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By any other name...

The auditory continuity phenomenon has been the subject of several communications earlier this month, and several names of people associated with this illusion were mentioned. Massimo Grassi correctly stated that Vicario’s name belongs on the list. He did indeed observe the effect in 1960, naming it “L'effetto tunnel acustico.” But Miller and Licklider seem to have been the first discoverers in 1950. Several other investigators, unaware of the earlier publications, made their own independent discoveries. This led to a multiplicity of terms describing the effect including “picket fence effect,” “auditory figure ground effect,” and more recently, “auditory continuity effect,” “auditory induction,” and “temporal induction.”

The communications this month seem to have limited this phenomenon to the illusory continuity of steady-state tones and tone glides through interruptions by a louder noise. But this phenomenon is much broader: portions of any sound can be restored if the interrupting louder sound stimulates the same peripheral receptors that would have been stimulated if the sound had indeed been present. In everyday life this effect represents a sophisticated process that can restore portions of signals (including speech) if they have actually been masked. This is accomplished by reallocating a portion of the neural representation of the louder interrupting sound for the perceptual synthesis of the fainter signal. In support of this mechanism, it had been shown that when illusory restoration of the fainter sound (either a tone or speech) occurred, it was accompanied by a decrease in the loudness of the interrupting sound [R.M. Warren et al., 1994, Auditory induction: Reciprocal changes in alternating sounds. Perception and Psychophysics, 55, 313-322].

For a review of the literature, see Chapter 6 “Perception of missing sounds” in R.M. Warren, 1999, Auditory Perception: A New Analysis and Synthesis, New York: Cambridge University Press (a third edition is now in production by Cambridge).