UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

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    THE INFLUENCE OF CUMULATIVE SLEEP RESTRICTION ON HUMAN PERFORMANCE: EXAMINATION OF BRAIN DYNAMICS AND SUSTAINED ATTENTION
    (2024) Kahl, Steven; Hatfield, Bradley; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Sustained attention (SA) impacts nearly every aspect of human performance. From the exactness of performing brain surgery to safely driving from one location to another, the ability to concentrate on a task for a period of time is important for success in work, school, relationships, and individual activities. As a key component of executive function (EF) and psychomotor performance, SA can be affected by many mental and physical processes. One process that can impact SA is restricted sleep, which is becoming more relevant in our ever-evolving technological society. Numerous studies have examined the impact of short bouts of restricted sleep on response time, a measure of SA, but few studies have examined the impact of the accumulating effect of sleep restriction (SR) on response time and brain dynamics as measured with electroencephalography (EEG). As part of a larger 40-day study, eight healthy participants (five female, average age 27.75) were observed for seven consecutive days and nights in a sleep lab, where they spent five hours in bed per night and engaged in numerous psychomotor vigilance tests (PVT), an indicator of SA, as part of their daytime activities. Through multiple one-factor ANOVAs, response time significantly slowed, and brain dynamic changes occurred, measured by slow wave activity (SWA) maxima change in the Fz electrode, located in the midline frontal region, over the course of the entire week of continual SR compared to an extended sleep night. Employing mixed method effects revealed a statistically significant relationship between response time and SWA maxima differences. The data show that not only does response time increase the day after rising first and last SWA maxima levels converge (i.e., flattening of the line slope connecting these values) caused by short bouts of SR, but these phenomena continue this progression with prolonged SR. Over the course of the week-long SR, the final SWA maximum increased at a higher rate than the first SWA maximum, leading to the maxima difference shrinking as response time increases. These findings indicate that brain dynamics highlight less restorative sleep occurring alongside a lack of sustained attention when sleep is restricted on a consistent basis.
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    MULTIMODAL ANALYSIS OF NEURAL SIGNALS RELATED TO SOURCE MEMORY ENCODING IN YOUNG CHILDREN
    (2024) Lei, Yuqing; Riggins, Tracy; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The emergence of source memory is an important milestone during memory development. Decades of research has explored neural correlates of source memory using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). However, connections between findings from the two approaches, particularly within children, remain unclear. This dissertation identified fMRI-informed cortical sources of two EEG signals during memory encoding, the P2 and the late slow wave (LSW), that predicted subsequent source memory performance in a sample of children aged 4 to 8 years. Both P2 and LSW were source localized to cortical areas of the medial temporal lobe (MTL), reflecting MTL’s crucial role in both early-stage information processing and late-stage integration of memory, which also validated LSW’s suspected role in memory updating. The P2 effect was localized to all six tested subregions of cortical MTL in both left and right hemispheres, whereas the LSW effect was only present in the parahippocampal cortex and entorhinal cortex. P2 was additionally localized to multiple areas in the frontoparietal network, a cortical network known as the “attention network”, highlighting interactions between memory encoding and other cognitive functions. These results reflect the importance of considering both spatial and temporal aspects of neural activity to decode memory mechanism, and demonstrated the potential of combining multimodal measures in children, paving the way for future developmental research.
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    EEG EFFECTS OF EVENT MODELS IN STORY COMPREHENSION
    (2023) Rickles, Ben Bogart; Bolger, Donald J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Cognitive models can offer deep insights into how stories are comprehended. Models which follow event segmentation theory (EST) focus on the processing of brief episodes or events within a narrative and the boundaries between events. To test the brain mechanisms proposed by EST to occur at the event boundaries we looked at electroencephalographs (EEG) recorded from 49 participants as they were tasked with both listening to and recalling 9 blocks of ~ 6 minute-long audio clips in one of three conditions: single ordered stories, unrelated events from unrelated stories, or single stories in scrambled order. All stimuli were designed to contain event boundaries spaced at semi-regular intervals. Accuracy during an inference recognition task administered after each block was highest in the single ordered stories condition. Analysis 1 examined the effects of event boundary vs. local semantic context on evoked negativities (N400) related to lexical processing of each word. Effects of condition suggest that narrative structure affected lexical processing, more so than event-level structure and sentence-level semantic context. Analysis 2 Examined changes in alpha (8.5-12.5 Hz) and theta (4-8 Hz) band power of the EEG induced by the onset of the event boundary. Boundary-induced changes in both frequencies were recorded, in all conditions. The largest increases were recorded during the ordered stories over large portions of the scalp. How these findings relate to cognitive mechanisms suggested by event segmentation theory is discussed.
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    Decoding the Brain in Complex Auditory Environments
    (2022) Rezaeizadeh, Mohsen; Shamma, Shihab; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Humans have an exceptional ability to engage with sequences of sounds and extract meaningful information from them. We can appreciate music or absorb speech during a conversation, not like anything else on the planet. It is unclear exactly how the brain effortlessly processes these rapidly changing complex soundscapes. This dissertation explored the neural mechanisms underlying these remarkable traits in an effort to expand our knowledge of human cognition with numerous clinical and engineering applications. Brain-imaging techniques have provided a powerful tool to access mental representations' content and dynamics. Non-invasive imaging such as Electroencephalography (EEG) and Magnetoencephalography (MEG) provides a fine-grained dissection of the sequence of brain activities. The analysis of these time-resolved signals can be enhanced with temporal decoding methods that offer vast and untapped potential for determining how mental representations unfold over time. In the present thesis, we use these decoding techniques, along with a series of novel experimental paradigms, on EEG and MEG signals to investigate the neural mechanisms of auditory processing in the human brain, ranging from neural representation of acoustic features to the higher level of cognition, such as music perception and speech imagery. First, we reported our findings regarding the role of temporal coherence in auditory source segregation. We showed that the perception of a target sound source can only be segregated from a complex acoustic background if the acoustic features (e.g., pitch, location, and timbre) induce temporally modulated neural responses that are mutually correlated. We used EEG signals to measure the neural responses to the individual acoustic feature in complex sound mixtures. We decoded the effect of attention on these responses. We showed that attention and the coherent temporal modulation of the acoustic features of the target sound are the key factors that induce the binding of the target features and its emergence as the foreground sound source. Next, we explored how the brain learns the statistical structures of sound sequences in different musical contexts. The ability to detect probabilistic patterns is central to many aspects of human cognition, ranging from auditory perception to the enjoyment of music. We used artificially generated melodies derived from uniform or non-uniform musical scales. We collected EEG signals and decoded the neural responses to the tones in a melody with different transition probabilities. We observed that the listener's brain only learned the melodies' statistical structures when derived from non-uniform scales. Finally, we investigated brain processing during speech and music imagery with Brain-Computer Interface applications. We developed an encoder-decoder neural network architecture to find a transformation between neural responses to the listened and imagined sounds. Using this map, we could reconstruct the imagery signals reliably, which could be used as a template to decode the actual imagery neural signals. This was possible even when we generalized the model to unseen data of an unseen subject. We decoded these predicted signals and identified the imagined segment with remarkable accuracy.
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    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.
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    Effect of spatial working memory depletion on cerebral cortical dynamics of cognitive-motor performance
    (2020) Shaw, Emma Patricia; Gentili, Rodolphe J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Prior work has validated the use of resource depletion to directly probe the role of specific cognitive functions on human performance. Specifically, intensive recruitment of cognitive resources to successfully perform a task has been shown to result in performance decrements and decreased neural activation on subsequent tasks. Much of this work, however, was not conducted within the context of cognitive-motor performance and/or did not examine the underlying brain dynamics. Therefore, this study examined the effects of depleted spatial working memory (SWM) resources, critical for spatial information processing, on performance and brain dynamics (attentional reserve and cognitive-motor effort). Performance and electroencephalography were collected as thirty-five individuals, randomly assigned to an experimental or control group, with minimal prior videogame experience completed a cognitive-motor task at an easy and a hard level of difficulty before and after undergoing SWM resource depletion (experimental) or non-depletion (control). The SWM depletion protocol required intensive mental rotation, while the non-depletion protocol did not. Attentional reserve was assessed via the novelty-P3 component of the event-related potential and cognitive-motor effort was assessed via spectral power within the theta, low- and high-alpha frequency bandwidths. The results revealed both groups exhibited similar performance improvement on the cognitive-motor task post- compared to pre-SWM depletion/non-depletion. This was accompanied with a more efficient engagement of attentional resources (decreased novelty-P3) and a refinement of cortical activity (low-/high-alpha synchrony), which may reflect a practice effect. Furthermore, the control group exhibited theta synchrony under the hard compared to the easy level of challenge across all cortical regions regardless of when the cognitive-motor task was performed. This adaptive response, however, was absent within the frontal and temporal cortical regions (important for working memory, attentional control and visuospatial processes) for the experimental group post-SWM depletion. Additionally, the experimental group, post-relative to pre-SWM depletion, exhibited temporal theta desynchrony and synchrony during the hard and easy level of challenge, respectively. These findings collectively suggest intensive cognitive task performance has a combined neurocognitive benefit (i.e., practice effect) and cost (i.e., lack of adaptive response due to depleted resources) during subsequent cognitive-motor performance requiring similar cognitive processes as that of the depleting task.
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    Development of Motivational Influences on Monitoring and Control Recruitment in the Context of Proactive and Reactive Control in Adolescent Males
    (2020) Bowers, Maureen; Fox, Nathan A; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Adolescence and the onset of puberty is a time period of physiological and behavioral changes that include a heightened reward sensitivity, but underdeveloped cognitive control. Cognitive control involves monitoring for salient stimuli and recruiting control to adapt behavior advantageously to reach a specific goal and is supported by the three domains of executive functioning (EF): inhibitory control, set-shifting, and working memory. Proactive control is engaged after an informative cue in preparation for an upcoming stimulus, while reactive control can be employed when preparation is not possible and you need to respond to a stimulus. Oscillations in the theta frequency (4-8Hz) during both cue presentation and stimulus presentation are implicated in proactive and reactive control processes. While reward has been shown to upregulate proactive control in adults, little work has assessed how reward influences theta oscillations during both proactive and reactive control throughout adolescence and pubertal development. Further, no work has sought to understand how EF abilities bolster reward-related changes in proactive or reactive control. Here, 68 adolescent males (Meanage=13.61, SDage=2.52) aged 9 – 17 years old completed a rewarded cued flanker paradigm while electroencephalogram (EEG) was collected. They also completed tasks from the NIH toolbox that tap the three EF domains. Behaviorally, reward hindered performance on proactive trials, particularly in mid-puberty, while enhancing performance on reactive trials. Reward was associated with increases in cue-locked theta power, but with overall reductions in cue-locked theta ICPS. Stim-locked theta power increased on reactive trials with increasing age, while stim-locked theta ICPS peaked in mid-adolescence for rewarded trials. Increased cue theta power was associated with worse performance on proactive trials. On proactive trials, adolescents with low levels of inhibitory control experience more reward-related interference, while reward-related interference was mitigated by better set-shifting abilities only in younger and older adolescents. In conclusion, reward differentially impacts proactive and reactive control throughout adolescent development and EF influences the impact of reward on proactive control throughout adolescence.
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    THE IMMEDIATE EFFECT OF VENTILATORY TRAINING ON HEART RATE VARIABILITY AND BRAIN DYNAMICS, DURING TRAINING AND CHALLENGE
    (2018) Lu, Calvin; Hatfield, Bradley D; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A Guided Ventilatory Maneuver (GVM) can lead to changes in the central and autonomic nervous systems. Chronic effects of GVM have been reported in the literature to enhance physical and mental health. Purpose: To investigate the immediate effects of GVM on cortical activity and cardiovascular activity. Method: Twenty healthy participants (age 18-30) were recruited. Eligibility for the study required no experience in any mindfulness training. Results: Measures of the study utilized electroencephalography and electrocardiogram to measure cortical and cardiovascular changes. The study provided support for acute effects of GVM on cortical dynamics and heart rate variability. Cortical activity exhibited an increase in cortical relaxation during GVM. And cardiovascular activity exhibited an increase in parasympathetic activity. Conclusion: The psychophysiological measures of this study provided evidence for GVM as a relaxation technique. Specifically, during GVM, participant’s cortical dynamics reflect an increase in relaxation.
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    INVESTIGATIONS TO UNDERSTAND THE UNDERLYING BRAIN PROCESSES WHICH ENHANCE COGNITIVE-MOTOR LEARNING AND PERFORMANCE
    (2018) Jaquess, Kyle James; Hatfield, Bradley D; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The ability to effectively and efficiently process task-relevant information is a critical element to a wide range of cognitive-motor activities. Indeed, various studies have illustrated that elite performers exhibit more refined neuro-cognitive processes than novices. However, it is unclear how these neuro-cognitive information processing abilities develop as skill is acquired. In this dissertation, I provide some evidence to address this gap in the literature. Study 1, entitled “Empirical evidence for the relationship between cognitive workload and attentional reserve” (Jaquess et al., 2017), provided evidence illustrating the relationship between mental workload and attentional reserve. Study 2, entitled “Changes in mental workload and motor performance throughout multiple practice sessions under various levels of task difficulty”, builds from the knowledge gained from Study 1 and extends it to a cognitive-motor learning/practice context over the course of four days. Finally, Study 3, entitled “How engaged are you? An investigation of the neurocognitive mechanisms of self-controlled practice during cognitive-motor learning”, was built upon the knowledge gained from Study 2 to further investigate how aspects of the practice environment, specifically the aspect of control, impact cognitive load and learning outcomes. Broadly, these studies illustrate how some of the neuro-cognitive processes related to information processing in cognitive-motor skills, specifically elements of the electroencephalogram (EEG), change with learning and the acquisition of skill.
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    Effects of Action-Outcome Agency on Feedback Processing
    (2016) Tootell, Anne; Bernat, Edward; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The current study investigated the effect of action-outcome agency, or one’s ability to guide behavior during reinforcement learning, on reward and loss processing in a gambling task. Thirty undergraduates (13 females; M age = 19.57, SD = 2.18) completed two computer gambling tasks, one designed to exhibit high levels of action-outcome agency and one with low, while attached to a 128-channel EEG system. Time-frequency event-related potential (TF- ERP) analysis was conducted on the acquired EEG data. ERP components associated with reward and loss processing were significantly dampened in the low action-outcome agency task relative to the high action-outcome agency task. Interestingly, TF-ERP analysis demonstrated a significant effect of action-outcome agency on gain-loss differences in theta but not delta frequencies, suggesting a more central role of loss processing in guidance of goal-directed behavior. These results challenge components of the well-established predicted response-outcome (PRO) model of reinforcement learning.