SECOND LANGUAGE LEXICAL REPRESENTATION AND PROCESSING OF MANDARIN CHINESE TONES

This dissertation investigates second language (L2) speech learning challenges by testing advanced L2 Mandarin Chinese learners’ tone and word knowledge. We consider L2 speech learning under the scope of three general hypotheses. (1) The Tone Perception Hypothesis: Tones may be difficult for L2 listeners to perceive auditorily. (2) The Tone Representation Hypothesis: Tones may be difficult for L2 listeners to represent effectively. (3) The Tone Processing Hypothesis: Tones may be difficult for L2 listeners to process efficiently. Experiments 1 and 2 test tone perception and representation using tone identification tasks with monosyllabic and disyllabic stimuli with L1 and advanced L2 Mandarin listeners. Results suggest that both groups are highly accurate in identification of tones on isolated monosyllables; however, L2 learners have some difficulty in disyllabic contexts. This suggests that low-level auditory perception of tones presents L2 learners with persistent long-term challenges. Results also shed light on tone representations, showing that both L1 and L2 listeners are able to form abstract representations of third tone allotones. Experiments 3 and 4 test tone representation and processing through the use of online (behavioral and ERP) and offline measures of tone word recognition. Offline results suggest weaknesses in L2 learners’ long-term memory of tones for specific vocabulary. However, even when we consider only trials for which learners had correct and confident explicit knowledge of tones and words, we still see significant differences in accuracy for rejection of tone compared to vowel nonwords in lexical recognition tasks. Using a lexical decision task, ERP measures in Experiment 3 reveal consistent L1 sensitivity to tones and vowels in isolated word recognition, and individual differences among L2 listeners. While some are sensitive to both tone and vowel mismatches, others are only sensitive to vowels or not at all. Experiment 4 utilized picture cues to test neural responses tied directly to tone and vowel mismatches. Results suggest strong L1 sensitivity to vowel mismatches. No other significant results were found. The final chapter considers how the three hypotheses shed light on the results as a whole, and how they relate to the broader context of L2 speech learning

Spoken English discrimination (SED) training with multilingual Malaysians: effect of adaptive staircase procedure and background babble in high variability phonetic training.

High variability phonetic training (HVPT) has been shown to improve non-native speakers’ perceptual performance in discriminating difficult second language phonemic contrasts (Bradlow, Akahane-Yamada, Pisoni, & Tohkura, 1999; Bradlow, Pisoni, Akahane-Yamada, & Tohkura, 1997; Lively, Logan, & Pisoni, 1993; Lively, Pisoni, Yamada, Tohkura, & Yamada, 1994; Logan, Lively, & Pisoni, 1991). The perceptual learning can be generalized to novel words (Wang & Munro, 2004), novel speakers (Nishi & Kewley-Port, 2007; Richie & Kewley-Port, 2008) and even to speech production (Bradlow et al., 1997). However, the rigidity of the laboratory training settings has limited applications to real life situations. The current thesis examined the effectiveness of a new phonetic training program - the Spoken English Discrimination (SED) training. SED training is a computerized individual training program designed to improve non-native speakers’ bottom-up perceptual sensitivity to discriminate difficult second language (L2) phonemic contrasts. It combines a number of key training features including 1) natural spoken stimuli, 2) highly variable stimuli spoken by multiple speakers, 3) multi-talker babble as background noise and 4) an adaptive staircase procedure that individualizes the level of background babble. The first experiment investigated the potential benefits of different versions of the SED training program. The effect of stimulus variability (single speaker vs. multiple speakers) and design of background babble (constant vs. adaptive staircase) were examined using English voiceless-voiced plosives /t/-/d/ phonemic contrast as the training materials. No improvements were found in the identification accuracy on the /t/-/d/ contrast in post-test, but identification improvements were found on the untrained English /ε/-/æ/ phonemic contrast. The effectiveness of SED training was re-examined in Chapter 3 using the English /ε/-/æ/ phonemic contrast as the training material. Three experiments were conducted to compare the SED training paradigms that had the background babble implemented either at a constant level (Constant SED) or using the adaptive staircase procedure (Adaptive Staircase SED), and the longevity of the training effects. Results revealed that the Adaptive Staircase SED was the more effective paradigm as it generated greater training benefits and its effect generalized better to the untrained /t/-/d/ phonemic contrast. Training effects from both SED paradigms retained six months after the last training section. Before examining whether SED training leads to improvements in speech production, Chapter 4 investigated the phonetics perception pattern of L1 Mandarin Malaysian speakers, L1 Malaysian English speakers and native British English speakers. The production intelligibility of the L1 Mandarin speakers was also evaluated by the L1 Malaysian English speakers and native British English speakers. Single category assimilation was observed in both L1 Mandarin and L1 Malaysian English speakers whereby the /ε/ and /æ/ phonetic sounds were assimilated to a single/æ/ category (Best, McRoberts, & Goodell, 2001). While the British English speakers showed ceiling performance for all phonetic categories involved, the L1 Malaysian English speakers had difficulty identifying the British English /ε/ phoneme and the L1 Mandarin speakers had difficulty identifying the /d/ final, /ε/ and /æ/ phonemes. As seen by their perceptual performance, the L1 Mandarin speakers also had difficulty producing distinct /d/ final, /ε/ and /æ/ phonemes. Two experiments in Chapter 5 examined whether the effects of SED training generalizes to speech production. The results showed that L1 Malaysian English speakers and native British English speakers found different SED paradigms to be more effective in inducing the production improvement. Only the production intelligibility of the /æ/ phoneme improved as a result of SED training. Collectively, the seven experiments in this thesis showed that SED training was effective in improving Malaysian speakers’ perception and production performance of difficult English phonemic contrasts. Further research should be conducted to examine the efficacy of SED training in improving speech perception and production across different training materials and in speakers who come from different language backgrounds

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