Juggling results. By UM1

Transcription

1 Juggling results By UM1

2 Review of skill acquisition in Juggling 1) Outline of concepts and approach 2) Overview of basic results 3) Examples of captured skilled performance (Oxford Metrics)

3 What is juggling? 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 timing constraints, hence one can anticipate a spatio-temporal organization between limbs

4 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

5 Illustration with a movie from OMG

6 Concepts and approach 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?

7 Organization imposed by the task Space: Location of throws, angle and velocity of release Time: Relative timing, phasing and frequency locking spatial clock However there is always variability

8 Basic results with expert and learning Consistent rhythm: Fixed dwell time, ratio a ball spends in one hand between two catches; 3/4, 2/3, 5/8 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) 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)

9 Basic results with expert and learning Expert assessment and longitudinal learning studies (20 hours over 7 weeks; 9 weeks) Variability expressed in serial negative correlations between two consecutive intervals: Long (short) intervals tend to precede short (long) intervals Smoothing of trajectories, decrease of variability of timing relation between balls and hands

10 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

11 Components embedding: Multiple measurements, analysis of relations Breathing Eyes Balls C.O.P.

12 Optical pick up of information Gaze: - Expert spot the ball earlier - Gaze at around the zenith of the ball trajectories: Gaze through adaptation (less fovea fixation: peripheral or other sensory channel (haptic)?) - Expert increase the total flight time (height; found in 3 Balls juggling) - And act quickly (decrease the time spent holding the ball) expand the time available to use optical information

13 Point-of-gaze & balls relations Illustration with a movie from OMG

14 Various type of point-of-gaze -balls relations for intermediate jugglers What 1:1 frequency locking 1:2 frequency locking

15 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

16 - Both gradual and abrupt transitions changes - A hierarchy of changes: Depending on the degree of direct relations between the variables and the outcome

17 Captured data by Vicon Oxford: From the balls only to full body kinematics

18 Illustration with movies from reconstructed 3D data

19 Z Stabilization of posture Y X

20 xxxx

21 Consequences

22 Consequences

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24 Multifrequency hand- ball coordination n:m, 3:2 frequency relations

25 Timing

26 Antero- posterior movement matters, totally absent from available literature May be key for assessment of learning Beginners often have to face a wall to prevent forward walking

27 Odd vs even basic patterns 0,24 sec. hand empty interval Cascade 3 Balls Fountain 4 Balls, In phase or Anti phase 0,16. sec hand empty interval (in phase = do the same thing in their respective local coordinates)

28 XXXXXXX Means: Gaze fixed at zenith, ball goes up and down, hence distance varies (see eyes in movie from OMG) Phase ball (0 rad: = zenith)

29 Model for the capture: ex one arm 7 dofs joint angles Right arm 3D endpoint coordinates redundancy 7 dofs again for Left arm And 3 balls x 3 D

30 Various type of point-of-gaze -balls relations for intermediate jugglers What 1:1 frequency locking 1:2 frequency locking