The Zwicker tone is a puzzling auditory illusion. It was discovered in 1964 by Eberhard Zwicker at Bell Labs and can be described as follows: A broadband noise with a spectral gap is presented for a few seconds. On a hi-fi this would look like all the lights on your graphic equalizer are lit up except for one column in the middle. The noise is then switched off abruptly. Although there is total silence, most listeners hear a faint pure tone for up to several seconds. The pitch of the tone is perceived in the gap, where no spectral components of the stimulus were present. Several noise configurations have been found that all lead to a Zwicker tone but its origin has always remained unclear. Biophysicists can now provide a neuronal model that can explain the Zwicker tone illusion. Suppression of background noise is the key ingredient in generating the effect.
The Zwicker tone as a transient auditory sensation is often thought of as a short-term tinnitus, the familiar ringing in the ears after a rock concert. Tinnitus is also a very irritating medical condition. Understanding Zwicker tone provides novel insight as to how tinnitus might be the result of persistent activation of a noise-reduction mechanism within the human brain.