Breaking It Down Is Better Haptic Decomposition of Complex Movements Aids in Robot-Assisted Motor Learning J. Klein, S. Spencer, & D. Reinkensmeyer IEEE Transactions on Neural Systems and Rehabilitation Engineering May 2012
Jan 18, 2016
Breaking It Down Is Better
Haptic Decomposition of Complex Movements Aids in Robot-Assisted Motor Learning
J. Klein, S. Spencer, & D. Reinkensmeyer
IEEE Transactions on Neural Systems and Rehabilitation Engineering
May 2012
Motivation – Klein et al.
• sports training• rehab from neurologic injury
– stroke– spinal-cord injury
Motivation – CHARM
• stroke rehab (Michele, Mike)• needle-steering training (Ann)• robot-assisted surgery (Ilana)
Background
HAPTIC GUIDANCE• of questionable effectiveness• to date, been used almost
exclusively to demonstrate entire movements
“PART-WHOLE” TRANSFER• sequential vs. continuous tasks• effectiveness correlated with
coordination requirements
shoulder rotation
elbow flexion/extension
desired trajectory
Hypothesis
“Decomposing” a movement into fewer-DOF components is more effective than training the movement as a whole. Moreover, the degree of effectiveness is dependent on the form of the decomposition.
Methods
4 DOFs1. shoulder abduction/adduction2. should flexion/extension3. shoulder int./ext. rotation4. elbow flexion/extension
EULER
Methods
2 Motions1. “main” (θ) ≈ tennis backhand2. transfer (θ’) ≈ front crawl swim
Reflection…
What if the task had been framed as a goal-directed movement?
That is, what if subjects had been told: “pretend
you are swinging a tennis racket”?
Methods
Experimental Protocol1. Baseline2. Baseline Transfer3. Training4. Assessment5. Assessment Transfer6. Retention7. Retention Transfer
4 Training Groups1. “Whole” (control)2. Euler3. Anatomical4. Visual
Reflection…
Klein et al. randomized the presentation order
of the joint components during Training. How necessary was this
control? Is component presentation order an area for further study?
rand{}
Methods
Assessment
“GLOBAL”
lower score = better learning
“LOCAL”
* accounting for time delay d
Reflection…
Why is it necessary to fit the shift parameter d? Shouldn’t d simply be the time between the
assessment start signal and movement onset? ...
Reflection…
… Are we assuming that subjects are “playing catch up” with the virtual arm? What if, instead of being
shown a virtual arm, subjects were given binary feedback (e.g., GREEN vs.
RED) based on their current performance?
Results“MAIN” TRANSFER
Results
• no Baseline differences between decomposition groups
• all groups significantly improved with Training• Anatomical decomposition exhibited greatest
improvement during all assessments– Training – no significant difference compared to “Whole”
– Short-Term – significant compared to all other groups
– Long-Term – only (weakly) significant compared to Visual
Reflection…
Why would there be greater learning at long-
term retention (vs. short-term retention) for
“Whole”, Euler, and Visual decompositions*?
Given enough time, would all groups
equalize?
* Anatomical was approximately the same
Results
• “global” performance correlated with
1. “local” performance2. proximity of training joint positions to those
required by whole motion
• no improvement for transfer motion haptic guidance training IS task specific
Discussion
“Part-Whole” Learning
• counterintuitive• success of Anatomical (vs.
Visual) decomposition suggests that spatiotemporal summation mechanism operates in joint (vs. visual coordinates)
* see (Kakei et al., 2001)
• NOT generalizable• more spatial than temporal
Reflection…
I am unconvinced by Klein et al.’s theory for why
(anatomical) movement decomposition aids in
learning a target motion more than practicing the motion itself. What other
explanations can we propose?
“One possibility is that the motor system has trouble determining where the problems lie in making, accurate, complex movements; breaking the movements down may allow better identification and then more focused practice on key problems.”
Discussion
“Part-Whole” Learning
• counterintuitive• success of Anatomical (vs.
Visual) decomposition suggests that spatiotemporal summation mechanism operates in joint (vs. visual coordinates)
* see (Kakei et al., 2001)
• NOT generalizable• more spatial than temporal
Robotic Movement Training
• opens the door for simpler robotic devices in rehab
• BUT, benefits of movement decomposition might only exist with haptic guidance
Reflection…
What does this mean for stroke rehabilitation? Is
there a “whole-part” mechanism that could
help decouple patients’ abnormal muscle
synergies?
shoulder rotation
elbow flexion/extension
desired trajectory
“Breakthrough” or just another addition to the pool of inconclusive
literature on haptic guidance?