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Octave Illusion

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The octave illusion is an auditory illusion discovered by Diana Deutsch in 1973. It is produced when two tones that are an octave apart are repeatedly played in alternation (‘high-low-high-low’) through stereo headphones.


The same sequence is played to both ears simultaneously; however when the right ear receives the high tone the left ear receives the low tone; and vice versa. Instead of hearing two alternating pitches, most subjects instead hear a single tone that alternates between ears while at the same time its pitch alternates between high and low. 


This is the Deutsch's Octave Illusion. Listen through high quality stereo headphones with the loudspeakers turned off.  (Don’t expect to hear the illusion via loudspeakers in a normal room environment.) Also make sure that the two headphone channels are carefully balanced for loudness.

If you hear a high tone in one ear and a low tone in the other ear, decide which ear is hearing the high tone. Then reverse the earphones while the pattern is playing, and decide again which ear is hearing the high tone.


Most righthanders hear the high tone on the right and the low tone on the left, regardless of how the earphones are positioned. Lefthanders and ambidextrous people are more varied in terms of where the high and low tone appear to be coming from.  They are also more likely to obtain complex percepts, such as three different tones that often change their apparent locations in space.


The next sound file presents Deutsch’s Octave Illusion first with the two channels in stereo, then with the channels mixed together, and then with the channels in stereo again. Notice that when the two channels are mixed together you only hear a single tone with clicks occurring four times a second. Yet when the two channels are presented in stereo, the pattern of high and low tones occurs instead.   


Octave illusion example 


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