Time was normalized based on the duration (D) measured between transition onset and the third toe-off. In both lower and upper panels, the left panel is the head forward condition and the right panel is the head left condition. As in Figure 1, the vertical red line shows the transition onset and the vertical grey line shows the transition end. Individual results (top) represent the average ± one standard deviation (n = 100 trials) of (from top to bottom): mediolateral centre of pressure, vertical forces (), shear force in the direction of the vestibular-induced perturbation ( = mediolateral; = anteroposterior), root mean square (RMS) of that same shear force, horizontal acceleration in the direction of the vestibular-induced perturbation, angular roll velocity of the head, and time-frequency coherence. The pooled results (bottom), represent the average ± one standard deviation (n = 1000 trials) of (from top to bottom): vertical forces (), shear force in the direction of the vestibular-induced perturbation and time-frequency coherence. Solid lines represent the average value while the dashed line is one standard deviation. The grey-shaded areas represent the double support periods during locomotion, in the head forward condition only. In the time-frequency coherence graphs, all non-significant coherence values have been set to zero based on a 99% confidence limit (single subject = 0.045, pooled data = 0.005). For illustrative purposes, vertical forces of the swing and stance foot (red and green curves, respectively) have been plotted relative to the first step. Note that the scale of coherence level for all subjects is half the scale presented in coherence graphs for the individual subject.