Rhythmic Fission and Perceptual Organization

Tone sequences presented at rates of about 10 tones/sec and constructed such that successive tones have large, and alternate tones small, frequency intervals between them, are heard as two simultaneous melodic patterns formed of the alternate tones. This effect, called rhythmic fission, can also be effected by intensity differences or stereophonic separation between the patterns. (1) The intensity difference can be in either direction. The softer, as well as the louder, of the two patterns can be attended to as “figure.” (2) More stereo separation is required to make a melody distinct from a random background than from most melodically patterned backgrounds. This is true even though the random sequences were already more separate from the melodies in terms of frequency differences between successive notes than were the other melodic patterns. (3) Embedding a melody in alternate tones of the same intensity and randomly selected from the same frequency range produces a meaningless jumble. However, when told...