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.

Browse

Filters

2009 - 200912010 - 20141

Settings

Author: search.filters.author.Logan, David Michael

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    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.
  • Thumbnail Image
    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.