Kinesiology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2784
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Item Closed Loop System Identification of Postural Control with Bilateral Vestibular Loss(2009) Amenabar, Katharine Elizabeth; Jeka, John J; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Human upright stance can be characterized as a combination of feedback and plant. Feedback consists of integrated sensory signals, producing estimates of position and velocity of the body segments while plant includes both musculotendon dynamics and body dynamics. Separating plant and feedback is possible mathematically through closed loop system identification. By studying bilateral vestibular loss (BVL) patients it is hoped knowledge regarding human posture and the role of the vestibular system will be gained. Two BVL patients and two age, height and gender matched controls had visual and mechanical perturbations applied simultaneously to determine these properties. Both leg and trunk kinematics and EMG data were collected. Using frequency response functions plant and feedback properties were calculated. Plant and feedback dynamics differ. BVL patients show more variable weighted hip EMG data, supporting the idea that this population can not properly use hip movement with their lack of vestibular system.Item The development of adaptive sensorimotor control in infant upright posture(2007-08-06) Chen, Li-Chiou; Clark, Jane E; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Postural control has been suggested as an important factor for early motor development, however, little is known about how infants acquire the ability to control their upright posture in changing environments and differing tasks. This dissertation addresses these issues in the first two years of life when infants learn to sit, stand, and walk. Three specific aims will be addressed: 1) to characterize the development of unperturbed infant upright postural sway; 2) to establish the influence of static somatosensory information on infant postural sway; and 3) to characterize the dynamic relationship between the infant's posture and sensory information. Three studies were conducted. The first study longitudinally examined infants' quiet stance and the influence of static touch in the 9 months following walk onset. With increasing walking experience, infants' upright postural sway developed toward lower frequency and slower velocity without changing the amount of sway. Additional touch information attenuated postural sway and decreased the sway velocity without affecting the frequency characteristics. We concluded that early postural development may involve increasing the use of sensory information to tune sensorimotor relationships that enhance estimating self-motion in the environment. The second study longitudinally characterized infants' unperturbed sitting postural sway and the influence of static touch. A temporary disruption of infant sitting posture was observed around walk onset. Light touch contact attenuated sitting postural sway only at this transition when infants' posture became unstable. These results suggest a sensorimotor re-calibration process in infant postural control to accommodate the newly emerging bipedal behavior of independent walking. The third study systematically examined the adaptive visual-postural dynamics, specifically the frequency- and amplitude-dependent features, in a cross-sectional sample of infants as they develop from sitting to standing and walking. The results revealed that infants as young as sitting onset were able to control their sitting posture responding to an oscillating visual stimulus as well as to re-weight the visual information as the stimulus amplitude changes. However, newly sitting infants, compared to experienced walkers, were more responsive but variable when the stimulus amplitude was small. We conclude from these three studies that infant postural development involves a complementary process between improving postural control of self-motion and an increasing sensitivity to environmental motionItem Postural Coordination Patterns: Visual Rotation and Translation(2006-04-19) Zhang, Yuanfen; Jeka, John; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recent studies have shown co-existing trunk-leg coordination patterns during quiet stance: in-phase and anti-phase for frequencies below and above 1 Hz, respectively. Two experiments investigated whether the nervous system assumes a multilinked internal model in sensory coupling? In the first experiment, we investigated the influence of the addition or removal of sensory information on these patterns. Trunk-leg coherence decreased with the addition of static vision and light touch, in the AP and ML directions, respectively, at frequencies below 1 Hz, suggesting the in-phase pattern may be more affected by neural control than the anti-phase pattern. In the second experiment, we compared translation of the visual field to a rotation relative to the ankle/hip. Gain and phase between the trunk/leg angles relative to the visual display showed only minor condition differences. The overall results suggest the nervous system adopts a simple control strategy of a single-link internal model at low frequencies.Item The Use of Vision in Children's Postural Control(2004-07-15) Kim, Stephen June; Clark, Jane E; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of the current thesis was to characterize age-related changes in postural control with variations in the properties of a dynamic visual stimulus. In the first study, seven 4-year-olds, seven 6-year-olds, and seven adults were presented with a visual stimulus that oscillated at 0.1, 0.3, and 0.5 Hz. Results showed the postural response amplitude and timing depended upon stimulus frequency and a reduction in the amplitude response variability indicated increased response precision with age. In the second study, ten 4-year-olds, ten 6-year-olds, and ten adults were presented with a visual stimulus that oscillated at 0.3 Hz, with amplitudes of 0, 2, 5, and 8 mm. The results characterized the response as a utilization of sensory information for postural control, with increased response precision with age. These findings indicate that the visuomotor coordination needed for postural control shows age-related improvements, consistent with the notion of a response tuning.