STOCHASTIC RESONANCE IN AN AUTONOMOUS SYSTEM WITH A NONUNIFORM LIMIT-CYCLE

In a recent numerical study, Gang et al. [Phys. Rev. Lett. 71, 807 (19 93)] presented the first example of stochastic resonance in an autonom ous system. They considered a two-variable model in which a limit cycl e is born as some parameter is varied. Their numerical experiments rev ealed various noise-induced effects, including a noise-induced shift i n the frequency of the limit-cycle oscillations, and noise-induced osc illations in the absence of a deterministic limit cycle. We show that both of these effects are simple consequences of the nonuniformity of the motion along the limit cycle.