  Physical notions of stochastic resonance for potential diffusions in
periodically changing double-well potentials such as the spectral power
amplification have proved to be defective. They are not robust for the passage
to their effective dynamics: continuous-time finite-state Markov chains
describing the rough features of transitions between different domains of
attraction of metastable points. In the framework of one-dimensional diffusions
moving in periodically changing double-well potentials we design a new notion
of stochastic resonance which refines Freidlin's concept of quasi-periodic
motion. It is based on exact exponential rates for the transition probabilities
between the domains of attraction which are robust with respect to the reduced
Markov chains. The quality of periodic tuning is measured by the probability
for transition during fixed time windows depending on a time scale parameter.
Maximizing it in this parameter produces the stochastic resonance points.
