Transitions between orbits of resonance attractors for spiral waves

Spiral waves rotating in a thin layer of the light-sensitive Belousov-Zhabotinsky reaction can he controlled by the application of short light pulses at instants corresponding to the passage of a wave front through a measuring point. It is shown that such a feedback results in a drift of the spiral wave core along a discrete set of stable circular orbits centered at the measuring point, in food quantitative agreement with the theory of the resonance attractor recently developed. Variations of parameters in the feedback loop initiate transitions between orbits of different size. Thus a spiral wave drift can he induced along a snail-shaped trajectory with permanently growing distance from the measuring point.