Auditory illusion

Causes

Many auditory illusions, especially those involving music and speech, arise from hearing sound patterns that are highly probable even when heard incorrectly, due to the influence of prior knowledge and experience. The human auditory system relates sounds from different spaces as coming from one source to prevent perceiving echo, yet this does not prevent being fooled by illusions. Embedded sounds found in words cause some illusions; a person's perception of a word can be influenced by seeing a speaker's mouth move, even if the sound is unchanged.

For example, looking at two people saying "far" and "bar" determines which word is heard. If these sounds loop, different words become audible within the same sound. People with brain damage can become more susceptible to auditory illusions.

In music

For a long time, composers have adjusted the spatial qualities of music to shape what listeners hear. A frequent technique involves combination tones, which are auditory illusions. These sounds do not exist as actual sound waves; instead, they are generated by the listener's own neurological processes. Purwins notes that effective uses of auditory illusions appear in works by Beethoven, Berg, Krenek, Ligeti, Honegger, and Stahnke.