Juggling results By UM1
Review of skill acquisition in Juggling
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1) Outline of concepts and approach 2) Overview of basic results 3) Examples of captured skilled performance (Oxford Metrics)
Oxford, October 23, 2007
1st SKILLS General Meeting
What is juggling? z
A juggler has to accommodate rather severe task constraints in order to juggle successfully.
Shannon theorem of juggling: (F + D)H = (V + D)N F time a ball spends in air, D time a ball spends in a hand, V time a hand is vacant, N number of balls, H number of hands z
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Æ timing constraints, hence one can anticipate a spatio-temporal organization between limbs
Oxford, October 23, 2007
1st SKILLS General Meeting
Most studied: 3 balls cascade juggling
-The hands move along more or less elliptical trajectories - One hand moves clockwise and the other anti-clockwise with an average phase difference of 180 deg. - Balls released at the inside of the ellipses and caught at the outside - The 3 balls are phase shifted by 2 pi/3 throws
catches Oxford, October 23, 2007
1st SKILLS General Meeting
Illustration with a movie from OMG
Oxford, October 23, 2007
1st SKILLS General Meeting
Concepts and approach
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Focus on coordination: Seeking the spatial and temporal order among components Stable, stationary, organized assembly of components Intricate perception and movement
The scales of learning in juggling: How the various subcomponents of the whole body coordination change?
Oxford, October 23, 2007
1st SKILLS General Meeting
Organization imposed by the task
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Space: Location of throws, angle and velocity of release
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Time: Relative timing, phasing and frequency locking Æ “spatial clock”
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However there is always variability
Oxford, October 23, 2007
1st SKILLS General Meeting
Basic results with expert and learning
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Consistent rhythm: Fixed “dwell time”, ratio a ball spends in one hand between two catches; 3/4, 2/3, 5/8
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Global coordination: The 3 balls motion in frontal plane settle onto lower dimension space for intermediate jugglers (PCA): from 9 to 4 dim., 2 dominants modes (78% variance, span a plane)
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Redundancy due to the spatio-temporal symmetry (2/3 pi phase shift between the 3 balls) reduces the dimensionality captured by the PCA (analytically demonstrated)
Oxford, October 23, 2007
1st SKILLS General Meeting
Basic results with expert and learning
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Expert assessment and longitudinal learning studies (20 hours over 7 weeks; 9 weeks)
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Variability expressed in serial negative correlations between two consecutive intervals: Long (short) intervals tend to precede short (long) intervals
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Smoothing of trajectories, decrease of variability of timing relation between balls and hands
Oxford, October 23, 2007
1st SKILLS General Meeting
Consistency of tosses in high expert
Balls trajectories
Accuracy of tosses
Location, direction, and velocity of tosses serve as an anchor for the global coordination Oxford, October 23, 2007
1st SKILLS General Meeting
Components embedding: Multiple measurements, analysis of relations
Breathing
Eyes
Balls C.O.P.
Oxford, October 23, 2007
1st SKILLS General Meeting
Optical pick up of information z
Gaze:
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Expert spot the ball earlier
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Gaze at around the zenith of the ball trajectories: “Gaze through” adaptation (less fovea fixation: peripheral or other sensory channel (haptic)?)
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Expert increase the total flight time (height; found in 3 Balls juggling) And act quickly (decrease the time spent holding the ball) Æ expand the time available to use optical information
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Oxford, October 23, 2007
1st SKILLS General Meeting
Point-of-gaze & balls relations Illustration with a movie from OMG
Oxford, October 23, 2007
1st SKILLS General Meeting
Various type of point-of-gaze -balls relations for intermediate jugglers z
What
1:1 frequency locking
Oxford, October 23, 2007
1:2 frequency locking
1st SKILLS General Meeting
Time scales of sub-components change with practice - Decrease of frequent locking variance faster than phase locking (represent stabilization in noisy system); Both monotonically saturate - These evolves faster than number of successful cycles (outcome), the latter tends to evolves explosively - No relations balls-breathing - Balls- COP relations 3:1 and 2:1 frequency ratios between vertical coordinate and both directions of the COP
Oxford, October 23, 2007
1st SKILLS General Meeting
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Both gradual and abrupt transitions changes
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A hierarchy of changes: Depending on the degree of direct relations between the variables and the outcome
Oxford, October 23, 2007
1st SKILLS General Meeting
Captured data by Vicon Oxford: From the balls only to full body kinematics
Oxford, October 23, 2007
1st SKILLS General Meeting
Illustration with movies from reconstructed 3D data
Oxford, October 23, 2007
1st SKILLS General Meeting
Stabilization of posture
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Oxford, October 23, 2007
1st SKILLS General Meeting
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Oxford, October 23, 2007
1st SKILLS General Meeting
Consequences
Oxford, October 23, 2007
1st SKILLS General Meeting
Consequences
Oxford, October 23, 2007
1st SKILLS General Meeting
Oxford, October 23, 2007
1st SKILLS General Meeting
Multifrequency hand- ball coordination n:m, 3:2 frequency relations
Oxford, October 23, 2007
1st SKILLS General Meeting
Timing
Oxford, October 23, 2007
1st SKILLS General Meeting
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Antero- posterior movement matters, totally absent from available literature
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May be key for assessment of learning
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Beginners often have to face a wall to prevent forward walking
Oxford, October 23, 2007
1st SKILLS General Meeting
Odd vs even basic patterns 0,24 sec. hand empty interval
“Fountain” 4 Balls, In phase or Anti phase
“Cascade” 3 Balls
0,16. sec hand empty interval
(in phase = do the same thing in their respective local coordinates) Oxford, October 23, 2007
1st SKILLS General Meeting
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Means: Gaze fixed at zenith, ball goes up and down, hence distance varies (see eyes in movie from OMG) Oxford, October 23, 2007
Phase ball (0 rad: = zenith) 1st SKILLS General Meeting
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Model for the capture: ex one arm
7 dofs joint angles Right arm Æ 3D endpoint coordinates redundancy
7 dofs…again for Left arm
And 3 balls x 3 D Oxford, October 23, 2007
1st SKILLS General Meeting
Various type of point-of-gaze -balls relations for intermediate jugglers z
What
1:1 frequency locking
Oxford, October 23, 2007
1:2 frequency locking
1st SKILLS General Meeting
