Tritone paradox

Roger Shepard in 1963 had argued that such tone pairs would be heard ambiguously as either ascending or descending.

Furthermore, the way these tone pairs were perceived varied depending on the listener's language or dialect.

The amplitudes of the sinusoids of both complexes are determined by the same fixed-amplitude envelope—for example, the envelope might be centered at 370 Hz and span a six-octave range.

Shepard predicted that the two tones would constitute a bistable figure, the auditory equivalent of the Necker cube, that could be heard ascending or descending, but never both at the same time.

In addition, Deutsch found that subjects from the south of England and from California resolved the ambiguity the opposite way.