Attempting to listen to another person talking in a crowded party room is more difficult than in a quiet room. The ability of the listener to understand the speaker (or of even recognizing that someone is speaking) is clearly diminished by the noise of the party. Because it is generally believed that noise degrades signals, much effort has been put into filtering out the noise. However, recent research has unveiled a wide class of systems that use noise to detect weak signals via a mechanism known as stochastic resonance (SR). Stochastic resonance was discovered in an electronic circuit and then in other physical systems. It is currently of interest in sensory biology and in psychophysics as a method of enhancing the ability of individuals to detect weak signals received from the environment.