Fig. 2. Straight walking of the intact stick insect on the slippery surface. (A) Pattern of straight walking stepping sequence on the slippery surface. The black bars mark the stance, the white gaps mark the swing phases for the six legs. From top to bottom; left front leg (lFL), left middle leg (lML), left hind leg (lHL) and right front leg (rFL), right middle leg (rML) and right hind leg (rHL). (B) Schematic drawing of a stick insect with the mean anterior extreme position (AEP) and posterior extreme position (PEP) values (and s.d.) for the straight walking animal. Dark gray marks the values for the averaged steps from the left and right side plotted separately, black marks the values for all pooled, averaged and mirror imaged data points. The light gray lines mark the respective x₀-value for the middle and hind legs. (C) Mean vectors of stance phase movement drawn to the mean step length as calculated between AEP and PEP. (D) Step-to-step variability in angle and length of all stance phase movement vectors for the front, middle and hind legs. All vectors of the right side legs were mirror imaged to show only left side-stepping.