The Measurement of

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Chapter 2

• The Measurement of
• Motor Performance
• Concept The measurement of motor performance is
  critical to understanding motor learning

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Why Study the Measurement of Motor Performance?

• Performance measurement essential for
• Performance assessment / evaluation
• Motor learning and control research

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Reaction Time

• Common measure indicating how long it takes a
  person to prepare and initiate a movement
• A stimulus or go signal is the indication to act
• Some 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?
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Reaction Time
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Reaction Time, contd

• Types of RT situations
• Simple RT One signal - One response
• Choice RT More than one signal - Each signal has
  a specific response
• Discrimination RT More than one signal - only
  one response

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RT Interval Components

• EMG enables us to fractionate RT to obtain more
  specific information about movement preparation
• Fractionated RT has two components
• Pre-motor time Quiet interval of time between
  the onset of stimulus and beginning of activity
• Motor time Interval of time from the initial
  increase in muscle activity until the actual limb
  movement

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Fractionated RT
EMG Recording
Pre-motor Time
Motor Time
Observable Movement
Go Signal
Initiation of muscle activity
Reaction Time
What do you think occurs in each RT component?
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Use of RT in Research

• RT has a long history as an index to assess
  specific aspects of human performance.
• RT is used as a means to
• Infer what a performer does to prepare to perform
  an action
• Identify the environmental context information a
  person uses to prepare to perform an action
• Assess the capabilities of a person to anticipate
  a required action and determine when to initiate
  it

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

• Three error measures
• 1. Absolute error (AE) Absolute value of
  difference between the actual performance on each
  trial and the criterion for each trial
• AE (performance criterion) / no. of trials
• Provides a general index of performance accuracy
• 16, 4, -10, 11, -9 50/5 10

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Assessing Error for One-Dimension Accuracy Goals,
contd

• 2. Constant error Algebraic value of difference
  between the actual performance on each trial and
  the criterion for each trial
• CE (performance criterion) / no. of trials
• Provides an index of a tendency for the
  performance error to be directionally biased
• 16, 4, -10, 11, -9 12/5 2.4
• 3. Variable error The standard deviation of the
  CE scores an index of performance consistency
  (i.e. variability)

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Assessing Error for One-Dimension Accuracy Goals,
contd

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

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Assessing Error for Two-Dimension Accuracy Goals

• When the outcome of performing a skill requires
  accuracy in the vertical and horizontal
  directions
• e.g. Golf putt
• Radial error General accuracy measure for
  two-dimensions
• See Figure 2.3

X2 Y2 h2 RE v h2
h
y
5 cm
x
X-axis distance 102 100 Y-axis distance 52
25 Sum 125
RE v125 11.2 cm
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Assessing Error for Two-Dimension Accuracy Goals,
contd

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

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Assessing Errors for Continuous Skills

• Many continuous skills require spatial accuracy
  over a period of time
• e.g. Driving a car on a highway
• Root-Mean Squared Error (RMSE) Common accuracy
  measure for continuous skills

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Kinematic Measures

• Kinematics description of motion without regard
  to force or mass
• Includes the following measures see Fig. 2.6
• Displacement Spatial position of a limb or joint
  over a period of time
• Velocity Rate of change in an object position
  with respect to time (i.e. speed)
• Displacement / Time
• Acceleration Change in velocity during movement
• Velocity / Time

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Kinetics

• Kinetics Force as a cause of motion
• Human movements involve both external and
  internal sources of force
• Importance of force as a movement measure All
  three Newtons laws of motion refer to force

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EMG Measures

• Movement involves electrical activity in the
  muscles
• Electrodes detect electrical activity
• Electromyography (EMG) Recording of muscle
  electrical activity
• Common use is to determine when a muscle begins
  and ends activation see Figure 2.9
• Also Recall our earlier discussion about use
  of EMG for fractionated RT as an index of
  movement preparation

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Brain Activity Measures

• Researchers have adopted brain activity measures
  commonly used in hospitals and clinics for
  diagnostic purposes
• Three measures commonly reported in motor
  learning and control research
• EEG
• PET
• fMRI

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Brain Activity Measures, contd

• Electroencephalography (EEG) Measures electrical
  activity in brain
• Active brain regions produce electrical activity

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• Positron Emission Topography (PET) Neuroimaging
  (i.e., brain scanning) technique that measures
  blood flow in the brain
• Active brain regions involve increased amounts of
  blood flow

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Brain Activity Measures, contd

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

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Measuring Coordination

• Assessment of the relationship of movement of
  limb-segments and joints
• Quantitative measurement of angle-angle diagrams
• Cross-correlation technique
• NoRMS
• Relative phase
• Relative phase see Figure 2.10

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Angle-Angle Diagram
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Measuring Coordination

• Assessment of the relationship of movement of
  limb-segments and joints
• Quantitative measurement of angle-angle diagrams
• Cross-correlation technique
• NoRMS
• Relative phase
• Relative phase see Figure 2.10

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Normalized Root Mean-squared Error
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Relative Phase

• Index of the coordination between two limb
  segments or limbs during a cyclic movement.
• Relative phase ranges from 0 to 180 degrees
• Relative phase near 0 indicates an in-phase
  relationship.
• Relative phase near 180 degrees indicates an
  out-of phase relationship.

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