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.