Date of Award

Spring 1-1-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Alaa A. Ahmed

Second Advisor

Lawrence E. Carlson

Third Advisor

Virginia L. Ferguson

Fourth Advisor

Rodger Kram

Fifth Advisor

Derek T. Reamon

Abstract

The ability to maintain stable, upright standing is a critical component of our daily activities. This ability requires that we generate appropriate postural control when making voluntary movements and when responding to perturbations, and appropriately adapt that control to compensate for changing conditions. Despite this, adaptation of whole-body postural control is not well understood.

This dissertation investigates the control strategies involved in the adaptation of whole-body postural control and how well this learning transfers to different environments. We used an experimental paradigm in which subjects made reaching movements while standing and holding the handle of a force-generating robotic arm that could apply novel perturbations to the arm and standing posture concurrently.

First, we sought to identify the signal driving postural adaptation. We examined adaptation in response to varying movement error sizes. Adaptation scaled near-proportionally with error, but was insensitive to very small errors. In a follow-up study, we investigated the effect of small yet consistent errors. Despite the small errors, subjects did adapt, indicating that both error size and consistency play a role in driving adaptation.

Next, we investigated how control strategies are affected by postural stability conditions. Results showed that stability conditions significantly affect how adaptation strategies are used; furthermore, transfer of adapted control between different conditions is affected by the condition in which the task is initially learned.

Lastly, we tested whether postural control can be adapted and transferred independently of arm control. When subjects failed to transfer their adapted arm control between arms, they also failed to transfer their postural control, even though the postural perturbation had not changed. Thus, arm control over-wrote the learned postural control, necessitating re-learning of a previously learned strategy. This suggests that postural control is dependent on information about the arm movement dynamics in this combined task.

Generally, this work demonstrates that postural adaptation manifests many characteristics of general motor adaptation. It also highlights how heavily postural control is influenced by and coordinated with concurrent arm movements. However, postural stability conditions play a significant role in determining how standing posture is controlled, adapted, and transferred between different contexts.

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