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Tonal Circularity -- Shepard Tones

Up until recently two succesive paradigms of pitch perception have prevailed within music psychology research literature.  The first of these understood pitch as a one-dimensional scale phenomenon.  The research of S. S. Stevens J. Volkman, and E. B. Newman exemplified the strengths of this paradigm (for a more detailed investigation of this notion of pitch, see the Pitch chapter  of the IPL audio unit).

The second paradigm called the single-dimensional perception of pitch into question, noting that pitch is too complex a perceptual phenomenon to be accurately represented in a single linear scale.  Of particular significance here is the observation that many people, particularly trained musicians, perceive tones in a cyclic manner, which cycle repeats at the octave.  This notion of tone can be represented graphically using a helix and thus articulating a dual-aspect concept of tone involving both height and chroma  (see Tone Perception for a more detailed discussion and set of demonstrations).