The ABA- triplet is an auditory signal consisting of tones A and B at fixed frequencies with '-' representing a brief gap of silence.  Each triplet lasts a total of 600ms.  For certain frequency differences between the A and B tones, a listener presented with repeated sequences of triplets can alternate between two perceptual states:

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• 1 stream in which the stimulus is integrated into a single, galloping like stream.

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• 2 streams in which the stimulus is separated into two distinct streams, like a morse code signal.

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On this page there are 2 audio files

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• Control audio.  In this file the stimulus (the frequency of the A tone) changes to induce switching between the perceptual states.  Play this file to get a sense of the two perceptual states.  Stimulus changes occur at the approximate time marks: (1 - 5 sec: 1 stream);  (5 - 27 sec: 2 streams); (27 - 37 sec: 1stream); (37 - 42 sec: 2 streams); and (42 - 50 sec: 1 stream).

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• Bistable audio.  In this file the the stimulus does not change for the entire duration of the clip.

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Play the bistable audio file.  How do you perceive the auditory stimulus?  Do you alternate between the perceptual states?