Controlled pulse reversal on a ring electrode

Oscillatory rotating activation pulses on a Pt ring electrode during formic acid oxidation were externally perturbed via a trigger electrode at one location of the ring. While usual phase resetting was obtained for small perturbation amplitudes, stronger perturbations resulted in reversal of the direction of pulse motion when applied behind the pulse over a wide phase interval. The results are in agreement with simulations carried out with a reaction–migration model and can be rationalized in terms of short-range positive and long-range negative coupling.