variation and variability
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Variation and Variability. Variation - a broad repertoire of behaviors for a specific motor function Variability the capacity to select from the repertoire the best motor strategy for the context. Variability and Error. Old view was that variability = error - PowerPoint PPT PresentationTRANSCRIPT
Variation and Variability
• Variation - a broad repertoire of behaviors for a specific motor function
• Variability the capacity to select from the
repertoire the best motor strategy for the context
Variability and Error
• Old view was that variability = error• Hypothesis: one correct form of movement• “mature form”
Contemporary Perspective
• Variability is good!
Good Variability
• Variability that preserves function• several ways to get out of bed– all support the goal task of independence
Good Variability
• Ability to vary force and speed within a strategy to meet environmental conditions
Good Variability
• Less noticeable– variation across synergistic muscles that enables
one to adjust forces across components of a movement pattern to preserve the outcome
– eg. consistent foul shot despite small variations in muscle forces
Bad Variability
• Inability to constrain force or speed – leads to misses, falls, collisions
• Ataxia
Neutral Variability
• Some variations don’t matter • If functional goal is preserved
Contemporary Approaches to Study Variability
• When is Variability Good or Bad?
Most Variability is Good
• person specific (anthropometric characteristics, age)
• task-specific (individual’s goal or motivation)• context –specific (situation specific
performances)
Discerning Good vs Bad
• separating variability – seen in outcome – seen during execution
Outcome Variability
• As long as goal task is accomplished – no harm done in outcome variability
Execution Variability
• variability during execution, – if goal accomplished… – elements that vary are considered part of a
“synergy”
Synergy
• parts working together for the common good
Manifold Concept
• The combination of all configurations seen during execution that produce the solution to the task
• concept borrowed from contemporary physics
Manifold Concept Research
• Examine variability in repeated trials of 1 task– gripping a cup – how do the individual digits
contribute to successful performance
Application to Clinical Practice
• Examine children with DS on a treadmill, • show variability of action across LE joints • yet stable outcome (no falls, etc)• suggests capacity to vary is functional
Another way to analyze variability
• Analyze the structure of performance across several trials of a task– a time series analysis – examine trajectories of a movement and see if the
patterns strictly overlap
Examining Movement Trajectories
Knee Joint Angle
Hip Joint Angle
180
45
-1085
Too Little Variation
Knee Joint Angle
Hip Joint Angle
180
45
-1085
Too much variation
Knee Joint Angle
Hip Joint Angle
180
45
-1085
Developmental Change in Variability
• Increased Consistency• Increased Flexibility
Increased consistency
• Practice leads to movements that are – smoother– more efficient– more accurate
• more consistent task outcomes
How to Structure Practice?
• Variable practice is best!
Variability between individuals
• Characteristics of the individual– anthropometrics– different experiences– temperament– motivation
Developmental Change in Variability
• Increased Flexibility in performance– practice in different contexts– scale control variables up and down– build capacity to vary