Auditory Illusions

Optical Illusions are a popular topic for children's books.  We're all familiar with the most famous ones.  Until recently, they were viewed as mere curiosities.  Today, they are studied by cognitive scientists as a path to reverse engineering the visual processing centers of the brain.

Auditory illusions are less familiar.  Sounds, groups of tones, and auditory patterns can form an equally boggling sensory experience.

Years of discovery, analysis, and reverse engineering of these illusions have born real fruit.  Through the field of psychoacoustics, researchers created MP3, AAC, and other modern computer audio formats. They reduce the size of sound files by throwing away huge portions of it.  The computer knows that you won't notice the missing bits.  MP3 can discard up to 90% of the original sound before you'll start to hear the gaps.

Not all auditory illusions have been discovered in modern times.  The Devil's Tritone is a musical illusion where the listener has difficulty figuring out if one needs to move up or down to find the home base.  Documented by medieval composers, its use was prohibited in sacred music written for the church. 

In modern times, Diana Deutsch discovered that listeners in California and England resolve a similar paradox in opposite ways.  The perception of sound can be influenced by culture.  Other illusions are perceived differently by left handed vs. right handed people reflecting differences in the way our brains are organized.