FIGURE 2.

Magnification of Figure 1 around the origin for the time interval of [–30, 0] s, prior to the perturbation-onset at t = 0 s. One of the remarkable features of the intermittent control model is that the postural state point ${({\mathrm{\theta }}_{\text{CoM}},{\stackrel{.}{\mathrm{\theta }}}_{\text{CoM}})}^T$ is not in a quiescent state even during quiet stance in the absence of noise as in panel (A), but it is oscillating periodically with a small amplitude of tilt angle about 0.01 rad, as confirmed by a closed trajectory (limit cycle) on the ${\mathrm{\theta }}_{\text{CoM}}-{\stackrel{.}{\mathrm{\theta }}}_{\text{CoM}}$ plane. Panel (B) is the case with small Gaussian white noise as a motor noise. Panels on the right-hand side of the phase planes are the corresponding waveforms of θ_a and θ_h, the corresponding joint torques, and the tilt angle θ_CoM. See text for details.