The role of timbre in the segregation of simultaneous voices with intersecting F0 contours.

When the fundamental frequency (F0) contours of two speakers' voices intersect, the listener is presented with a problem. The listener must decide which of the F0 contours emerging from the intersection is a continuation of which contour entering the intersection: have the F0 contours crossed or merely approached and parted? In the present experiment, subjects listened to two simultaneous diphthong-like sounds with F0 contours that either approached and diverged or crossed over. The task was to report whether the pitches "crossed" or "bounced" away from each other. Despite the changing timbres of the two sounds, the subjects were able to discriminate crossing and bouncing F0s, provided that the timbres of the vowels differed at the moment when their F0s were the same. When the timbres were the same, the subjects could not make the discrimination and tended to hear a bouncing percept. These results are consistent with the idea that listeners use continuity of timbre rather than continuity of F0 movement to disambiguate F0 intersections.