Page 45 - Human Environment Interface (3)

Learning Intermittent Strategy

Subject 1 (Two-sided Intermittent) Subject 9 (Two-sided Intermittent) Subject 2 (One-sided Intermittent)

1 1 1

InactR, DCR, QR, 15Dis, 15SD 0.75 InactR, DCR, QR, 15Dis, 15SD 0.75 InactR, DCR, QR, 15Dis, 15SD 0.75

0.5 0.5 0.5

0.25 0.25 0.25

0 0 0
InactR DCR QR 15*Dis 15*SD InactR DCR QR 15*Dis 15*SD InactR DCR QR 15*Dis 15*SD

Subject 3 (One-sided Intermittent) Subject 5 (One-sided Intermittent) Subject 8 (One-sided Intermittent)

1 1 1

InactR, DCR, QR, 15Dis, 15SD 0.75 0.75 0.75 InactR, DCR, QR, 15Dis, 15SD InactR, DCR, QR, 15Dis, 15SD

0.5 0.5 0.5

0.25 0.25 0.25

0 0 0
InactR DCR QR 15*Dis 15*SD InactR DCR QR 15*Dis 15*SD InactR DCR QR 15*Dis 15*SD

Subject 4 (Continuous) Subject 7 (Continuous) Subject 11 (Continuous)

1 1 1

InactR, DCR, QR, 15Dis, 15SD 0.75 0.75 0.75 InactR, DCR, QR, 15Dis, 15SD InactR, DCR, QR, 15Dis, 15SD

0.5 0.5 0.5

0.25 0.25 0.25

0 0 0
InactR DCR QR 15*Dis 15*SD InactR DCR QR 15*Dis 15*SD InactR DCR QR 15*Dis 15*SD

Figure 7. Multiple indices characterizing sway of the virtual inverted pendulum for each subject. In each panel, values of five indices are
plotted as thick black bars. From the left-most index, they represent the ratio of inactive interval to the whole trial time span (Inactive-Ratio) denoted
as InactR, the ratio of time interval with DCw0:8 to the whole single trial time span (DC-Ratio) denoted as DCR, the ratio of the number of off-points
(an off-point is a state point at a time instant when an inactive interval began) located in specific areas of the 2nd and the 4th quadrants of the phase
plane to the total number of off-points (Q-Ratio) denoted as QR, the average of distance between off-points and the v-axis in the phase plane
denoted as Dis (15 times of Dis-value for scaling: 15Dis), and the average standard deviation of h-coordinates of off-points denoted as SD (15 times of
SD for scaling: 15SD). See text for detailed definitions of indices. Thick black bars are for average values of the indices for successful trials. Thin gray
bars are the corresponding values for F5 trials. See text for the meaning of configuration of panels for nine subjects.
doi:10.1371/journal.pone.0062956.g007

backward position, and also switched from TA to MG at an the forward-tilted posture and backward velocity moved toward
instant when the pendulum moved from backward to forward the upright saddle point transiently if no active torques were
position, by which the subjects could keep the pendulum’s position present. Similarly, the state point in the second quadrant with the
as close to the upright as possible. backward-tilted posture and forward velocity also moved close to
the stable manifold, resulting in the transient approach toward the
In the subjects of one and two-sided intermittent types, on the upright saddle point with no help of muscle activations. These
other hand, the off-points did not necessarily tend to be close to changes in the off-point distribution were characterized by the
the v-axis. Instead, they moved into the second and/or the fourth ratio of the number of off-points located in the triangular areas
quadrants (Figs. 8E and F). Since the off-points in the fourth defined in the second and the fourth quadrants to the total number
quadrant were close to the stable manifold of the saddle point of of off-points. We referred to this ratio as Q-Ratio (Quadrant-Ratio).
the pendulum in the absence of active control, the state point with

PLOS ONE | www.plosone.org 12 May 2013 | Volume 8 | Issue 5 | e62956