Central Contributions To Motor Control (1+2) Flashcards
What two basic things do we do when making an action?
- plan a goal or intention
- guide the action to achieve the goal
What is closed loop control?
The use of sensory information during action allows for movement guidance or correction - this type of movement is called closed loop control
How is an action goal achieved?
Achieved by modifying behaviour with use of incoming sensory information
The output cycle refers to what??
The sensory inputs (vision, proprioception, auditory etc.)
What did Woodworth (1899) consider?
That an action plan would first execute, and once underway, would be guided by the senses to achieve the goal.
Also considered that feedback for correction would be dependent on capacity and time.
What did Woodworth (1899) test and what did he find?
Tested the effects of making actions with and without visual guidance, and measured performance error.
The results showed that 200-400ms of vision reduced error, and 400-1000ms of vision showed stable performance
What did Keele and Posner (1968) find to back up the data of Woodworth (1899)?
Showed there was no difference between vision conditions with 200ms, hence more than 250ms of vision was required to increase the chances of hitting the target
What are some problems with closed-loop control?
We can execute some movements without sensory feedback
The sensory feedback loop may be too long to control fast movements
What is the sequence of events in the sensory feedback loop?
Goal - reference mechanism - executive/effectors - environment
How did Schmidt (1988) define a motor program?
“A motor program as a prestructured set of central commands capable of carrying out movement essentially open-loop”
The motor programme is an open-loop process, meaning no need for sensory feedback
Describe the sequence of events in a motor program (open loop)
Input Instructions Output
-> executive -> effector
What does reference refer to??
A feedforward or efferent copy mechanism , which is a copy of the motor programme
What is ‘efferent copy’ used for?
To compare the state of ongoing action through the senses with that originally intended.
In addition it appears to prepare the sensory feedback systems
What are the 2 main problems of the theoretical model of open and closed loop motor control??
The storage problem : questions whether there are set programs that we learn and execute for every type of response
The novelty problem : this questions how we adapt the set programs to make new responses
What is a generalised motor program?
An abstract memory structure that governs a class of movement pocessing a common movement pattern
What does the GMP consist of?
Certain characteristics of an action that are invariant, such as the order of events, relative time and relative force.
For a particular class of action, a motor program is stored in memory, a unique pattern of activity will result if the program is executed.
At the time a specific action must be produced, the abstract program must be parametrised to accommodate the demands of the specific situation
What are the main invariants of a GMP?
Relative duration, relative force and order of events
What are the two main parameters are?
Overall duration and overall force
What did Schmidt propose that a motor response consists of?
Fixed and modifiable patterns.
Similarly there is an overall force parameter that controls the relative action forces contained in the movement sequence. Increasing the force of the muscles over the same time makes bigger movements
What are the 2 types of movement error ?
- Programme selection (incorrect action selection)
- Programme execution (incorrect execution)
What are some examples of errors in programme selection?
Typically involve catching a ball instead of heading it, moving right instead of left.
To correct selection errors, a completely new plan must be generated, therefore these errors cannot be corrected online
Timing of movement correction depends upon the nature of the error. How do selection and execution errors differ ?
Selection errors require a new plan and so can take as long as 120-200ms to correct
Execution errors can modify the ongoing plan with 30-50ms of detecting the error
What is the sequence of events in the open-loop control system?
Movement commands
Movement control centre -> Movement effectors
What is the sequence of events in the closed loop control system?
Movement commands
Movement control centre ->. Movement effectors
Referring to diagram of the motor programme, what does plan, feedforward correction and guidance include?
Plan includes executive, stimulus identification and response selection
FF correction includes reference
Guidance involves muscles, movement, changes in environment and feedback
What is an internal model (Kawato, 1999)
Internal models are neural mechanisms that can mimic the input/output characteristics , or their inverses, of the motor apparatus.
What are the two types of internal models?
Internal forward models
Internal inverse models
What do internal forward models do?
Capture the forward or causal relationship between the inputs to the system and the outputs (Kawato et al,1997)
‘Forward internal models can predict sensory consequences from efference copies of issued motor commands’ (Kawato, 1999)
Provides predicted sensory feedback / states of movements
Motor -> sensory information
Forward models act as the predictors (Miall et at, 1993)
What’s the basic premise of inverse dynamic models?
Inverts the forward models
A motor command that will cause a desired change in state
Sensory to motor information
Inverse models act as the controllers (Miall et all, 1993) amd as the motor command
What did Kawato (1999) state about inverse internal models?
” inverse internal models can calculate necessary feedforward motor commands from desired trajectory information “
Describe the sequence of events in an inverse dynamic model?
Desired trajectory Feedforward motor command Realised trajectory
->. Inverse model. ->. Controlled object. ->.
The cerebellar cortex is highly regular and densely packed, what are the effects of cerebellar damage??
- coordination of movements
- some effects on posture/muscle tone
- no effect on muscle strength, sensory perception or higher order processes
How does the cerebellum affect motor coordination?
Corrects ongoing movements when they deviate from the intended course and modifies descending output and central motor programs
Cerebellum could be inverse model?
