Deutsch tritone paradox

The Deutsch tritone paradox is an auditory illusion created by Diana Deutsch (creator of a number of auditory illusions) 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: one will consistently find the same tone as higher or lower, and this is determined by the tones' absolute pitch. This is consistently done by a large portion of the population, despite the fact that responding differently to different tones must involve the ability to hear absolute pitch, which was thought to be extremely rare. Deutsch also found that British and Californian subjects consistently resolved the ambiguity the opposite way.