Binaural Beat Technology, a Premature Market
ABSTRACT: Certain training devices and some sound effects can modify the global electrical activity of your brain. From epilepsy to some mood disorders targets for possible clinical uses keep growing. Though insufficiently studied an aggressively appealing new age industry is flooding the market with recordings that give promise of enhancing brain power; from meditation to memorizing, from relaxation to alert states of more efficient functioning.
The confusing information around this not-so-new market and the Binaural Beats upon which it is construed have led this comprehensive review that explores the fundamentals of sound location, the Binaural Beat effect, brain waves and EEG biofeedback, in order to provide some basic information with which to confront the believe-it-or-not bet of new age "brain training".
(leer artículo en Castellano)
Introduction
A Binaural Beat is a sound effect that creates a wave "inside the head" of the listener. As the frequency range of these waves is equivalent to that of electrical waves generated by brain activity binaural beats can be used to induce specific brain waves and thus, supposedly, to generate specific mental states.
The whole matter is really that simple. The aim of this review is to discover how and to what extent all this is true and how and to what extent can the marketed promises of products such as Hemi-Sync or iMusic recordings be given any credit.
The first part of this article is dedicated to sound location which will allow an understanding of what Binaural Beats are. Then some general ideas on the electrical activity of the brain and electroencephalographic (EEG) measures are purported to later discover how can those be modified, either with EEG biofeedback or Binaural Beat recordings, and its implications.
Sound Location
Under normal conditions any sound will stimulate both, left and right ears, independently.
From the very beginning the brain processes auditory information binaurally (this is, from the conveying information coming from both, left and right ears). Binaural 
processing allows the brain to identify single auditory "objects", interpreting left and right different inputs not as two distinct sounds but as only one percept.
Imagine there is someone shouting right at your left ear. Not only the left but also the right auditory system will be stimulated by the shouting although their information (left and right) will differ as far as, for example, distance to the sound differs from one or the other ear. These differences will be compensated by particular assemblies of neurons to form a combined (single) perception and serve to calculate, for example, the location of sound in space.
Location of sound depends on inter-aural (left-right) differences in volume (sound intensity), time and phase differences (Fig 1) and on the Head Related Transfer Function (HRTF), which is an expression of the particular characteristics of ears and cranial configuration and the way these relate to sounds of different locations in space. Basically the HRTF purports information of distance to the sound in a sagittal plane while intensity and time and phase differences provide an angular value in a transversal (horizontal) plane (Fig 2). Jointly a three-dimensional spotting of the source of sound is thus calculated.
Let us say left and right ears are stimulated with sounds such as those expressed in Fig 3 and let us convey that the HRTF function for these sounds locate them 2 meters in front of the listener. As far as there are no intensity or phase differences no left-right angular deviation will be perceived and so the source of the sound will be located right in front of the listener. But let us now imagine that the HRTF informs that the distance to both ears is null; in this case the source of the sound will be located inside the cranium of the listener (Fig 4). This is precisely what happens when one listens to (non-stereo) music with headphones; sounds are perceived as if located somewhere inside the head.
When using headphones a slight difference in phase of left and right sounds (Fig 1) will shift the location of the sound (still perceived as if inside the cranium) a little bit towards the side of the wave interpreted to come first (Fig 5; in Fig 1 the Blue (right) wave would be interpreted as arriving before the Red (left) one).
Binaural Beats
The pitch of a sound (Fig 6) is determined by its wavelength (deeper sounds have larger wavelengths than high-pitched ones). "Binaural Beat" is the name given to the sound effect that is perceived when listening to sounds in the left and right ears (using headphones) that differ slightly in pitch.
This slight difference in pitch produces a progressive displacement of right and left waves (Fig 7). As already seen in Fig 5 a mismatch in the phase of right and left waves displaces the perceived location of the sound towards one side. A progressive mismatch will be perceived as if the location of the sound (always inside the cranium) was moving (Fig 8). When the difference in pitch is small the mismatch-rematch of both waves occurs so fast that the "movement" of the sound is perceived as a vibration, as if the source of the sound was vibrating inside the cranium. This vibration can itself be expressed as a wave and the value of its wavelength is exactly the right-left wavelength difference (pitch difference in cycles per second). This value (the wavelength of the perceived movement of the sound) is very interesting as already mentioned and as we will soon see.
For the binaural beat (the perception of a vibrating sound inside the cranium) to take place the right-left pitch difference must be less than 30 Hz (cycles per second) or else the listener will perceive two different sounds, produced at the right and left ears (as it is actually the case), instead of interpreting them as a single sound.
Jeff Fletcher in his highly recommendable article describes Binaural Beats as hallucinations. Not wanting to lessen a bit the magic of sound effects the truth is that every perceptual process in the brain is a "hallucination", a construct of "objects" from small pieces of information, many times unrelated. Allow me a digression to show you The Dancer (and please take a trip to the amazing web-page of Dr. Hugo; also, for visual "hallucinations", check out this link). You may perceive The Dancer (click on the image) as turning around anti-clockwise or maybe clockwise. If you try you can get yourself to perceive The Dancer turning the other way around. Some people do perceive spontaneously The Dancer as constantly changing the direction of her movement. Dr. Hugo oversimplifies when explaining that the turning direction perceived depends on right-left hemispheric dominance but whatever the explanation truth is that her very movement is a "hallucination". Anyway, hallucination in this sense only means an effect produced by a perceptual system that tries to convey information into single percepts or objects.
EEG and the Electrical Activity of the Brain
Neuronal cells are believed to be the functional substrate of mental activity. It is well known that a neuron can release molecules -at the synaptic spaces- that are able to change the membrane properties of the cell such stimulated. These membrane properties are related to the balance of certain ions, inside and outside the neuron, which is cause of the electrical changes that can be measured at this level.
The electrical activity of single neurons can be measured, even in humans, by inserting electrodes in the neuronal tissue. Costly -and rather aggressive- single neuron measures are of limited interest when trying to understand "mental states" or general brain function. The Electroencephalogram (EEG) is a far less specific but a non-invasive way to measure the global electrical activity of the brain.
Usually 10 to 20 electrodes are placed around the skull and measures of global electrical activity of different regions of the brain are thus obtained. Functional Magnetic Resonance Imaging (fMRI), which measures oxygen uptake, can also obtain indirect rates of brain activity but it is important to note here that either EEG or state-of-the-art fMRI measures are but crude approximations to brain functioning.
An EEG will show brain waves of different frequencies as it detects the adding electrical activity of enormous groups of neurons at a given time. Depending on general activity patterns it is observed that some kind of waves appear more often than others. Generally, a relaxed subject with closed eyes -or listening to Mozart- will show waves that range from 8 to 12 Hz, mainly on the posterior regions of the skull. These waves are called "alpha waves", as they were the first to be identified.
A "beta rhythm" corresponds to EEG waves of 12 to 30 Hz and appears often related to active and sometimes anxious thinking. On the opposite side very slow waves of less than 3 Hz are usually found during deep sleep in normal adult subjects.
Some pathological conditions do show particular wave patterns. For instance EEG studies are widely used to determine epileptic predisposition, observing spikes and sharp waves intermingled within the otherwise normal and chaotic "beta" or "alpha" rhythms. Some neurological conditions, drug induced states or mood disorders do show general deficits or excesses of particular wave frequency ranges. For example there are studies that suggest that some forms of attention-deficit hyperactivity disorder (ADHD) are related to an excess of low frequency waves and some anxiety and mood disorders are believed to be related to scarce "alpha" wave production.
Although not always consistent these results that point to more or less specific brainwave-frequency deficits or excesses as related to certain pathologies constitute the foundation of brainwave-oriented treatments. EEG biofeedback (or 'neurofeedback') is the particular form of biofeedback with which an individual can learn to stimulate and/or avoid certain brain wave frequencies.
Biofeedback
Basically biofeedback is a procedure in which a physiological variable (such as the cardiac frequency or the electrical conductance of the skin) is amplified and brought forward to the attention of a subject. Then the subject is motivated to find a way to change that variable in a specified direction which will (almost magically) enable him to (consciously) control an otherwise autonomic response.
A common way of biofeedback presentation is as a computer game in which the subject must try to control for example the movements of a spot on a screen (that changes its left-right position accordingly to the physiological variable being measured), following explicit instructions and with no other tools than his "mind" and the electrodes connected to the machine.
Thus defined biofeedback might seem a silly and inappropriate joke but truth is that it is an incredibly simple but powerful learning procedure. Its efficacy has been widely probed. Paradoxically enough best results have been found when the subject does not know what variable is he trying to affect.
As previously noted when the physiological variable being measured is (a localized) brain wave frequency the subject ends up learning how to facilitate the appearance of specific frequencies over others (a process that is sometimes called entraining). Many controversial and still germinal studies point to the efficacy of such a training method in certain mood disorders (facilitating slow "alpha" -relaxing- brain rhythms), ADHD (stimulating normal EEG patterns) or epilepsy (stimulating midrange brainwave frequencies).
Binaural Beats and the Frequency Following Effect
Binaural Beats are said to allow yet a different way of "tuning" the brain into specific wave frequencies. It has been mentioned before that binaural beats frequency range is below 30 Hz, which is similar to the brain wave frequency range found on EEG recordings. That range equivalence allows the Frequency Following Effect (FFE) to take place, by which brainwaves should slowly shift towards the frequency of the beat.
"Christiaan Huygens found out in 1665 that two pendulum clocks suspended by the side of each other did establish an odd kind of sympathy; the pendulum clocks swung with exactly the same frequency and 180 degrees out of phase. Synchronization has been found out to relay on platform motion such that damping effects favor antiphase motion (of the pendulums) while inphase oscillations induce additional counter-motion of the frame" (from Huygen's Clocks)
Synchronization means adjustment of rhythms of self-sustained periodic oscillators due to their weak interaction; this adjustment can be described in terms of phase locking and frequency entrainment. Biological systems do also show synchronization effects and the FFE would be but an example.
It has been described that the act of listening to binaural beats does promote a general brainwave pattern shift towards the (stable) frequency of the beat. Although this forced change of brainwave pattern has never been related to spontaneous mood or "mental state" corresponding changes "alpha" range Binaural Beats were promptly marketed as able to enhance meditative states or as anti-stress devices, embedded in natural sounds (waterfalls, bird singing, etc), slow repetitive mantras or rhythms and hypnotic or guided imagery chat.
The Hemi-Sync provides one of the oldest such recordings I know of; iMusic is one of the newest ones. iMusic amplifies the range of binaural beat frequencies extending it up to slow and not so slow "beta" rhythms and also down towards the slower side of "delta" sleep-facilitating waves, embedding the binaural beats in just normal music. Still very far from probe iMusic is said to enhance brain power, to turn you smarter, faster and probably happier.
As already mentioned an "alpha" rhythm is found on relaxed subjects. A biological cause-consequence confusion has led to believe that "alpha" wave stimulation must provoke a relaxed state. This has not been found.
Furthermore even the general brainwave shift after binaural beat stimulation is controversial. The FFE is actually related with short latency auditory evoked potentials and not with general effects over the brain. The Monroe Institute has led the investigation on this field and its consistently positive results relating binaural beat and global brainwave shifts have been called to caution after lack of independent similar results and patent links of this Institute with Hemi-Sync products (for further discussion read this experiment and critical review)
Conclusive Remarks
Passive training is probably one of the marks of our times. Devices for no-effort cooking, washing or physical shaping are in fashion. Passive brain training is no exception.
Neurofeedback is a fascinating tool that could well be used not only as a therapeutic instrument but also as a training device to prevent and equilibrate pre-morbid states. Although deeper and more ample studies are still needed preliminary results do show promising trends.
The sliding towards binaural beat technology and its appealing low-effort "training" combined with an aggressive marketing and biased "scientific" articles do only serve as a drawback for the more serious investigation that the field requires.
There is yet no proof that listening to binaural beats can change the mental state of the listener in spite of the observations that there might exist a brainwave shift. Few independent studies have been published on possible binaural beat effects. Among the most interesting experiences a single case study with positive results on an epileptic dog is described by David S. Walonick. On the contrary, depression enhancement and some recall impairments have been described in a small study with 7 Hz binaural beat exposition (Wahbeh H et al)
Neurofeedback as a clinical procedure is still under investigation. Its positive trends though are confused as proof of Binaural Beat technology. The truth is that the results of Neurofeedback are till scarce and contradictory and that there exists no relation yet between the possible effects of EEG biofeedback active training and the passive exposition to Binaural Beats.
Finally it is important to remember that, specially in healthy subjects, the EEG patterns are excessively unspecific and interindividually variable so as to pretend, even accepting a particular brainwave shift, that such a shift should be paralleled by specific brain function empowerment of just any subject.
On EEG related treatments the most promising fields of investigation today seem to be both compensation therapies and specific brainwave frequency range facilitation attending to individualized activity patterns.
Chema Nieto
Figures & Graphics by Elisa Robles and Chema Nieto
Further Reading & Links:
. Binaural Beats by Jeff Fletcher
. Binaural Beats (Wiki)
. Psychology Wikia
. Binaural beat technology in humans: a pilot study to assess neuropsychologic, physiologic, and electroencephalographic effects
. Role of Neurofeedback in the Treatment of ADHD
. Neurofeedback in Addictive Disorders Treatment
. Effect of neurofeedback training on the neural substrates of selective attention in children with attention-deficit/hyperactivity disorder: A functional magnetic resonance imaging study
. The frequency-following response in subjects with profound unilateral hearing loss.
. Human frequency-following responses to monaural and binaural stimuli
. Monroe Institute Research Papers
. Silva Related
. Critical Review from Penn Engineering
. Are neocortical gamma waves related to consciousness?
. Human Central Auditory Plasticity Associated With Tone Sequence Learning
. Huygens’ pendulums (abstract)
. The Story of Maynooth
. De la Localización del Sonido al iMusic (artículo en Castellano)
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