Chapter 5
Motor Control Theories

Do we decide how we move?
• Are you in control of your body?
– Sure…
• But to what extent?
– To what degree are the movements you make strictly down to your choice?
– To what degree is choice an illusion?

1.
How are intentions translated into action?
2.
What information guides movement?
3.
How does intention shape movement?
4.
How does learning one movement help in learning another?
5.
What is best practice in training/coaching movement skills?

What sort of problem are we facing?
• The problem of ‘control’ is one of choices and variety
– 792 muscles, 100 joints.
– That’s a lot of decisions to make (“ degrees of freedom problem” )
– We never make the same movement twice, but something is similar across repetitions of behavior
– We can learn

What sort of problem are we facing?
• “ degrees of freedom problem”
1.
– Problem for who?
– Car example – how many steering wheels on a normal car?
– Constraints/affordances – how are the wheels made “free to vary?
2.
• Axles joined together.
• Wheels of rear axle locked pointed in same direction
• Front wheels can be turned using steering wheel
3.

What sort of problem are we facing?
• “ degrees of freedom problem”
1.
2.
• Car example – how many steering wheels on a normal car?
– What if you freed the rear axle too, so that you’d have another steering wheel?
– How would it affect complexity of system control ?
– How would it affect complexity of system output ?
» How about if you freed all 4 wheels (so you had 4 steering wheels?
• Biological systems and degrees of freedom
– e-coli bacteria vs. humans
3.
4.

What sort of problem are we facing?
• The problem of ‘control’ is one of choices and variety
– Redundancy ( motor equivalence – a good thing )
• In the car example, freeing the back wheels means you can steer in two different ways.
– Consciousness vs. control
• When you write a word, what are you attending to?
• When you perform best at your chosen sport (or any other physical activity), what sort of stuff are you thinking about?

Making a start: A basic model
• 2 streams of information:
– One out – efference, output (e.g muscle contractions)
– One in – afference, feedback (e.g. sight, sound, proprioception)
• But they’re both going on completely continuously, so breaking them down and focusing on one may be a mistake
• One theory (motor program theory) focuses on the “out” stream
• The other ( dynamic pattern theory , which we’ll focus on) takes a more interactive approach, looking for properties within us and around us that may determine how movements (the patterns referred to) form

Making a start: A basic model
Defn: feedback = sensory information
• The simplest control model:
Input Processing Output


This model uses OPEN-LOOP control
Def: Open-loop control = outgoing messages only. No ‘feedback’

Making a start: A basic model
Processing Effectors Output
Feedback (= input)


This model uses Closed-Loop control
Def: Closed-loop control = use of feedback to guide behavior

Making a start: A basic model
3.
2.
• Moving closer to reality
1.
– How many senses do you have?
• http://www.youtube.com/watch?v=CUn7zy8Ya20
• Each of these are sensory inputs (feedback)
– How many muscles/fibres/motor neurons do you have?
• Each of these are motor outputs (grouped, form effectors – muscles or even limbs)
– William James (1891) & others – careful observation...

Making a start: A basic model
• The reality...
– There are many studies that suggest the interaction between these two sources of information is in reality far more complex than simply one
“upstream” (feedback) and one “downstream”
(motor commands)
– The signals seem to interact at every available level of the system, resulting in a complexity of signal processing that is very daunting
– So what’s the message behind this?

Making a start: the next step
• No final answer...(robotics, artificial intelligence, neuroscience etc...)
• So we need a theory that is one step removed from the final answer
– Dynamic pattern theory works at every level of the system (neural, behavioral)
– It does a decent job of helping us to understand where movements “come from”