stream segregation · Bregman (1978) · van Noorden (1975)
Two alternating pure tones — low and high — play in sequence. At slow rates or small frequency gaps, most listeners hear a single integrated melody: the pitches weave together. At fast rates or large gaps, the sequence splits into two independent streams — a low one and a high one, each with its own rhythm. The transition is not a decision. The streams emerge from mutual inhibition between frequency channels in the auditory cortex. No module decides "stream these." The streams are what happens when the inhibition settles.
The diagram (right) shows where current settings fall in the perceptual phase space mapped by van Noorden (1975): boundary curves separate regions where integration or streaming reliably occur, with an ambiguous zone between them. This page cannot know which state you are in. It schedules sine-wave bursts. The rest happens in you.
Presentation rate
6.0/s
Tones per second (low and high alternate)
Frequency gap
6 st
Semitones between tones (low = 440 Hz reference)
Current frequencies
low: 440 Hz
high: 622 Hz
Phase space · van Noorden (1975)
Tone sequence (scrolling · blue = low · orange = high)
Adjust sliders, then play
What the simulation cannot show: whether the tones are one stream or two. The visualization always displays both tones together — the low blocks and high blocks, side by side — because it has no access to the perceptual state occurring in whoever is listening. The mutual inhibition that produces streaming (or doesn't) runs in the auditory cortex, not in the code. The phase diagram is the historical trace of where the boundary tended to fall across many subjects in van Noorden's experiments — a probabilistic description of the perceptual territory, not a measurement of your current state. In the ambiguous zone, you may be able to tip between percepts deliberately: attend to just the low tones and hear them emerge as a separate rhythm, then release. The page cannot detect this. Both states are generated by the same two-tone sequence. See entry 560.