Interpersonal synergies: static prehension tasks performed by two actors

Area of Science:

• Biomechanics
• Human Motor Control
• Robotics

Background:

• Understanding how multiple digits coordinate to stabilize forces is crucial for grasping and manipulation.
• Previous research often focuses on single-person tasks, limiting insights into collaborative manipulation.

Purpose of the Study:

• To compare multidigit force synergies between single-person (bimanual) and two-person static prehension tasks.
• To investigate the role of sensory feedback in stabilizing force output during collaborative tasks.

Main Methods:

• Quantified intertrial variance of digit forces and moments using the uncontrolled manifold framework.
• Analyzed synergies at multiple levels: between hands, between virtual digits, and within a single hand.
• Performed correlation and phase synchronization analyses on resultant and internal forces.

Main Results:

• Single-person tasks showed higher intertrial variance in forces not affecting the resultant normal force.
• Two-person tasks exhibited stronger synchronization of normal forces between hands.
• Evidence suggests reliance on non-visual feedback (haptic, proprioceptive) in two-person tasks.

Conclusions:

• Multidigit synergies adapt based on the number of individuals involved in the task.
• Non-visual sensory information plays a critical role in coordinating forces during collaborative manipulation.
• Findings highlight limitations of generalizing synergies from visually-dependent tasks to naturalistic interactions.