Pitch circularity as found in Shepard tones was examined by using complex tones that had various degrees of exactness in their spectral periodicities on the logarithmic frequency dimension. This dimension was divided into periods of 1400 cents by tone components, and each period was subdivided into two parts of a fixed ratio of 700:700, 600:800, 550:850, 500:900, 450:950, 400:1000, or 0:1400. Subjects made paired comparison judgments for pitch. When the subdividing ratio was 0: 1400 or 400:1000, the subjects responded to the spectral periodicity of 1400 cents, and, when the ratio was 700:700 or 600:800, they responded to the periodicity of 700 cents. Some seemingly intermediate cases between these two extremes or some qualitatively different cases were obtained in the other conditions. As we have asserted before, the human ear appears to detect a global pitch movement when some tone components move in the same direction by similar degrees on the logarithmic frequency dimension.
Emergent pitch perception using short term plasticity
