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Fig. 3. Spatial and temporal effects of perturbation. The impact of perturbation on
the perturbed leg itself was investigated over a walking sequence of three
subsequent steps (-1, 0, +1), step 0 being the perturbed step (white). Bars
indicate mean values of step parameters ± s.d. (Inner, N=51;
Straight, N=64; Outer, N=58). Perturbation affected swing
distance (A), swing duration (B), and duty cycle, i.e. the fraction of the
step cycle spent in stance (C). Data of the perturbed step 0 and the
subsequent unperturbed step +1 (grey) were tested with reference to step -1
(black), prior to perturbation (Wilcoxon test). Perturbation caused a
reduction of swing distance and duty cycle and a prolongation of the swing
duration, the only exception being swing distance of inner legs, which
remained unchanged (A, left). Step parameters in unperturbed walking depend on
the behavioural context and differ between straight and curve walking
(Mann-Whitney U-test). Significance levels:
***P<0.001; **P<0.01;
*P<0.05.