Dissociating variability and effort as determinants of coordination

Area of Science:

• Neuroscience
• Motor Control
• Biomechanics

Background:

• The nervous system must coordinate redundant effectors for movement.
• Distinguishing between minimizing motor output variability and effort has been challenging in prior research.
• Previous studies on movement temporal shape could not differentiate between effort and variability minimization.

Purpose of the Study:

• To investigate how humans distribute force between two fingers to minimize both variability and effort.
• To quantify the relative importance of variability and effort in motor coordination.
• To determine if effort or variability costs are more significant in multi-effector control.

Main Methods:

• Participants produced target forces using two fingers on isometric transducers.
• Variability was measured using the coefficient of variation for each finger's force output.
• Effort was quantified using the sum of squared forces, both normalized and unnormalized.

Main Results:

• The study estimated the relative importance of variability to effort in force distribution as 1:7.
• Unnormalized effort was found to be the most significant factor in force distribution.
• Actual force distribution by participants aligned with predictions prioritizing effort minimization.

Conclusions:

• The nervous system utilizes multi-effector redundancy to reduce both output variability and effort.
• Effort minimization plays a more dominant role than variability minimization in motor control.
• These findings provide insight into the neural strategies for optimizing movement with redundant systems.