Octave illusion

It is produced when two tones that are an octave apart are repeatedly played in alternation ("high-low-high-low") through stereo headphones.

Of the remaining subjects, nearly three times as many right-handers than left-handers heard a tone that switched ears but not pitch.

[2] Deutsch proposed that when a single tone that alternates between octaves is heard, this illusion results from the combined operation of two decision mechanisms.

[3] This is known as the two-channel model, since it is proposed that the operation of two separate "what" and "where" decision mechanisms combine to produce the illusion.

They performed an experiment similar to Deutsch’s original, except the two tones that were used ranged in interval from a minor third to an eleventh.

Chambers, Moss, and Mattingley believe that the illusion is caused by a combination of harmonic fusion and binaural diplacusis, a condition in which a pitch is perceived slightly differently between ears.

This does not necessarily conflict with other studies, as the number of subjects used in this experiment was small and there are individual differences in perception of the illusion.

Deutsch (2004a)[12] used a new procedure, which provided more explicit documentation of the octave illusion; here musically trained subjects notated precisely what they heard.

The experiment confirmed that subjects, on listening to the illusion, perceive an octave difference between the ears.

This result cannot be explained by diplacusis, which refers to a difference of a fraction of a semitone between the ears.

For example, Oehler and Reuter recently replicated the handedness correlate in a study of 174 subjects[14] Lamminmaki and Hari (2000)[15] and Lamminmaki et al. (2012)[16] in MEG studies provide an explanation of the illusion at the neurophysiological level that is in accordance with Deutsch’s two-channel model.