Transcript Turvey et al (1982)

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:
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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
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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.