  Noise can induce time order in the dynamics of nonlinear dynamical systems.
For example, coherence resonance occurs in various neuron models driven by a
noise. In studies of coherence resonance, ensemble-averaged measures of the
coherence are often used. In the present study, we examine coherence resonance
for time-averaged measures. For the examination, we use a Hodgkin-Huxley neuron
model driven by a constant current and a noise. We firstly show that for large
times, the neuron is in a stationary state irrespective of initial conditions
of the neuron. We then show numerical evidence that in the stationary state, a
given noise sample path uniquely determines the dynamics of the neuron. We then
present numerical evidence suggesting that time-averaged coherence measures of
the dynamics is independent of noise sample paths and is equal to
ensemble-averaged coherence measures. On the basis of this property, we show
that coherence resonance is not only a phenomenon related to ensemble-averaged
measures but also a phenomenon that holds for time-averaged measures.
