The role of spectral and periodicity cues in auditory stream segregation, measured using a temporal discrimination task

In a previous paper, it was shown that sequential stream segregation could be based on both spectral information and periodicity information, if liste ners were encouraged to hear segregation [Vliegen and Oxenham, J. Acoust. S ec. Am. 105, 339-346 (1999)]. The present paper investigates whether segreg ation based on periodicity information alone also occurs when the task requ ires integration. This addresses the question: Is segregation based on peri odicity automatic and obligatory? A temporal discrimination task was used, as there is evidence that it is difficult to compare the timing of auditory events that are perceived as being in different perceptual streams. An ABA ABA ABA... sequence was used, in which tone B could be either exactly at t he temporal midpoint between two successive tones A or slightly delayed. Th e tones A and B were of three types: (1) both pure tones; (2) both complex tones filtered through a fixed passband so as to contain only harmonics hig her than the 10th, thereby eliminating detectable spectral differences, whe re only the fundamental frequency (f0) was varied between tones A and B; an d (3) both complex tones with the same f0, but where the center frequency o f the spectral passband varied between tones. Tone A had a fixed frequency of 300 Hz (when A and B were pure tones) or a fundamental frequency (f0) of 100 Hz (when A and B were complex tones). Five different intervals, rangin g from 1 to 18 semitones, were used. The results for all three conditions s howed that shift thresholds increased with increasing interval between tone s A and B, but the effect was largest for the conditions where A and B diff ered in spectrum (i.e., the pure-tone and the variable-center-frequency con ditions). The results suggest that spectral information is dominant in indu cing (involuntary) segregation, but periodicity information can also play a role. (C) 1999 Acoustical Society of America. [S0001-4966(99)04908-5].