ASA 19 - Pitch Streaming


It is clear in listening to melodies that sequences of tones can form coherent patterns. This is called temporal coherence. When tones do not form patterns, but seem isolated, that is called fission.

Temporal coherence and fission are illustrated in a demonstration first presented by van Noorden (1975) and included in the "Harvard tapes" (1978). Van Noorden describes it as a "galloping rhythm."

We present tones A and B in the sequence ABA ABA. Tone A has a frequency of 2000 Hz, tone B varies from 1000 to 4000 Hz and back again to 1000 Hz. Near the crossover points, the tones appear to form a coherent pattern, characterized by a galloping rhythm, but at large intervals the tones seem isolated, illustrating fission.


A.S.Bregman (1978), "Auditory streaming: competition among alternative organizations," Percept. Psychophys. 23, 391-98.

L.P.A.S.van Noorden (1975), Temporal Coherence in the Perception of Tone Sequences. Doctoral dissertation with phonograph record (Institute for Perception Research, Eindhoven, The Netherlands).

Harvard University Laboratory of psychophysics (1978), "Auditory demonstration tapes," No. 18.

Time Delay


In this experiment a fixed tone A and a variable tone B alternate in a fast sequence ABA ABA. At some places you may hear a "galloping rhythm," while at other places the sequences of tone A and B seem isolated.