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

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

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

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

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

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.

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

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

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

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

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).

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