| Homepage | Imprint |
|
||
 |
Binaural beatsBinaural beats or binaural tones are auditoryprocessing artifacts, i.e. apparent sounds, the perceptionof which arises in the brain independent of physical stimuli. In nature, two sounds that are similar but slightly shifted in frequencywill heterodyneto produce two new frequencies which are the sumand differencesof the original two sounds. The brain produces a similar phenomenon internally, resulting in low-frequency pulsations in the loudnessof a perceived sound when two tones at slightly different frequencies are presented separately, one to each of a subject's ears, using stereo headphones. The frequency of the tones must be below about 1,000 to 1,500 hertz. The difference between the two frequencies must be small (below about 30 Hz) for the effect to occur; otherwise the two tones will be distinguishable and no beat will be perceived. The effect was discovered in 1839by Heinrich Wilhelm Dove. Interest in binaural beats can be classified into two categories. First, they are of interest to neurophysiologists investigating the sense of hearing. Second, there are those who believe that binaural beats may influence the brain in more subtle ways through the entrainmentof brainwavesand can be used to produce relaxation and other health benefits.
PhysiologyThe sensation of binaural beats is believed to originate in the superior olivary nucleus, a part of the brainstem. They appear to be related to the brain's ability to locate the sources of sounds in three dimensions. Hypothetical effects on brain functionOverviewSome people believe that binaural beats can 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 (see Dreamachine). However, using alpha frequencies with such stimuli can trigger photosensitive epilepsy. Directly using an infrasonicauditory stimulus is impossible, since the ears cannot hear sounds low enough to be useful for brain stimulation. Therefore, binaural beat frequencies must be used. According to this view, when the perceived beat frequencycorresponds to the delta, theta, alphaor betarange of brainwavefrequencies, 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 supposed to be entrained towards the beat frequency (10 Hz, in the alpha range). Since alpha range is usually associated with relaxation, it is supposed to have a relaxing effect. Brain waves
(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 your alpha waves dominate, you are in the alpha state (this happens when you are relaxed but awake). However, also other frequencies will be present, albeit with smaller amplitudes. Gamma waves aren't usually your dominant frequencies. The brain entraining is more effective if the entraining frequency is close to your current dominant frequency. Therefore, it is suggested to start with a frequency near to your current dominant frequency (if you're awake it is likely to be about 20 Hz or little less), and then slowly decreasing it towards the desired frequency. To some people, pure sine waves are unpleasant, therefore a pink noiseor 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 won't improve the effectiveness, therefore using a low volume is usually suggested. Some people say that the volume should be so low that the beating should not even be clearly audible, but this does not seem to be the case (see the next paragraph). It should be made clear that binaural beats are not magic: just passively listening to binaural beats does not necessarily alter your state of consciousness. An active mental participation by the subject is needed to produce the synchronization. Experiments in which beats were not audible [{{fullurl:Template:FULLPAGENAME}}#endnote_http://www.seas.upenn.edu/courses/belab/LabProjects/2001/be309f01m5.doc] (e. g. with a background pink noise 15 dBlouder than the sine waves) have failed to report any effect. Therefore it is also possible that the effect of binaural beats is due to placebo. However, to prove this one would have to make people believe to listen to binaural beats without really listening to them, which is only possible if the subject cannot distinguish between binaural beats and non-binaurals. (The difference is that binaural beats seem to originate from inside your head, whereas the same monaural beatingplayed into both ears is clearly heard as coming from outside.) On the other hand, it is possible to examine the EEG of a person before and after a binaural beat session to check whether the relaxing effect is merely subjective or there really is a change in the EEG. Nevertheless, it seems that no objective, serious, extensive research has been performed in this area. Other usesIn 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, some say that using specific frequencies you can stimulate certain glandsto produce desired hormones, sometimes even relating them with chakras. This is highly disputed, and even among people who consider this possible many agree that the precise frequencies may vary from person to person. 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, 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 dreamingand even for achieving out-of-body experiences, astral projection, telepathyand psychokinesis. However, most people believe that these phenomena (except lucid dreams, which are acknowledged even by mainstream science) do not exist, let alone that they can be achieved by training the brain to a specific frequency. They 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. ExampleBinbeat_sample.ogg: 30 seconds of steady 10 Hz binaural beats with background pink noise. (244 KB) Binbeats2.ogg: Frequency starts at 20 Hz, falls to 7.83 Hz in 10 minutes, stays constant for 15 minutes and rises back to 16 Hz in 5 minutes. Warning: this file is nearly 4 MB. External links
Categories: Articles to be merged| Neurology
|
