Within-trial modulation of multi-digit forces to friction

Area of Science:

• Neuroscience
• Biomechanics
• Human motor control

Background:

• Tactile feedback from fingertips is essential for effective object manipulation.
• Humans dynamically adjust grip forces based on object properties like friction to prevent slippage.

Purpose of the Study:

• To investigate how multi-digit grip forces adapt to varying friction levels within and across manipulation trials.
• To determine the timing and extent of force adaptation to friction during object grasping and lifting.

Main Methods:

• Ten healthy participants grasped, lifted, held, and released a device with five digits under four distinct surface texture conditions.
• Quantified changes in digit normal force, center of pressure, safety margins, and force sharing patterns across texture conditions.
• Analyzed force adaptation within the first trial and across subsequent trials.

Main Results:

• Altering surface textures significantly changed digit forces and force distribution from initial contact to lift-off.
• Force adaptation to friction was evident from the first trial and persisted throughout the experiment.
• A strong linear relationship was found between safety margin at lift-off and object hold, indicating pre-lift adaptation.

Conclusions:

• Tactile input enables rapid, within-trial adaptation of multi-digit forces to surface friction.
• This adaptation occurs early in the manipulation process, before object lift-off.
• Findings highlight the critical role of tactile feedback in modulating grip forces for dexterous object handling.