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Sensorimotor feedback[ edit ] Response to stimuli[ edit ] The process of becoming aware of a sensory stimuli and using that information to influence an action occurs in stages, and reaction time of simple tasks can be used to reveal information about these stages.
Reaction time refers to the period of time between when the stimulus is presented, and the end of the response.
Movement time is the time it takes to complete the movement. Some of the first reaction time experiments were carried out by Franciscus Donderswho used the difference in response times to a simple reaction task and a choice reaction task to determine the length of time needed to process the stimuli and choose the correct response.
Further research has provided evidence that these stages do exist, but that the response selection period of any reaction time increases as the number of available choices grows, a relationship known as Hick's law.
There is a reference that specifies the desired value for the system, and the output of the system is fed back and compared to the reference for error detection and, if necessary corrected A closed loop system is self regulating by compensating for deviating from the reference.
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May Learn how and when to remove this template message Most movements that are carried out during day-to-day activity are formed using a continual process of accessing sensory information and using it to more accurately continue the motion.
This type of motor control is called feedback controlas it relies on sensory feedback to control movements. Feedback control is a situated form of motor control, relying on sensory information about performance and specific sensory input from the environment in which the movement is carried out.
This sensory input, while processed, does not necessarily cause conscious awareness of the action. Closed loop control  is a feedback based mechanism of motor control, where any act on the environment creates some sort of change that affects future performance through feedback. Closed loop motor control is best suited to continuously controlled actions, but does not work quickly enough for ballistic actions.
Ballistic actions are actions that continue to the end without thinking about it, even when they no longer are appropriate. Open loop control[ edit ] The classical definition from Jack. The input events for a system exert their influence, the system effects its transformation on the input and the system has an output A traffic light with fixed timing snarls traffic when the load is heavy and impedes the flow when the traffic is light.
The system has no compensatory capability. Open loop control is a feed forward form of motor control, and is used to control rapid, ballistic movements that end before any sensory information can be processed.
To best study this type of control, most research focuses on deafferentation studies, often involving cats or monkeys whose sensory nerves have been disconnected from their spinal cords. Monkeys who lost all sensory information from their arms resumed normal behavior after recovering from the deafferentation procedure.
Most skills were relearned, but fine motor control became very difficult.
The motor system is highly complex, composed of many interacting parts at many different organizational levels Peripheral neurons receive input from the central nervous system and innervate the muscles.
In turn, muscles generate forces which actuate joints. Getting the pieces to work together is a challenging problem for the motor system and how this problem is resolved is an active area of study in motor control research. Reflexes[ edit ] In some cases the coordination of motor components is hard-wired, consisting of fixed neuromuscular pathways that are called reflexes.
Reflexes are typically characterized as automatic and fixed motor responses, and they occur on a much faster time scale than what is possible for reactions that depend on perceptual processing. Some reflex loops are routed solely through the spinal cord without receiving input from the brain, and thus do not require attention or conscious control.
Others involve lower brain areas and can be influenced by prior instructions or intentions, but they remain independent of perceptual processing and online control. The simplest reflex is the monosynaptic reflex or short-loop reflex, such as the monosynaptic stretch response. In this example, Ia afferent neurons are activated by muscle spindles when they deform due to the stretching of the muscle.
In the spinal cord, these afferent neurons synapse directly onto alpha motor neurons that regulate the contraction of the same muscle. As the name and the description implies, monosynaptic reflexes depend on a single synaptic connection between an afferent sensory neuron and efferent motor neuron.
In general the actions of monosynaptic reflexes are fixed and cannot be controlled or influenced by intention or instruction. However, there is some evidence to suggest that the gain or magnitude of these reflexes can be adjusted by context and experience.
These loops may include cortical regions of the brain as well, and are thus slower than their monosynaptic counterparts due to the greater travel time.
However, actions controlled by polysynaptic reflex loops are still faster than actions which require perceptual processing. Synergies[ edit ] A motor synergy is a neural organization of a multi-element system that 1 organizes sharing of a task among a set of elemental variables; and 2 ensures co-variation among elemental variables with the purpose to stabilize performance variables.
Synergies are learned, rather than being hardwired like reflexes, and are organized in a task-dependent manner; a synergy is structured for a particular action and not determined generally for the components themselves.
Nikolai Bernstein famously demonstrated synergies at work in the hammering actions of professional blacksmiths.Internal Control Procedures The Copedia Internal Control Templates include our accounting, management, and operational internal controls, questionnaires, checklists, and evaluation tools.
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