Dividing attention between two segregated tone streams

Abstract

Listeners were presented with pure-tone sequences which had a high speed (25–50 tones/s) and consisted of two interleaved melodies, M1 and M2, spanning separate frequency ranges (624–786 Hz and 1483–1869 Hz). M1 and M2 were renewed from sequence to sequence and could be either (1) perfectly correlated, or (2) perfectly anticorrelated, or (3) independent of each other. The main task, performed in a 2I-2AFC paradigm, was to discriminate sequences of type 1 (perfect correlation) from sequences of type 2 or 3. This appeared to be relatively easy when, in the type-1 sequences, each note of M2 immediately preceded or followed the corresponding note of M1. In that case, however, listeners were unable to tell whether M2 preceded or followed M1, which shows that the two melodies were perceptually segregated. In another series of experimental sessions, listeners knew that M2 would always follow M1 after a fixed delay, corresponding to one tone in some sessions and three tones in other sessions. The main discrimination task was performed better for the one-tone delay, but performance was still well above chance for the three-tone delay. Overall, the data suggest that two segregated tone streams can be attended to simultaneously.