  We show that scaling arguments are very useful to analyze the dynamics of
periodically modulated noisy systems. Information about the behavior of the
relevant quantities, such as the signal-to-noise ratio, upon variations of the
noise level, can be obtained by analyzing the symmetries and invariances of the
system. In this way, it is possible to predict diverse physical manifestations
of the cooperative behavior between noise and input signal, as for instance
stochastic resonance, spatiotemporal stochastic resonance, and stochastic
multiresonance.
