Deutsch's scale illusion
Discovered by Diana Deutsch in 1973, Deutsch's "scale illusion" is an auditory illusion in which principles of grouping by frequency, proximity, and spatial location are put into conflict and in which frequency proximity wins out. It is produced by simultaneous ascending and descending major scales beginning in separate stereo channels with each successive note being switched to the opposite channel. With the left channel: C'-D-A-F--A-D-C'; and the right: C-B-E-G-E-B-C; the ear hears both: C'-B-A-G--A-B-C'; and: C-D-E-F--E-D-C. The tones are equal-amplitude sine waves, and the sequence is played repeatedly without pause at a rate of four tones per second. (Listen to the Stereo Sound Example linked below.)
When listening to the illusion over headphones, most right-handers hear a melody corresponding to the higher tones as on the right and a melody corresponding to the lower tones as on the left. When the earphone positions are reversed, the higher tones continue to appear to be coming from the right and the lower tones from the left. Other people experience different illusions, such as the higher tones on the left and the lower tones on the right, or a pattern in which the sounds appear to be localized in different and changing ways. Right-handers and left-handers differ statistically in how the scale illusion is perceived.
The above example, played first a channel at a time, then simultaneously.
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- Deutsch, D. (1974). "An illusion with musical scales". Journal of the Acoustical Society of America 56: s25. doi:10.1121/1.1914084. Abstract
- Deutsch, D. (1975). "Two-channel listening to musical scales". Journal of the Acoustical Society of America 57 (5): 1156–1160. doi:10.1121/1.380573. PMID 1127169. Abstract PDF Document
- Deutsch, D. (1975). "Musical Illusions". Scientific American 233 (4): 92–104. doi:10.1038/scientificamerican1075-92.
- Deutsch, D. (1979). "Binaural integration of melodic patterns". Perception & Psychophysics 25 (5): 399–405. doi:10.3758/BF03199848. PMID 461100. PDF Document
- Deutsch, D. (1983). "Auditory illusions, handedness, and the spatial environment". Journal of the Audio Engineering Society 31: 607–618.
- Deutsch, D. (1985). "Dichotic Listening to Melodic Patterns and Its Relationship to Hemispheric Specialization of Function". Music Perception 3: 127–154. doi:10.2307/40285329. PDF Document
- Deutsch, D. (1987). "Illusions for Stereo Headphones". Audio Magazine: 36–48. PDF Document
- Radvansky GA, Hartmann WM, Rakerd B. (1992). "Structural alterations of an ambiguous musical figure: the scale illusion revisited". Perception & Psychophysics 52 (3): 256–62. doi:10.3758/bf03209143. PMID 1408637.
- Deutsch, D. (1999). "Grouping mechanisms in music. In D. Deutsch (Ed.)". The psychology of music, 2nd Edition: 299–348. doi:10.1016/b978-012213564-4/50010-x. PDF Document
- Bregman, Albert (1994). Auditory Scene Analysis: The Perceptual Organization of Sound, p.76. ISBN 0-262-52195-4.