls below the threshold of perception of adult speakers of this language) in the development of one child learning the contrast between /ɹ/ and /w/ in English. More specifically, using a longitudinal corpus documenting the development of American English by one child learner, I compare data obtained by impressionistic means of phonetic transcription against acoustic measurements of the same speech tokens. As we will see, the results from both the transcription data and the acoustic measurements mirror one another in ways that undermine the claim that covert contrast represents a necessary stage in acquisition (Scobbie et al. 1996). Additionally, the current study reveals a disparity in the time of acquisition for /ɹ/ in coronal stop-initial onsets vs. all other onset environments which highlights the influence of articulatory factors on the production of /ɹ/ across different phonological contexts. Finally, the acoustic component of the study uncovers what can be termed a ‘covert allophone’ in the case of /w/ in that same coronal-initial complex onset environment. I conclude this thesis with a discussion of both the theoretical and methodological implications for future research on the development of phonological contrasts by children

A joint model of word segmentation and phonological variation for English word-final /t/-deletion

Word-final /t/-deletion refers to a common phenomenon in spoken English where words such as /wEst / “west ” are pronounced as [wEs] “wes ” in certain contexts. Phonological variation like this is common in naturally occurring speech. Current computational models of unsupervised word segmentation usually assume idealized input that is devoid of these kinds of variation. We extend a non-parametric model of word segmentation by adding phonological rules that map from underlying forms to surface forms to produce a mathematically well-defined joint model as a first step towards handling variation and segmentation in a single model. We analyse how our model handles /t/-deletion on a large corpus of transcribed speech, and show that the joint model can perform word segmentation and recover underlying /t/s. We find that Bigram dependencies are important for performing well on real data and for learning appropriate deletion probabilities for different contexts. 1

Markedness and implicational relationships in phonological development: a longitudinal, cross-linguistic investigation

This dissertation sets out to evaluate theoretical and empirical issues involved in referring to implicational relationships (i.e., that a marked or complex sound or phonological process implies the presence of an unmarked or simpler sound or process) for the treatment of speech sound disorders (e.g., Gierut 2007). Due to the relatively untested and unexplored nature of implicational relationships, and because of their potential relevance to Speech-Language Pathology practice, I investigated the following research questions: (1) Are implicational relationships warranted cross-linguistically in the description of phonological development? (2) Can factors outside of universal markedness account for attested patterns of phonological development? I conducted six detailed longitudinal case studies documenting typical phonological systems in English, French, German, and Portuguese, as well as atypical development in one English-learning child. Based on these studies, I claim that implicational relationships based on universal markedness are theoretically and empirically questionable. The results from my investigation highlight the influence of speech phonetics and phonological distributions in all aspects of development. Additionally, the few implicational relationships that appear to make valid predictions can be described in terms of articulatory complexity: the sounds that the children acquired first are easier to articulate for a number of reasons (e.g., motoric, perceptual, grammatical). As claims based on universal markedness generally do not account for the data, I investigate whether a phonetically driven view of markedness could apply. This inquiry led me to advocate for a markedness-through-mechanism (Hume 2011) approach to phonological development, which combines perceptual distinctiveness, phonetic variability, and articulatory simplicity; which, in child language, can be rather salient due to anatomical and motor properties of child speech production. I combine this view of phonetically conditioned markedness with the A-map model (McAllister Byun, Inkelas & Rose 2016), which provides a formal link relating perceptual targets and the dimensions involved in the motor-acoustic mappings of these objects on to patterns of speech production. In a nutshell, combining markedness-through-mechanism with the A-map provides a way to frame the phonological patterns that we observe in child phonological development that is both theoretically consistent and clinically applicable. This approach expands on our understanding of the underpinnings of speech sound disorders and provides a new model that can guide Speech- Language Pathologists in their selection of treatment approaches to speech disorders