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Chapter 2 – The Measurement of Motor Performance 01/21/2015 

Why Study the Measurement of Motor Performance? 

The measurement of performance is essential for: o

Performance assessment/evaluation

o

Motor control and learning research

o

Tracking progress (deterioration)

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How to Assess Performance 

1. Determine which aspects of performance should be measured to make (a) valid performance assessment(s)

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2. Determine how to measure the identified aspects of performance

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Tracking Process 

Patient (or client)



What will determine his/her progress during rehabilitation/deterioration

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Measure types: o

Performance outcome measures (motor skill RESULT)

o

Performance production measures (specific aspects of motor skill during performance)

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The 2 General Categories of Skill Performance Measures: 

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Performance outcome o

Measures of the result of performing a skill

o

Action related measures

Performance production o

Measures related to specific performance characteristics that produced the performance outcome

o 

Movement related measures

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Reaction Time 

Interval between the onset of a stimulus and the onset of the action

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Reaction time and relative difficulty

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Reaction time and anticipation

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Movement time begins when the RT ends

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Response time is RT+MT (reaction time + movement time)

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Figure on slide 7: Response time: go signal, (RT), movement begins, (MT), movement ends

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Types of RT Situations o

1. Simple RT (100 meters dash: gun shot then run. 1 response after the go stimulus)

o

2. Choice RT (Traffic lights: there are 2 go signals)

o

3. Discrimination RT (Running around lakes: do nothing if you see tree on the side but must jump over a tree in the road: 3 different stimuli. But should only react if you see one specific color)

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RT Interval components o

Premotor time (time that muscles are still at rest) 

2 patients have slow reaction time but one has dementia so can’t process stimuli fast so has slower premotor time

o

Motor time (there is reaction of muscles but can’t measure any movement yet)

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Basic Considerations for measures 

Objectivity o



Two or more observers arrive at the same measurements

Reliability o

Measurement is repeatable under similar conditions

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Validity o

Does the method of measurement measure what the researcher intends to measure

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Error Measures 

Performance accuracy



Causes of performance problems



o

Consistency

o

Bias

One dimension movement goals o

Absolute error: Absolute difference between performance on each trial and goal (what is magnitude of the error. Do they have the same number of total dots)

o

Constant error: Signed difference between performance on each trial and goal (is there a bias. If more dots are on one side then they are more bias towards that side. If they are evenly distributed on both sides then there’s no bias)

o

Variable error: Standard deviation of the person’s mean score for the series of trials (if all the dots are on one side then have smaller SD than if the dots were evenly distributed on both sides)

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Two dimension movement goals. o

Radial error (similar to AE=absolute error) (how far away it is from the target (magnitude))

o

Qualitative assessment of bias and consistency  Look at scatter (something has larger bias and more consistency if the darts are not scattered but all in the same spot)

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Continuous skills o

Root-mean-squared-error (RMSE) 

General index for performance accuracy



Comparison between the profile of the performance and criterion (if drinking then can’t walk in straight line)



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Kinematic Measures 

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Motion without regard to force or mass o

Displacement (position)

o

Velocity (different from speed because has direction)

o

Acceleration

o

Jerk (how smooth movements are)

o

Linear motion

o

Angular motion- rotate around a joint

Measures that reveal the forces that (could) cause motion o

o

External and internal sources of force 

Internal- Muscles contracting that make us move



External- ex. Someone pushing you, wind, friction, gravity, etc.

Newton’s laws of motion 

1. Force is necessary to start, change, stop motion

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2. Force influences the rate of change in the momentum of an object

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3. Force is involved in the action and reaction that occurs between two objects 

ex. Someone pushes you and you fall

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Electrical Activity Measures 

Electromyography (EMG) (measures motor behavior) o

Reaction time- pre-motor

o

Motion time is when there is a beginning of movement before contraction time



Electroencephalography (EEG) o

Ex. Can measure different waves such as beta waves—means you are active



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Positron emission topography (PET) o

Look at metabolic activity/blood flow is measured

o

What structures are involved when performing action? The neon

Functional Magnetic resonance imaging (fMRI) o

No needles involved

o

More popular, increased resolution with improvement in computer technology

o

Look at hydrogen atoms

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Measuring Coordination 



Angle-angle diagrams o

Cross-correlation technique

o

Normalized root mean-squared error technique

Relative phase (ex. phase relations for right and left hands or feet. Rhythmic tests) o

Popular in dynamic systems theories

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SHORT REFRESHER OF STATISTICAL MEASURES:

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The Mean 

Arithmetic average of scores in a distribution

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The scores need to be at least interval-scale

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The mean is the central point in a data-set with a normal distribution

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Standard Deviation 

Square root of the variance

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Variance is the mean of the squared deviations about the mean

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Between the Mean–SD and Mean+SD lays about 68.2% of the distribution

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Between the Mean–2xSD and Mean+2xSD lays about 95.4% of the distribution

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The Median 

The median is the point on a scale of measurement below which 50% of the scores fall (also called the 50th percentile).

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To find the median: o

Rank order the measures from low to high

o

Count the number of measures and add one.

o

Divide by 2 => the measure at the (N+1)/2-place is the median.

o

When N is even. The median it is the value halfway the two measures in the middle of the series.

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(N+1)/2

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Correlation

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01/21/2015 

Marching leader needs to pick a drummer with a drum beat with exact

time intervals for 10 minutes. What measure should be used to figure out who is best?  VE—variable error  Because you want exact time intervals (which are unknown)  Want consistency  Time is a one dimensional measure      

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Average radial  2D, shooting at target Average CE  Constant error Averaged AE  Absolute error  Magnitude of error VE  Variable error

CLICKERS

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(top is A, bottom

is B) 

Average absolute error o is about the same in task B

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Average constant Error o is worse in task B

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Variable error o is better in in task B

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Average absolute error—number of dots  is about the same in task C Average constant error—deviation from target  is about the same in task C  Variable Error is--- consistency  About the same in task C  ...