School of Public Health

Permanent URI for this communityhttp://hdl.handle.net/1903/1633

The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

Note: Prior to July 1, 2007, the School of Public Health was named the College of Health & Human Performance.

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Subject: search.filters.subject.Vision

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    Asymmetric Sensory Reweighting in Human Upright Stance
    (PLoS One, 2014-06-24) Logan, David; Kiemel, Tim; Jeka, John J.
    To investigate sensory reweighting as a fundamental property of sensor fusion during standing, we probed postural control with simultaneous rotations of the visual scene and surface of support. Nineteen subjects were presented with pseudo-random pitch rotations of visual scene and platform at the ankle to test for amplitude dependencies in the following conditions: low amplitude vision: high amplitude platform, low amplitude vision: low amplitude platform, and high amplitude vision: low amplitude platform. Gain and phase of frequency response functions (FRFs) to each stimulus were computed for two body sway angles and a single weighted EMG signal recorded from seven muscles. When platform stimulus amplitude was increased while visual stimulus amplitude remained constant, gain to vision increased, providing strong evidence for inter-modal reweighting between vision and somatosensation during standing. Intra-modal reweighting of vision was also observed as gains to vision decreased as visual stimulus amplitude increased. Such intra-modal and inter-modal amplitude dependent changes in gain were also observed in muscular activity. Gains of leg segment angle and muscular activity relative to the platform, on the other hand, showed only intra-modal reweighting. That is, changing platform motion amplitude altered the responses to both visual and support surface motion whereas changing visual scene motion amplitude did not significantly affect responses to support surface motion, indicating that the sensory integration scheme between somatosensation (at the support surface) and vision is asymmetric.
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    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.