Grip force anticipation of nonlinear, underactuated load force

Area of Science:

• Motor control
• Robotics
• Neuroscience

Background:

• Feedforward internal model-based control, using efference copies of motor commands, is the leading theory for motor anticipation.
• Grip force control during object manipulation is a key piece of evidence supporting this theory.
• This approach has not adequately addressed the complexities of manipulating objects with nonlinear dynamics.

Purpose of the Study:

• To investigate grip force control during the manipulation of mechanically complex objects.
• To test the prediction of the internal forward model approach regarding grip force coordination with unpredictable load forces.
• To determine if efference copies of motor commands are necessary for anticipatory grip force control.

Main Methods:

• Participants manipulated a complex object with nonlinear, underactuated degrees of freedom.
• Grip force and load force dynamics were recorded during manipulation.
• Analysis focused on the anticipatory coupling between grip force and load force.

Main Results:

• Strong, precise, and anticipatory grip force control was observed during complex object manipulation.
• Grip force exhibited precise coupling with changing load forces.
• The observed control was inconsistent with predictions from the efference copy-enabled feedforward control scheme.

Conclusions:

• Efference copies of motor commands are not necessary for anticipatory control during active object manipulation.
• The internal forward model approach is insufficient to explain grip force control with complex objects.
• Alternative theoretical frameworks are required to account for anticipatory grip force control in such scenarios.