The subtractive nature of illusory continuity: Reciprocal changes in alternating sounds.

Abstract

When portions of one sound are replaced by a louder sound, the missing segments may be restored if the louder inducing sound is a potential masker. This phenomenon has been examined extensively using pulsation threshold, auditory induction, and phonemic restoration paradigms to measure the conditions required for perceptual synthesis of the fainter sound. These studies have generally neglected to examine changes produced in the inducing sound. Decreases have been measured in apparent level of the inducer using inducer/inducee pairs consisting of tone/tone, noise/noise, and noise/speech. Interestingly, changes in the inducer occurred even when the inducee was above the pulsation threshold. Under some conditions loudness reduction was coupled with a marked alteration in timbre: Especially profound changes in the quality of the inducer occurred when the alternating sounds differed only in intensity (e.g., two levels of a 1000-Hz sinusoidal tone)−apparently, a residue with anomalous neural representation remains following subtraction of components corresponding to the inducee. These observations involving the inducer require modification of current theories concerning the apparent continuity and restoration of absent sounds. [Work supported by NIH Grant No. DC00208.]