Turvey et al (1982)

1. Turvey et al (1982) Notes on general principles of action and control of action

2. Turvey, Fitch, Tuller. • Inertia and reactive forces. • Keyboard – open loop control – cortex sends commands to lower levels • Model arm example: • 7 d.f. for joints • 26 for muscles • 2600 for motor units • Need to lessen the role of homunculus • “don’t want a tennis player in the head” • Infinite regress

3. Turvey, Fitch, Tuller. • Step one: only consider configurations that are useful or possible. • Degrees of freedom = ND-C (elements, dimensions, constraints). Linkages reduce df

4. Turvey, Fitch, Tuller. • 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

5. Turvey, Fitch, Tuller. • Context-conditioned variability • Sources • 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

6. Turvey, Fitch, Tuller. • 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.

7. Tuller, Turvey, Fitch • Coordinative structures • Linkages • Arm control in shooting: wrist-shoulder • Breathing: cervical- thoracic-pelvic • Handstand: shoulders-hips • Plane example like the car example (more complex) • Locomotion: leg position relative to each other • Nesting of linkages

8. Tuller, Turvey, Fitch • Mass-spring systems • Equilibrium points set by tension in spring and amount of mass. • Final location of finger is well reproduced. Not amplitude. • Limit-cycle oscillators • “capable of returning to stable mode despite disturbances that may speed up or slow down the cycle” • Cyclicity is an “obligatory manifestation of a universal design principle for autonomous systems.” Yates (1980). • Entrainment – mutual constraint of cycles • Kelso et al. (1981) – “human interlimb coordination and limit cycle oscillators” • Timing of forcing – see clock example later

9. Fitch, Tuller, Turvey • Tuning coordinative structures via perception • Overall ratio of activity remains the same, but absolute values change • Piano roll metaphor • Timing of force determined by coordinative structure – only allowed at certain times in the movement, learned through experience. • Pendulum clock example

10. Pendulum clock example (Kugler, Kelso, & Turvey, 1980) • Pendulum clock function • 3 components • oscillatory component • potential energy source (hanging weights) • escapement to correlate each of these two. • Escapement has two parts: • escape wheel (flywheel) • oscillatory component with teeth that engage alternately with the escape wheel • Clock function: • pendulum swings • pendulum reaches equilibrium point • wheel escapes engagement for one notch • allows hanging weights to descend a bit • releases small amount of kinetic energy • fed back into pendulum via the teeth of the escape wheel

11. Fitch, Tuller, Turvey • Optical array • Exteroception (environment) • Proprioception (body) • “Exproprioception” (Lee) • Time-to-contact (tau - τ) • Swinging room • Arrays need not be optical • can be tactile too (or any other sensory modality).

12. Fitch, Tuller, Turvey • Posture-preserving system • Transport system • Combine…gives more linkages and constraints.