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Chapter 4 Continued

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If too much time elapses between when the movement is initiated and when ... Time- the amount of time that elapses from beginning to end of a person's movement ... – PowerPoint PPT presentation

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Title: Chapter 4 Continued


1
Chapter 4 Continued
  • Sources of Sensory Information

2
Rapid Tracking Behavior
  • Remember that the information processing model
    stages require time and attention so closed-loop
    systems that include these stages are slow as
    well
  • In the model corrections occur a few hundred
    milliseconds after an error occurs
  • Error processed (stimulus-ID stage)
  • Movement Correction (Response selection stage)
  • Modification organization/initiation (response
    programming stage)
  • Adequate if only 2-3 changes required per second

3
Discrete Tasks of Brief Duration
  • Closed-loop system also inadequate when it comes
    to such brief skills as hitting, striking
    throwing, catching common in sport (the actual
    action itself, not the preparation phase)
  • If too much time elapses between when the
    movement is initiated and when correction can be
    made, success may not occur
  • Therefore, the first few hundred milliseconds of
    a brief, rapid movement occur more or less
    without modification
  • Finally, scientists have determined that there is
    an all or nothing point where a go signal is
    initiated and the movement proceeds without
    interruption (Slater-Hamel experiment)

4
Reflexive Modulations in Movement Skills
  • To this point we have been talking about
    consciously controlled movement adjustments based
    on sensory information. However, there are other
    adjustments, called reflexes, that occur at the
    spinal cord and brain stem level that go on at
    the same time as controlled movement.

5
Types of Compensation
  • M1 Response
  • One of the most rapid underlying limb control,
    prompted when and unexpected load is added to a
    limb. 30-50 ms, involves 1 synapse, is
    non-conscious and automatic
  • M2 Response
  • 50-80 ms after the load comes the functional
    stretch reflex, which also travels to the spinal
    cord, but then moves on to the brain stem. Here
    muscles are activated to help with the load
    (knee-jerk reflex). Not affected by SR
    alternatives, but we can adjust the amplitude of
    the response

6
  • Triggered Reaction
  • 80-120 ms too fast to be voluntary, but too slow
    for M1 or M2. This is the little slip of the
    glass (called wineglass effect) made before you
    are even aware the glass is slipping, caused by
    awareness of slippage against the cells of your
    skin
  • Voluntary Reaction-Time Response (M3)
  • 120-180ms, voluntary response, powerful and
    sustained, can affect all muscles in the body,
    not just those being stretched. This response is
    sensitive to Hicks Law.
  • Coordinating compensations
  • If more flexibility is needed more sources of
    sensory information must be taken into account
    before the action is defined, so more time is
    needed to process information

7
  • Reflexes in the conceptual Model
  • M1 and M2 occur in the effector stage
  • Final common path and loops within loops
  • Role of Movement Time- the amount of time that
    elapses from beginning to end of a persons
    movement
  • Only when the action takes longer than 300 ms is
    there potential for all responses to be active
  • Choices among modes of control
  • If performer can choose then the system can be
    preprogrammed
  • We do this when we tell a student to
    concentrate or focus on a particular source
    of feedback
  • Voluntary feedback leads to over-control- when
    perhaps preprogrammed operation corrected by
    inner feedback loops would be best

8
Role of Two Visual Systems in Movement Control
  • We have two different visual systems
  • Focal vision for object identification and
    ambient vision for movement control

9
Focal Vision
  • Used to identify objects in the center of your
    visual field
  • Answers the question what is it?
  • It is conscious
  • It is biased by movement
  • It is diminished by dim light

10
Ambient Vision
  • Uses both central and peripheral portions of the
    visual field
  • Not degraded by dim light
  • Believe it is specialized for movement control,
    to detect motion as well as the position of
    objects in the environment
  • Answers the questions where is it? and where
    am I in relation to it?
  • Contributes to fine control of movement

11
Visual Control of Movement Skills
  • Focal Vision and Movement Control
  • Vision processed as another source of
    exteroceptive information
  • Particularly important when we fail to accurately
    identify objects in our environment, such as
    during night driving

12
  • Ambient vision and movement control
  • Optical flow- movement of patterns of light rays
    from the environment over a persons retina,
    allowing the person to perceive motion, position
    and timing
  • Aids in stability and balance, velocity of
    movement through the environment, direction of
    movement relative to fixed objects, movement of
    environmental objects relative to the observer,
    time until contact between observer and object
  • Visual proprioception- information about movement
    of your body in space

13
  • Concept of Tau
  • As objects approach us, the retinal image
    expands. That rate of expansion (how fast or
    slow) tells us the speed of the approaching
    object. So, images that expand on our retina are
    approaching more quickly.
  • This is important for people who perform
    interceptive actions (catching a ball) or
    coincident-timing tasks (preparing the body for
    entry into the water at the proper time of a
    springboard dive)

14
  • Balance
  • Strongly affected by varying the visual
    information presented to the person (spotting on
    a wall)
  • Vision in the Conceptual Model
  • Focal system is exteroceptive
  • Ambient system is more non-conscious

15
Visual Dominance and Visual Capture
  • Visual dominance
  • Tendency for visual information to supersede
    information coming from other senses
  • Visual capture
  • Tendency for visual information to attract a
    persons attention more easily than other forms
    of information
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