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1

Multi- Level Approach

Two most important bodies of knowledge for motor behavior are Neurophysiology and Psychology

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Motor Behavior (3)

Motor control
Motor learning
Motor development

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Motor Control

Snapshot
What your body is capable of doing right now
When you're standing how your body is capable to do that exact muscle contraction

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Motor Learning

Effects of practice
How the control of the movements change with practice

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Motor Development

Long periods of time
How movement skills change over long periods of time (toddler v. elderly)

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Intro to Motor Control

In order to understand the nature of motor control, it is necessary to discover what is actually being controlled and how the various processes of governing that control are organized

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What is Motor Control?

Motor control is the study of postures and movements and the mechanisms which underlie them

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Types of Motor Control

Open-loop control
Closed-loop control

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Open-Loop Control

Does not require sensory feedback to be available and/or used to control movements

Want to see how far the golf ball goes after you hit it
Basketball free-throw
Find out the score after you are done (time, placement, etc)

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Closed-loop Control

Feedback is involved in the planning and execution of movements

As you are producing the movement, you are receiving feedback
How you swing towards the golf ball

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Input Process: Open-Loop

Input > Movement control center (cortex) > effectors (muscles, joints)

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Input Process: Closed-Loop

Input > movement control center (cortex) > Movement commands > Effectors (muscles, joints) > movement center (repeat)

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Open-loop system of control

fast movements
well learned movements
NO feedback used DURING execution

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Closed-loop system of control

Slow/precise movements
Feedback is used during execution = afferent (sensory) information is used to control movement

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Motor control theories

Reflex theories
Hierarchical Theories
Dynamical Approaches
Ecological Approaches

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Theory

A set of ideas used to explain a specific phenomenon

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Hypothesis

A testable statement about observed events

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Reflex Theories

Sherrington
Skinner

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Reflex Theories: Basic Assumptions

The reflex is the fundamental unit of motor control
A stimulus triggers the response (movement)
- There is no involvement of higher cortical centers, only the spinal cord (reflex)
Complex movements occur as a result of a chain of reflexes (reflex chaining models)
The individual is a passive recipient of externally produced sensory input

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Reflex Theories: Strengths and Weaknesses

Strength: simple explanation
Weak: TOO simple to account for a person's ability to perform a wide variety of goal-directed actions (ex. anticipation)
Unable to explain how movements performed in the absence of sensory information (stimulus from environment)

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Hierarchical Theories: Basic Assumptions

All aspects of movement planning and execution are the sole responsibility of one or more cortical centers
-"top down" view of motor control
Sensory feedback is not essential for the execution of movements
Memory representations (Motor Programs): pre-structured sets of motor commands developed at the highest cortical level and sent to lower spinal centers

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Support for Hierarchical Models

Deafferentation Studies
Limb Block Studies
Response Complexity Studies

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Deafferentation Studies

Hierarchical Model
Show that movements can be performed in absence of feedback

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Limb Blocking Studies

Hierarchical Model
Show that activation pattern for agonist and antagonist muscles are planned in advanced for short duration movements

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Response Complexity Studies

Hierarchical Model
Reaction time increases as complexity of response increases (more time for planning movements)

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Strength of Hierarchical Models

1. Accounts for the ability to perform movements in the absence of feedback
2. The GMP allows the performance of a variety of movements by manipulating parameters
3. New movements are possible

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Dynamical/Ecological Approach

These theories represent a big "break" from the previous theories
Both rely heavily on concepts "borrowed" from physics, mathematics, and/or ecological psychology

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Dynamical Systems

Self-Organization
From chaos into order

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Dynamical Systems: Self Organization

MOVEMENT: Individual > Environment > Task

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Dynamical Approach: Basic Assumptions

Self Organization: patterns emerge as a result of the interaction among the components of a system (individual, task, and environment)
Attractor states: preferred patterns of coordination are adopted to enhance stability

New movement patterns emerge as a result of scalar changes in one or more control parameters (control parameter: variable that can lead to change in behavior)

The parameters that exhibit the nonlinear changes are identified using order parameters (order parameter: variables that are used to quantify the effect of a change in behavior)

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Ecological Approach: Basic Assumption

Focus on the perceptual interface between the individual and the environment

Affordances: lawful properties of the environment that permit certain action
Optical properties specific to an affordance can directly trigger action
Continuous interaction occurring between the processes of perceiving and acting (perception/action coupling)

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Does one theoretical approach better explain how movements are controlled?

Hierarchical (GMP) theories are better in explaining a performer's actions in rule-based sport settings.

Dynamical and ecological approaches better explain how well-learned skills (walking, standing...) are performed.

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Four characteristics of Human Actions

Flexibility
Uniqueness
Consistency
Modifiability

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Flexibility

the ability to recruit different muscles and joints to achieve the same aciton

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Uniqueness

no two movements are ever performed in exactly the same way

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Consistency

temporal/spatial characteristics of a movement remain relatively stables from one performance to the next.

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Modifiability

the ability to alter a movement pattern, even as it is being executed.

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The Degrees of Freedom Problem (Bernstein)

How do individuals successfully organize a complex system of bones, joints, musculature that moves in a variety of different ways.

Degree-of-Freedom: number of ways in which any given unit of control is capable of moving.
-unit of control may be a joint, a muscle, or even a motor unit

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Two ways to solve the DOF problem

Muscle response synergy
Mechanical properties of the limbs

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Muscle Response Synergy

A group of muscles constrained to act as a single behavioral unit
Some are innate: reaching, grasping, walking
Some are learned: any sport skill

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Mechanical properties of the limbs

Using characters of muscles/joints and gravity can help movement without the need of muscles activation