Incomplete auditory induction of tones alternated with noise: Effects occurring below the pulsation threshold

Abstract

Alternation of two sounds can give rise to illusory continuity of the fainter when the sounds have appropriate spectral and intensity relations [Warren, Obusek, and Ackroff, Science 176, 1149–1151 (1972); Houtgast, J. Acoust. Soc. Am. 51, 1885‐1894 (1972)]. We have found effects occurring below the continuity threshold when listeners estimate onset and offset times of a sinusoid (1000 ms duration; 12 frequencies, 180–8000 Hz) alternated with a narrow band noise (500 ms, 1000 Hz center frequency). For tonal frequencies corresponding to those within the noiseband, apparent offset was late and apparent onset early; effects opposite in direction to those corresponding to forward and backward masking by noise. At tonal frequencies outside those of the noiseband, onset/offset estimates were accurate. Frequency dependent effects found for illusory lengthening appear similar to those reported for continuity in auditory induction/pulsation threshold experiments, and in a direction which compensates for effects of masking. Illusory continuity appears to be the limiting case of the apparent temporal expansion found for conditions below the continuity threshold. [Research supported by NSF.]