The process by which the ear's sensitivity to sound is changed by the presence of a constant sound or DRONE. The state of fatigue caused by such a load on the sensory cells and nerve fibres results in a gradual decrease in the apparent LOUDNESS of a constant tone or noise. In the following diagrams, it can be seen how a SINE TONE decreases in apparent loudness over a three minute period; a similar effect occurs when one is exposed to loud sounds. Also called aural fatigue or habituation.


Decrease of loudness sensation through fatigue when the ear is taxed with a permanent sine wave, measured over 3 minutes. Hatched area shows time course of the signal for three cases: a) constant sound pressure; b) doubling of the pressure after 2 minutes; c) halving of the pressure after 2 min. (from F.Winckel, Music, Sound and Sensation, Dover, 1967, p. 104, used by permission).