Example of stochastic resonance. (a) When the sensory signal and noise are low and do not exceed the sensory threshold, the system perceives nothing. (b) When an optimal amount of noise is added to the signal, the signal and noise exceed the sensory threshold whenever the signal reaches its peak, thus assisting the system to perceive the signal. (c) When high noise is added to the signal, the sensory threshold crossings occur most of the time irrespective of the signal shape, thus hindering the system from perceiving the signal.