  We study an extended system that without noise shows a spatially homogeneous
state, but when submitted to an adequate multiplicative noise, some
"noise-induced patterns" arise. The stochastic resonance between these
structures is investigated theoretically in terms of a two-state approximation.
The knowledge of the exact nonequilibrium potential allows us to obtain the
output signal-to-noise ratio. Its maximum is predicted in the symmetric case
for which both stable attractors have the same nonequilibrium potential value.
