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Figure 5


Fig. 5. Motion components before and after perturbation. Joint angle velocities and motion components during the 20 ms immediately before and after obstacle contact in the three behavioural contexts. (A) Positive thorax-coxa (ThC) joint velocity causes protraction of the leg. (B) Positive coxa-trochanter (CTr) joint velocities result in levation of the femur. (C) Positive femur-tibia (FTi) joint velocities are due to extension of the tibia. Median velocities are indicated by arrowheads. Before perturbation, the combination of motion components is context-dependent. The swing phase of straight walking is characterised by protraction, depression and extension (centre), whereas in curve walking, only one motion component predominates: FTi extension in the inner leg (left) and ThC protraction in the outer leg (right). In contrast, the avoidance reflex consists of the same motion components in all three behavioural contexts: retraction, levation and flexion (Mann-Whitney U-test of median velocities against zero). Significance levels: ***P<0.001; **P<0.01; *P<0.05.





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