Abstract
In the advent of intelligent robotic tools for physically assisting humans, user experience, and intuitiveness in particular have become important features for control designs. However, existing works predominantly focus on performance-related measures for evaluating control systems as the subjective experience of a user by large cannot be directly observed. In this study, we therefore focus on agency-related interactions between control and embodiment in the context of physical human-machine interaction. By applying an intentional binding paradigm in a virtual, machine-assisted reaching task, we evaluate how the sense of agency of able-bodied humans is modulated by assistive force characteristics of a physically coupled device. In addition to measuring how assistive force profiles influence the sense of agency with intentional binding, we analyzed the sense of agency using a questionnaire. Remarkably, our participants reported to experience stronger agency when being appropriately assisted, although they contributed less to the control task. This is substantiated by the overall consistency of intentional binding results and the self-reported sense of agency. Our results confirm the fundamental feasibility of the sense of agency to objectively evaluate the quality of human-in-the-loop control for assistive technologies. While the underlying mechanisms causing the perceptual bias observed in the intentional binding paradigm are still to be understood, we believe that this study distinctly contributes to demonstrating how the sense of agency characterizes intuitiveness of assistance in physical human-machine interaction.
Highlights
In the face of growing elderly population, automated assistive technologies such as powered exoskeleton and rehabilitation devices are expected to play a crucial role for meeting societal demands (Beckerle et al, 2017)
User experience is of high relevance for designing assistive technologies in which the human is at the center of a control loop (Limerick et al, 2014; Beckerle et al, 2017) and methodologies for objective monitoring of user experience will be valuable for advancements of human-machine interactions (HMI) systems
While the underlying mechanisms causing the perceptual bias observed in the intentional binding paradigm are still to be understood, we believe that this study distinctly contributes to the understanding of how a control design in physical HMI modulates sense of agency (SoA)
Summary
In the face of growing elderly population, automated assistive technologies such as powered exoskeleton and rehabilitation devices are expected to play a crucial role for meeting societal demands (Beckerle et al, 2017). In order to meet user-dependent requirements in guiding behavior, usually explicit control objectives are minimized These cost functions are task-oriented and use a set of performance indices such as the muscular effort (Hamaya et al, 2017) or the task completion time (Erdogan and Argall, 2017) to define the utility of the autonomous behavior of a system. It is considered that coupling of the self-induced motion and its outcome in the conscience experience attracts the temporal experience of the two sensory events, resulting in perception of a selfinduced action outcome being perceived as earlier than it physically is This subjective contraction of time is considered to be an implicit measure of SoA as it reflects the internal representation of self-produced motion. We hypothesized IBE is sustained when guiding force adheres to a desired motion of the participants, while IBE is diminished when the force results in undesirable outcome
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