Document Type


Date of Degree

Summer 2017

Degree Name

PhD (Doctor of Philosophy)

Degree In

Physical Rehabilitation Science

First Advisor

Shields, Richard K

First Committee Member

Anderson, Steven

Second Committee Member

DeJong, Stacey

Third Committee Member

Frey-Law, Laura

Fourth Committee Member

Wilken, Jason


A broad understanding of motor control has been achieved through research performed on upper extremity reaching, walking on level ground, and static balance. Though invaluable insights have been achieved under these testing paradigms, inherent limitations result in less being known regarding functional movement in weight-bearing. Gait studies require large numbers of consecutive steps to achieve high reliability, static balance is limited to the goal of no movement, and upper extremity reaching lacks insights into feedback from the vestibular system. Here we describe (and provide a supplemental video of) a system for testing and training the performance of a weight-bearing, visuomotor task in the form of a mini-squat according to a sinusoidal trace on a screen.

In this work, we determined that by altering both task movement rate and resistance at the knee, a hierarchy of difficulty was achieved at all ages. As age increases, there is a velocity-error tradeoff; speed of movement is attempted to be maintained while error is sacrifieced. When introducing an unexpected force perturbation (rapid release of the resistance of the squat for less than a second), older adults who are least able to match the frequency of the task experience the greatest error and velocity rates during the perturbation. This exposes a possible deficit in the feedback control system of even healthy older adults, where future studies may determine if early intervention to prevent such changes may prevent future injury and disability.

When older and younger adults learned to perform the visuomotor task while performing a simultaneous cognitive task, learning was slowed as complexity of the cognitive task increased. In older adults, a difficult cognitive task inhibited acquisition of the squatting task with no apparent improvement in trial error nor coherence. Upon retesting of the motor task, there was no difference between dual-task and single-task trained ability to consolidate the motor task in both age groups, though those that trained under a dual-task condition were more able to automate the motor task as measured by a smaller dual-task cost. This may indicate that dual-task training leads to freeing cognitive resources from attending to a functional movement so that they may attend to other tasks such as what may be happening in the environment. Finally, executive function as measured by the Flanker Test, explained 80% of the variability of final day visuomotor error, being a possible prognostic factor for dual-task interventions. Future directions will determine if increased automaticity of a mini-squat will lead improvement to overall improved functional mobility and reduced lower extremity injuries when functioning in a busy community.


Cognitive-Motor Interference, Feedback Control, Long-latency response, Motor Learning, Single limb squat, Weight-Bearing


x, 161 pages


Includes bibliographical references (pages 136-153).


Copyright © 2017 Keith R. Cole

Additional Files

SLS Video with visuomotor task.mpg (5900 kB)