1. Turvey Fitch & Tuller (1982)
…and some additional notes.

2. The focus questions
On page the first page - the notion of the inclusion of reactive forces and inertia in the theory of movement is first mentioned. Give a couple of examples of how these are referred to elsewhere in the paper.
Why does Turvey suggest the homunculus concept must be trimmed down (or eliminated)?
How do equations of constraint help with the degrees of freedom problem?
Define context conditioned variability (CCV)
Briefly explain each of the three types of CCV
What is the alternative approach to the non-muscular forces suggested at the foot of p.249?
How does Turvey characterize the use of the degrees of freedom in learning at the end of the paper?

3. The “straw person” argument
Turvey et al present a simplified version of hierarchical control
We’ll go over the most successful (?) theory, from the 70s
Richard Schmidt’s Schema theory of discrete motor skill learning (1975)

4. Schmidt’s schema theory
The schema
The concept has a rich history
Kant (1787) – critique of pure reason
Transcendental schema
Triangles – how do we know something is a triangle?
Categories of things as a means to understand them
The rule for the category stays the same, while the individual properties of the items within the category can vary.
Triangle:
Fixed Rule = 3 sides, internal angles add to 180
Variable properties = size of sides, individual angles.

5. Schmidt’s schema theory
The schema
The concept has a rich history
Bartlett (1932) – “Remembering”
‘When I [play a tennis shot], I am not producing something entirely new, and I never repeat something old...’
Movements are prototypical.
Each movement is novel, because it is generated from an abstraction, rather than a specific command
Formation of general rules used to interpret stimuli and drive movement organization

6. Schmidt’s schema theory
Using schema to explain movement (see Schmidt, 1975, 1988, 1991):
Three concepts central to Schmidt’s schema theory
Generalized motor program (GMP)
Basic prototype of the movement
Has variant and invariant features (just like Kant’s original idea)
Recall schema
Provides parameter values (variant parameters) to the GMP
Built through experience
Recognition schema
Expected feeling of the movement

7. Schmidt’s schema theory
Using schema to explain movement (see Schmidt, 1975, 1988, 1991):
What is stored after moving?
After each movement (for a short while):
Initial conditions (body position, context, environment)
Response specifications (direction, speed, force)
Sensory consequences (during and after moving)
Response outcome (desired, actual)
After many repetitions, the program parameters are generated from the recall schema, which stores the relationship between:
past response specifications
past response outcomes
past and present initial conditions

8. Schmidt’s schema theory
Using schema to explain movement (see Schmidt, 1975, 1988, 1991):
Defining features of a Generalised Motor Program
Some features of the GMP were held to be variant:
overall force
overall timing
muscle selection
Some features of the GMP were held to be invariant:
relative force
relative timing

9. Schmidt’s schema theory
Using schema to explain movement (see Schmidt, 1975, 1988, 1991):
Example:
Walking and running

10. Schmidt’s schema theory
Using schema to explain movement (see Schmidt, 1975, 1988, 1991):
Example:
Handwriting
Change effectors, outcome still the same

11. Schmidt’s schema theory
Reconsider?
Do either of these actually show invariant features?
What exactly stays the same here from one attempt to the next?
What about the bit in the middle?

12. Back to Turvey… Bernstein’s synergies Degrees of freedom
Blacksmith example
Car example
Links reduce complexity
But also reduce d of f to control

13. Back to Turvey…
So synergies reduce complexity, but it’s still very complex
Context conditioned variability
Changes in movements arising from muscle forces forces due to context into which these forces are “injected”
Homunculus must know of context to know the required force

14. Back to Turvey…
So synergies reduce complexity, but it’s still very complex
Context conditioned variability
Anatomical
Muscle contraction has different effect due to initial position of limb segment
Mechanical
Muscle force has different movement effect depending on context
Kinetic energy created by movement in one joint affects others
Physiological
Neural signals do not descend uninterrupted – they are acted on and interpreted by the assemblies in the spinal cord. It is not a simple hierarchical process

15. Overall message
Muscular and non-muscular forces must complement each other.
Learning is about integrating non-muscular forces with muscular forces.
Freezing and freeing degrees of freedom as reactive forces are learned, anticipated, and absorbed
What’s important about the different perspectives?

16. Overall message What’s important about the different perspectives?
From the schema theory perspective:
Mistakes arise from incorrect calibration of recall schema
Mistakes arise because the GMP is not well adapted to current consitions
All central problems
Central organization
From the Bernstein perspective
Reactive forces are not sufficiently integrated with active forces in such a way as to exploit the “free” energy of the movement
E.g. walking, golf swing.
Definitely a peripheral problem
Listen to the periphery
What is it supposed to feel like? [Hula hoop example]
Self-organization
Turing machine vs. the Watt governor – for next time!