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NROC64H3 Lecture Notes - Deeper And Deeper, Semicircular Canals, Motor Control

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Chapter 9 Motor Systems
Why Studying Motor System is Difficult
- To stimulate it have to know what is appropriate pattern of stimulation to apply in order to get
a response
o 2nd - Sensory system is largely straightforward way from level to level but a
characteristic of motor control is that every action necessarily results in sensory
feedback (from muscle, join and vision and other special senses)
- Better approach apply real stimuli to the senses & trace the resultant pattern as they
penetrate deeper & deeper through levels of NS & emerge at motor end as movements
o Not possible w complex system ( e.g. movement of hand) but w number of levels is
much smaller ( i.e. primate brain of insects or in simpler sub-system of mammalian brain
like eye movements ) this is feasible
- Generally have learned lot by studying complete system w output compared with purely
sensory system
Motor control & Feedback
- Feedback using info about result to improve performance is important in control of
No Feedback: Ballistic control
- Many circumstances where motor system is forced to act blindly b/c for one reason or another
they are deprived of normal sensory feedback e.g. tossing orange peel into a waste bin
once it leaves hand & no sensory feedback helps w/ trajectory
o So have to work it before hand (e.g. the muscular contraction)
o classic e.g. is nest-building behaviour of brown rat (by Lorenz) once it decided to
build , it goes through stereotypic movements even if there is no material left to finish it
- Motor type of this act called ballistic (thrown) can be drawn in diagram
o Desired results (or goal) - e.g. orange peel into basket this is translated by controller
into appropriate pattern of commands
o These commands then produce the actual result through their effect on plant (i.e.
o How well actual result compare with desired results depends on how good the
controller is more it knows about how plant will behave in response to any particular
command , the better it will perform - it needs a library of motor programs

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E.g. ballistic missiles
- But the this system has flaw it vulnerable to noise noise is any kind of unpredictable
disturbance that makes actual result differ from what the controller expects (e.g. wind)
- World is unpredictable particular pattern of activation in motor nerves will produce diff
movements of limbs depending on host of internal factors (e.g. temperature, fatigue etc.)
- More important effect of load when using limbs , given degree of muscle activity will
generate quite different movements depending what you have (e.g. feather vs. rock)
o Most of lower levels that control limbs are devoted to solving noise introduced by
unpredictable load
Parametric adjustment: Feed-forward & Feedback
- One way of dealing w/ noise to have some kind of sensor that monitors the noise before it
affects system & to use this info to adjust parameters of controller to allow for it
o Is called parametric feed-forward controller parameters to anticipate the effects of
noise e.g. adjusting for wind before launching the missile
- Much of info is used by the brain in this way especially for allowing different load e.g. neural
circuits controlling muscle length use info from force-detectors in the skin & tendons that make
appropriate adjustments of motor commands
- This is system also has flaw there are infinite of things can cause perturbations & brain cannot
have plan for every one of them in advance so approach is to have system that learn from its
own mistakes parametric feedback
- Need comparator compares actual result w desired results by subtracting one from another
if generates error singal that is used to modify controllers parameter
o Advantage to feedback is its flexibility rather than having stored program ready in
advance for anything can have rather simple all-purpose programs that maybe
redefine via trial & error for needed task that are actually encountered
- such that great deal of learning motor skills can be thoughts as parametric feedback in which
errors is used to modify our stored motor programs - e.g. playing darts or cricket
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