Musical Illusion

This Is Your Brain on Music: The Science of a Human Obsession. 

Daniel J. Levitin wrote about musical illusions reporting that:  “In piano works such as Sindig’s ‘The Rustle of Spring’ or Chopin’s Fantasy-Impromptu in C-sharp Minor, op. 66, the notes go by so quickly that an illusory melody emerges. Play the tune slowly and it disappears. Due to stream segregation, the melody ‘pops out’ when the notes are close enough together in time—the perceptual system holds the notes together—but the melody is lost when its notes are too far apart in time. As studied by Bernard Lortat-Jacob at the Musée de l’Homme in Paris, the Quintina (literally ‘fifth one’) in Sardinian a capella vocal music also conveys an illusion: A fifth female voice emerges from the four male voices when the harmony and timbres are performed just right. (They believe the voice is that of the Virgin Mary coming to reward them if they are pious enough to sing it right.)”