Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xxvii, 166 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 121-126).

In order to provide the means to set up a control theory lab experiment involving position control of a brushed DC motor with current feedback, a pulse-width modulated motor controller was designed. The output voltage is controlled by an analog reference signal and the magnitude of the output current and voltage are measured and output. These inputs and outputs are connected to a DAQ I/O-unit such that the lab experiment can be implemented digitally. In addition, defining equations for the whole system were derived. Comparison between measurements and model showed it possible to use the current as feedback if low-pass filtered and the angular displacement controlled over a small angular interval.

As of 2005, there were over 1.5 million amputees living in the United States, more than 548,000 of them with upper extremity involvement. The total number of amputees is projected to rise to at least 2.2 million by 2020. Unfortunately, full functional use of upper extremity prosthetic devices is low. Knowledge gained regarding the cortical systems active in amputees performing motor tasks may reveal atypical motor control strategies that contribute to these issues. Substantial evidence demonstrates a strong dependence on left parietofrontal cortical areas to successfully plan and execute tool-use movements and pantomimes. It was previously unclear how this network functioned in users of prostheses. The hypothesis of this dissertation is that in order to optimally engage the typical parietofrontal network during action imitation with a prosthetic device, the action being imitated should be performed by a matching prosthesis. Also, that greater engagement of the parietofrontal network will result in increased ability to perform tool-use movements. First, this dissertation showed that when imitating motor tasks performed by intact actors, prosthesis users exhibit lower engagement of the parietofrontal action encoding system. This network is crucial for motor adaptation. Left parietofrontal engagement was only observed when prosthesis users imitated matched limb prosthesis demonstrations, which suggests that matched limb imitation may be optimal to establish motor representations. Next, intact subjects donned a fictive amputee model system (FAMS) to simulate the limb movement that transradial amputees experience. Matched limb imitation in FAMS users yielded better movement technique compared to mismatched imitation. Finally, the longitudinal effects of a matched limb training paradigm on the cortical action encoding activity and motor behavior in FAMS users were investigated. Matched limb imitation subjects showed greater engagement of the parietofrontal network and better movement technique compared to those trained with mismatched limb. This dissertation has clinical relevance as it supports the notion that matched limb imitation could play an important role in the performance of motor tasks using a prosthetic device. These findings could be used to inform the development of improved rehabilitation protocols that may lead to greater functional adaptation of prosthetic devices into the lives of amputees.

Understanding possible variations in muscle activation patterns and its functional implications to movement control is crucial for rehabilitation. Inter-/intra-subject variability is often observed in muscle activity used for performing the same task in both healthy and impaired individuals. However, the extent to which muscle activation patterns can vary under specific neuromuscular conditions and differ in function are still not well understood. Current musculoskeletal modeling approaches using optimization techniques to identify a unique solution cannot adequately address such questions. Here I developed a novel computational framework using detailed musculoskeletal model to reveal the latitude the nervous system has in selecting muscle activation patterns for a given task regarding neuromechanical constraints. I focused on isometric hindlimb endpoint force generation task relevant to balance behavior in cats. By identifying the explicit bounds on activation of individual muscles defined by biomechanical constraints, I demonstrate ample range of feasible activation patterns that account for experimental variability. By investigating the possible neuromechanical bases of using the same muscle activation pattern across tasks, I demonstrate that demand for generalization can affect the selection of muscle activation pattern. By characterizing the landscape of the solution space with respect to multiple functional properties, I demonstrate a possible trade-off between effort and stability. This framework is a useful tool for understanding principles underlying functional or impaired movements. We may gain valuable insights to developing effective rehabilitation strategies and biologically-inspired control principles for robots.

A computational neural and biomechanical system for human bicycle pedaling is developed in order to study the interaction between the central nervous system and the biomechanical system. It consists of a genetic algorithm, artificial neural network, muscle system, and skeletal system. Our first finding is that the genetic algorithm is a robust tool to formulate human movement. We also find that our developed models are able to handle mechanical perturbation and neural noise. In addition, we observe variability and repeatability of pedaling motion with or without perturbation and noise. Movement phase dependent feedback nature is seen through computation too. This system shows many human movement qualities and is useful for further neural and motor control investigations. / text

published_or_final_version / Sports Science / Master / Master of Science in Sports Science

Exercise induced fatigue can have a negative impact on motor skill performance. While part of the decline is attributable to physiological factors that directly influence the coordination of movement, psychological factors may also contribute. Typically, motor learning environments encourage the accumulation of task-relevant declarative knowledge, which can be depended on to consciously support performance. The literature suggests that skills learnt in this way are vulnerable to demanding performance environments, including those in which the performer is fatigued. Recent empirical work has demonstrated that ‘implicit’ motor learning environments, devised to limit declarative knowledge buildup and/or dependence on working memory, promote resilient skill performance even after exhaustive fatigue protocols. Such findings imply that dependence on declarative knowledge to support motor skill execution may be a limiting factor under physiologically fatigue. However, it remains unclear the effect fatigue has on attentional resources, such as working memory. Using established experimental paradigms and EEG methodology, a research project was designed to investigate. Two explanations were considered: (1) fatigue distracts attention away from the control of movement or (2) fatigue directs attention to the skill, which interferes with automated control of the movement. In this study novice participants were allowed to freely accumulate declarative knowledge before completing a targeted muscle-fatigue protocol. A probe response paradigm assessed participants’ ability to recall the position of movement at the time a tone sounded, under the assumption that better recall reflects skill-focused attention. Neural activity was monitored by wireless EEG technology. Neural co-activation (or coherence) between brain regions associated with motor planning (Fz or F3) and with verbal-analytical processing (T3) has been suggested to reflect conscious control of motor skills. Therefore, a fatigue induced increase in T3-F3 coherence can be interpreted as increased conscious involvement in movement control, whereas, a decrease suggests a shift of attention away from movement control. The data collected suggests that to some extent fatigue raises visual-spatial and verbal-analytical contributions to motor control, but highlights methodological issues and limitations of the work. / published_or_final_version / Human Performance / Master / Master of Philosophy

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