Open and Closed Loops Generic ClosedLoop System What

Open and Closed Loops

Generic Closed-Loop System What constitutes the desired state? What are the extero- and intero- sources of feedback? Set Temp Actual Temp What self-regulating mechanisms are involved in action? How does the athlete judge the discrepancy between desired and actual state? What can a coach do to facilitate this analysis?

Basic Feedback Loop Internal Feedback: Instantly feel your muscles are Proprioceptive Feedback: Youyou can make anwhat immediate evaluation doing and make corrections andbeen adjustments if possible Exteroceptive Feedback: You can make an evaluation of youron own of your own performance after it has completed based the External Feedback: My coach told me that my timing performance after it has been completed based onitthe feedback your senses. it feelmyright? Did hurt? Was my was off. I seefrom on the video that I Did dropped head from your I contact the ball theball. rightwhen place? I landed? Did I step weight transferred Dideye I feel balanced too soon. It senses. looks like. Did Ismoothly? am taking my offinthe line? Were hands correctly Iover was instructed to takemy two steps, positioned not three before I on the club? Was I lined up with my target? jump.

Closed-Loop Model Expanded 1. Executive 2. Effector 3. Feedback 4. Comparator Slower/Longer Duration Responses (3 corrections/sec) Tracking - Driving Cycling Running Rowing

The Dewhurst (1967) study on a perturbed movement : �Had a subject hold a weight with his hand so that the elbow was at 90 0; maintains position on computer monitor-dot on oscilloscope that matched the elbow angle. �Unexpectedly a weight was applied to the limb. �What feedback did “s” receive?

Faster Closed-Loop Control Dewhurst, 1967

Patella Reflex (M 1 and M 2)

Assorted reflexes - Closed-loop Control

But can closed loop control explain how all movements are controlled? �Slater-Hammel (1960) –S instructed to lift finger off of key when clock reaches 800 ms –Occasionally clock stop early, and S is told to inhibit the response –How much time does S need to inhibit response? 800

Open Loop Control Input Executive Effector Output • Used for rapid, brief, & forceful movements • Cannot process error of movements due to limited time • Used when environment is predictable & stable • Executive initiates but does NOT control movement – Which muscles to contract – What order to contract – When to contract – Duration of contraction

Practice of Motor Programs as Open Loops • New Skills – More stable – More precise – Longer operating motor programs • Motor Programs – More elaborate – Capable of controlling longer strings of behavior – Modify reflex activities that support overall behavior

Control Options: 1. Slower responses or of long duration can operate under open-loop, but can also operate under feedback control. 2. Very fast or brief then open-loop tends to dominate

Conceptual Model: Open-Closedloop Model with M 1 and M 2 Final Common Path: = Final Response is a result of: 1. Original set of movement commands 2. M 1 Response 3. M 2 Response

The Problems: Storage and Novelty? • Conceptualizing the human body as an aggregate of just hinge joints like the elbow would result in about 100 mechanical degrees of freedom, freedom each characterized by two states, states position and velocity, to yield a state space of, minimally, 200 dimensions! dimensions • Add to this the regulation of the approximately 792 muscles in the human body, body and the number of degrees of freedom become seemingly inordinate!

Motor Control is a problem of organization, but at what level? • One way to look at organization is as information processing theorists do. Control comes from an “executive. ”

An alternative view that is becoming more mainstream is that , motor control can be considered as a problem in self-organization. • There are no external instructions. The parts cooperate through some kind of mutual understanding in achieving a common goal.