  The main objective of this work is to explore aspects of stochastic resonance
(SR) in noisy bistable, symmetric systems driven by subthreshold periodic
rectangular external signals possessing a large duty cycle of unity. Using a
precise numerical solution of the Langevin equation, we carry out a detailed
analysis of the behavior of the first two cumulant averages, the correlation
function and its coherent and incoherent parts. We also depict the
non-monotonic behavior versus the noise strength of several SR quantifiers such
as the average output amplitude, i.e. the spectral amplification (SPA), the
signal-to-noise ratio (SNR) and the SR-gain. In particular, we find that with
subthreshold amplitudes and for an appropriate duration of the pulses of the
driving force the phenomenon of stochastic resonance (SR), is accompanied by
SR-gains exceeding unity. This analysis thus sheds new light onto the interplay
between nonlinearity and the nonlinear response which in turn yields
nontrivial, unexpected SR-gains above unity.
