Binaural beats

A binaural beat is an auditory illusion perceived when two different pure-tone sine waves, both with frequencies lower than 1500 Hz, with less than a 40 Hz difference between them, are presented to a listener dichotically (one through each ear). For example, if a 530 Hz pure tone is presented to a subject's right ear, while a 520 Hz pure tone is presented to the subject's left ear, the listener will perceive the auditory illusion of a third tone, in addition to the two pure-tones presented to each ear. The third sound is called a binaural beat, and in this example would have a perceived pitch correlating to a frequency of 10 Hz, that being the difference between the 530 Hz and 520 Hz pure tones presented to each ear.

The term 'binaural' literally signifies 'to hear with two ears ', and was introduced in 1859 to signify the practice of listening to the same sound through both ears, or to two discrete sounds, one through each ear. It was not until 1916 that Carl Stumpf (1848-1936), a German philosopher and psychologist, distinguished between dichotic listening, which refers to the stimulation of each ear with a different stimulus, and diotic listening, the simultaneous stimulation of both ears with the same stimulus.

Later, it would be become apparent that binaural hearing, whether dichotic or diotic, is the means by which the geolocation and direction of a sound is determined.

Scientific consideration of binaural hearing began before the phenomenon was so named, with the ideas articulated in 1792 by William Charles Wells (1757–1817), a Scottish-American printer, and physician at Saint Thomas' Hospital, London. Wells sought to theoretically examine and explain aspects of human hearing, including the way in which listening with two ears rather than one might affect the perception of sound, which proceeded from his research into binocular vision.

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