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Binaurale Beats

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Binaural beats or binaural tones are auditory processing artifacts, that is apparent sounds, the perception of which arises in the brain independent of physical stimuli. This effect was discovered in 1839 by Heinrich Wilhelm Dove.

In nature, two sounds that are similar but slightly shifted in frequency will beat to produce two new frequencies which are the average and the difference of the original two sounds. For example, a 400 Hz tone and a 410 Hz tone will form a ~405 Hz tone pulsating 10 times per second.

The brain produces a similar phenomenon internally, 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.

Interest in binaural beats can be classified into two categories. First, they are of interest to neurophysiologists investigating the sense of hearing. Second, some protoscientists believe that binaural beats may influence the brain in more subtle ways through the entrainment of brainwaves and can be used to produce relaxation and other health benefits.

History

Heinrich Wilhelm Dove discovered binaural beats in 1839. While research about them continued after that, the subject basically remained 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 paper was landmark not so much for its own new laboratory findings, but rather that in the way in which it identified and tied together the isolated islands of relevant research done since Dove, in a way that gave the subject fresh insight and relevance to scientific research.

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 (because they involved different neurological pathways than ordinary auditory processing) for more general neurological conditions. For example, Oster found that a number of the subjects he worked with that were incapable of perceiving binaural beats suffered from Parkinson's disease. In one case, Oster was able to follow one such subject through a week-long treatment of Parkinson's disease; at the outset the patient couldn't perceive binaural beats, but by the end of the week of treatment, the patient could hear them again.

Oster also reported (in corroborating an earlier study) that there were gender differences in the perception of beats. Specifically, women seemed to experience two separate peaks in their ability to perceive binaural beats that seemed to correlate with specific points in the menstrual cycle (one at the onset of menstruation, one around 15 days later), which led Oster to wonder if binaural beats could be used as a tool for measuring relative levels of estrogen.

Physiology

Vorlage:Expand-section The sensation of binaural beats is believed to originate in the superior olivary nucleus, a part of the brain stem. They appear to be related to the brain's ability to locate the sources of sounds in three dimensions.

Hypothetical effects on brain function

Vorlage:Weasel Vorlage:Details

Overview

Binaural beats may influence functions of the brain besides those related to hearing. This phenomenon is called frequency following response. The concept is that if one receives a stimulus with a frequency in the range of brain waves, the predominant brain wave frequency is said to be likely to move towards the frequency of the stimulus (a process called entrainment).

The stimulus does not have to be aural; it can also be visual (e.g. Dreamachine). However, using alpha frequencies with such stimuli can trigger photosensitive epilepsy.

Directly using an infrasonic auditory stimulus is impossible, since the ears cannot hear sounds low enough to be useful for brain stimulation. Human hearing is limited to the range of frequencies from 20 Hz to 20,000 Hz, while the frequencies of human brain waves are below about 40 Hz. To account for this, binaural beat frequencies must be used. (Actually, rhythmic sounds such as a metronome could be used if fast enough, but since they do not affect the same areas in the brain as binaural beats do, binaural beats advocates claim Vorlage:Fact that the latter are more effective.)

When the perceived beat frequency corresponds to the delta, theta, alpha or beta range of brainwave frequencies, the brainwaves entrain to or move towards the beat frequency. For example, if a 315 Hz sine wave is played into the right ear and a 325 Hz one into the left ear, the brain is entrained towards the beat frequency (10 Hz, in the alpha range). Since alpha range is associated with relaxation, this has a relaxing effectVorlage:Fact.

Brain waves

Frequency range Name Usually associated with:
> 40 Hz Gamma waves  Higher mental activity, including perception, problem solving, fear, and consciousness
13–40 Hz Beta waves Active, busy or anxious thinking and active concentration
7–13 Hz Alpha waves Relaxation (while awake)
4–7 Hz Theta waves Dreams, deep meditation
< 4 Hz Delta waves Deep dreamless sleep

(The precise boundaries between ranges vary among definitions, and there is no universally accepted standard.)

The dominant frequency determines your current state. For example, if in someone's brain alpha waves are dominating, they are in the alpha state (this happens when one is relaxed but awake). However, also other frequencies will be present, albeit with smaller amplitudes.

The brain entraining is more effective if the entraining frequency is close to the user's starting dominant frequency. Therefore, it is suggested to start with a frequency near to one's current dominant frequency (likely to be about 20 Hz or little less for a waking person), and then slowly decreasing it towards the desired frequency.

Some people find pure sine waves unpleasant, so a pink noise or another background (e.g. natural sounds such as river noises) can also be mixed with them. In addition to that, as long as the beat is audible, increasing the volume is supposed not to improve the effectiveness, therefore using a low volume is usually suggested. One theory is to reduce the volume so low that the beating should not even be clearly audible, but this does not seem to be the case (see the next paragraph).

Vorlage:POV-section

Other uses

In addition to lowering the brain frequency to relax the listener (or to raise it to help focusing), there are other controversial, alleged uses for binaural beats. For example, using specific frequencies you can stimulate certain glands to produce desired hormones, sometimes even relating them with chakras.Vorlage:Fact This is highly disputed, especially given the lack of reliable studies to support such claims and even among people who consider this possible many agree that the precise frequencies may vary from person to person.Vorlage:Fact

Among other alleged uses, there are reducing learning time and sleeping needs (theta waves are thought to improve learning, since children, who have stronger theta waves, and remain in this state for a longer period of time than adults, usually learn faster than adults; and some people find that half an hour in the theta state can reduce sleeping needs up to four hours; however, this is supposed to happen with any way to get into theta state, e.g. meditation); some use them for lucid dreaming and even for achieving out-of-body experiences, astral projection, telepathy and psychokinesis. However, most people believe that these phenomena (except lucid dreams, which are acknowledged even by mainstream science)Vorlage:Fact do not exist, let alone that they can be achieved by entraining the brain to a specific frequency.

Binaural beats have also been used experimentally for the treatment of addictions, and for the recovery of repressed memories, but as with other techniques this can lead to false memories.Vorlage:Fact

Example

Vorlage:Listen Vorlage:Listen

See also

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