1. Performance and Motor Control Characteristics of Functional Skills
Chapter 7
Performance and Motor Control Characteristics of Functional Skills
Concept: Specific characteristics of the performance of various motor skills provide the basis for much of our understanding of motor control
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2. ©2011 McGraw-Hill Higher Education.
Introduction
This chapter extends discussion of motor control theory issues in chapters 5 & 6 to:
Consider how motor control processes are involved when we perform specific motor skills
Provide guidance for practitioners for teaching these skills
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3. _______________________________
___________________________________________________________________speed-accuracy trade-off
i.e., when speed is emphasized, accuracy is reduced and vice-versa
What are some examples of motor skills that require both speed and accuracy?
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4. Speed-Accuracy Skills: __________________________
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If we know the spatial dimensions of two variables:
_________________________
MT = a + b log2 (2D/W)
Also demonstrated that an index of difficulty could be calculated based on this equation: log2 (2D/W)
See Fig. 7.1 for examples of different IDs for manual aiming tasks, and predicted MTs
Note how same task (i.e., action goal) can have different levels of performance difficulty
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5. Application of Fitts’ Law to Non-Laboratory Skills
Research has demonstrated that Fitts’ Law predicts MT for various non-laboratory motor skills, e.g.,
Dart throwing
Peg-board manipulation task
Used in physical rehab assessment and training
Reaching and grasping containers of different sizes
Moving a cursor on a computer screen
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6. Speed-Accuracy Skills: Motor Control Processes
General agreement that two motor control processes involved in performance of speed-accuracy skills:
1. Open-loop control – At movement initiation
_____________________________________________________________________________________
2. Closed-loop control – At movement termination
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7. Speed-Accuracy Skills: Role of Vision
Relate to Manual Aiming Skills
(e.g., putting key in keyhole – see Fig. 7.2)
Role of vision depends on movement phase:
_____________________– Assess regulatory conditions of environmental context
_____________________– Monitor limb displacement and velocity; shift gaze to keyhole at 50% time-to-contact
____________________– Provide spatial-temporal info to correct movement accuracy errors to ensure insertion of key
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8. _______________________
________________________________________________________________
Three components
____________________
Movement of the hand to the object
The hand taking hold of the object
_________________________
The hand carrying out the intended use for the object (e.g. drinking from it, moving it to another location)
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9. Relationship of Prehension Components
Motor control question concerns the ________________________between the transport and grasp components
Initial views proposed the independence of the components
Recent evidence shows
___________________________________
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10. Relationship of Prehension Components, cont’d
Example of research demonstrating temporal relationship of reach and grasp
Goodale and colleagues (1991, 2005) showed:
1. Object’s size influences:
_________________________________________
2. Regardless of object’s size or distance
Max. grip aperture (point of beginning of hand closure for grasp) ____________________________
Other research shows:
Relationship of movement kinematics for prehension components exemplify characteristics of a “coordinative structure”
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11. Role of Vision in Prehension
________________________________
Assesses regulatory conditions
Central vision directs hand to object – provides time-to-contact info to initiate grasp
Peripheral vision provides hand movement feedback
______________________________
Supplements tactile and proprioceptive feedback to ensure intended use achieved
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12. Prehension and Fitts’ Law
______________________________________________________________________________________________________
______________________________
____________________for grasping containers of different sizes and quantities of liquid
Developed by Latash & Jaric (2002)
See “A Closer Look,” p. 144
Critical component is % of fullness
Ratio of mug size and liquid level
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13. ____________________________
____________________________________________________________________________
People demonstrate much individual variation in terms of limb segment involvement
Person can adapt to various context demands (e.g., write on different surfaces, write large or small)
Handwriting motor control demonstrates characteristics of a coordinative structure
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Handwriting, cont’d
___________________________________________________________________
Write on a piece of paper:
I like to sit and read books
Write the same sentence with your eyes closed
How do the similarities and differences with eyes open and closed demonstrate the role vision plays in the control of handwriting?
See the experiment by Smyth & Silvers (1987) – Results in Fig. 7.3
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15. __________________________________________________________________
Skill may require two arms to move with the same or different spatial and/or temporal characteristics
_____________________________
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16. Bimanual Coordination Skills, cont’d
____________________________________________________________________
Demonstrates why it is difficult to rub your stomach and pat your head at the same time, or draw a circle with one hand while drawing a straight line with the other hand
Research demonstrates temporal and spatial coupling of the two arms when initially performing asymmetric bimanual skill
____________________________________________________________________________
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17. __________________________
________________________________________________________________________________________________
Provide basis for stereotypic rhythmicity of walking and running gait patterns
But, proprioceptive feedback from muscle spindles and GTOs also influence gait
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Locomotion, cont’d
_______________________________________
Components of a step cycle (discussed in ch.5 in experiment by Shapiro et al.)
Rhythmic relationship between arms and legs
Pelvis and thorax relationship during walking
________________________________________________________________________________
Allows for assessment of coordination problems of trunk and legs (e.g. Parkinson’s Disease)
Another important motor control characteristic of locomotion
Head stability
Consider why and implications of head stability problems
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Locomotion, cont’d
_______________________________
An important motor control characteristic of locomotion (Initially discussed in ch.5)
People spontaneously change from walking to running gait (and vice-versa) at critical speed (specific speed varies across people)
Why do spontaneous gait transitions occur?
Various hypotheses
Most popular: Minimize metabolic energy use (i.e., VO2)
Some agreement that no one factor responsible
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Locomotion and Vision
When we walk or run, vision is important to enable us to contact objects and avoid contact with objects
Contacting objects
Experiment by Lee et al. (1982) showed long-jumpers use tau as basis for contacting take-off board accurately [See Fig. 7.4]
Avoiding contact with objects
_________________________________________________________________________________________
Vision provides body-scaled info to determine how to walk through a door, or step on a step
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21. _________________________________
Three phases
__________________________________________
Movement analysis evidence of the three phases – Experiment by Williams & McCrirrie (1988)
Figure 7.6 – Illustrates movement characteristics related to % ball flight time
Notable finding (not in figure) – Successful ball catchers initiated final hand and finger shaping 80 msec earlier than non-catchers
What do you think are the roles of tactile, proprioceptive, and visual information in the stages of catching a moving object
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22. Catching a Moving Object, cont’d
___________________________________________________________________
Two critical time periods
______________________
_______________________
Between the two critical periods
Brief, intermittent visual snapshots sufficient
Specific amounts of time not known
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23. Catching a Moving Object, cont’d
Is vision of the hands necessary to catch a moving object?
Key factor in answer is amount of experience
Inexperienced – Yes
Experienced – No
Describe how experience with using vision to catch an object influences a person’s capability to rely on proprioceptive feedback to position hands to catch an object
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24. Striking a Moving Object
Ball speed effect
Skilled ”strikers” demonstrate similar ”bat” movement time for all ball speeds, change amount of time before initiating bat movement
Visual contact with moving ball
Skilled ”strikers” do not maintain visual contact with ball throughout ball flight but visually ”jump” from early flight to predicted location in area to strike ball
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