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 An Investigation of Inhibitory Control in Bilingual Aphasia(2015) Sampson, Monica; Faroqi-Shah, Yasmeen; Hearing and Speech Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Speaking involves selecting words and syntactic structures from among numerous competing options. It has been suggested that constant practice in using inhibitory control (IC) to limit within and cross-language competition may be associated with better lexical-semantic IC in proficient bilingual speakers relative to monolingual speakers. This advantage is also theorized to generalize to IC advantages in non-linguistic tasks (bilingual advantage hypothesis; BAH; Bialystok, 2001). However, conflicting evidence with regard to bilingual IC advantages abound, and the nature of relationship between linguistic and domain-general inhibitory control abilities is poorly understood. Since IC is proposed to be critical for lexical retrieval, it is important to understand the nature of IC engaged in individuals with lexical retrieval deficits (aphasia). Bilingual speakers with aphasia provide an ideal platform to examine the relationship between language processing and IC because there are seemingly contradictory effects at play: while bilingualism may render an IC advantage, acquired brain injury may be associated with less efficient IC. These contrasting effects allow one to tease apart the effects of bilingualism on IC, the domain generality of the bilingual IC advantage, and relationship between bilingualism, IC and lexical selection. It is important to examine these effects relative to matched monolingual controls to understand (i) if there is a bilingual advantage in lexically based IC and, (ii) the domain generality of any bilingual IC advantage. To address these aims, IC engaged in (i) lexical retrieval (semantically blocked cyclic naming task), (ii) linguistic processing (Stroop task), and (iii) non-linguistic processing (flanker task) was compared in ten each of bilingual (Tamil-English) and monolingual (English) neurologically healthy speakers and participants with aphasia. Results from neurologically healthy participants revealed a bilingual advantage in the blocked cyclic naming task (lexical IC) but no advantages in the non-lexical Stroop and flanker tasks. Results from participants with aphasia revealed no support for the proposed bilingual advantages in all three experiments. Furthermore, there was no significant association between inhibitory control measures in the three experimental tasks for all participants. Contrary to the predictions of the BAH, the collective results of this study indicate that there is insufficient evidence for the role of bilingualism in modulating non-lexical IC advantages. This lack of consistent support for BAH questions the influence of bilingual experience in modulating non-linguistic inhibitory control. These findings also reveal that the relationship between inhibitory control and lexical retrieval is not influenced by language background (monolingual versus bilingual) in persons with aphasia.Item The response-monitoring mechanism: Influence of feedback and temperament(2008-05-06) Martin McDermott, Jennifer; Fox, Nathan A; Human Development; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of the current study was to examine behavioral and physiological processes underlying response-monitoring and to document the manner in which these processes are expressed during early childhood. As well, this study examined two factors important in understanding individual differences in monitoring: performance feedback and temperament. A total of seventy-four children (mean age 7.5 years) were tested using a modified flanker paradigm administered in both no-feedback and feedback conditions. Accuracy and reaction time measures of behavioral performance were assessed as well as event-related potentials linked to response execution and feedback presentation. Data were also examined in relation to the temperamental dimensions of shyness and inhibitory control. The results indicate a strong impact of trial-by-trial feedback on both behavioral and physiological measures. Overall, feedback served to increase children's task engagement as evidenced by fewer errors of omission and faster reaction times. Similarly, the physiological measures also varied as a function of feedback such that the error-related Positivity (Pe) and the feedback-related negativity (FRN) were more pronounced on incorrect as compared to correct trials in the feedback condition. Larger FRN responses were also associated with fewer errors of commission. These findings were further moderated by individual differences in temperament. Specifically, feedback was particularly influential in increasing task involvement for children low in inhibitory control and enhancing performance accuracy for children low in shyness Overall these results confirm a strong impact of feedback on task engagement as assessed by children's behavioral performance and physiological reactivity. Findings are presented in the framework of individual differences in cognitive control and variations in children's physiological measures of response-monitoring are discussed. Several avenues for future research are provided which emphasize the need for investigations of response-monitoring in young children and also highlight the importance of exploring the applicability of these assessments across various cognitive and social contexts.