Kinesiology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2784
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Item Human-Human Sensorimotor Interaction(2019) Honarvar, Sara; Shim, Dr. Jae Kun; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We investigated the role of sensory feedback in inter-personal interactions when two co-workers are working together. Twenty-five co-workers completed two isometric finger force production experiments. In Experiment 1, co-workers isometrically produced finger forces such that combined force will match a target force and/or torque under different visual and haptic conditions. In Experiment 2, without participants’ knowledge, each performed the same task with the playback of his/her partner’s force trajectory previously recorded from Experiment 1. Results from both experiments indicated that co-workers performed the task worse in the presence of haptic and visual feedback. Since, in latter as opposed to the former condition, they adopted a compensatory strategy to accomplish the task accurately. Further analysis showed that co-workers achieved the same level of motor performance with similar control strategies, suggesting that they did not work synergistically to achieve better performance, but one co-worker processed another as disturbance when they worked together.Item Muscular Fatigue Influences Motor Synergies During Push-ups(2018) Bell, Elizabeth M; Shim, Jae Kun; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This research used the push-up as an experimental paradigm for the study of adaptations in motor synergies throughout the challenge of muscular fatigue. Fatigue was expected to lead to greater synchronization of power production (greater motor synergy) by the Central Nervous System (CNS). Greater between and within-limb synergies would be necessary to overcome the reduced force production of fatigued muscles. Different changes in joint power synergies were expected for eccentric and concentric phases due to muscle properties and direction of gravity. Eleven subjects performed push-ups repetitions to self-selected failure. Subjects initially performed push-ups using positive between and within-limb joint power synergies, however synergies reduced throughout reps. Congruent with hypotheses, between and within-limb synergy reduced at a lesser rate throughout eccentric movements. The strategy used relied on bilateral elbow and shoulder joint production. The CNS was not able to adapt control strategies, but instead the dominant strategy was affected throughout fatigue.Item INVESTIGATIONS TO UNDERSTAND THE UNDERLYING BRAIN PROCESSES WHICH ENHANCE COGNITIVE-MOTOR LEARNING AND PERFORMANCE(2018) Jaquess, Kyle James; Hatfield, Bradley D; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to effectively and efficiently process task-relevant information is a critical element to a wide range of cognitive-motor activities. Indeed, various studies have illustrated that elite performers exhibit more refined neuro-cognitive processes than novices. However, it is unclear how these neuro-cognitive information processing abilities develop as skill is acquired. In this dissertation, I provide some evidence to address this gap in the literature. Study 1, entitled “Empirical evidence for the relationship between cognitive workload and attentional reserve” (Jaquess et al., 2017), provided evidence illustrating the relationship between mental workload and attentional reserve. Study 2, entitled “Changes in mental workload and motor performance throughout multiple practice sessions under various levels of task difficulty”, builds from the knowledge gained from Study 1 and extends it to a cognitive-motor learning/practice context over the course of four days. Finally, Study 3, entitled “How engaged are you? An investigation of the neurocognitive mechanisms of self-controlled practice during cognitive-motor learning”, was built upon the knowledge gained from Study 2 to further investigate how aspects of the practice environment, specifically the aspect of control, impact cognitive load and learning outcomes. Broadly, these studies illustrate how some of the neuro-cognitive processes related to information processing in cognitive-motor skills, specifically elements of the electroencephalogram (EEG), change with learning and the acquisition of skill.Item A NEW APPROACH TO ASSESS HIGH LEVEL PLANNING UNDERLYING COGNITIVE-MOTOR PERFORMANCE DURING COMPLEX ACTION SEQUENCES(2018) Hauge, Theresa Christine; Gentili, Rodolphe J; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While much work has examined low-level sensorimotor planning, only limited efforts have studied high-level motor planning processes underlying the cognitive-motor performance of complex action sequences. Such sequences can generally be successfully executed in a flexible manner and typically involve few constraints. In particular, no past study has examined the concurrent changes of high-level motor plans along with those of mental workload and confidence during practice of a novel complex action sequence. To address this gap, first a computational approach providing markers capturing performance dynamics of action sequences during practice had to be developed since past relevant works only employed fairly rough metrics. Such an approach should provide concise performance markers (e.g., distances, scalar) while still capturing accurately the changes of structure of high-level motor plans during the acquisition of novel complex action sequences. Thus, by adapting the Levenshtein distance (LD) and its operators to the motor domain, a computational approach was first proposed to assess in detail action sequences during an imitation practice task executed by various performers (humans, a humanoid robot) and with flexible success criteria. The results revealed that this approach i) could support accurately comparing the high-level plans generated between performers; ii) provides performance markers (LD, insertion operator) able to differentiate optimal (using a minimum of actions) from suboptimal (using more than a minimum of actions but still reaching the task goal) sequences; and iii) gives evidenced that the deletion operator is a marker of action sequence failure. This computational approach was then deployed to examine during practice the concurrent changes in high-level motor plans underlying action sequence execution with modulation of mental workload and an individual’s confidence in performing the task. The results revealed that as individuals practiced, performance improved (reduction of LD, insertion/substitution and movement time) while the level of mental workload and confidence decreased and increased, respectively. Also, by late practice the sequences were still suboptimal while being executed faster, possibly suggesting different dynamics between the generation of high-level motor plans and their execution. Overall, this work complements prior efforts to assess complex action sequences executed by humans and humanoid robots in the context of cognitive-motor practice, and it has the potential to inform not only human cognitive-motor mechanisms, but also human-robots interactions.Item The Impact of Acute Aerobic Exercise on Semantic Memory Activation in Healthy Older Adults(2018) Won, Junyeon; Smith, Jerome C; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Background: A growing body of exercise literature use functional magnetic resonance imaging (fMRI) technique to measure the effects of exercise on the brain. Findings suggest that regular participation of long-term exercise is associated with enhanced cognitive function. However, fundamental questions regarding the beneficial effects of acute exercise on semantic memory have been ignored. Purpose: This study investigated the effects of a single session of exercise on brain activation during recognition of Famous names and Non-Famous names compared to seated-rest in healthy older adults (age 65-85) using fMRI. We also aimed to measure whether there are differences in brain activation during retrieval of Famous names from three distinct time epochs (Remote, Enduring, and Recent) following acute exercise. Methods: Using a within-subjects counterbalanced design, 30 participants (ages 55-85) will undergo two experimental visits on separate days. During each visit, participants will engage in 30-minutes of rest or stationary cycling exercise immediately followed by the famous name discrimination task (FNT). Neuroimaging and behavioral data will be processed using AFNI (version 17.1.06) and SPSS (version 23), respectively. Results: HR and RPE were significantly higher during exercise. Acute exercise was associated with significantly greater semantic memory activation (Famous > Non-Famous) in five out of nine regions (p-value ranged 0.027 to 0.046). In an exploratory epoch analysis, five out of 14 brain regions activated ruing the semantic memory task showed significantly greater activation intensity following the exercise intervention (Enduringly Famous > Non-Famous). Conclusions: Enhanced semantic memory processing is observed following acute exercise, characterized by greater fMRI response to Famous than Non-Famous names. Enduringly Famous names exhibited significantly greater activation after exercise compared to Non-Famous names. These findings suggest that exercise may improve semantic memory retrieval in healthy older adults, and may lead to enhancement of cognitive function.Item NEURAL CONTROL OF SPEED IN HUMAN WALKING(2018) Ehtemam, Farzad; Kiemel, Tim; Hatfield, Bradley D; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The central nervous system in humans continuously controls the speed of walking by modulating muscle activities. The underlying mechanisms of this control process are not well understood. Recent studies have probed the neural control of walking using sensory and mechanical perturbations. It has been suggested that transient responses to perturbations show patterns in the modulation of muscle activations not previously observed. This dissertation aims to systematically investigate differences in modulations of muscle activations between transient responses and steady-state walking. Three studies were designed to explore these modulations using visual and mechanical perturbations. The first study compared the qualitative patterns from transient responses to visual perturbations to those observed during steady-state walking. Small changes in the average muscle activations between two steady-state speeds were compared to small transient changes due to perturbations. We demonstrated that the decrease in the plantarflexor activity during transient responses that potentially contributed to an increase in speed was unique to these responses and not reproducible in steady-state walking conditions. The second study quantified the effects of average walking speed on transient responses to visual perturbations and compared these effects to steady-state walking conditions. A scaling effect on the amplitude of responses was shown across different treadmill speeds. Finally, in the last study, we explored characteristics of transient responses to mechanical perturbations of the treadmill. We examined the effects of perturbations at two different amplitudes on both kinematics and muscle activations. The responses of the neurofeedback to kinematic deviations were quantified and it was shown that the local limit cycle approximation was reasonable to describe the system. Together these studies shed light on how modulations of muscle activity are utilized by the nervous system to regulate the key variable of walking speed, as well as other aspects of human locomotion.Item Lower-Body Mechanical Perturbation of Gait to Identify Neural Control(2017) Rafiee, Shakiba; Kiemel, Tim; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Neural feedback plays a key role in maintaining locomotor stability in face of perturbations. In this study, we systematically identified properties of neural feedback that contribute to stabilizing human walking by examining how the nervous system responds to small kinematic deviations away from the desired gait pattern. We applied small continuous mechanical perturbation, forces at the ankles, as well as small continuous sensory perturbation, movement of a virtual visual scene, in order to compare how neural feedback responds to actual and illusory kinematic deviations. Computing phase-dependent impulse response functions (φIRFs) that describe kinematic and muscular responses to small brief perturbations (impulses), enabled us to identify critical phases of the gait cycle when the nervous system modulates muscle activity. In particular, our results suggest that an early-stance modulation of anterior leg-muscles is a general control mechanism that serves multiple functions, including controlling walking speed and compensating for errors in foot placement.Item THE IMPACT OF ACUTE EXERCISE AND SLEEP QUALITY ON EXECUTIVE FUNCTION: THE POTENTIAL MEDIATING EFFECTS OF FUNCTIONAL CONNECTIVITY IN OLDER ADULTS(2017) Alfini, Alfonso J.; Smith, J. Carson; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Background: Although, improved longevity is a major public health accomplishment, the prevalence of chronic disease, including cognitive impairment, increases with age. Insufficient sleep and physical inactivity exacerbate chronic disease and may accelerate the onset of dementia. While a cure remains elusive, a growing body of evidence demonstrates that exercise training facilitates better sleep and enhanced cognition. Exercise-altered patterns of neural activity, including resting state functional connectivity (rsFC) and task-based functional activation, likely coincide with and may facilitate cognitive improvements in the aging brain. Purpose: This study sought to examine the joint impact of acute exercise and sleep quality on executive function in older adults. We also aimed to determine the degree to which exercise-induced changes in prefrontal rsFC influence the relationship between sleep and executive function performance/functional activation. Methods: Using a within subjects counter-balanced design, 21 participants (aged 55-85) underwent at least three days of objective sleep monitoring (actigraphy), followed by two experimental visits on separate days. During each visit, participants engaged in 30-minutes of rest or exercise followed immediately by resting state and task-based functional MRI. After the MRI scanning session, participants completed several executive function assessments. Neuroimaging and behavioral data were processed using AFNI (version 17.1.06) and SPSS (version 23), respectively. Results: Repeated measures ANOVA and multivariate linear regression revealed two significant voxel-wise interactions in the (L) precuneus. Our findings demonstrated that acute exercise increased prefrontal rsFC and functional activation in long sleepers (> 7.5 hours/night), while decreasing these parameters for individuals with less total sleep time. Moreover, these results correspond to behavioral data demonstrating that acute exercise and adequate sleep improved select aspects of executive function performance, while decreasing inhibitory control in short sleepers alone (< 7.5 hours). Conclusion: These findings suggest that the effects of acute exercise on prefrontal rsFC are similar, or even related, to the effects of acute exercise on conflict-dependent functional activation, and that this relationship may depend on sleep duration. Moreover, our results imply that although acute exercise elicited improved executive function for those with adequate sleep, it may weaken already vulnerable, and perhaps fatigued, executive function networks among short sleepers.Item THE ORGANIZATION OF MOTOR SYNERGIES IN ONE-PERSON AND TWO-PERSON MULTI-FINGER FORCE PRODUCTION TASKS(2017) Christensen, Kelsey Ann; Shim, Jae K; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Humans perform motor tasks every day, both individually and with others. Performing motor tasks involves the organization of motor synergies, task-specific groupings of individual motor effectors that are temporarily constrained to act as a single unit and whose total combined output ensures stability of the overall task performance. Both intra- and inter-personal motor synergies have been found to exist in one-person and two-person motor tasks, respectively. Not as clear, however, is whether separate synergies can exist simultaneously on multiple levels of control within a given task. The purpose of the current study is to investigate the organization of force-stabilizing motor synergies during one-person and two-person finger-force production tasks using the Uncontrolled Manifold Analysis. We expect to find both intra- and inter-personal motor synergies, an increase in synergy strength as tasks require more motor effectors, but the lack of simultaneously-occurring motor synergies on multiple levels of control within the given tasks.Item LEARNING PROCESSES UNDERLYING IMPLICIT MOTOR SEQUENCE ACQUISITION IN CHILDREN AND ADULTS(2016) Du, Yue; Clark, Jane E; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Children and adults are able to learn a motor sequence quickly, usually over a course of one learning session consisting of 4-8 learning blocks. This initial acquisition is referred to as fast learning. However, little is known about the learning processes underlying the fast acquisition of motor sequences. Therefore, the overarching objective of this dissertation was to examine the underlying processes that drive rapid motor sequence learning in children and adults. In a series of studies, children and adults performed a modified serial reaction time (SRT) task, a primary window into understanding implicit motor sequence learning. Study I demonstrated that fast learning of implicit motor sequences in six- and 10-year-old children was comparable to adults, while the performance (i.e., reaction time, RT) during learning was reflected by two age-related processes. Learning in six-year-old children dominantly relied on an offline process where RT improved after a short rest, while offline enhancement as well as online progressive improvement in RT reflected sequence learning in 10-year-old children and adults. In studies II, III, and IV, we demonstrated that the online and offline processes were neither by-products of task pacing constraints nor illusory effects of fatigue or reactive inhibition. Instead, these two age-related processes were more likely to be functional mechanisms underlying implicit motor sequence learning, which could be modulated by the involvement of procedural and declarative memory. In addition, study III characterized the developmental landscape of 5- to 14-year-old children and found that the developmental changes of online and offline learning were primarily present in early childhood. As fast learning is known to enable generalization (or transfer) of sequences learning, we expected, given the findings in studies I through IV, age-related differences in the generalization of implicit motor sequence learning. The results in study V, interestingly, demonstrated that the generalization of implicit motor sequence learning was better in children than in adults. However, in study VI, when greater procedural memory was required in the SRT task, learning in adults largely depended on offline learning; and, the age-related differences in learning generalization vanished, suggesting that offline learning may facilitate the generalization of implicit motor sequence learning. Taken together, results from these studies found two age-related learning processes (i.e., online and offline learning) that drive the fast implicit sequence acquisition and demonstrated that the age-related online and offline learning may lead to children a superior ability in the generalization of motor sequence learning. These results extend our understanding of the age-related development of implicit motor sequence learning and provide potential insights into the question of why childhood is an optimal period for learning.