Kinesiology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2784

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Subject: search.filters.subject.Psychology, Developmental

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    On the Development of Postural Stability During Infancy as a Process of Growth and Active, Exploratory Sensorimotor Tuning
    (2007-12-04) Metcalfe, Jason Scott; Clark, Jane E; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The process by which humans stabilize bipedal stance represents a confluence of changes associated with musculoskeletal maturation and experience-based sensorimotor learning. While investigations have documented a variety of changes with increased bipedal experience, such as reduced velocity and frequency of postural sway and concomitant refinements in muscle activation sequences, the extent to which these changes may be ascribed to growth versus learning processes has not been well characterized. For example, reduced sway frequency is a natural consequence of increasing body height but alternatively, may be explained by active modulations in motor commands specifying the timing and magnitude of muscular activation sequences. It is clear that both types of influences are needed to explain postural development. However, a parsimonious framework for understanding and explaining postural development has yet to be clearly articulated and validated against empirical observations. As such, the purpose of this dissertation was to initiate the development of such an account through a combination of empirical and computational studies. In this dissertation, data are presented from a longitudinal study of upright posture in infants ranging from the onset of independent sitting until 9 months of walking experience; this dissertation focused on the particular period spanning from walk onset onward. Infants participated in a quiet stance task involving hand contact with a surface that was either static or dynamic as well as an independent stance condition. Empirical analyses were performed to estimate the statistical properties of sway and characterize adaptations to static and dynamic manipulations utilizing the touch surface. An unexpected lack of significance for sway magnitude was observed in all conditions. Robust effects, however, were found across measures of rate properties of sway. Taken in the context of previous literature, the empirical observations were used to guide a final study utilizing computational techniques to test hypotheses regarding potential sources of change in postural development. First, the mechanical and computational requirements for postural stabilization were systematically assessed through a review of extant models of both stance and motor learning. Armed with insights from this review, the final study examined an autonomous reinforcement learning algorithm, that was designed to capture the essence of how a human may stabilize his or her posture under the tutelage of exploratory action. Simulation results provided evidence in support of conclusions regarding changes in rate-properties of postural sway and underlying associations with physical growth as well as calibration of both sensory and motor system parameters. Further, simulations emphasized the importance of inclusion of noise in biologically-relevant aspects of the model, such as in sensory and motor processes, as well as the need to consider physical morphology as a primary constraint on sensorimotor learning in the context of upright postural development.
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    Age-related Difference in Kinematics and Cerebral Cortical Processes during Discrete Drawing Movements in Children and Adults
    (2007-06-06) Pangelinan, Melissa Marie; Clark, Jane E; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Research has shown developmental improvements in drawing movements during childhood. These changes may be related to protracted structural development and myelination of cortical brain structures underlying motor planning and control. However, no study to our knowledge has examined the relationship between cortical development and the emergence of accurate visuomotor behavior. This thesis characterized age-related differences in kinematics and cerebral cortical processes during the performance of discrete drawing movements in children, as compared to adults. Three groups were included in the study: young girls (6- to 7-year-olds), older girls (9- to 11-year-olds), and adult females (n=15, each). Participants performed 5cm center-out drawing movements with the dominant hand (right hand), while electroencephalography (EEG) was recorded. All participants exhibited similar task-related cortical communication (coherence) and activation (relative spectral power) in several frequency bands. Activation of motor neural resources (motor cortical potentials) in the midline pre-motor and motor regions was also similar across age groups. The similarity of the brain activation patterns for these measures may contribute to the comparable behavioral performance among all groups for root mean squared error (straightness) and movement length. However, other features of the young children's brain activation patterns and motor control were different than the older children and/or adults. Specifically, the young children showed increased activation of frontal (executive process) areas, whereas the older children and adults exhibit increased relative activation in task-relevant sensorimotor areas (as measured by spectral power) in frequencies related to sensorimotor processes and attention. Similarly, increased coherence in the lower beta and gamma bands, indicative of local networking, was found in the adults between the frontal and central regions, and the frontal and parietal areas. Moreover, the adults show increased activation of the contralateral sensorimotor areas time-locked to the onset of movement, compared with the young children. The increased activation of the motor areas and visuomotor networks during movement planning may contribute to faster, smoother, and more consistent behavioral performance for the older children and adults, not evident in the young children.
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    THE RELATIONSHIP BETWEEN TOUCH AND INFANTS' UPRIGHT POSTURE DURING THE FIRST YEAR OF WALKING
    (2004-04-29) Chang, Tzu-Yun; Clark, Jane E; Kinesiology
    Much of the research on postural development has focused on changes in trunk and lower limb control. However, the hands may also play an integral role as young infants learn to stand and walk. In this study, we examine the hypothesis that with increasing walking experience infants improve their ability to use the hand adaptively for postural control. Six infants were studied longitudinally from 1-month pre-walking to 9-months post-walking while they stood touching a static contact surface. Touch forces (TF) were examined across 10 confidence ellipses each containing 10% of the infants' postural sway. The results indicated that as infants gained walking experience they applied more TF the farther they were away from their postural center. With development, infants gain an understanding of their body position and use touch differently depending on their current position relative to their "functional boundaries."