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 Phonological form in L2 lexical access: Friend or Foe?(2012) Cook, Svetlana V.; Kira, Gor; Second Language Acquisition and Application; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The aim of this dissertation is to investigate the contribution of lexical factors that affect second language (L2) lexical access, such as size of L2 mental lexicon, lexical frequency, and number of competitors. It introduces and explores an additional L2-specific dimension that plays a differential role in L2 lexical access, which is the degree of familiarity with the L2 lexical item, in particular, familiarity with its phonological form as it maps onto its meaning. The current thesis focuses on this factor's main consequence, which is the underspecification of the phonological representation of less-known words in the L2 mental lexicon. The combination of traditional lexical factors with the proposed L2-specific lexical factor makes it possible to propose an L2-specific model that accounts for the interactions not found in L1 lexical access mechanisms. The Second Language Lexical Access Model (SLLAM) proposed in the dissertation incorporates L2 specific factors, such as the underspecification of phonological representations and the proficiency-defined size of the mental lexicon, and makes predictions about the process of lexical access in L2. The dissertation compares lexical access mechanisms in three groups of subjects, two of which are L2 learners of Russian at different stages of acquisition (Intermediate learners and Advanced learners), and uses novel empirical evidence from five behavioral experiments: lexical decision task without priming, lexical decision task with phonological priming, lexical decision task with semantic priming, lexical decision task with pseudo-semantic priming, and a translation task. The results of the experiments are discussed in light of the proposed SLLAM model. The dissertation argues that the majority of the observed results can be accommodated by the assumptions made by SLLAM, compatible with the postulated underspecification at the lexical level of L2 phonological representations. Moreover, the study concludes that some of the L2-specific lexical access mechanisms, commonly attributed to a lack of semantic links within the lexicon, may be more parsimoniously explained as resulting from phonological underspecification as well.Item Neural Basis and Computational Strategies for Auditory Processing(2004-11-29) Elhilali, Mounya; Shamma, Shihab A; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Our senses are our window to the world, and hearing is the window through which we perceive the world of sound. While seemingly effortless, the process of hearing involves complex transformations by which the auditory system consolidates acoustic information from the environment into perceptual and cognitive experiences. Studies of auditory processing try to elucidate the mechanisms underlying the function of the auditory system, and infer computational strategies that are valuable both clinically and intellectually, hence contributing to our understanding of the function of the brain. In this thesis, we adopt both an experimental and computational approach in tackling various aspects of auditory processing. We first investigate the neural basis underlying the function of the auditory cortex, and explore the dynamics and computational mechanisms of cortical processing. Our findings offer physiological evidence for a role of primary cortical neurons in the integration of sound features at different time constants, and possibly in the formation of auditory objects. Based on physiological principles of sound processing, we explore computational implementations in tackling specific perceptual questions. We exploit our knowledge of the neural mechanisms of cortical auditory processing to formulate models addressing the problems of speech intelligibility and auditory scene analysis. The intelligibility model focuses on a computational approach for evaluating loss of intelligibility, inspired from mammalian physiology and human perception. It is based on a multi-resolution filter-bank implementation of cortical response patterns, which extends into a robust metric for assessing loss of intelligibility in communication channels and speech recordings. This same cortical representation is extended further to develop a computational scheme for auditory scene analysis. The model maps perceptual principles of auditory grouping and stream formation into a computational system that combines aspects of bottom-up, primitive sound processing with an internal representation of the world. It is based on a framework of unsupervised adaptive learning with Kalman estimation. The model is extremely valuable in exploring various aspects of sound organization in the brain, allowing us to gain interesting insight into the neural basis of auditory scene analysis, as well as practical implementations for sound separation in ``cocktail-party'' situations.