京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第21704号 / 人健博第70号 / 新制||人健||5(附属図書館) / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 青山 朋樹, 教授 黒木 裕士, 教授 松田 秀一 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

<p>Tool use is an important area of research in psychology, neurophysiology, and motor behavior because it provides insights into the organization of perception, cognition, and action. Tool use research has traditionally focused on the neural structures or cognitive processes that contribute to body-tool integration, while there has been comparatively little interest in motor control. When tool use actions are studied, adaptations have mainly been examined at the level of manual control, while postural control and multi-segment coordination have received less attention. Examining these components of behavior in the context of tool use is vital for developing a better understanding of how humans integrate tools into goal-directed actions.</p><p>The goals of this dissertation were to 1) characterize adaptations to postural control over time when performing a manual task with a tool under different levels of postural constraint and determine their relation to manual task performance, 2) examine postural-manual coupling under different levels of postural constraint during tool use, and 3) determine how multi-segment coordination supports postural stability and suprapostural task performance under different levels of postural constraint during tool use. To address these questions, we adopted a sensorimotor adaptation paradigm to examine postural-manual control and multi-segment coordination before, during, and after an extended bout of tool use.</p>Tool-use adaptations were found to extend beyond the end-effector. Postural control played a crucial role in facilitating improvements in the manual control of tools. Placing constraints on posture interfered with these adaptations, disrupting the coordination of postural-manual behaviors during tool use. However, multi-segment coordination was modified to overcome this challenge and facilitate postural stability and manual performance. These results demonstrate that healthy young adults are capable of flexibly recruiting and exploiting available degrees of freedom in a task-dependent manner the potential challenges associated with integrating tools into movements. This dissertation provides preliminary support for the importance of considering postural control in tool use actions and highlights the utility of examining interactions across multiple levels of motor behavior—postural control, manual control, postural-manual coupling, and multi-segment coordination—to elucidate how tools are integrated into complex, goal-directed behaviors.

<p>  </p> <p>Falls mostly occur when people are walking. Investigations of control of gait stability have focused primarily on the single stance phase. My dissertation focused on the double support phase of gait because (1) responses to perturbations occur during the double support (2) the portion of the gait cycle spent in double support is increased with old age, and, more importantly, (3) since both feet can push off the ground simultaneously, there are more kinetic degrees of freedom (DoF) and therefore greater control authority over body motion during this phase. However, how these kinetic DoFs are coordinated during the double support phase is not fully understood. Thus, the goal of this dissertation was to identify the inter-leg coordination to stabilize whole-body motion and quantify how the inter-leg coordination is affected by intrinsic and extrinsic factors. Specifically, Study 1 focused on healthy aging (an intrinsic factor) and varying task demands (an extrinsic factor that changed while curb ascent versus curb descent). Study 2 investigated another extrinsic factor of future uncertain environmental demands (fixed versus uncertain foot targeting demand for the step after descending a curb). Using the uncontrolled manifold analysis, I identified ground reaction variable (GRV) synergies, i.e., synergistic covariations between the ground reaction forces and moments under the two feet that stabilize whole-body linear and angular motions. Furthermore, I found that GRV synergies were modulated by extrinsic factors: GRV synergies were sensitive to current fixed environmental demands (Study 1), whereas they were robust to future environmental demands on foot placement (Study 2). Lastly, I found that GRV synergies were not changed by the intrinsic factor of age, despite the physiological declines with aging (Study 1). The absence of an age effect on GRV synergies indicates that older adults have the preserved ability to exploit the control authority during the double support phase to maintain stability while negotiating a curb. The work extends the current body of literature on gait stability mechanisms and improves our understanding of changes in stability control as a function of different environmental demands.</p>