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.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Computational Methods for Natural Walking in Virtual Reality(2024) Williams, Niall; Manocha, Dinesh; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Virtual reality (VR) allow users to feel as though they are really present in a computer-generated virtual environment (VE). A key component of an immersive virtual experience is the ability to interact with the VE, which includes the ability to explore the virtual environment. Exploration of VEs is usually not straightforward since the virtual environment is usually shaped differently than the user's physical environment. This can cause users to walk on virtual routes that correspond to physical routes that are obstructed by unseen physical objects or boundaries of the tracked physical space. In this dissertation, we develop new algorithms to understand how and enable people to explore large VEs using natural walking while incurring fewer collisions physical objects in their surroundings. Our methods leverage concepts of alignment between the physical and virtual spaces, robot motion planning, and statistical models of human visual perception. Through a series of user studies and simulations, we show that our algorithms enable users to explore large VEs with fewer collisions, allow us to predict the navigability of a pair of environments without collecting any locomotion data, and deepen our understanding of how human perception functions during locomotion in VR.Item Neural Modulation of Leg Stiffness in Response to Neuromuscular Fatigue(2016) Chu, Edward; Shim, Jae Kun; Miller, Ross H; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The spring-mass model is able to accurately represent hopping spring-like behavior (leg and joint stiffness), and leg and joint stiffness changes can reveal overall motor control responses to neural and muscular contributors of neuromuscular fatigue. By understanding leg stiffness modulation, we can determine which variables the nervous system targets to maintain motor performance and stability. The purpose of this study was to determine how neuromuscular fatigue affects hopping behavior by examining leg and joint stiffness before and after a single-leg calf raise fatiguing protocol. Post-fatigue, leg stiffness decreased for the exercised leg, but not for the non-exercised leg. Ankle and knee joint stiffness did not significantly change for either leg. This indicates that leg stiffness decreases primarily from muscular fatigue, but was not explained by ankle and knee joint stiffness. The decrease in leg stiffness may be an attempt to soften landing impact, while at the same time maintaining performance.Item Subtask Control in Human Locomotion(2014) Logan, David Michael; Jeka, John J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Maintenance of upright posture during walking is one the most important tasks to ensure flexible and stable mobility, along with speed adjustment, wayfinding and obstacle avoidance. These underlying functions, or subtasks, are simultaneously coordinated by the nervous system, which relies heavily on sensory feedback to obtain continual estimates of self-motion. This dissertation reports the findings of four experiments which made use of visual and mechanical perturbations to probe the interplay of these subtasks during treadmill walking. To confront the inherent nonlinearity of human gait, novel frequency domain analyses and impulse response functions that take into account phase of the gait cycle were used to characterize perturbation-response relationships. In the first experiment, transient visual scene motion was used to probe how visual input simultaneously influenced multiple subtasks, but at different phases of the gait cycle. In the second experiment, kinematics and muscle activity response variables showed an amplitude dependency on visual scene motion during walking that indicates vision is reweighted in a manner similar to standing posture. The third experiment used a metronome to constrain walking, revealing two time scales of locomotive control. The final experiment made use of both visual and mechanical perturbations simultaneously to probe the subtasks of postural orientation upright and positional maintenance on the treadmill. Doing so revealed that the nervous system prioritizes control of postural orientation over positional maintenance. In sum, this dissertation shows that sensory and mechanical perturbations provide insight as to how the nervous system controls coexisting, underlying functions during walking.Item Probing Postural Stability Mechanisms in Locomotion(2009) Logan, David Michael; Jeka, John J; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)It is not currently known if those upright stability mechanisms utilized in standing posture are present in locomotion. In this investigation, subjects walked or stood on a treadmill in three speed conditions (posture, 1 km/h, 5 km/h) in front of a visual scene consisting of randomly oriented triangles. The triangles translated in the Anterior-Posterior (A/P) direction in either a low or high amplitude condition. Frequency response functions (FRFs) of both the A/P displacement of bilateral kinematic markers and their corresponding segment angles in response to the visual scene translations were computed. Gain and phase of these FRFs had consistent responses in high amplitude visual conditions in the trunk (hip and shoulder displacements, trunk angle), which motivated further comparisons within the trunk during posture and locomotion. In doing so, the postural processes of orientation and equilibrium control were teased apart during locomotion.Item The Role of Epistemic Motivation in the Link between Arousal and Focus of Attention(2009) Orehek, Edward; Kruglanski, Arie W; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Over 60 years of research has led to a law-like acceptance of the Easterbrook (1959) hypothesis. Easterbrook (1959) famously reviewed the evidence on the arousal-attention link and concluded that as arousal increases, the range of cues utilized decreases, and the focus of attention narrows. However, the present set of eight studies suggests that the Easterbrook hypothesis needs to be seriously qualified. Recent developments in the understanding of the role of arousal in information processing suggests that rather than invariably leading to a focus of attention, arousal instead serves as information regarding the urgency and/or importance of active processing strategies (Storbeck & Clore, 2008). Because some processing strategies lead to a broadening of attention, arousal should sometimes be negatively related to a focusing of attention. A first set of four studies investigated the need for closure as it relates to the arousal-attention link. The need for closure refers to the motivation to make quick, firm judgments, and has been shown to lead to the use of fewer available cues. Because of this, it seems that the need for closure should lead to a tendency to focus one's attention. However, when need for closure is low, individuals tend to process more available cues, broadening attention in order to avoid reaching premature closure. The results indicate that when individuals are high on the need for closure, arousal is positively related to focus of attention, whereas when individuals are low on the need for closure, arousal is negatively related to focus of attention. A second set of four studies investigated the influence of the regulatory modes of locomotion and assessment on the arousal-attention link. Because locomotion is oriented towards movement, it should lead to a focus of attention. Because assessment is oriented towards making evaluations based on comparisons among alternatives, it should lead to a broadening of attention. The results show that when a locomotion mode is active, arousal is positively related to focus of attention, whereas, when an assessment mode is active, arousal is negatively related to focus of attention.