Fig. 7. Large perturbation mis-steps. A small number of rough terrain steps included a leg that failed to contact the substrate during stance. Here, the hind left leg (three pink points in image 1) swings through a trough formed by several particularly high obstacles (A). Normal activation of muscle 179 occurs even though contact is absent (B); however, there is a subsequent increase in stride period in the following step (B,C), indicating a stride-to-stride change in the clock-like activation of 179. This change requires neural feedback. Stride period returns to the original time within two strides of the mis-step following kinematic recovery from the perturbation. Histograms in C are normalized with respect to the baseline stride period taken 2 steps before the perturbation.