INTER-PERSONAL MOTOR INTERACTIONS DURING HUMAN-HUMAN JOINT-ACTION SHARED OBJECT HANDLING TASKS

Abstract

Physical human-human collaborative interactions, often referred to as “joint-action” or “dyad partner” tasks, are a common part of many activities in our everyday lives and in workplace settings. This includes various actions such as shaking hands, playing sports, dancing with a partner, moving furniture, etc. Previous studies on the control and performance of human movements have largely focused on investigations of the mechanisms of an individual person’s actions. However, the knowledge of how two people, involving two independent central nervous systems (CNSs), work together to complete shared motor tasks is limited. Given the ubiquity of human-human dyad partner interactions, understanding how two people work together to perform a shared object-handling task and navigate various alterations to task conditions is critical to enhancing our understanding of collaborative motor performance. Therefore, the overarching purpose of this dissertation was to investigate inter-personal motor interactions in dyad partners performing shared object-handling tasks with the manipulation of various task conditions to increase task difficulty including obscuring visual feedback between partners and altering object inertial properties, such as total object mass and unequal load sharing of total object mass. In Study 1, we examined inter-personal level and inter-hand level force-stabilizing and moment stabilizing indices of synergy exhibited by dyad partners during a quasi-static object-holding task and found distinct strategies at the two hierarchal levels. In Study 2, we investigated an object-carrying task which employed sideways walking and found no significant differences inter-personal kinematic coordination of whole-body center of mass positions, leading feet positions, or trailing feet positions between dyad partners. In Study 3, we investigated an object-lifting task to examine dyad partner coordination of joint moment and joint power trajectories and found that only at the ankle level were there significant differences in coordination between dyad partners with obscured visual feedback and increased total object mass. Taken together, these findings suggest that dyad partner synergy and coordination in object-handling task performance is relatively robust to increases in task difficulty via changes to visual feedback and object inertial properties. In future research, the mechanisms which permit for this robustness of inter-personal synergies and coordination despite increases to overall task difficulty and a lack of a shared central neural controller should be further expanded to investigations outside of the laboratory setting using real-world task environments and paradigms.