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 RELATIONSHIP OF PERCEIVED WORKLOAD AND PSYCHOMOTOR PERFORMANCE TO BRAIN DYNAMICS DURING VARYING DEGREES OF TASK DEMAND AND CONTROLLABILITY IN A FLIGHT-RELATED COMPENSATORY TRACKING TASK(2024) Pietro, Kyle; Hatfield, Bradley D.; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The assessment and prediction of cognitive-motor performance holds great importance for any discipline connected to human operators in the context of safety-critical behavior. A study of mental workload is essential to understanding the intrinsic limitations of the human information processing system, and the resultant cognitive-motor behavior. Mental workload and the quality of cognitive-motor performance are generally known to be impacted by task demand. However, one feature of task demand far less understood is the controllability of a system (e.g. the responsiveness of a flight platform and its handling qualities). In the realm of Human-Machine Interface, the assessment of system controllability has typically been conducted through subjective measurements, such as the Cooper-Harper Rating Scale, a widely used metric in aircraft design to measure perceived operator workload and handling qualities, first proposed in 1969. A fundamental element of the decision making process for handling qualities associated with operator workload includes the reporting of the control compensation required to overcome deficiencies and errors that could impact and inhibit the successful completion of a task. Yet, the Cooper-Harper Rating Scale, and all other subjective rating scales are limited by a lack of objectivity, reliability, reduced sensitivity to dynamic changes in operator workload, and, are solely dependent on subjective estimates of effort to control compensation within a system, despite such wide usage in the field. To overcome such limitations, the contribution of this dissertation is the estimation of perceived operator workload, based on objective brain dynamics captured during varying levels of task demand and controllability. Therefore, the objective of this dissertation was to ascertain how objective brain dynamics and subjective ratings would respond to flight-related compensatory tracking tasks when handling qualities and task demand are manipulated. More specifically, this dissertation assessed the relationship between objective brain dynamics and subjective rating scales explicitly related to mental workload, as reported during compensatory tracking tasks of varying complexity, while also challenged with progressively increasing levels of controllability (i.e., levels of handling qualities). Thus, Aim 1 was to assess the effects of varying levels of handling qualities (i.e., HQR1, HQR2, HQR3) on mental workload and psychomotor performance. Aim 2 was to investigate the effects of increased task demand (i.e., Single-axis vs. Multi-axis) on mental workload and psychomotor performance. Finally, Aim 3 was to examine the empirical relationship between objective brain dynamics and subjective ratings of workload. Accordingly, this dissertation employed a 2 Condition (Single-axis vs. Multi-axis) x 3 Level of Handling Qualities (HQR1, HQR2, HQR3) design. Perceived workload, psychomotor performance, and brain dynamics, derived from EEG power spectra and spectro-temporal analyses, were assessed in twenty-two volunteer participants in the Naval Reserve Officers’ Training Corps. Overall, the findings of this dissertation support a characterization of the human information processing system as a finite resource with a limited capacity. When challenged with increasing levels of handling qualities, parietal alpha power decreased, behavioral performance was significantly attenuated, and subjective ratings of workload were higher, as was expected. Accordingly, there was a significant relationship between objective brain dynamics and subjective ratings of workload. Furthermore, an exploratory wavelet-based analysis revealed some generally high cross-correlations between brain dynamics and psychomotor performance, which may inform future research efforts of more dynamic measurement strategies to capture perceived workload with increased fidelity. Therefore, the results of this dissertation underscore the usage of objective brain dynamics to supplement subjective rating scales, which can provide additional insights to enhance our understanding of brain and motor coordination under varying levels of task demand and system handling qualities.Item HACKING THE NERVOUS SYSTEM: PROMOTION OF PSYCHOMOTOR EFFICIENCY THROUGH VAGUS NEUROMODULATION(2021) Lu, Calvin; Hatfield, Bradley D; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Research in performance optimization aims to improve cognitive-motor performance under arduous conditions. From a kinesiology perspective, effectiveness in performance optimization can be quantified through the neurophysiological economy of goal-directed motor behavior. Derived from the psychomotor efficiency hypothesis, the cognitive-affective-motor (CAM) model discusses the brain's complex intersections of cognitive-motor and cognitive-affective processes. The CAM model subscribes to the principle that superior performance is achieved by minimizing nonessential motoric processes, such as mental stress management. When stress response becomes unmanageable, there will be an elevation in nonessential motoric processes and negatively impact motor preparation. The resulting disfluency within the central nervous system will ultimately manifest in the motor and autonomic sections of the peripheral nervous system. To combat the disruptive effects of mental stress, employing autonomic regulation techniques such as Vagus nerve neuromodulation can remedy the inefficiencies of the nervous systems and promote an adaptive state for performance. This dissertation aimed to assess the CAM model empirically by investigating the integrative model of the cortical, autonomic, and motor nervous systems during a precision motor task (i.e., dart-throwing). A thorough examination was conducted on preserving the nervous system’s efficiency and positive impacts on the quality of motor performance through Vagus nerve neuromodulations. Specifically, the study focused on varying levels of mental stress to determine inoculation capabilities. Twenty-three participants were enrolled in a repeated-measures within-subjects design. Neurophysiological measures of nervous system activity were captured before motor execution to determine the amalgamated influence of Vagus nerve neuromodulation and mental stress. The observed results revealed an elevation in psychomotor efficiency through the Vagus nerve neuromodulations. Participants exhibited improved performance, as seen through a reduction of accuracy variability. This was accompanied by nervous system alterations of increased left temporal alpha power, reduced motor unit engagements, and reduced mental workload during the preparation of motor execution. In summary, the observed effects of Vagus nerve neuromodulation techniques successfully promoted nervous system efficiency and an adaptive state for goal-directed motor behavior. The dissertation outcomes provide evidence on the benefits of ergonomic aids such as Vagus nerve neuromodulation on facilitating an adaptive nervous system to enhance cognitive-motor performance.Item THE IMPACT OF ETHNIC AND RACIAL IDENTITY ON THE RELATION BETWEEN AFRICAN AMERICAN TEST ANXIETY AND LATER ACHIEVEMENT(2019) Daye, Alyssa Lauren; O'Neal, Colleen; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The present study tests a protective factor which may mitigate the negative impact of test anxiety on academic outcomes. This study examines ethnic and racial identity as a moderator of the impact of test anxiety on grades and academic ability self-concept among African American adolescents. The study relies on the existing longitudinal Maryland Adolescent Development in Context Study (MADICS) dataset, a public use dataset collected from 1991-2000. The subsample consists of 533 African American youths in Wave 3 and 399 African American youths in Wave 4. The present study uses two waves of data from participants aged 13 to 18. This study employs self-reported questionnaires of test anxiety, ethnic and racial identity, grades, and academic ability self-concept. Moderation analyses are conducted to test ethnic and racial identity as a protective factor mitigating the impact of test anxiety on later grades and academic ability self-concept, while adjusting for gender, socioeconomic status, and age. Results indicate that ethnic and racial identity moderated the relation between test anxiety and GPA, such that the lower the level of ethnic and racial identity, the more protective it becomes. Discussion centers on potential causes for the unexpected trend in moderation.Item AN INITIAL EVALUATION OF IBI VIZEDIT: AN RSHINY APPLICATION FOR OBTAINING ACCURATE ESTIMATES OF AUTONOMIC REGULATION OF CARDIAC ACTIVITY(2018) Barstead, Matthew; Rubin, Kenneth H; Human Development; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Photoplethysmogram (PPG) sensors are increasingly used to collect individual heart rate data during laboratory assessments and psychological experiments. PPG sensors are relatively cheap, easy to use, and non-invasive alternatives to the more common electrodes used to produce electrocardiogram recordings. The downside is that these sensors are more susceptible to signal distortion. Often, the most relevant measures for understanding psychological processes that underlie emotions and behaviors are measures of heart rate variability. As with all measures of variability, outliers (i.e., signal artifacts) can have outsized effects on the final estimates; and, given that these scores represent a primary variable of interest in many research contexts, the successful elimination of artefactual points is critical to the ability to make valid inferences with the data. Prior to the development of IBI VizEdit, there was no single, integrated processing and editing pipeline for PPG data. The present pair of studies offers and initial evaluation of the program’s performance. Study 1 is focused on the efficacy of a novel approach to imputing sections of particularly corrupted PPG signal. Study 2 tests the ability of trained editors to reliably use IBI VizEdit as well as the validity of estimates of cardiac activity during a prescribed set of laboratory tasks. Study 1 suggests that the novel imputation approach, under certain conditions and using certain parameterizations may hold promise as a means of accurately imputing missing sections of data. However, Study 1 also clearly demonstrates the need for further refinement and the consideration of alternative implementations. The results from Study 2 indicate that IBI VizEdit can be reliably used by trained editors and that estimates of cardiac activity derived from its output are likely valid.Item Psychological and Neurobiological Outcomes of Parent-Child Adrenocortical Concordance(2017) Merwin, Stephanie; Dougherty, Lea R; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Emerging work has examined parent-child concordance of hypothalamic-pituitary-adrenal (HPA) axis functioning (i.e., adrenocortical concordance) which reflects the attunement or association of the stress hormone cortisol between the parent and child. The cortisol awakening response (CAR) is a critical aspect of HPA axis functioning that is sensitive to environmental factors and uniquely predicts psychopathology in youth. HPA axis functioning has also been linked to alterations in brain structure, specifically the hippocampus. The hippocampus is a critical brain region involved in learning and emotional processing and is sensitive to the parenting context, and undergoes change across early childhood. Despite these critical links between the parent-child dyad, HPA axis functioning, and hippocampal structure, no study has examined the longitudinal outcomes of adrenocortical concordance. The current study examined early parent-child adrenocortical concordance and its concurrent and longitudinal associations with parenting and children’s psychopathology and psychosocial functioning, as well as its longitudinal associations with children’s hippocampal structure in middle childhood. Participants included 142 parent-child dyads. Parents and children provided cortisol at Wave 1 when children were 3-5 years-old, and 98 dyads returned for the Wave 2 assessment three years later when children were 5-9 years-old. At Wave 1, parents and children provided salivary cortisol samples at waking, and 30 and 45 minutes post-waking across two days to assess the CAR. At Waves 1 and 2, child psychopathology and functioning were assessed through a parent-report clinical interview, and the parenting context was assessed through a laboratory-based parent-child interaction task. At Wave 2, a subsample of 51 children completed an anatomical magnetic resonance imaging assessment to measure hippocampal structure. Stronger parent-child concordance was associated with children’s poorer outcomes, namely increases in parental hostility from early to middle childhood, and children’s greater psychiatric symptoms and poorer psychosocial functioning in early and middle childhood. Moreover, parent- and child-level risk factors moderated several associations between stronger concordance and children’s poor outcomes. Parent-child concordance was not related to children’s hippocampal volumes in middle childhood. Importantly, our findings highlight adrenocortical concordance as a process underlying the parent-child relationship that plays a role in the development of psychopathology and functional impairment in children.Item NEURAL CHRONOMETRY OF VISUAL ATTENTION & THREAT PROCESSING(2018) Haas, Sara A; Fox, Nathan A; Human Development; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most anxiety disorders in adults emerge during adolescence, and if left untreated, pediatric anxiety disorders predict adverse mental and physical health outcomes in adolescents and adults. While genetic heritability is a contributing risk factor, a heightened tendency to direct attention preferentially to threat represents one of the strongest information-processing correlates of anxiety; such an attention bias may shape both the development and maintenance of anxiety symptoms. Attentional performance differences have been observed on emotion cueing visual attention tasks as a function of both clinical and sub-clinical anxiety levels. Previous work in adults observed that for adults with higher anxiety symptoms, efficiency of visual search was degraded by threat-cueing faces. However, further work is required to clarify the emergence attentional biases in adolescents, to inform methods for early identification, intervention and treatment of individuals at risk for anxiety. The present study examined the impact of emotional priming on attention as a function of anxiety using a task in which emotional faces were used as primes for a visual search task. Event Related Potentials (ERP) (P1, N170 and N2pc) were recorded in concert with behavioral responses to address the chronometry and quality of attentional processing as a function of anxiety symptoms in adolescents, 12-17 years of age. Early P1 and N170 processing in the first few hundred milliseconds of viewing face primes, differed as a function of both anxiety and prime emotion. Moreover, these anxiety-related early processing differences related to subsequent behavior. Variability in the N2pc attention-related processing during visual search also varied as a function of anxiety and prime type, as well as affected subsequent behavior. This dissertation found both early and later occurring attentional processes have significant ramifications for individuals with higher anxiety scores, such that in addition to neural differences, high anxious individuals also display significant differences in behavior. While early and late neural processes varied in lower anxious individuals as a function of face prime type, relations with behavior were minimal in comparison. These findings are discussed as they relate to emotion processing, threat responsivity to facial stimuli, and applicability to pediatric and adult clinical anxiety.Item Neural Mechanisms of Approach and Avoidance(2017) Gentry, Ronny; Roesch, Matthew R; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Using environmental cues to acquire good things and avoid harmful things is critical for survival. Rewards and punishments both drive behavior through reinforcement learning mechanisms and sometimes occur together in the environment, but it remains unclear how these signals are encoded within the brain and if signals for positive and negative reinforcement are encoded similarly. The dopaminergic system and, more broadly, the corticomesolimbic circuit are known to be involved in the processing of positive and negative reinforcement. Here, I investigated neural correlates of decision-making and associated behavioral patterns within two key corticomesolimbic regions: the ventromedial prefrontal cortex (vmPFC), which is thought to generate contextually appropriate responses, and the nucleus accumbens (NAc), which is thought to use dopamine (DA) prediction error signals to motivate behavior. The goal of this work was to uncover the underlying brain mechanisms encoding positive and negative reinforcement signals and to explore individual differences in neural and behavioral patterns that arise during learning and performance. To achieve this, I recorded from single neurons within vmPFC and measured DA release within NAc core during two behavioral tasks examining distinct aspects of learning: initial Pavlovian responses, as well as more complex combined positive and negative reinforcement. I found that, within the vmPFC, cell firing was modulated more often and more robustly by cues predicting reward than by cues preceding avoidable shock; overall, we found very few cells that responded to shock cues, and responses to shock avoidance and reward cues were not colocalized within the same cells. Alternatively, I found that DA release within the NAc increased to both reward and shock avoidance cues compared to neutral cues, and these changes occurred within the same microdomain of the NAc. Additionally, we uncovered intriguing individual differences in NAc DA release and behavioral responses during both our combined approach avoidance and autoshaping tasks and, in the final chapter, shifted these responses by manipulating task parameters and inhibiting VTA-NAc DA neurons. Together, these results help further our understanding of how differences in vmPFC activity and accumbal DA release influence cue-driven learning and behavioral performance across various contexts.Item UNDERSTANDING THE CONTRIBUTION OF THE CENTRAL EXTENDED AMYGDALA TO DISPOSITIONAL NEGATIVITY(2017) Tillman, Rachael; Shackman, Alexander; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dispositional negativity (DN) is a key risk factor for a spectrum of adverse outcomes, including anxiety disorders, depression, and comorbid substance abuse. The central extended amygdala (EAc; an anatomical concept encompassing the bed nucleus of the stria terminalis [BST] and central nucleus of the amygdala [Ce]) is implicated in the development and maintenance of these disorders. However, disorders, like other psychological processes, reflect the coordinated actions of widely distributed networks. Yet, the functional architecture of the human EAc and its relation to individual differences in DN remains poorly understood. We investigated intrinsic functional connectivity (iFC) of the EAc in 185 healthy adults. Whole-brain regression analyses revealed that the BST and Ce show iFC with one another via the sublenticular extended amygdala. While both regions showed significant iFC with the ventromedial prefrontal cortex and with cingulate territories involved in adaptive control of anxiety-related behavior, the BST showed more robust coupling. Contrary to expectations, EAc iFC was not significantly associated with individual differences in DN. These observations provide a novel neurobiological framework for understanding a range of stress-sensitive disorders.Item TRANSFORMATIONS OF TASK-DEPENDENT PLASTICITY FROM A1 TO HIGHER-ORDER AUDITORY CORTEX(2016) Elgueda Gonzalez, Diego Enrique; Shamma, Shihab A; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Everyday, humans and animals navigate complex acoustic environments, where multiple sound sources overlap. Somehow, they effortlessly perform an acoustic scene analysis and extract relevant signals from background noise. Constant updating of the behavioral relevance of ambient sounds requires the representation and integration of incoming acoustical information with internal representations such as behavioral goals, expectations and memories of previous sound-meaning associations. Rapid plasticity of auditory representations may contribute to our ability to attend and focus on relevant sounds. In order to better understand how auditory representations are transformed in the brain to incorporate behavioral contextual information, we explored task-dependent plasticity in neural responses recorded at four levels of the auditory cortical processing hierarchy of ferrets: the primary auditory cortex (A1), two higher-order auditory areas (dorsal PEG and ventral-anterior PEG) and dorso-lateral frontal cortex. In one study we explored the laminar profile of rapid-task related plasticity in A1 and found that plasticity occurred at all depths, but was greatest in supragranular layers. This result suggests that rapid task-related plasticity in A1 derives primarily from intracortical modulation of neural selectivity. In two other studies we explored task-dependent plasticity in two higher-order areas of the ferret auditory cortex that may correspond to belt (secondary) and parabelt (tertiary) auditory areas. We found that representations of behaviorally-relevant sounds are progressively enhanced during performance of auditory tasks. These selective enhancement effects became progressively larger as you ascend the auditory cortical hierarchy. We also observed neuronal responses to non-auditory, task-related information (reward timing, expectations) in the parabelt area that were very similar to responses previously described in frontal cortex. These results suggests that auditory representations in the brain are transformed from the more veridical spectrotemporal information encoded in earlier auditory stages to a more abstract representation encoding sound behavioral meaning in higher-order auditory areas and dorso-lateral frontal cortex.Item Multidimensional psychophysics and verbal associations(1953) Ray, William S.; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)