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

Front. Bioeng. Biotechnol., 2021 · DOI: 10.3389/fbioe.2020.574006 · Published: January 13, 2021

Simple Explanation

This study explored how changing the way a computer display reflects a user's grasp force affects their sense of control and how well they perform the grasp, considering both rigid and flexible surfaces. The results showed a link between the feeling of control and grasp performance. The experiment involved participants using their grasp force to control a trace on a screen, trying to match a target. Different control modes were tested, involving changes in force needed, adding slight noise, or some automation. The type of surface being grasped (rigid or flexible) was also considered. The findings suggest that rehabilitation interfaces for people recovering from neurotraumas should be designed considering these cognitive aspects. Specifically, the type of surface (rigid or flexible) matters when designing interfaces for virtual reality training and assistive devices like exoskeletons and prostheses.

Study Duration

Not specified

Participants

16 able-bodied volunteers (12 male, 4 female, 21 ± 3 years)

Evidence Level

Original Research

Key Findings

1
A positive correlation was observed between implicit agency (measured by time-interval estimation) and grasp performance (measured by force-tracking error) across varying control modes for each surface type.
2
Grasp on the compliant surface resulted in greater dependence of performance on agency and increases in agency and performance with the addition of mild noise.
3
Introducing automation in control decreased agency and performance for both surfaces, suggesting the value in continuous user control of grasp.

Research Summary

This study investigated how modifications in the display of a computer trace under user control of grasp forces can co-modulate agency (perception of control) and performance of grasp on rigid and compliant surfaces. We observed positive correlation (p < 0.01) between implicit agency, measured from time-interval estimation for intentional binding, and grasp performance, measured by force-tracking error, across varying control modes for each surface type. In conclusion, agency and performance of grasp can be co-modulated across varying modes of control, especially for compliant grasp actions.

Practical Implications

Cognition-Centered Device Interfaces

Design rehabilitation interfaces that consider cognitive aspects to improve user integration with virtual reality training and powered assistive devices.

Importance of Continuous User Control

Assistive devices should prioritize continuous user control to enhance agency and performance, avoiding excessive automation.

Surface Compliance Considerations

Grasp training and assistive devices should account for the compliance of the grasped surface, as it affects the relationship between agency and performance.

Study Limitations

1
Examination of only one level for each control mode type.
2
Gender-based differences for movement agency and precision grasp have not been well established, but not considering gender as a factor is a potential study limitation.
3
Future studies should also consider alternative measurements of agency.

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