Dongpyo Lee

"Kinematic Rules Underlying Unrestricted and Restricted Reaching Movements"

In the context of target-reaching movements that involve the arms, trunk and legs, we attempted to delineate the rules for apportioning motions amongst body segments, which would be valid for a range of target locations. We also attempted to determine whether the rules would be altered when motion is restricted at one joint - the knee. For each participant moving with unrestricted joints to nine target locations, Principal Component Analysis of the changes in orientation of six chosen segments revealed two effective degrees of freedom; these can be interpreted as movement modules, whose weighted combinations account for the segmental motions. Investigating inter-participant similarities, we found that a set of two movement modules could account for the segment motions among a group of participants who flex their knees, and another set of two modules among a group who extend their knees. Comparing the motions with and without the knee joints braced, we found that for each individual participant a set of two (or in some cases three) modules derived from the unrestricted segment motions could account well for the altered segment motions when the participant reached for the targets with the knees restricted. Our findings imply that the redundancy of kinematic degrees of freedom can be resolved by reliance on a small number of movement modules, and, in light of the robustness of the modules against mechanical restriction of joint motion, suggest a neural rather than mechanical origin of the modules. 

Dongpyo Lee is a postdoctoral candidate visiting UCSD.