Representative traces of the vertical displacement of the head from midstance to subsequent midstance for a vaulting trial (A) and a bouncing trial (B). Dotted red lines represent original trials with head bobbing, thick dashed grey lines represent simulated trials without head-bobbing, and thick solid grey lines represent trials in which head-bobbing was inversed. Thin grey lines represent stepwise modifications of the onset of thrust. Each step was an increase (solid lines) or decrease (dashed lines) by 10% of stride duration. In the vaulting trial the quail moved at 0.15 m/s and % Congruity was 24.7. In the bouncing trial the quail moved at 0.55 m/s and % Congruity was 93.8. Note that in the vaulting trial the initial hold phase begins slightly before the initial midstance and the subsequent hold phase continues beyond the subsequent midstance. In the bouncing trial the thrust phase begins slightly before the initial midstance and the hold phase continues slightly beyond the subsequent midstance. In both cases, the timing of the thrust phase (experimental data) results in smaller vertical head displacement in comparison to simulated head-trunk-coordination patterns in the respective gait.