Band Tones: Auditory Stream Segregation with Alternating Frequency Bands

An alternating tone sequence may be perceptually integrated into one stream or segregated into two streams based on pitch and timbre differences between the tones (sequential stream segregation). However, the effect of the spectral dispersion of harmonic complex tones on sequential stream segregation has been largely unexplored. We introduced band tones that were harmonic complex tones divided into several frequency bands, in which frequency components in every other frequency band were removed. Here, we show that segregation was reported more often with fewer frequency bands and larger separation in fundamental frequency. Listeners generally responded to 2–8-band stimuli as segregated most of the time. However, the percentages of segregation responses for 16-band stimuli were generally dominated by fundamental frequency separations and whether the movements of fundamental frequencies and band-like spectral patterns were congruent or incongruent. The results suggest that the auditory system cannot organize rapidly alternating frequency component blocks spanning a wide frequency range into one stream.