Chapter 2

1. Chapter 2 The Measurement of Motor Performance Concept: The measurement of motor performance is critical to understanding motor learning

2. Why Study the Measurement of Motor Performance? Performance measurement essential for: • Performance assessment / evaluation • Motor learning and control research

3. 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?

4. Warning signal “Go” signal Initiation of the response Termination of the response Foreperiod Reaction Time (RT) Movement Time (MT) Response Time Reaction Time

5. Reaction Time, cont’d • 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

6. 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

7. Fractionated RT EMG Recording Pre-motorTime MotorTime Observable Movement Go Signal Initiation of muscle activity Reaction Time What do you think occurs in each RT component?

8. 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

9. 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?

10. 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

11. Assessing Error for One-Dimension Accuracy Goals, cont’d 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)

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

13. 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 = √ h2 h 5 cm y x X-axis distance = 102 = 100 Y-axis distance = 52 = 25 Sum = 125 RE = √125 = 11.2 cm

14. Assessing Error for Two-Dimension Accuracy Goals, cont’d • Performance bias and consistency are difficult to quantitatively assess, although can do qualitative assessment easily

15. 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

16. 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

17. 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 Newton’s laws of motion refer to force

18. 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

19. 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

20. Brain Activity Measures, cont’d • Electroencephalography (EEG): Measures electrical activity in brain • Active brain regions produce electrical activity

21. 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

22. Brain Activity Measures, cont’d • Functional Magnetic Resonance Imaging (fMRI):Neuroimaging (i.e., brain scanning) technique that measures blood flow changes in the brain by detecting blood oxygenation characteristics

23. 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]

24. Angle-Angle Diagram

25. 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]

26. Normalized Root Mean-squared Error

27. 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.