Date of Award

Summer 2022

Document Type

Open Access Dissertation


Exercise Science

First Advisor

Jill C Stewart


The Index of Difficulty value (ID) derived from Fitts’ Law’s speed-accuracy trade-off is commonly used to determine the difficulty of a targeted reaching movement and balance difficulty in sequence learning tasks. However, this value does not account for the mechanical difficulty of multi-directional movements which could affect both performance and learning. Where we direct our focus when completing a task/skill can also have an effect on how we perform and learn that task, however, the manner in which differing focus instructions affect learning a whole-arm reaching task is relatively unknown. The purpose of this dissertation was to examine 1) how Fitts’ Law translates to multi-directional targeted reaching movements and 2) examine how differing focus of attention instructions affect the learning of a multi-directional, whole-arm sequence task. The first study found that while reaches to targets of increasing ID and same direction resulted in scaling of kinematic measures consistent with Fitts’ Law, reaches between targets of the same ID but differing directions resulted in variations in movement time and other movement kinematic measures. These variations are likely the result of differences in mechanical difficulty due to changes in inertia and joint demands with direction. The results of Study 1 suggest that studies which use multi-directional, whole-arm reaching movements should either try to account for this effect and/or understand this limitation to Fitts’ Law. The second study found that both External (EF) and Internal (IF) focus instructions resulted in similar improvements in overall performance (Response Time) on the sequence task over practice but did so via different approaches. The EF instructions resulted in shorter hand paths indicating straighter hand trajectories during the task while the IF instructions resulted in higher peak velocities indicating higher movement speeds. The results of Study 2 suggest that both EF and IF instructions can be effective when learning a motor sequence task which requires both speed and accuracy but do so via differing control mechanisms. This finding suggests that instructions could be tailored to the task at hand and toward the control parameter (spatial, temporal) where change is most desired.


© 2022, Charles R Smith