Chapter 2Chapter 2The Measurement ofThe Measurement ofMotor PerformanceMotor Performance

Concept: The measurement of motor performance is critical to understanding motor learning

Why Study the Measurement of Why Study the Measurement of Motor Performance?Motor Performance?

Performance measurement essential for:Performance measurement essential for:

Performance assessment / evaluation Performance assessment / evaluation

Motor learning and control researchMotor learning and control research

Reaction TimeReaction Time

Common measure indicating how long it Common measure indicating how long it takes a person to prepare and initiate a takes a person to prepare and initiate a movementmovement

A stimulus or go signal is the indication to A stimulus or go signal is the indication to actact

Some type of warning signal also givenSome type of warning signal also given

What are some motor skill performance examples in which RT is important for achieving the goal of the skill?

Reaction TimeReaction Time

Warningsignal

“Go”signal

Initiation of the response

Termination of the response

Foreperiod

Reaction Time (RT) Movement Time (MT)

Response Time

Reaction Time, cont’dReaction Time, cont’dTypes of RT situationsTypes of RT situations– Simple RT: One signal - One responseSimple RT: One signal - One response– Choice RT: More than one signal - Each signal has a specific Choice RT: More than one signal - Each signal has a specific

responseresponse– Discrimination RT: More than one signal - only one responseDiscrimination RT: More than one signal - only one response

Stimulus lights

Response key(s) Index

finger Index Middle Ring Index

finger

Simple RT Choice RT Discrimination RT

RT Interval ComponentsRT Interval Components

EMG enables us to fractionate RT to EMG enables us to fractionate RT to obtain more specific information about obtain more specific information about movement preparationmovement preparationFractionated RT has two componentsFractionated RT has two components– Pre-motor time:Pre-motor time: Quiet interval of time between Quiet interval of time between

the onset of stimulus and beginning of activitythe onset of stimulus and beginning of activity– Motor time:Motor time: Interval of time from the initial Interval of time from the initial

increase in muscle activity until the actual limb increase in muscle activity until the actual limb movementmovement

Fractionated RTFractionated RT

Pre-motor Time

Go Signal Initiation of muscle activity

Motor TimeObservable Movement

EMG Recording

What do you think occurs in each RT componentWhat do you think occurs in each RT component??

Reaction Time

Use of RT in ResearchUse of RT in Research

RT has a long history as an “index” to RT has a long history as an “index” to assess specific aspects of human assess specific aspects of human performance.performance.RT is used as a means toRT is used as a means to – Infer what a performer does to prepare to Infer what a performer does to prepare to

perform an action perform an action – Identify the environmental context information Identify the environmental context information

a person uses to prepare a person uses to prepare to perform an to perform an actionaction– Assess the capabilities of a person to Assess the capabilities of a person to

anticipate a required action and determine anticipate a required action and determine when to initiate itwhen to initiate it

Error MeasuresError Measures

Error measures allow us to evaluate performance for skills that have spatial or

temporal accuracy action goals

What are some examples of skills for which spatial or temporal accuracy determines performance success?

Assessing Error for Skills with One-Assessing Error for Skills with One-Dimension Accuracy GoalsDimension Accuracy Goals

Three error measures Three error measures 1. Absolute error (AE):1. Absolute error (AE): Absolute value of Absolute value of

difference between the actual performance difference between the actual performance on each trial and the criterion for each trial on each trial and the criterion for each trial – AE =AE = |(performance – criterion)| / no. of trials|(performance – criterion)| / no. of trials

– Provides a general index of performance Provides a general index of performance accuracyaccuracy

+16, +4, -10, +11, -9 = 50/5 = +16, +4, -10, +11, -9 = 50/5 = 1010

Assessing Error for One-Dimension Assessing Error for One-Dimension Accuracy Goals, cont’dAccuracy Goals, cont’d2. Constant error:2. Constant error: Algebraic value of difference Algebraic value of difference

between the actual performance on each trial between the actual performance on each trial and the criterion for each trial and the criterion for each trial – CE =CE = (performance – criterion) / no. of trials(performance – criterion) / no. of trials– Provides an index of a tendency for the Provides an index of a tendency for the

performance error to be directionally biasedperformance error to be directionally biased

+16, +4, -10, +11, -9 = 12/5 = +16, +4, -10, +11, -9 = 12/5 = 2.42.4

3. Variable error:3. Variable error: The standard deviation of the The standard deviation of the CE scores; an index of performance CE scores; an index of performance consistency (i.e. consistency (i.e. variabilityvariability))

Assessing Error for One-Dimension Assessing Error for One-Dimension Accuracy Goals, cont’dAccuracy Goals, cont’d

See “A Closer Look” on p. 31 for an example See “A Closer Look” on p. 31 for an example of calculating AE, CE, and VE to of calculating AE, CE, and VE to determine the accuracy characteristics of determine the accuracy characteristics of stride lengths for walkingstride lengths for walking

Assessing Error for Two-Dimension Assessing Error for Two-Dimension Accuracy GoalsAccuracy Goals

When the outcome of When the outcome of performing a skill performing a skill requires accuracy in requires accuracy in the vertical and the vertical and horizontal directionshorizontal directions– e.g. Golf putte.g. Golf putt

Radial error =Radial error = General General accuracy measure for accuracy measure for two-dimensionstwo-dimensions– See Figure 2.3See Figure 2.3

y

x

5 cm h

X2 + Y2 = h2

RE = √ h2

X-axis distance = 102 = 100

Y-axis distance = 52 = 25

Sum = 125

RE = √125 = 11.2 cm

Assessing Error for Two-Dimension Assessing Error for Two-Dimension Accuracy Goals, cont’dAccuracy Goals, cont’d

Performance bias and Performance bias and consistency are difficult consistency are difficult to quantitatively assess, to quantitatively assess, although can do although can do qualitative assessment qualitative assessment easily easily

Assessing Errors for Continuous Assessing Errors for Continuous SkillsSkills

Many continuous skills Many continuous skills require spatial require spatial accuracy over a accuracy over a period of timeperiod of time– e.ge.g. Driving a car on a . Driving a car on a

highwayhighway

Root-Mean Squared Root-Mean Squared Error (RMSE) Error (RMSE) Common accuracy Common accuracy measure for measure for continuous skillscontinuous skills

Kinematic MeasuresKinematic Measures

Kinematics: description of motion Kinematics: description of motion without regard to force or masswithout regard to force or massIncludes the following measures Includes the following measures [[see Fig. 2.6see Fig. 2.6]:]:– Displacement Displacement =Spatial position of a =Spatial position of a

limb or joint over a period of timelimb or joint over a period of time– Velocity Velocity = = Rate of change in an Rate of change in an

object position with respect to time object position with respect to time ((i.ei.e. speed). speed)

= Displacement / Time= Displacement / Time

– AccelerationAcceleration = Change in velocity = Change in velocity during movementduring movement

= Velocity / Time= Velocity / Time

KineticsKinetics

KineticsKinetics:: Force as a cause of motion Force as a cause of motion

Human movements involve both external Human movements involve both external and internal sources of forceand internal sources of force

Importance of force as a movement Importance of force as a movement measuremeasure: All three Newton’s laws of : All three Newton’s laws of motion refer to forcemotion refer to force

EMG MeasuresEMG MeasuresMovement involves electrical Movement involves electrical activity in the muscles activity in the muscles Electrodes detect electrical Electrodes detect electrical activityactivityElectromyography (EMG)Electromyography (EMG) = = Recording of muscle electrical Recording of muscle electrical activityactivity– Common use is to determine Common use is to determine

when a muscle begins and ends when a muscle begins and ends activation activation [[see Figure 2.9see Figure 2.9]]

– Also – Recall our earlier Also – Recall our earlier discussion about use of EMG for discussion about use of EMG for fractionated RT as an index of fractionated RT as an index of movement preparationmovement preparation

Brain Activity MeasuresBrain Activity Measures

Researchers have adopted brain activity Researchers have adopted brain activity measures commonly used in hospitals and measures commonly used in hospitals and clinics for diagnostic purposesclinics for diagnostic purposesThree measures commonly reported in Three measures commonly reported in motor learning and control researchmotor learning and control research– EEGEEG– PETPET– fMRIfMRI

Brain Activity Measures, Brain Activity Measures, contcont’d’d

Electroencephalography (EEG):Electroencephalography (EEG): Measures Measures electrical activity in brainelectrical activity in brain– Active brain regions produce electrical activityActive brain regions produce electrical activity

Positron Emission Positron Emission TopographyTopography (PET):(PET): Neuroimaging (Neuroimaging (i.e., brain i.e., brain scanningscanning) technique that ) technique that measures blood flow in measures blood flow in the brain the brain – Active brain regions involve Active brain regions involve

increased amounts of increased amounts of blood flowblood flow

Brain Activity Measures, Brain Activity Measures, contcont’d’d

Functional Magnetic Functional Magnetic Resonance Imaging Resonance Imaging (fMRI):(fMRI): Neuroimaging Neuroimaging ((i.e., brain scanningi.e., brain scanning) ) technique that measures technique that measures blood flow changes in blood flow changes in the brain by detecting the brain by detecting blood oxygenation blood oxygenation characteristicscharacteristics

Measuring CoordinationMeasuring Coordination

Assessment of the relationship of Assessment of the relationship of movement of limb-segments and joints movement of limb-segments and joints

Quantitative measurement of angle-angle Quantitative measurement of angle-angle diagramsdiagrams– Cross-correlation techniqueCross-correlation technique– NoRMSNoRMS

Relative phaseRelative phase– Relative phase Relative phase [see Figure 2.10][see Figure 2.10]

Angle-Angle DiagramAngle-Angle Diagram

Measuring CoordinationMeasuring Coordination

Assessment of the relationship of Assessment of the relationship of movement of limb-segments and joints movement of limb-segments and joints

Quantitative measurement of angle-angle Quantitative measurement of angle-angle diagramsdiagrams– Cross-correlation techniqueCross-correlation technique– NoRMSNoRMS

Relative phaseRelative phase– Relative phase Relative phase [see Figure 2.10][see Figure 2.10]

Normalized Root Mean-squared Normalized Root Mean-squared ErrorError

Relative PhaseRelative Phase

Index of the coordination between two limb Index of the coordination between two limb segments or limbs during a cyclic segments or limbs during a cyclic movement.movement.

Relative phase ranges from 0 to 180 Relative phase ranges from 0 to 180 degreesdegrees– Relative phase near 0 indicates an in-phase Relative phase near 0 indicates an in-phase

relationship.relationship.– Relative phase near 180 degrees indicates an Relative phase near 180 degrees indicates an

out-of –phase relationship.out-of –phase relationship.