Phys. Rev. Lett. 90, 178103 (2 May 2003).

Zwicker tone illusion and noise reduction in the auditory system.

J.-M. P. Franosch, R. Kempter, H. Fastl, and J. L. van Hemmen.

The Zwicker tone is an auditory aftereffect. For instance, after switching off a broad-band noise with a spectral gap, one perceives it as a lingering pure tone with the pitch in the gap. It is a unique illusion in that it cannot be explained by known properties of the auditory periphery alone. Here we introduce a neuronal model explaining the Zwicker tone. We show that a neuronal noise-reduction mechanism in conjunction with dominantly unilateral inhibition explains the effect. A pure tone's `hole burning' in noisy surroundings is given as an illustration.

Zwicker's Auditory Illusion and the Origin of Tinnitus

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 broad-band 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. Until today several noise configurations have been found that all lead to a Zwicker tone but its origin has always remained unclear. We 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. We show how the Zwicker tone provides novel insight as to how tinnitus might be the result of persistent activation of a noise-reduction mechanism.