torso.
The expert (subject A) moves in a different way.
While his torso is synchronised, a delay is found in his
elbows. This delay suggests that this subject pressed
the clay in swinging back phase of the torso. The arms
also helped his torso to swing back and thus the motion
became quick. To avoid to dry up the clay, this quick
method has an advantage.
We now investigate the movement of the knees. In
the expert (Figure 5), each knee has a peak on the other
sides of the Y axis. The forward motion of torso is gen-
erated by the right knee (i.e., the aft leg) and swing back
by the left (fwd) knee. The body motion is thus not like
a single pendulum, but a double pendulum which is piv-
oted around the hip. In other subjects, a peak is found
only at the left (fwd) knee while the right (aft) knee does
not have a peak. In such cases the body swings like a
single pendulum although it is not stiff because of the
relatively weak synchronisation than the expert.
We found a hierarchical organisation in the expert’s
motion. That is, within strong synchronisation, a phase
differentiation is established. If we represent a motion as
a rhythm, the experienced persons’ are fluctuated single
beat while the expert’s is four beat whose intervals are
not equal. To master this rhythm and correct pressing
strength at once seems to be difficult for short period of
time.
4.З samba shaking
For shaking, we employed two subjects X and Y, both
of whom we think were intermediate level players. We
asked them to play the shaker on the samba rhythm on
different tempos: 90 bpm, 100 bpm, 110 bpm, and 120
bpm. Each session continued for three minutes. The
tempo was given by a metronome and no rhythmic hint
was given to the subjects.
Figures 8 and 9 show the frequency distributions of
relative phases, which we calculated from the data taken
from the two sub jects, X and Y. Due to limited space,
we only present the distributions for two cases for each
subject. For each figure, the upper plots show the distri-
butions of the lumbar and the right knee and the lower
plots those of either side of the hip, i.e., the left hip for
X and the right hip for Y.
Both subjects reported that they felt most comfortable
when they played the shaker on 100 bpm. Contrary to
our intuition, the trajectories on the tempo are worst
coordinated compared with those on other tempos as
long as we judge the degree of coordination in terms of
synchronisation. Take the sub ject X (see Figure 8). His
degree of synchronisation got better when he played on
90 bpm (right). The peaks are sharper than those found
for 100 bpm (left). On faster tempo of 100 bpm, the
left hip is desynchronised and even exhibits two peaks
while we observe only one peak for 90 bpm. For tempos
>,1400
⊂ 1200
1000
σ- 800
4= 600
400
200
0
|
left elbow - |
Figure 5: distributions of relative phase of subject A (expert)
rienced)
Figure 6: distributions of relative phase of sub ject B (expe-
1600
1400
1200
1000
800
600
400
200
0
1400
1200
1000
800
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200
0
-3
-2
-1
0
1
2
3
1600
1400
1200
1000
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0
|
T I I |
I I Γ left knee ^ |
-3 -2 -1 0 1 2 3
relative phase [rad]
1400
1200
1000
800
600
400
200
0
|
right hip - |
-3-2-10123
1400
1200
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0
|
right elbow - |
900
800
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500
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100
0
right hip
right hip
1600
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0
1600
1400
1200
1000
800
600
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0
-3 -2 -1 0 1 2 3
relative phase [rad]
Figure 7: distributions of relative phase of subject C (expe-
rienced)
101