In the octave illusion, one tone is presented to one ear while another tone, exactly one octave higher or lower, is presented simultaneously to the other ear. However, the next note combination is of the same two notes, but to the opposite ears. That is, if a middle C is presented to the left ear, and the C an octave lower is presented to the right ear, the next notes will be a middle C presented to the right ear and the C an octave lower presented to the left ear.
What do you actually hear? What most people report hearing is the following: You hear a single note (the middle C) in your right ear followed by a single note an octave lower in your left ear. And then a continuous alternation between the two occurs, regardless of which ear the higher C is actually being presented to.
In this illustration, you can listen to the octave illusion and manipulate a few features of the tones to see what the illusion might be dependent upon.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
Below is a list of the ways that you can alter the illustration. The settings include the following:
Play: will play to tone combination alternating which ear gets the lower
and higher pitch.
Play Series: will play a series of tone combinations to help you hear the octave illusion.
Play in: play the tones in the Left Ear only, Both Ears, or the Right Ear only. The octave illusion can be only experienced when the tones are played to both ears.
Interval: the tones differ by an Octave, a Fifth, or a Third. You can also play the tones that are an octave apart but in the right ear the tones are Up a Semitone or Up a Third from the tones in the left ear.
Duration (ms): the duration of the tones in milleseconds.
Pressing this button restores the settings to their default values.