Deutsch's Musical Illusions
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Here we describe and illustrate some of Deutsch’s musical illusions and paradoxes. They show that people can differ strikingly in the way they hear very simple musical patterns. These disagreements do not reflect variations in musical ability or training. Even the finest musicians, on listening to the stereo illusions described here, may disagree completely as to whether a high tone is being played to their right ear or to their left. And the most expert musicians, on listening to the tritone paradox, can engage in long arguments as to whether a pattern of only two tones is moving up or down in pitch.
How do we explain these striking perceptual discrepancies? In the case of the stereo illusions, disagreements tend to arise between righthanders and lefthanders, indicating that they reflect variations in brain organization. In contrast, the way the tritone paradox is perceived varies with the geographical region in which listener grew up, so differences here are related to the languages or dialects to which people are exposed.
The illusions and paradoxes described here lead us to wonder what other curiosities of music perception might exist that have not yet been discovered. But using the principles that generate these illusions, we can now produce music that sounds radically different from one listener to another, and even from one audience to another.
A few of the illusions are posted here as sound examples, but these and others are contained in Deutsch’s compact discs ‘Musical Illusions and Paradoxes’ (Philomel Records, 1995) and 'Phantom Words and Other Curiosities' (Philomel Records, 2003)
In listening to these illusions, it is important to use equipment with a flat frequency response so as to avoid spectral distortion. For example, enhanced high frequency transients tend to degrade the effects. And features that alter the signal in any way, such as spatialization features, should be turned off. Also make sure that the playback amplitude is not too high. With many sound systems, this amplitude needs to be set at a different level depending on whether you are listening through headphones or loudspeakers, and you might want to determine the appropriate settings before you begin. When you are listening to the stereo illusions through loudspeakers, it is best to be positioned equidistant between the speakers, with one to your left and the other to your right.
