Error compensation during finger force
production after one and four-finger
voluntarily fatiguing exercise.
E. S. Kruger, J. A. Hoopes, R. J. Cordial, and S. Li
By Kelsey Christensen
• Motor Variability• Bernstein “repetition without repetition”.
Background
• Motor Variability• Bernstein “repetition without repetition”.
• Degrees of Freedom (DOF)• Number of independent elements in a
system.
Background
• Motor Variability• Bernstein “repetition without repetition”.
• Degrees of Freedom (DOF)• Number of independent elements in a
system.
• DOF Problem/Problem of Motor Redundancy• How does the CNS select a particular
solution from the infinite number of solutions?
Background
Introduction• Error Compensation• DOFs work together to accomplish a
given task by compensating for errors made.
• Utilizing motor variability and redundant DOFs.
Introduction• Error Compensation• DOFs work together to accomplish a
given task by compensating for errors made.
• Utilizing motor variability and redundant DOFs.
• How is error compensation affected when parts of the motor system are impaired (number of DOFs is reduced)?
Methods• Apparatus• Procedures• Data Analysis
Methods• Apparatus• Procedures• Data Analysis
Methods• Apparatus• Procedures• Data Analysis
Procedures• 13 young, healthy adults• 2 sessions, 2-3 days apart• Index finger fatigued• All four fingers fatigued
3 6 9
Force (N)
Time (s)
3 6 9
Force (N)
Time (s)
3 6 9
Force (N)
Time (s)
Ftot
FI
FM
FR
FL
Ftot = FI+ FM+ FR+ FL
Methods• Apparatus• Procedures• Data Analysis
Data Analysis• Force signals from individual sensors to
analyze force profiles.
• ΣVarFi = sum of the variances of individual finger forces
• VarFtot = variance of total force• Error Compensation Index (ECI) = ratio of
ΣVarFi to VarFtot.
From force profiles:
Results
• Variance (A) and Error Compensation Index (B) averaged over entire force ramp and across all subjects.
• Average Error Compensation Index over the 1st, 2nd, and 3rd one-second segments of the ramp phase (seconds 4,5,6).
Discussion
Summary• The CNS is able to utilize the abundant
DOFs to compensate for motor system impairments to maintain the desired performance.• Problem of Motor Redundancy is a GOOD
thing.• Principle of Abundance – but there is a
limit.