Deutsch tritone paradox

An auditory illusion the Deutsch tritone paradox was created to test the Shepard scale if proximity information was removed. Thus two Shepard tones exactly half an octave apart, a tritone, are played. Diana Deutsch found that perception of which tone was higher was dependent on the absolute frequencies involved, that one will consistently find the same tone as higher or lower, and that this is determined by absolute pitch, which is, however, thought to be extremely rare. Deutsch also found that British and Californian subjects consistently resolved the ambiguity the opposite way.