  Coherent stochastic resonance is explained in terms of first passage time
density functions. Scaling relation between first passage time density
functions at resonance for different lengths of the medium is obtained. A
formula for first passage time density function at resonance is derived in
terms of two universal functions, which demonstrates the universal feature of
coherent stochastic resonance. A simple approximate expression for first
passage time density function at resonance is proposed which is shown to
explain the behavior at resonance fairly accurately.
