Survey
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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: cervicalthoracic-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.