Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item The Effects of Transcranial Direct Current Stimulation on Narrative Abilities in Primary Progressive Aphasia(2018) Colantuoni, Deborah Elise; Faroqi-Shah, Yasmeen; Hearing and Speech Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Transcranial direct current stimulation (tDCS) is a neuromodulation technique that has recently been studied as an adjunct to speech-language therapy in persons with primary progressive aphasia (PPA). Preliminary studies have shown improved language abilities with tDCS-supplemented therapy, primarily in naming, as well as improved generalization and maintenance of skills. However, the effects of tDCS on narrative abilities have not yet been well studied in this population. The present study examined whether the addition of tDCS to anomia therapy improved narrative language measures in 16 participants with PPA versus sham stimulation plus therapy. Results demonstrated that tDCS did not significantly improve narrative language measures in participants with PPA.Item EXPLORING THE ACCESSIBILITY OF HOME-BASED, VOICE-CONTROLLED INTELLIGENT PERSONAL ASSISTANTS(2018) Pradhan, Alisha; Lazar, Amanda; Library & Information Services; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)From an accessibility perspective, home-based, voice-controlled intelligent personal assistants (IPAs) have the potential to greatly expand speech interaction beyond dictation and screenreader output. This research examines the accessibility of off-the-shelf IPAs (e.g., Amazon Echo) by conducting two exploratory studies. To explore the use of IPAs by people with disabilities, we analyzed 346 Amazon Echo reviews mentioning users with disabilities, followed by interviews with 16 visually impaired IPA users. Although some accessibility challenges exist, individuals with a range of disabilities are using IPAs, including unexpected uses such as speech therapy and memory aids. The second study involved a three-week deployment of Echo Dot, a popular IPA, with five older adults who use technology infrequently. Findings indicate preferences for using IPAs over traditional computing devices. We identify design implications to improve IPAs for this population. Both studies highlight issues of discoverability and the need for feature-rich voice-based applications. The findings of this research can inform future work on accessible voice-based IPAs.Item CORTICAL REPRESENTATION OF SPEECH IN COMPLEX AUDITORY ENVIRONMENTS AND APPLICATIONS(2017) Puvvada, Venkata Naga Krishna Chaitanya; Simon, Jonathan Z; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Being able to attend and recognize speech or a particular sound in complex listening environments is a feat performed by humans effortlessly. The underlying neural mechanisms, however, remain unclear and cannot yet be emulated by artificial systems. Understanding the internal (cortical) representation of external acoustic world is a key step in deciphering the mechanisms of human auditory processing. Further, understanding neural representation of sound finds numerous applications in clinical research for psychiatric disorders with auditory processing deficits such as schizophrenia. In the first part of this dissertation, cortical activity from normal hearing human subjects is recorded, non-invasively, using magnetoencephalography in two different real-life listening scenarios. First, when natural speech is distorted by reverberation as well as stationary additive noise. Second, when the attended speech is degraded by the presence of multiple additional talkers in the background, simulating a cocktail party. Using natural speech affected by reverberation and noise, it was demonstrated that the auditory cortex maintains both distorted as well as distortion-free representations of speech. Additionally, we show that, while the neural representation of speech remained robust to additive noise in absence of reverberation, noise had detrimental effect in presence of reverberation, suggesting differential mechanisms of speech processing for additive and reverberation distortions. In the cocktail party paradigm, we demonstrated that primary like areas represent the external auditory world in terms of acoustics, whereas higher-order areas maintained an object based representation. Further, it was demonstrated that background speech streams were represented as an unsegregated auditory object. The results suggest that object based representation of auditory scene emerge in higher-order auditory cortices. In the second part of this dissertation, using electroencephalographic recordings from normal human subjects and patients suffering from schizophrenia, it was demonstrated, for the first time, that delta band steady state responses are more affected in schizophrenia patients compared with healthy individuals, contrary to the prevailing dominance of gamma band studies in literature. Further, the results from this study suggest that the inadequate ability to sustain neural responses in this low frequency range may play a vital role in auditory perceptual and cognitive deficit mechanisms in schizophrenia. Overall this dissertation furthers current understanding of cortical representation of speech in complex listening environments and how auditory representation of sounds is affected in psychiatric disorders involving aberrant auditory processing.Item TEMPORAL CODING OF SPEECH IN HUMAN AUDITORY CORTEX(2012) Ding, Nai; Simon, Jonathan Z; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Human listeners can reliably recognize speech in complex listening environments. The underlying neural mechanisms, however, remain unclear and cannot yet be emulated by any artificial system. In this dissertation, we study how speech is represented in the human auditory cortex and how the neural representation contributes to reliable speech recognition. Cortical activity from normal hearing human subjects is noninvasively recorded using magnetoencephalography, during natural speech listening. It is first demonstrated that neural activity from auditory cortex is precisely synchronized to the slow temporal modulations of speech, when the speech signal is presented in a quiet listening environment. How this neural representation is affected by acoustic interference is then investigated. Acoustic interference degrades speech perception via two mechanisms, informational masking and energetic masking, which are addressed respectively by using a competing speech stream and a stationary noise as the interfering sound. When two speech streams are presented simultaneously, cortical activity is predominantly synchronized to the speech stream the listener attends to, even if the unattended, competing speech stream is 8 dB more intense. When speech is presented together with spectrally matched stationary noise, cortical activity remains precisely synchronized to the temporal modulations of speech until the noise is 9 dB more intense. Critically, the accuracy of neural synchronization to speech predicts how well individual listeners can understand speech in noise. Further analysis reveals that two neural sources contribute to speech synchronized cortical activity, one with a shorter response latency of about 50 ms and the other with a longer response latency of about 100 ms. The longer-latency component, but not the shorter-latency component, shows selectivity to the attended speech and invariance to background noise, indicating a transition from encoding the acoustic scene to encoding the behaviorally important auditory object, in auditory cortex. Taken together, we have demonstrated that during natural speech comprehension, neural activity in the human auditory cortex is precisely synchronized to the slow temporal modulations of speech. This neural synchronization is robust to acoustic interference, whether speech or noise, and therefore provides a strong candidate for the neural basis of acoustic background invariant speech recognition.Item Windows into Sensory Integration and Rates in Language Processing: Insights from Signed and Spoken Languages(2011) Hwang, So-One K.; Idsardi, William J.; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation explores the hypothesis that language processing proceeds in "windows" that correspond to representational units, where sensory signals are integrated according to time-scales that correspond to the rate of the input. To investigate universal mechanisms, a comparison of signed and spoken languages is necessary. Underlying the seemingly effortless process of language comprehension is the perceiver's knowledge about the rate at which linguistic form and meaning unfold in time and the ability to adapt to variations in the input. The vast body of work in this area has focused on speech perception, where the goal is to determine how linguistic information is recovered from acoustic signals. Testing some of these theories in the visual processing of American Sign Language (ASL) provides a unique opportunity to better understand how sign languages are processed and which aspects of speech perception models are in fact about language perception across modalities. The first part of the dissertation presents three psychophysical experiments investigating temporal integration windows in sign language perception by testing the intelligibility of locally time-reversed sentences. The findings demonstrate the contribution of modality for the time-scales of these windows, where signing is successively integrated over longer durations (~ 250-300 ms) than in speech (~ 50-60 ms), while also pointing to modality-independent mechanisms, where integration occurs in durations that correspond to the size of linguistic units. The second part of the dissertation focuses on production rates in sentences taken from natural conversations of English, Korean, and ASL. Data from word, sign, morpheme, and syllable rates suggest that while the rate of words and signs can vary from language to language, the relationship between the rate of syllables and morphemes is relatively consistent among these typologically diverse languages. The results from rates in ASL also complement the findings in perception experiments by confirming that time-scales at which phonological units fluctuate in production match the temporal integration windows in perception. These results are consistent with the hypothesis that there are modality-independent time pressures for language processing, and discussions provide a synthesis of converging findings from other domains of research and propose ideas for future investigations.Item The relationship between maternal speech clarity and infant language outcomes(2011) McColgan, Kerry; Ratner, Nan B; Hearing and Speech Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mothers' use of infant-directed speech (IDS) may assist infants in decoding language input. IDS is characterized by exaggerated prosodic features (Fernald, 1989), shorter mean length of utterance (Cooper, 1997; Bernstein Ratner, 1996), repetition (Bernstein Ratner, 1996), and more highly clarified acoustic qualities (Bernstein Ratner, 1984; Malsheen, 1980) in comparison to speech directed to adults. However, it is not yet known to what extent such measures of maternal input have long-term impacts on language development. This thesis seeks to test the overarching hypothesis that children who receive more clarified speech input during the prelinguistic stage may be expected to have better language skills at an earlier age than children who receive poorer quality input.Item Infant Speech-in-Noise Perception and Later Phonological Awareness: A Longitudinal Study(2008-10-20) Stimley, Sarah Elizabeth; Newman, Rochelle; Hearing and Speech Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While differences have been found in the ability of infants on a variety of speech perception skills including speech perception in the presence of background noise, the implications of these differences on later language skills are currently unknown. This study examines the relationship between a specific measure of infant speech perception in noise and later phonological awareness outcomes. In order to test this relationship, individuals who participated in Newman's (2005) study on infant speech perception in the presence of background noise were administered a battery of language, phonological awareness, and intelligence tests. Scores from these tests were analyzed to see if performance differences existed between those who had performed well as infants in the original study and those who had not. No significant differences between these two groups were found on the phonological awareness measures. Potential reasons for these findings and suggestions for future research are discussed.Item CORTICAL DYNAMICS OF AUDITORY-VISUAL SPEECH: A FORWARD MODEL OF MULTISENSORY INTEGRATION.(2004-08-30) van Wassenhove, Virginie; Poeppel, David; Grant, Ken W.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In noisy settings, seeing the interlocutor's face helps to disambiguate what is being said. For this to happen, the brain must integrate auditory and visual information. Three major problems are (1) bringing together separate sensory streams of information, (2) extracting auditory and visual speech information, and (3) identifying this information as a unified auditory-visual percept. In this dissertation, a new representational framework for auditory visual (AV) speech integration is offered. The experimental work (psychophysics and electrophysiology (EEG)) suggests specific neural mechanisms for solving problems (1), (2), and (3) that are consistent with a (forward) 'analysis-by-synthesis' view of AV speech integration. In Chapter I, multisensory perception and integration are reviewed. A unified conceptual framework serves as background for the study of AV speech integration. In Chapter II, psychophysics testing the perception of desynchronized AV speech inputs show the existence of a ~250ms temporal window of integration in AV speech integration. In Chapter III, an EEG study shows that visual speech modulates early on the neural processing of auditory speech. Two functionally independent modulations are (i) a ~250ms amplitude reduction of auditory evoked potentials (AEPs) and (ii) a systematic temporal facilitation of the same AEPs as a function of the saliency of visual speech. In Chapter IV, an EEG study of desynchronized AV speech inputs shows that (i) fine-grained (gamma, ~25ms) and (ii) coarse-grained (theta, ~250ms) neural mechanisms simultaneously mediate the processing of AV speech. In Chapter V, a new illusory effect is proposed, where non-speech visual signals modify the perceptual quality of auditory objects. EEG results show very different patterns of activation as compared to those observed in AV speech integration. An MEG experiment is subsequently proposed to test hypotheses on the origins of these differences. In Chapter VI, the 'analysis-by-synthesis' model of AV speech integration is contrasted with major speech theories. From a Cognitive Neuroscience perspective, the 'analysis-by-synthesis' model is argued to offer the most sensible representational system for AV speech integration. This thesis shows that AV speech integration results from both the statistical nature of stimulation and the inherent predictive capabilities of the nervous system.Item Vocal Dysfunction in Young-onset Parkinson's Disease(2004-08-10) Bassich-Zeren, Celia J.; McCall, G N.; Hearing and Speech Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Vocal dysfunction is well established in persons with older-onset Parkinson's disease (PD), but has not been investigated in the young-onset PD (YOPD) population. Voice deficits associated with older-onset PD mirror the characteristics of vocal aging, suggesting that our current knowledge base of laryngeal dysfunction in the PD population is confounded by aging effects. The purpose of this study was threefold: (a) to examine perceptual voice characteristics and the potential impact of voice symptoms on quality of life; (b) to compare YOPD and healthy control (HC) speakers' performance on two routinely used clinical tasks (sustained vowel phonation and laryngeal diadochokinesis); and (c) to experimentally manipulate and compare speakers' performance in producing phonatory offset-onset gestures as reflected in four phonetic contexts (each eliciting a different mechanism) across three speaking modes. Twelve YOPD speakers and twelve healthy control (HC) speakers participated. YOPD speakers reported voice symptoms of hypophonia, tremor, hoarseness, monotone, and impaired speech intelligibility. They demonstrated a mild to moderate voice handicap. Findings revealed no speaker group differences for speech intensity on sustained vowel phonation and reading tasks. YOPD speakers demonstrated a significantly decreased rate of syllable repetition and used a significantly greater number of pauses during production of one of two laryngeal diadochokinetic tasks. Acoustic measures associated with mechanisms of phonatory offset-onset demonstrated trends of speaker group differences, suggesting that YOPD speakers have impaired voicing control for mechanisms of phonatory offset-onset not associated with oral constriction. Intra-speaker group variability was observed for YOPD speakers. Inspection of speaker groups' performance across speaking modes suggested a disruption in the habitual setting of laryngeal posture in YOPD speakers; namely, they use a laryngeal postural setting that is similar to that observed in HC speakers when speaking in an aspirant or breathy voice mode. Speech masking facilitated a speaking mode change in YOPD speakers and could provide an effective and efficient treatment method for training persons with YOPD to speak in a projected mode. Vocal dysfunction is associated with YOPD and voice symptoms can appear early in the disease process, sometimes preceding onset of limb symptoms. Persons with YOPD should be routinely assessed for vocal dysfunction.