Agency and Performance of Reach-to-Grasp With Modified Control of a Virtual Hand: Implications for Rehabilitation

Abstract

This study investigated how modified control of a virtual hand executing reach-to-grasp affects functional performance and agency (perception of control). The objective of this work was to demonstrate positive relationships between reaching performance and grasping agency and motivate greater consideration of agency in movement rehabilitation. We hypothesized that agency and performance have positive correlation across varying control modes of the virtual hand. In this study, each participant controlled motion of a virtual hand through motion of his or her own hand. Control of the virtual hand was modified according to a specific control mode. Each mode involved the virtual hand moving at a modified speed, having noise, or including a level of automation. These specific modes represent potential control features to adapt for a rehabilitation device such as a prosthetic arm and hand. In this study, significant changes in agency and performance were observed across the control modes. Overall, a significant positive relationship (p < 0.001) was observed between the primary performance metric of reach (tracking a minimum path length trajectory) and an implicit measurement of agency (intentional binding). Intentional binding was assessed through participant perceptions of time-intervals between grasp contact and a sound event. Other notable findings include improved movement efficiency (increased smoothness, reduced acceleration) during expression of higher agency and shift toward greater implicit versus explicit agency with higher control speed. Positively relating performance and agency incentivizes control adaptation of powered movement devices, such as prostheses or exoskeletons, to maximize both user engagement and functional performance. Agency-based approaches may foster user-device integration at a cognitive level and facilitate greater clinical retention of the device. Future work should identify robust and automated methods to adapt device control for increased agency. Objectives include how virtual reality (VR) may identify optimal control of real-world devices and assessing real-time agency from neurophysiological signals.

Influence of levels of automation on the sense of agency during continuous action

“…We performed two step-wise experiments in light of these aims. In Experiment 1, we replicated the findings of past experiments 11 – 13 , whereby the sense of agency increases with an increase in apparent task performance due to automation and decreases in the full automation condition. In Experiment 2, we identified the turning point where the participants’ sense of agency decreases to lower than that in the complete control condition.…”

“…Interestingly, this observation of the increase in the sense of agency was replicated even when the participants were given instructions about the assistance 12 . In addition, Nataraj et al 13 , by using a virtual reality environment in which the participants controlled a virtual hand to perform reach-to-grasp movements, showed that the sense of agency decreased if modifications in the movement of the virtual hand due to the automation degraded task performance. These results suggest a positive relationship between apparent task performance as modified by automation and the sense of agency in situations where people continuously operate a tool featuring some automation.…”

Control Modification of Grasp Force Covaries Agency and Performance on Rigid and Compliant Surfaces

“…Improved motor control may be enacted from training the person to move better independently or with the assistance of a powered device. Regardless of the rehabilitation approach, the person should be cognitively engaged and integrated with the therapeutic platform or the assistive device ( Moore and Fletcher, 2012 ; Nataraj, 2017 ; Nataraj et al, 2020a , b , c ). Improved perception of involvement and control of movement should better ensure continued participation and positive functional outcomes ( Doyle, 2002 ; Behrman et al, 2005 ).…”

“…Agency is naturally implicated with rehabilitation through perception of neuromuscular action and related functional consequences ( Moore and Obhi, 2012 ). Agency contributes to the performance of functional movements such as reaching ( Nataraj et al, 2020c , d ) and is impaired in the presence of neurological disorders ( Jeannerod, 2009 ; Ritterband-Rosenbaum et al, 2012 ). Agency can also be compromised during the use of powered assistive devices, such as exoskeletons ( Hartigan et al, 2015 ) or sensorimotor prostheses ( Antfolk et al, 2013 ; Hebert et al, 2013 ), due to distortions in embodiment ( Kilteni et al, 2012 ; Caspar et al, 2015 ).…”

Training with Agency-Inspired Feedback from an Instrumented Glove to Improve Functional Grasp Performance

“…The notable limitation in this study was that we did not explicitly measure agency and directly relate it to performance. Our previous work has made the positive connection between agency and performance [ 16 ] but relied on verbal estimation of randomly presented time-intervals [ 15 ] to assess agency. In this study, subject onus to estimate time-intervals may be prohibitive to the perceptual conditioning we sought to achieve.…”