Open and closed loop control Flashcards
What does the brain care about?
No single answer for this question.
Brain must think about safety, force, direction, functional goal, timing, precision, energy conservation, etc.
We must keep in mind changes in control of movement that occur from birth to adulthood
What are 2 control processes of motor control?
open loop control
closed loop control
What is a closed circuit?
Using feedback about the movement that is being performed to help control or adjust that action
What is an open circuit?
Movement is too quick to adjust using vision, proprioception, or other sensation so the cycle of action and evaluation is open. We get feedback after the movement is completed
How do you control movements that happen very quickly?
have preprogrammed, stereotypical responses
What movements are under open loop control?
Serve in tennis, gold swing, regaining balance after slipping on ice, getting up from sitting to answer doorbell, grasping vase as it starts to fall of the shelf
What is an easy way to think of open loop control
Furnace with no thermostat just on off switch. You want to keep warm but you have no control other than to turn on and off furnace. You can use feedback but action itself is highly stereotyped and not responsive to changing climate in house
What are key features of open loop control?
Movements occur so rapidly (150 ms or less) that they can’t use sensory feedback to alter movement.
Movement is programmed
What is the average reaction time for simple tasks?
150 ms
What is CPG?
central pattern generator
Spinal cord can produce rhythmical movements of limbs, even if not connected to brain and receiving no feedback from periphery.
Flexor and extensor muscle groups are alternately activated when isolated SC is stimulated.
What are important concepts about CPG from the many experiments (5)?
CPGs appear to be prewired in the spinal cord.
They can be turned on in various ways and they continue until they are stopped by some other input.
Patterns can be modified.
Basic reflexes are still active and can influence output of CPG
Reflexes are not stereotyped
What is the reflex reversal phenomenon?
Sensory input to top of foot can cause limb flexion during swing but same stimulus has no response or slight extension if limb is in stance phase.
What are areas of interest in regards to CPG and PT?
Greatest gains for those with incomplete spinal cord injury.
Training foot placement and weight bearing, taking advantage of rhythmicity of limb movement at spinal cord level has promise in regaining locomotion.
Much research still needs to be done.
Lack of postural stability and inability to initiate gait continue to interfere with functional gait.
What is a motor program?
Restructured set of central commands capable of carrying out movement.
What is evidence that skilled movement can occur without sensory feedback?
Feedback is too slow (movements can be performed faster than feedback can be processed)
Time to react to stimulus is longer for complex movements compared to simple.
Individuals who can’t receive sensory info can still perform some skilled movements.
T/F: in open loop systems it means that sensory info is completely disregarded?
False: sensory info must be taken into account
How is sensory info integrated into motor programs?
Prior to movement: need to know initial position of body to complete movement
During movement: errors are monitored during a movement so it can be used to modify future movements
After movement: feedback from outcome may be used for subsequent movements (think of baseball hitter making changes to swing after a mistake)
What are two types of errors
Error in program selection: from misperception of the environment or an error in selection of goal
Error in program execution: from unexpected difference or alteration in environment
What is an analogy for closed loop control systems?
Furnace with a thermostat
Uses feedback to monitor air until it reaches goal temp
What are key features of closed loop control?
Movements are slow enough to allow feedback to be processed (120-250 ms).
Movement in closed loop are much longer or continuous.
Examples: driving, painting, eating
What is hierarchical levels of control?
adapts open loop control to allow for known influence of sensory feedback.
Output of program is dictated only for span of one reaction time. After that sensory info can be used to select a different motor program.
Corrections can also be made during execution at times faster than reaction time.
What are two concerns with concept of motor program?
How does our brain store all of these programs?
How do we produce movements that we have never done before?
What did the concerns for motor programming lead to?
GMP- generalized motor program
GMP would have certain invariant features- features are fixed and identify actions as coming from that motor program
GMP can be parameterized- certain features of template can be adjusted
What are invariant features of GMP?
Order of events
Relative timing of components of the movement
Relative force of components
What are parameters of GMP?
Duration of movement
Overall force required
Selection of muscles to complete the movement
What are sources of sensory info from the environment?
Interoceptors: ie hunger, little relation to movement
Exteroceptors: info about movement of objects in environment
What are the types of exteroceptors?
Vision: most important, rapid system, provide feedback that alters movement in as little as 100 ms
Auditory:
Smell: movement in environment
Proprioceptors: info about our own movement
