Thesis (M.S.)--Eastern Illinois University, 2010. / Includes bibliographical references (leaves 57-62).

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 203-213).

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 142-146).

Thesis (M. Communication Pathology)--University of Pretoria, 2006. / Summary in English and Afrikaans. Includes bibliographical references.

Thesis (M. Log.)--Universiteit van Pretoria, 2000.

Fluent speech production requires rapid coordination among respiratory, laryngeal, and articulatory processes and is mediated by multiple neural systems (Bohland & Guenther, 2006). Stuttering is a fluency disorder characterized by core deficits in speech motor planning. Previous research indicates people who stutter (PWS) exhibit deficits in speech motor sequence learning and are slower and less accurate over practice relative to fluent speakers (Ludlow, Siren, & Zikira, 2004; Namasivayam & VanLieshout, 2004; Smits-Bandstra & De Nil, 2007; Smits-Bandstra, De Nil, & Saint-Cyr, 2006). Furthermore, the neural bases of impaired speech motor sequence learning in PWS are not well understood. We present a study in which PWS (n=18) and persons with fluent speech (PFS) (n=17) were taught phonotactically illegal (e.g. gbesb) and phonotactically legal (e.g. blerk) speech motor sequences over two practice sessions. Functional magnetic resonance imaging (fMRI) was used to investigate brain regions underlying the production of learned illegal syllables and novel illegal syllables. With practice, subjects produced syllables more accurately, which is indicative of motor sequence learning. Our findings suggest a speech motor performance deficit in PWS. Furthermore, these findings indicate speech motor sequence learning relies on a speech motor sequence learning network.

Non-native tones are considered challenging for adult second language speakers to perceive and produce. The current study examined the effect of a laboratory-based intensive training in improving American English speakers’ tone production. Participants’ task was to repeat Mandarin words after the model. There were two conditions in the experiment: in one condition, participants did not get any external feedback; whereas in the other condition, participants received detailed visual feedback, which was the pitch contour of their tone production alongside the native version. Eight participants completed training with no feedback and another eight participants were trained with visual feedback. Results revealed that participants in both groups did not improve their tone production after training, and participants trained with visual feedback did not show more improvement than those trained with no feedback. Given the lack of improvement in participants’ tone production after training, methodological and theoretical limitations with respect to the use of a repetition-based training paradigm are discussed.

abstract: Distorted vowel production is a hallmark characteristic of dysarthric speech, irrespective of the underlying neurological condition or dysarthria diagnosis. A variety of acoustic metrics have been used to study the nature of vowel production deficits in dysarthria; however, not all demonstrate sensitivity to the exhibited deficits. Less attention has been paid to quantifying the vowel production deficits associated with the specific dysarthrias. Attempts to characterize the relationship between naturally degraded vowel production in dysarthria with overall intelligibility have met with mixed results, leading some to question the nature of this relationship. It has been suggested that aberrant vowel acoustics may be an index of overall severity of the impairment and not an "integral component" of the intelligibility deficit. A limitation of previous work detailing perceptual consequences of disordered vowel acoustics is that overall intelligibility, not vowel identification accuracy, has been the perceptual measure of interest. A series of three experiments were conducted to address the problems outlined herein. The goals of the first experiment were to identify subsets of vowel metrics that reliably distinguish speakers with dysarthria from non-disordered speakers and differentiate the dysarthria subtypes. Vowel metrics that capture vowel centralization and reduced spectral distinctiveness among vowels differentiated dysarthric from non-disordered speakers. Vowel metrics generally failed to differentiate speakers according to their dysarthria diagnosis. The second and third experiments were conducted to evaluate the relationship between degraded vowel acoustics and the resulting percept. In the second experiment, correlation and regression analyses revealed vowel metrics that capture vowel centralization and distinctiveness and movement of the second formant frequency were most predictive of vowel identification accuracy and overall intelligibility. The third experiment was conducted to evaluate the extent to which the nature of the acoustic degradation predicts the resulting percept. Results suggest distinctive vowel tokens are better identified and, likewise, better-identified tokens are more distinctive. Further, an above-chance level agreement between nature of vowel misclassification and misidentification errors was demonstrated for all vowels, suggesting degraded vowel acoustics are not merely an index of severity in dysarthria, but rather are an integral component of the resultant intelligibility disorder. / Dissertation/Thesis / Ph.D. Speech and Hearing Science 2012

abstract: Working memory (WM) and attention deficits have been well documented in individuals with aphasia (IWA) (e.g. Caspari et al., 1998; Erickson et al., 1996; Tseng et al., 1993; Wright et al., 2003). Research into these cognitive domains has spurred a theoretical shift in how aphasia is conceptualized - from a purely linguistic disorder to a cognitive-information processing account. Language deficits experienced by IWA may result from WM impairments or from an inability to allocate cognitive effort to the tasks. However, how language impacts performance on these tasks has not been readily investigated. Further, there is a need for a more direct measure of effort invested to language tasks. Heart rate variability (HRV) is a physiological measure of cognitive workload that has been used to measure effort in neurologically intact participants. Objectives of the study included: (1) determining the feasibility of using HRV as a measure of effort IWA invest into verbal compared with spatial WM tasks, (2) Comparing participants' performance on verbal and spatial WM tasks; and (3) determining the relationship among performance, perceived task difficulty, and HRV across verbal and spatial tasks. Eleven IWA and 21 age- and education-matched controls completed verbal and spatial n-back tasks at three difficulty levels. Difficulty ratings were obtained before and after each task. Results indicated spatial WM was relatively preserved compared with verbal WM for the aphasia group. Additionally, the aphasia group was better at rating task difficulty after completing the tasks than they were at estimating task difficulty prior to completing the tasks. Significant baseline-task differences in HRV were found for both groups. Relationships between HRV and performance, and HRV and task difficulty were non-significant. Results suggest WM performance deficits in aphasia may be primarily driven by their language deficit. Baseline-task differences in HRV indicate effort is being allocated to the tasks. Difficulty ratings indicate IWA may underestimate task demands for both verbal and spatial stimuli. However, the extent to which difficulty ratings reflect effort allocated remains unclear. Additional research is necessary to further quantify the amount of effort IWA allocate to verbal and non-verbal tasks. / Dissertation/Thesis / Ph.D. Speech and Hearing Science 2012

abstract: Differentiating bilingual children with primary language impairment (PLI) from those with typical development in the process of learning a second language has been a challenge. Studies have focused on improving the diagnostic accuracy of language measures for bilinguals. However, researchers are faced with two main challenges when estimating the diagnostic accuracy of new measures: (a) using an a priori diagnosis of children (children with and without PLI), as a reference may introduce error given there is no gold standard for the a priori classification; and (b) classifying children into only two groups may be another source of error given evidence that there may be more than two language ability groups with different strengths and weaknesses or, alternatively, a single group characterized by a continuum of language performance. The current study tested for the number of distinct language ability groups and their characteristics in predominately Spanish-speaking children in the U.S. without using an a priori classification as a reference. In addition, the study examined to what extent the latent groups differed on each measure, and the stability of language ability groups across three assessment methods in Spanish (standardized tests, language sample analyses, and comprehensive assessment), taking in to account English and non-verbal cognitive skills. The study included 431 bilingual children attending English-only education. Three latent profile analyses were conducted, one for each method of assessment. Results suggested more than two distinct language ability groups in the population with the method of assessment influencing the number and characteristics of the groups. Specifically, four groups were estimated based on the comprehensive assessment, and three based on standardized assessment or language sample analysis in Spanish. The stability of the groups was high on average, particularly between the comprehensive assessment and the standardized measures. Results indicate that an a priori classification of children into two groups, those with and without PLI, could lead to misclassification, depending on the measures used. / Dissertation/Thesis / Ph.D. Speech and Hearing Science 2012