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File:Binaural beats.svg

Binaural beats (or binaural tones or binaural shift) 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.

The brain produces a phenomenon resulting in low-frequency pulsations in the loudness 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 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.

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[1][2] and can be used to reduce anxiety[3] and provide other health benefits such as control over pain.[4]

Acoustical background Edit

File:Acoustics BinauralBeats.JPG

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. [5] The perceived sound is also evaluated from the analysis of both ear signals.

If different pure tones (=sinus signals with different frequencies) are presented to both ears, there will be time dependent phase and time differences between both ears (see figure above). 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 more follow the changes in the interaural parameters. A diffuse auditory event appears. The sound corresponds to an overlay of both ear signals, this 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 observed without headphones, they appear when playing two different pure tones thru 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 . [6]

History Edit

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 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.[1]

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.[7] 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.

Physiology Edit

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.[8] 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.[9] 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.[10]

Hypothetical effects on brain function Edit

For more details on this topic, see brainwave synchronization.

Overview Edit

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).[11] 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.[12][13][14][15][16]

The stimulus does not have to be aural; it can also be visual[17] or a combination of aural and visual[18] (one such example would be Dreamachine). However, using alpha frequencies with such stimuli can trigger photosensitive epilepsy.

Perceived human hearing is limited to the range of frequencies from 20 Hz to 20,000 Hz, though Infrasound - sound below 20Hz - still has scientifically observable effects on humans, however, it is not readily audible, especially at low volume levels. While 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.[19]

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.[20] 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.[21][22]

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.[2] Studies have shown that with repeated training to distinguish close frequency sounds that a plastic reorganization of the brain occurs for the trained frequencies[23] and is capable of asymmetric hemispheric balancing.[24]

Brain waves Edit

Main article: Electroencephalography
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, arousal, cognition
7–13 Hz Alpha waves Relaxation (while awake), pre-sleep and pre-wake drowsiness
4–7 Hz Theta waves Dreams, deep meditation, REM 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, 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 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 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 Edit

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, 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,[25] and dopamine with binaural beats.[26] 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] however, this is supposed to happen with any way to get into 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.)[27][28][29]

Alpha-theta brainwave training has also been used successfully for the treatment of addictions,[25][30][31] for the recovery of repressed memories, but as with other techniques this can lead to false memories.[32]

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[26] and has been successfully shown to decrease mild anxiety[33]. A randomised, controlled study concluded that binaural beat audio could lessen hospital acute pre-operative anxiety.[34]

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.[35] In more recent times has come more understanding of the role of theta brain waves in behavioural learning.[36] The presence of theta patterns in the brain has been associated with increased receptivity for learning and decreased filtering by the left hemisphere.[35][37][38] 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.[39]

See also Edit

References Edit

  1. 1.0 1.1 Oster G (1973). Auditory beats in the brain. Sci. Am. 229 (4): 94–102.
  2. 2.0 2.1 Hutchison, Michael M. (1986). Megabrain: new tools and techniques for brain growth and mind expansion, New York: W. Morrow.
  3. http://pt.wkhealth.com/pt/re/emmednews/abstract.00000524-200509000-00006.htm
  4. Hemispheric-synchronisation during anaesthesia: a double-blind randomised trial using audiotapes for intra-operative nociception control, Jan 2000, Kliempt, Ruta, Ogston, Landeck & Martay
  5. Blauert, J.: Spatial hearing - the psychophysics of human sound localization; MIT Press; Cambridge, Massachusetts (1983), ch. 2.4
  6. Slatky, Harald (1992): Algorithms for direction specific Processing of Sound Signals - the Realization of a binaural Cocktail-Party-Processor-System, Dissertation, Ruhr-University Bochum, ch. 3
  7. "My Big TOE" book 1, Thomas Campbell, p79 ISBN 978-0972509404
  8. Spitzer MW, Semple MN (1998). Transformation of binaural response properties in the ascending auditory pathway: influence of time-varying interaural phase disparity. J. Neurophysiol. 80 (6): 3062–76.
  9. Thaut MH (2003). Neural basis of rhythmic timing networks in the human brain. Ann. N. Y. Acad. Sci. 999: 364–73.
  10. Barr DF, Mullin TA, Herbert PS. (1977). Application of binaural beat phenomenon with aphasic patients. Arch Otolaryngol. 103 (4): 192–194.
  11. Gerken GM, Moushegian G, Stillman RD, Rupert AL (1975). Human frequency-following responses to monaural and binaural stimuli. Electroencephalography and clinical neurophysiology 38 (4): 379–86.
  12. Dobie RA, Norton SJ (1980). Binaural interaction in human auditory evoked potentials. Electroencephalography and clinical neurophysiology 49 (3-4): 303–13.
  13. Moushegian G, Rupert AL, Stillman RD (1978). Evaluation of frequency-following potentials in man: masking and clinical studies. Electroencephalography and clinical neurophysiology 45 (6): 711–18.
  14. Smith JC, Marsh JT, Greenberg S, Brown WS (1978). Human auditory frequency-following responses to a missing fundamental. Science 201 (4356): 639–41.
  15. Smith JC, Marsh JT, Brown WS (1975). Far-field recorded frequency-following responses: evidence for the locus of brainstem sources. Electroencephalography and clinical neurophysiology 39 (5): 465–72.
  16. Yamada O, Yamane H, Kodera K (1977). Simultaneous recordings of the brain stem response and the frequency-following response to low-frequency tone. Electroencephalography and clinical neurophysiology 43 (3): 362–70.
  17. Cvetkovic D, Simpson D, Cosic I (2006). Influence of sinusoidally modulated visual stimuli at extremely low frequency range on the human EEG activity. Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 1: 1311–4.
  18. [Abstract The Induced Rhythmic Oscillations of Neural Activity in the Human Brain]. URL accessed on 2007-11-14.
  19. Schwarz DW, Taylor P (2005). Human auditory steady state responses to binaural and monaural beats. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology 116 (3): 658–68.
  20. Rogers LJ, Walter DO (1981). Methods for finding single generators, with application to auditory driving of the human EEG by complex stimuli. J. Neurosci. Methods 4 (3): 257–65.
  21. Lane JD, Kasian SJ, Owens JE, Marsh GR (1998). Binaural auditory beats affect vigilance performance and mood. Physiol. Behav. 63 (2): 249–52.
  22. Beatty J, Greenberg A, Deibler WP, O'Hanlon JF (1974). Operant control of occipital theta rhythm affects performance in a radar monitoring task. Science 183 (127): 871–3.
  23. Menning H, Roberts LE, Pantev C (2000). Plastic changes in the auditory cortex induced by intensive frequency discrimination training. Neuroreport 11 (4): 817–22.
  24. Gottselig JM, Brandeis D, Hofer-Tinguely G, Borbély AA, Achermann P (2004). Human central auditory plasticity associated with tone sequence learning. Learn. Mem. 11 (2): 162–71.
  25. 25.0 25.1 Peniston EG, Kulkosky PJ (1989). Alpha-theta brainwave training and beta-endorphin levels in alcoholics. Alcohol. Clin. Exp. Res. 13 (2): 271–9.
  26. 26.0 26.1 Wahbeh H, Calabrese C, Zwickey H (2007). Binaural beat technology in humans: a pilot study to assess psychologic and physiologic effects. Journal of alternative and complementary medicine (New York, N.Y.) 13 (1): 25–32.
  27. Ogilvie RD, Hunt HT, Tyson PD, Lucescu ML, Jeakins DB (1982). Lucid dreaming and alpha activity: a preliminary report. Perceptual and motor skills 55 (3 Pt 1): 795–808.
  28. Korabel'nikova EA, Golubev VL (2001). [Dreams and interhemispheric asymmetry]. Zhurnal nevrologii i psikhiatrii imeni S.S. Korsakova / Ministerstvo zdravookhraneniia i meditsinskoĭ promyshlennosti Rossiĭskoĭ Federatsii, Vserossiĭskoe obshchestvo nevrologov Vserossiĭskoe obshchestvo psikhiatrov 101 (12): 51–4.
  29. Spoormaker VI, van den Bout J (2006). Lucid dreaming treatment for nightmares: a pilot study. Psychotherapy and psychosomatics 75 (6): 389–94.
  30. Saxby E, Peniston EG (1995). Alpha-theta brainwave neurofeedback training: an effective treatment for male and female alcoholics with depressive symptoms. Journal of clinical psychology 51 (5): 685–93.
  31. Watson CG, Herder J, Passini FT (1978). Alpha biofeedback therapy in alcoholics: an 18-month follow-up. Journal of clinical psychology 34 (3): 765–9.
  32. Loftus EF, Davis D (2006). Recovered memories. Annual review of clinical psychology 2: 469–98.
  33. Le Scouarnec RP, Poirier RM, Owens JE, Gauthier J, Taylor AG, Foresman PA. (2001). Use of binaural beat tapes for treatment of anxiety: a pilot study of tape preference and outcomes. Altern Ther Health Med. 7 (1): 58–63.
  34. Padmanabhan R, Hildreth AJ, Laws D (2005). A prospective, randomised, controlled study examining binaural beat audio and pre-operative anxiety in patients undergoing general anaesthesia for day case surgery. Anaesthesia 60 (9): 874–7.
  35. 35.0 35.1 Harris, Bill (2002). Thresholds of the Mind, Appendix 1, pp151–178, Centerpointe Press.
  36. Berry SD, Seager MA (2001). Hippocampal theta oscillations and classical conditioning. Neurobiol Learn Mem 76 (3): 298–313.
  37. Seager MA, Johnson LD, Chabot ES, Asaka Y, Berry SD (2002). Oscillatory brain states and learning: Impact of hippocampal theta-contingent training. Proc. Natl. Acad. Sci. U.S.A. 99 (3): 1616–20.
  38. Griffin AL, Asaka Y, Darling RD, Berry SD (2004). Theta-contingent trial presentation accelerates learning rate and enhances hippocampal plasticity during trace eyeblink conditioning. Behav. Neurosci. 118 (2): 403–11.
  39. Vernon D, Egner T, Cooper N, et al. (2003). The effect of training distinct neurofeedback protocols on aspects of cognitive performance. International journal of psychophysiology : official journal of the International Organization of Psychophysiology 47 (1): 75–85.

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