Synchrony of separate or antidirectionally coupled hand and foot oscillations with the external clock. A. When the hand and the foot were moved either separately or antidirectionally coupled, the clk-mov delay remained constant (no significant effect of frequency) as the frequency increased from 0.4 to 1.8 Hz. Same representation and symbols as in Fig. 2. Constancy of the clk-mov was achieved despite the increasing lag of the hand and foot movements with respect to the EMG activation (mech curves, filled symbols in B), thanks to the progressive phase-advance of the motor activation with respect to the clock signal (neur curves, open symbols in B). All curves obtained during antidirectionally coupled hand-foot oscillations virtually overlap the corresponding curves obtained during separate oscillations of the two segments (green lines). Vertical bars in A and B = Standard Error of the Mean (covered by the symbol in most instances).