Circularity in relative pitch judgments for inharmonic complex tones: The Shepard demonstration revisited,again

The Shepard illusion, in which the presentation of a cyclically repetitive sequence of complex tones composed of partials separated by octave intervals (Shepard, 1964) gives the illusion of an endlessly increasing sequence of pitch steps, is often cited as evidence for octave equivalence. In this paper, evidence is presented which demonstrates that this illusion can be produced using (inharmonic) complex tones whose partials are separated by equal ratios other than octaves. Therefore, the illusion is not evidence for octave equivalence.