Binaural Beats
Binaural beats are of interest to neurophysiologists investigating the sense of hearing. Second, binaural beats reportedly influence the brain in more subtle ways through the entrainment of brainwaves and can be used to produce relaxation and other health benefits such as pain relief.
The brain produces a phenomenon resulting in low-frequency pulsations in the loudness of a perceived sound when two tones at slightly different frequencies are presented separately, one to each of a subject's ears, using stereo headphones. A beating tone will be perceived, as if the two tones mixed naturally, out of the brain. The frequency of the tones must be below about 1,000 to 1,500 hertz for the beating to be heard. The difference between the two frequencies must be small (below about 30 Hz) for the effect to occur; otherwise, the two tones will be heard separately and no beat will be perceived.
A Brief History
Heinrich Wilhelm Dove discovered binaural beats in 1839. While research about them continued after that, the subject remained somewhat of a scientific curiosity until 134 years later, with the publishing of Gerald Oster's article "Auditory Beats in the Brain" (Scientific American, 1973). Oster's article identified and assembled the scattered islands of relevant research since Dove, offering tremendous fresh insight (and new laboratory findings) to research on binaural beats.
In particular, Oster saw binaural beats as a powerful tool for cognitive and neurological research, addressing questions such as how animals locate sounds in their three-dimensional environment, and also the remarkable ability of animals to pick out and focus on specific sounds in a sea of noise (what is known as the "cocktail party effect").
Oster also considered binaural beats to be a potentially useful medical diagnostic tool, not merely for finding and assessing auditory impairments, but also for more general neurological conditions. (Binaural beats involve different neurological pathways than ordinary auditory processing.) For example, Oster found that a number of his subjects that could not perceive binaural beats suffered from Parkinson's disease. In one particular case, Oster was able to follow the subject through a week-long treatment of Parkinson's disease; at the outset the patient could not perceive binaural beats; but by the end of the week of treatment, the patient was able to hear them.
In corroborating an earlier study, Oster also reported gender differences in the perception of beats. Specifically, women seemed to experience two separate peaks in their ability to perceive binaural beats- peaks possibly correlating with specific points in the menstrual cycle (onset of menstruation and approx. 15 after). This data led Oster to wonder if binaural beats could be used as a tool for measuring relative levels of estrogen.
The effects of binaural beats on consciousness were first examined by physicist Thomas Campbell and electrical engineer Dennis Mennerich, who under the direction of Robert Monroe sought to reproduce a subjective impression of 4Hz oscillation that they associated with out-of-body experience. On the strength of their findings, Monroe spawned the binaural self-development industry by forming The Monroe Institute, now a charitable binaural research and education organization.
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