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Bistable stimuli can be perceived in two separate ways. The sound you hear can be heard in two ways: as triplets of an A-B-A pattern or as two simultaneous streams of an A-A-A-A pattern and a B-B-B-B pattern.
Typically, discussions of illusory experiences focus on visual illusions. But auditory illusions (and illusions in other sensory modalities, including cross-modal ones) are also interesting. Illusions in general provide us with cases in which what we experience doesn't seem to match reality. If that's right, we are not experiencing reality, and we can ask what it is that we are experincing. If that's not right, then we can ask why we appear to experience something that doesn't match reality, and whether we really are experiencing what we take ourselves to be experiencing. Illusions in sensory modalities other than vision show us that this issue affects experiences in other modalities, such as audition, touch, taste, smell, and so on.
An interesting question is whether there are any interesting similarities in illusory experiences across different sensory modalities. Bistable auditory stimulus illusions support an affirmative answer to this question. The experience of being able to auditorily experience two different tunes in response to the one stimulus is reminiscent of visual ambiguous figures, such as the Duck-Rabbit, which is one image that can elecit two very different visual experiences: that of a duck or that of a rabbit. Common to all these illusions is that they can cause two (or more) different experiences. You may want to search for other ambiguous stimuli in the Illusions Index.
