Multistable perception of ambiguous melodies and the role of musical expertise

Whereas visual demonstrations of multistability are ubiquitous, there are few auditory examples. The purpose of the current study was to determine whether simultaneously presented melodies, such as underlie the scale illusion [Deutsch (1975). J. Acoust. Soc. Am. 57(5), 1156-1160], can elicit multiple mutually exclusive percepts, and whether reported perceptions are mediated by musical expertise. Participants listened to target melodies and reported whether the target was embedded in subsequent test melodies. Target sequences were created such that they would only be heard if the listener interpreted the test melody according to various perceptual cues. Critically, and in contrast with previous examinations of the scale illusion, an objective measure of target detection was obtained by including target-absent test melodies. As a result, listeners could reliably identify target sequences from different perceptual organizations when presented with the same test melody on different trials. This result demonstrates an ability to alternate between mutually exclusive percepts of an unchanged stimulus. However, only perceptual organizations consistent with frequency and spatial cues were available and musical expertise did mediate target detection, limiting the organizations available to non-musicians. The current study provides the first known demonstration of auditory multistability using simultaneously presented melodies and provides a unique experimental method for measuring auditory perceptual competition.