Binaural beats or
binaural tones are
auditory processing artifacts, or apparent sounds, the
perception of which arises in the brain for specific physical
stimuli. This effect was discovered in 1839 by
Heinrich Wilhelm Dove, and earned greater public awareness in the late 20th century based on claims that binaural
beats
could help induce relaxation, meditation, creativity and other
desirable mental states. The effect on the brainwaves depends on the
difference in frequencies of each tone: for example, if 300 Hz was
played in one ear and 310 in the other, then the binaural beat would
have a frequency of 10 Hz.
[1][2]
The brain produces a phenomenon resulting in low-frequency pulsations in the
amplitude and
sound localization
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 frequencies of the tones must be below 1,000
hertz for the beating to be noticeable.
[3]
The difference between the two frequencies must be small (less than or
equal to 30 Hz) for the effect to occur; otherwise, the two tones will
be heard separately and no beat will be perceived.
Binaural beats are of interest to
neurophysiologists investigating the
sense of hearing.
[4][5][6][7]
Binaural beats reportedly influence the brain in more subtle ways through the
entrainment of
brainwaves[3][8][9] and have been claimed to reduce anxiety
[10] and to provide other health benefits such as control over pain.
[11]
Acoustical background
Interaural time differences (ITD) of binaural beats
For
sound localization the human
auditory system analyses
interaural time differences between both ears inside small frequency ranges, called
critical bands. For frequencies below 1000 to 1500
Hz interaural time differences are evaluated from interaural phase differences between both ear signals.
[12] The perceived sound is also evaluated from the analysis of both ear signals.
If different
pure tones (
sinusoidal
signals with different frequencies) are presented to each ear, there
will be time dependent phase and time differences between both ears (see
figure). The perceived sound depends on the frequency difference
between both ear signals:
- If the frequency difference between the ear signals is lower than
some hertz, the auditory system can follow the changes in the interaural
time differences. As a result an auditory event
is perceived, which is moving through the head. The perceived direction
corresponds to the instantaneous interaural time difference.
- For slightly bigger frequency differences between the ear signals
(more than 10 Hz) the auditory system can no longer follow the changes
in the interaural parameters. A diffuse auditory event appears. The
sound corresponds to an overlay of both ear signals, which means
amplitude and loudness are changing rapidly (see figure in the chapter
above).
- For frequency differences between the ear signals of above 30 Hz the cocktail party effect
begins to work, and the auditory system is able to analyze the
presented ear signals in terms of two different sound sources at two
different locations, and two distinct signals are perceived.
Binaural beats can also be experienced without headphones, they
appear when playing two different pure tones through loudspeakers. The
sound perceived is quite similar: with auditory events which move
through the room, at low frequency differences, and diffuse sound at
slightly bigger frequency differences. At bigger frequency differences
apparent localized sound sources appear.
[13] However, it is more effective to use headphones than loudspeakers.
History
Heinrich Wilhelm Dove discovered binaural beats in 1839. While
research about them continued after that, the subject remained something
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 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
(which 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 during the
luteal phase. This data led Oster to wonder if binaural beats could be used as a tool for measuring relative levels of
estrogen.
[3]
The effects of binaural beats on consciousness were first examined by physicist
Thomas Warren Campbell and electrical engineer Dennis Mennerich, who under the direction of
Robert Monroe sought to reproduce a subjective impression of 4 Hz oscillation that they associated with
out-of-body experience.
[14] On the strength of their findings, Monroe created the binaural-beat technology self-development industry by forming
The Monroe Institute, now a charitable binaural research and education organization.
Unverified claims
There have been a number of claims regarding binaural beats, among
them that they may simulate the effect of recreational drugs, help
people memorize and learn, stop smoking, help dieting, tackle erectile
dysfunction and improve athletic performance.
Scientific research into binaural beats is very limited. No
conclusive studies have been released to support the wilder claims
listed above. However, one
uncontrolled pilot study[15]
of 8 individuals indicates that binaural beats may have a relaxing
effect. In absence of positive evidence for a specific effect, however,
claimed effects may be attributed to the power of suggestion (the
placebo effect).
In a blind study (8 participants) of binaural beats' effects on
meditation, 7 Hz frequencies were found to enhance meditative focus
while 15 Hz frequencies harmed it.
[16]
Physiology
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 and to track moving sounds, which also
involves inferior colliculus (IC) neurons.
[17]
Regarding entrainment, the study of rhythmicity provides insights into
the understanding of temporal information processing in the human brain.
Auditory rhythms rapidly entrain motor responses into stable steady
synchronization states below and above conscious perception thresholds.
Activated regions include primary sensorimotor and cingulate areas,
bilateral opercular premotor areas, bilateral SII, ventral prefrontal
cortex, and, subcortically, anterior insula, putamen, and thalamus.
Within the cerebellum, vermal regions and anterior hemispheres
ipsilateral to the movement became significantly activated. Tracking
temporal modulations additionally activated predominantly right
prefrontal, anterior cingulate, and intraparietal regions as well as
posterior cerebellar hemispheres.
[18]
A study of aphasic subjects who had a severe stroke versus normal
subjects showed that the aphasic subject could not hear the binaural
beats whereas the normal subjects could.
[19]
Hypothetical effects on brain function
Overview
Binaural beats may influence functions of the brain in ways 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).
[20]
In addition, binaural beats have been credibly documented to relate to
both spatial perception & stereo auditory recognition, and,
according to the frequency following response, activation of various
sites in the brain.
[21][22][23][24][25]
The stimulus does not have to be
aural; it can also be visual
[26] or a combination of aural and visual
[27] (one such example would be
Dreamachine).
Perceived human hearing is limited to the range of frequencies from
20 Hz to 20,000 Hz, but the frequencies of human brain waves are below
about 40 Hz. To account for this lack of perception, binaural beat
frequencies are used. Beat frequencies of 40 Hz have been produced in
the brain with binaural sound and measured experimentally.
[28]
When the perceived
beat frequency corresponds to the
delta,
theta,
alpha,
beta, or
gamma range of
brainwave frequencies, the brainwaves entrain to or move towards the beat frequency.
[29]
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 effect or if in the beta range,
more alertness. An experiment with binaural sound stimulation using beat
frequencies in the Beta range on some participants and Delta/Theta
range in other participants, found better vigilance performance and mood
in those on the awake alert state of Beta range stimulation.
[30][31]
Binaural beat stimulation has been used fairly extensively to induce a
variety of states of consciousness, and there has been some work done
in regards to the effects of these stimuli on relaxation, focus,
attention, and states of consciousness.
[8]
Studies have shown that with repeated training to distinguish close
frequency sounds that a plastic reorganization of the brain occurs for
the trained frequencies
[32] and is capable of asymmetric hemispheric balancing.
[33]
Brain waves
| Frequency range |
Name |
Usually associated with: |
| > 40 Hz |
Gamma waves |
Higher mental activity, including perception, problem solving, fear, and consciousness |
| 13–39 Hz |
Beta waves |
Active, busy or anxious thinking and active concentration, arousal, cognition, and or paranoia |
| 7–13 Hz |
Alpha waves |
Relaxation (while awake), pre-sleep and pre-wake drowsiness, REM sleep, Dreams |
| 8–12 Hz |
Mu waves |
Sensorimotor rhythm Mu_rhythm, Sensorimotor_rhythm |
| 4–7 Hz |
Theta waves |
deep meditation/relaxation, NREM sleep |
| < 4 Hz |
Delta waves |
Deep dreamless sleep, loss of body awareness |
(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, other
frequencies will also 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 less for a waking person), and
then slowly decreasing/increasing 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 should not necessarily 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).
Other uses
In addition to lowering the brain frequency to relax the listener,
there are other controversial, alleged uses for binaural beats. For
example, that by using specific frequencies an individual can stimulate
certain
glands to produce desired
hormones. Beta-endorphin has been modulated in studies using alpha-theta brain wave training,
[34] and dopamine with binaural beats.
[1]
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;
[citation needed] and some people find that half an hour in the theta state can reduce sleeping needs up to four hours;
[citation needed] similar to another method of achieving a theta state, e.g.
meditation;
[citation needed]) some use them for
lucid dreaming and even for attempting
out-of-body experiences,
astral projection,
telepathy and
psychokinesis. However, the role of alpha-wave activity in lucid dreaming is subject to ongoing research).
[35][36][37]
Alpha-theta brainwave training has also been used successfully for the treatment of
addictions.
[34][38][39]
It has been used for the recovery of
repressed memories, but as with other techniques this can lead to
false memories.
[40]
An uncontrolled pilot study of Delta binaural beat technology over 60
days has shown positive effect on self-reported psychologic measures,
especially anxiety. There was significant decrease in trait anxiety, an
increase in quality of life, and a decrease in insulin-like growth
factor-1 and dopamine
[1] and has been successfully shown to decrease mild anxiety.
[41] A randomised, controlled study concluded that binaural beat audio could lessen hospital acute pre-operative anxiety.
[42]
Another claimed effect for sound induced brain synchronization is
enhanced learning ability. It was proposed in the 1970s that induced
alpha brain waves enabled students to assimilate more information with
greater long term retention.
[43] In more recent times has come more understanding of the role of theta brain waves in behavioural learning.
[44]
The presence of theta patterns in the brain has been associated with
increased receptivity for learning and decreased filtering by the left
hemisphere.
[43][45][46]
Based on the association between theta activity (4–7 Hz) and working
memory performance, biofeedback training suggests that normal healthy
individuals can learn to increase a specific component of their EEG
activity, and that such enhanced activity may facilitate a working
memory task and to a lesser extent focused attention.
[47]
A small media controversy was spawned in 2010 by an Oklahoma Bureau
of Narcotics official comparing binaural beats to illegal narcotics, and
warning that interest in websites offering binaural beats could lead to
drug use.
[48]
See also
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