Resilience of English vowel perception across regional accent variation

In two categorization experiments using phonotactically legal nonce words, we tested Australian English listeners’ perception of all vowels in their own accent as well as in four less familiar regional varieties of English which differ in how their vowel realizations diverge from Australian English: London, Yorkshire, Newcastle (UK), and New Zealand. Results of Experiment 1 indicated that amongst the vowel differences described in sociophonetic studies and attested in our stimulus materials, only a small subset caused greater perceptual difficulty for Australian listeners than for the corresponding Australian English vowels. We discuss this perceptual tolerance for vowel variation in terms of how perceptual assimilation of phonetic details into abstract vowel categories may contribute to recognizing words across variable pronunciations. Experiment 2 determined whether short-term multi-talker exposure would facilitate accent adaptation, particularly for those vowels that proved more difficult to categorize in Experiment 1. For each accent separately, participants listened to a pre-test passage in the nonce word accent but told by novel talkers before completing the same task as in Experiment 1. In contrast to previous studies showing rapid adaptation to talker-specific variation, our listeners’ subsequent vowel assimilations were largely unaffected by exposure to other talkers’ accent-specific variation

Perceptual sensitivity to stress in native English speakers learning Spanish as a second language

Second language (L2) learners of Spanish whose first language (L1) is English tend to find Spanish lexical stress patterns difficult to acquire. This study investigates whether such difficulty derives, at least in part, from an obstacle encountered during perceptual processing: reduced perceptual sensitivity to stress distinctions. Participants were adult L1 English L2 Spanish learners of various proficiency levels. The experiment was a categorical matching task with triads of auditory stimuli minimally contrasting in stress (target) or segmental composition (baseline), an ABX task. The results show that learners were more accurate in the baseline condition than in the target condition, suggesting reduced perceptual sensitivity to stress relative to other contrasts. The reduction in accuracy, however, was restricted to trials in which matching items were not adjacent, further suggesting an obstacle with phonological processing in working memory rather than perceptual categorization. The default stress processing routines of L1 English L2 Spanish learners, optimized for their L1 (not their L2), may be responsible for their acquisitional obstacles with this feature of the Spanish language

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

Effects of forensically-relevant facial concealment on acoustic and perceptual properties of consonants

This thesis offers a thorough investigation into the effects of forensically-relevant facial concealment on speech acoustics and perception. Specifically, it explores the extent to which selected acoustic-phonetic and auditory-perceptual properties of consonants are affected when the talker is wearing ‘facewear’ while speaking. In this context, the term ‘facewear’ refers to the various types of face-concealing garments and headgear that are worn by people in common daily communication situations; for work and leisure, or as an expression of religious, social and cultural affiliation (e.g. surgical masks, motorcycle helmets, ski and cycling masks, or full-face veils such as the niqāb). It also denotes the face or head coverings that are typically used as deliberate (visual) disguises during the commission of crimes and in situations of public disorder (e.g. balaclavas, hooded sweatshirts, or scarves). The present research centres on the question: does facewear influence the way that consonants are produced, transmitted, and perceived? To examine the effects of facewear on the acoustic speech signal, various intensity, spectral, and temporal properties of spoken English consonants were measured. It was found that facewear can considerably alter the acoustic-phonetic characteristics of consonants. This was likely to be the result of both deliberate and involuntary changes to the talker’s speech productions, and of sound energy absorption by the facewear material. The perceptual consequences of the acoustic modifications to speech were assessed by way of a consonant identification study and a talker discrimination study. The results of these studies showed that auditory-only and auditory-visual consonant intelligibility, as well as the discrimination of unfamiliar talkers, may be greatly compromised when the observer’s judgements are based on ‘facewear speech’. The findings reported in this thesis contribute to our understanding of how auditory and visual information interact during natural speech processing. Furthermore, the results have important practical implications for legal cases in which speech produced through facewear is of pivotal importance. Forensic speech scientists are therefore advised to take the possible effects of facewear on speech into account when interpreting the outcome of their acoustic and auditory analyses of evidential speech recordings, and when evaluating the reliability of earwitness testimony

The role of experience in processing foreign-accented speech

The present study examines the perceptual accommodation of the bilabial stop-consonant voicing contrast (i.e., /b/ vs. /p/), in several English- and Spanish-accented contexts, by native Spanish listeners with different degrees of experience with accented speech. In a series of four experiments, we confronted three potential mechanisms for the perceptual accommodation of foreign-accented sounds. According to the first mechanism (phonetic relaxation), listeners accommodate foreign-accented sounds by relaxing the phonetic boundary between native speech sound categories. According to the second mechanism (phonetic calibration), listeners accommodate foreign-accented sounds by adjusting the location of native perceptual boundaries according to the phonetic realization of native categories in the foreign-accented speech context. Finally, according to the third mechanism (phonetic switching), foreign-accented speech sounds are accommodated by switching to a non-native system of phonetic representations that was previously developed through long-term experience with the speech norm of the foreign accent. Experimental results indicate that Spanish listeners did not relax the phonetic boundary between /b/ and /p/ in an English-accented Spanish context (Experiments 1 and 3). However, they accommodated English-accented Spanish voicing differently, depending on their degree of experience with the English-accented speech norm. When Spanish listeners had little or no experience with the English norm, they calibrated the location of the perceptual boundary between /b/ and /p/ according to the Spanish or English phonetic realization of these sounds in the speech context (Experiment 4). Alternatively, when they had a high degree of experience with English-accented speech, they accommodated English-accented Spanish /b/ and /p/ by using an English-like system of phonetic representations that was not predictable from the phonetic realization of /b/ and /p/ in the speech context (Experiments 1 and 2). These experimental results contribute to a better understanding of the role played by non-native experience in the perceptual accommodation of foreign-accents. In particular, they indicate that native listeners may rely on previous long-term experience with the native language of the foreign-accented speaker to efficiently accommodate foreign-accented speech variability in a different way to which they accommodate speech variability from different native-accented speakers

Ultra-high-speed imaging of bubbles interacting with cells and tissue

Ultrasound contrast microbubbles are exploited in molecular imaging, where bubbles are directed to target cells and where their high-scattering cross section to ultrasound allows for the detection of pathologies at a molecular level. In therapeutic applications vibrating bubbles close to cells may alter the permeability of cell membranes, and these systems are therefore highly interesting for drug and gene delivery applications using ultrasound. In a more extreme regime bubbles are driven through shock waves to sonoporate or kill cells through intense stresses or jets following inertial bubble collapse. Here, we elucidate some of the underlying mechanisms using the 25-Mfps camera Brandaris128, resolving the bubble dynamics and its interactions with cells. We quantify acoustic microstreaming around oscillating bubbles close to rigid walls and evaluate the shear stresses on nonadherent cells. In a study on the fluid dynamical interaction of cavitation bubbles with adherent cells, we find that the nonspherical collapse of bubbles is responsible for cell detachment. We also visualized the dynamics of vibrating microbubbles in contact with endothelial cells followed by fluorescent imaging of the transport of propidium iodide, used as a membrane integrity probe, into these cells showing a direct correlation between cell deformation and cell membrane permeability