Polyrhythm perception
One way to study auditory pattern perception is to observe what subjects perceive when two auditory sequences are presented simultaneously. Depending upon the physical relation between the two sequences, they will merge into a single line or be perceived as two separate, simultaneously proceeding lines. For example, with two (alternating) tone sequences “A . A . A” and “B . B . B,” one will perceive two separate sequences if the pitch distance between them is large. This phenomenon has been called fission (Van Noorden, 1975) or streaming (Bregman, 1990; Bregman & Campbell, 1971). When the pitch interval gets smaller, there will be a switch to the perception of a single alternating auditory pattern “ABABAB. . . .” The precise frequency separation at which the transition between the two percepts occurs depends upon the tempo and the attention of the observer (Van Noorden, 1975).
These two strains of research show that both the pitch interval and the tempo difference play a role in the formation of auditory pattern percepts.