Binaural beats were first described in Germany by H.W.Dove in the 1830s. they were first generated by the use of tuning forks. Modern research is able to use the more efficient and adaptable tone generators, but the underlying principle is the same. In essence, two tone generators producing pure tones of very similar pitch, will be heard as “beats” which are the result of the summating effects of the two wave forms as they travel through the air. To the observer they will appear to hear a sound that will cyclically fluctuate in volume but not in pitch. These are monaural beats. A characteristic of these monaural beats is that they can be heard with one ear occluded.
(Smith, J. C et al 1978).
Binaural beats are produced in a similar way with two pure tones being produced, but each is specifically and separately delivered to a single ear. Because the monaural beats are the physical result of pressure summation in the transmitting medium (air), there is clearly no possibility of this phenomenon being implicated in the genesis of binaural beats. These are a brain-generated phenomenon described by Oster (1973) as being synthesised in the auditory processing pathways inside the brain.
It would appear that the brain computes a subjective synthetic sound from the information that it receives from both ears, which is characteristically experienced as emanating from the centre of the subject’s head. The frequency of the binaural beats is exactly the difference between the two frequencies, for example if the subject is played a pure tone frequency of 500 Hz in one ear and 520 Hz in the other ear a binaural beat frequency of 20 Hz will be “heard” by the subject even though there can be no physical (non-physiological) explanation of the phenomenon.
It follows from what has already been stated, that the frequency of the induced binaural beat is a result of the difference between the two primary frequencies. It follows that a resultant beat of 20 Hz can not only be produced by 500 and 520 Hz as outlined above. It can equally well be produced by primary frequencies of 250 and 270 Hz or alternatively 890 and 910 Hz. The working envelope is that the sound should be of an amplitude that is capable of being heard and that it should be below about 1000Hz. The phenomenon does not occur above these frequencies simply because of the anatomical size of the skull allows higher frequencies to be distorted by its size. (Cozby, P.C. 1989).
More sophisticated studies,( Licklider JCR et al 1950), of the physiological mechanisms, suggest that the most efficient frequency for producing binaural beats is in the region of 400 Hz and the beats heard the most consistently at that frequency were at 35 Hz, which would be firmly in the beta range. (see on).
The technical side of this finding relies on finding a biological explanation of why this should be. A rational explanation relies on both elements of the Wever's volley theory with elements of the Hill-Rashevsky theory of the excitation of neurones.
At the lower frequencies, neurones can discharge in a degree of synchronisation with the stimulus, but the physical time interval may be too low for synaptic summation at a chemical neurotransmitter level. Higher frequencies do not allow for the absolute refractory period of the neurone and therefore only a few neurones in each nerve can fire off at any given high frequency stimulus. (McFadden D et al 1975).
At frequencies around the 35 Hz, each individual neurone can participate individually, and as a result each can fire virtually simultaneously with the others that have been stimulated. As the two pathways join at the Olivary nucleus, at these frequencies there is likely to be the maximal neural input and this is when the maximal amplitude of binaural beats is experienced.
EEG studies have shown that this synthesising of the binaural beats is associated with a phenomenon known as hemispheric synchronisation. (Peniston, E. G. et al 1990), where the detectable electrical activity on both sides of the brain recorded over the auditory cortex appears to unite into a synchronous pattern which has a basic frequency that matches the difference in the frequencies of the two tones heard. (Edrington, D et al. 1985).
A further characteristic of the binaural beats phenomenon is described called entrainment. If the difference between the two tones produces beats that match a specific subset of brainwave activity, then the whole brain will tend to adopt activity of that particular frequency. This is referred to as the Frequency Following Response (FFR). (Stillman AJ et al. 1978).
This response can be utilised to artificially induce specific brainwave frequencies over the whole of the cerebral cortex and can also help to maintain those states once they have been generated. (Ochs, L 1993)
The FFR is widely cited as being the basis of many “learning enhancement” techniques. It should be noted that, although the effect undoubtedly exists, the response signal (as detected by the EEG), is actually very small, and represents only a tiny fraction of the detectable electrical activity of the alert brain. (Atwater FH 1991)
By way of supporting evidence for this phenomenon we can cite work that has elicited a similar response to photic stimulation. (Nogawa KA et al. 1976), Alpha rhythms are particularly responsive to photic stimulation of a specific type. Lights flickering at a frequency within the normal alpha range can entrain the endogenous alpha rhythms to become more synchronous with the lights(Arinibar & Pfurtscheller, 1978;).
Other mechanisms have also been explored including tactile stimuli and click-based stimuli. These latter two do not appear to be anything like as effective as the binaural beats.
It appears that there are two demonstrable pathways by which auditory entrainment can occur. It has been demonstrated in association with bursts of sound such as regular drum beats in addition to the binaural beats mechanism that we have described above. (Neher, 1961)
There are four major subdivisions of brainwave frequencies which are known by Greek letters. Rather confusingly, they are not allocated in an order that corresponds with the appropriate frequency. This fact is a reflection of the original order of discovery of the significance of the frequency, rather than a completely illogical mind.
Name Frequency State of mind
Delta 0.5 - 4 Hz Deep sleep
Theta 4 - 8 Hz Drowsiness
Alpha 8 - 14 Hz Relaxed but alert
Beta 14 - 30 Hz Highly alert and focused
It is important to appreciate that the terminology of the wave from relates to the dominant wave form. It should not be considered that the wave form suppresses all of the others, which are still generally detectable, but with reduced amplitude
Examination of EEG material suggests that the range of naturally occurring frequencies is from 0 to 40 Hz. If one contrasts this with the normal auditory range of frequencies (about 20 to 20,000 Hz), one can see that there is only a very small overlap. Pure tones below 20 HZ simply will not be heard, and therefore it is not possible that entrainment below these frequencies can occur as a result of external stimuli.
This situation can be artificially manipulated by the phenomenon of binaural beats which can be generated down to 1 Hz.. The mechanism is thought to be due to the action of the Olivary nucleus, a small centrally placed nucleus in the brain stem, phylogenetically the most primitive part of the brain, which lies on the path of the VIIIth cranial nerve on its way to the auditory cortex. (Empson, J. 1986).
This pathway is able to be modified by efferent impulses from the higher brain centres, particularly those centres which are involved in both motivational and attentional factors. Areas which have been specifically implicated are the frontal lobes and the limbic system (Evans, F. J. 1972).
The entrainment phenomenon has been observed in the complete frequency range of 0 to 40 Hz. (Dobie & Norton, 1980). The phenomenon of entrainment is observed most strongly when the binaural beats are closest to the dominant wave frequency of the brain at the time.
It is also clear that in order for any degree of entrainment to occur there must be an intact VIIIth nerve with intact decussations across the Corpus Callosum (Zeng FG et al 2005)
There is some evidence to suggest that binaural beats can be used to not only entrain the brain’s own frequencies, but also to enhance some mentally demanding cognitive tasks (Hutchinson, 1994).
Atwater (FH 1991) suggests that the mechanism of binaural beat enhancement is modulated through the extended reticular-thalamic activating system. To quote him verbatim:-
Binaural beating, a sensory-information stimulus, provides potential consciousness-altering information to the reticular-thalamic activating system which in turn alters arousal states, attentional focus, and level of awareness (crucial elements of consciousness itself).
He suggests that, with the use of binaural beat techniques, particularly if enhanced and used in conjunction with other cognition aids such as social-psychological conditioning tools, and educational curriculum, it is quite possible to “provide access to a variety of applications…… and expanded states of consciousness”
It has to be observed that a brief examination of the literature on the subject shows that there are a huge number of effects that are claimed for the application of binaural beats. Some appear to be based in fact and are capable of critical analysis (Mohammed, D et al 2003), thereby allowing for a degree of security when constructing an evidence base for the subject, other applications appear to be little more than overtly cranky with no published evidence to support the professed view. (Berwick D 2005)
Many of the so-called trials, if carefully examined, are either not properly blinded or do not necessarily control for many of the important confounding variables, which makes them exceedingly unreliable for our purposes.
Some of the more rigorously constructed studies have centred upon the educational field. Owens (1984) has reported a decrease in distractibility and increase in academic performance when binaural beats are used in a classroom setting. While Edrington (1983)carried out rather more quantitative studies, one of which showed that students appeared to perform academically better in the presence of binaural beat augmentation
There is some evidence to suggest that the Alpha and Theta stages are the most useful in terms of learning enhancement. There appears to be a biological precedent for this insofar as children spend more time in the theta state than do adults and this may well correlate with the enhanced learning capacity of children (Oertel D 2005)
Kennerly (RC 1992) carried out some impressive work on the subject of the education-enhancing possibilities of the binaural beats phenomenon by carrying out a double blind trial of different elements of memory function with and without binaural beats. A cohort of fifty students were split into two (blinded) groups and played music. One set had binaural beat signals playing below the music. Each group were asked to perform four different memory process tests.
The trial is well written, analysed and presented, with an extremely involved analysis section. In overview, the results showed that three of the four process groups (the word list recall test, the digit symbol subtest, and the digit span subtest) all performed statistically better in the presence of binaural beats. The one group that didn’t demonstrate any performance enhancement was the group with the word list recognition/recall subtest. The authors were able to conclude that:
Beta frequency binaural-beat audio signals are an effective method for facilitating simple free recall memory, ability to attend, and the ability to persevere at routine motor tasks.
Other well constructed studies in this area included an intriguing study by Waldkoetter, (1982) who examined the ability of students to learn and interpret Morse code and demonstrated a 30% increase in efficiency of learning in students who were augmented with binaural beats. There is less robust evidence presented by the US Army in support of the ability to acquire a second language (Pawelek, & Larson 1985)
There is also some less well researched evidence from a study by Owen (JD et al 1998) which purports to demonstrate a causal linkage between vigilance, performance and mood. While this may be the case, it has to be said that the study is not well constructed and the statistical analysis is far from robust.
A brief overview of some of the less well substantiated claims would suggest that there is some form of potentially exploitable enhancement from binaural beats. It is fair to say that many of these papers are comparatively old and therefore they do not stand up to the more modern scientific scrutiny that we would expect today.
Hiew (1995) produced a (non-randomised) study which links binaural beats with states of increased relaxation, meditative and creative states (not published in a peer review journal).
Waldkoetter & Sanders (1997) examined the possibility of reducing depressive symptoms in alcoholic patients and found a robust statistically significant result .
Binaural beats have been found to be associated with increased states of alertness and concentration by Monroe (1985), while Kennerly (1994) presented a case study of four mentally retarded adults who were demonstrated to have increased focus of attention
It has to be noted that there appears to have been an explosion of interest and activity in this field in the 70s and 80s with the potential promises of educational enhancement being explored. There is no doubt that cognitive changes can occur in association with binaural beats and that some statistically significant effects can be demonstrated with careful statistical analysis. It would also appear that interest has largely waned, as evidenced by a comparative dearth of academic papers after this time.
There are many claims being put forward by manufacturers of binaural beat “black boxes” who claim to be able to produce all manner of changed states from heightened awareness to profound relaxation on what appears to be rather flimsy evidence.
A critical analysis of the literature that we have found and presented here, would suggest that the physiological effects of binaural beats are undoubtedly real but unfortunately not very profound.
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