Dr. Atcherson (left) is an assistant professor and the director of the auditory electrophysiology and rehabilitation laboratory; Ms. Kennett (middle) is a third-year doctor of audiology student; and Dr. Nicholson (right) is an associate professor and an audiology program director, all in the department of audiology and speech pathology at the University of Arkansas for Medical Sciences, Little Rock. Dr. Musiek, the clinical editor of Pathways, is a professor and the director of auditory research in communication sciences at the University of Connecticut in Storrs.
Sound therapy is hardly new, but binaural beats are being touted as ways to induce well-being and relaxation, enhance mood or cognition, and treat neurophysiologic abnormalities. The benefit of binaural beat technology is largely unsubstantiated, however, and the technology touted for its health benefits is unregulated. One thing is for certain, using binaural beats with personal listening devices can put listeners at risk for noise-induced hearing loss. As an auditory phenomenon, it hits close to home for hearing professionals.
The dichotic presentation of two sinusoids with a small frequency difference produces a perceptual fluctuation called a binaural beat. The listener perceives a fused auditory image around 105 Hz that beats at a rate of 10 per second when a 100 Hz-tone is presented in one ear and 110 Hz is presented in the other ear. Binaural beats can be perceived for closely spaced tones up to about 1,000 Hz, and have been investigated in numerous reports over the past 100 years for sound lateralization and localization, pitch perception, signal extraction in noise, and temporal processing. (J Acoust Soc Am 1950;22:468; Sci Am 1973;229:94; Ear Hear 2012;33:187.)
Physiology and Brainwaves
The perception of binaural beats is not a physical manifestation but a convergence of neural activity in the central auditory nervous system (CANS) that begins with phase differences between the two ears. Sinusoidal phase-locking of pure tones is preserved from the cochlea to the spherical bushy cells by way of the auditory nerve. (Brain Res 1973;64:35; Hear Res 1986;24:1.) The superior olivary complex is well established as the first anatomical site in the CANS to receive input from both ears with binaural beat detection specifically within the medial superior olives. (J Comp Neurol 1993;331:245; J Neurophysiol 1969;32:613.)
Neurons in the inferior colliculus and primary auditory cortex have also been found to respond to binaural beats. (J Neurophysiol 1990;64:1247; Science 1979;206:586.) Binaural sensitive neurons in the inferior colliculus help develop the perception of sound motion and spatial hearing. (J Neurophysiol 1998;80:3062.) Remarkably, binaural beats have also been reported to give rise to far-field neurophysiologic correlates within the auditory brainstem and temporal lobes. (Clin Neurophysiol 2005;116:658; Clin Neurophysiol 2009;120:1514; J Neurophysiol 1968;31:428.) Taken together, binaural beat representation is reflected broadly throughout the CANS and promotes a number of auditory skills and behaviors.
The perceived beat frequency that is induced in the CANS may correspond with a range of brainwave frequencies, such as delta (<4 Hz), theta (4-7 Hz), alpha (7-13 Hz), beta (13-39 Hz), and gamma (>40 Hz). Perhaps listening to beats at a particular brainwave frequency can cause brainwave entrainment or synchrony to promote relaxation (e.g., 8 Hz) versus active concentration while performing a task (e.g., 12 Hz). Some investigators have suggested that binaural beat auditory training may help control attention, arousal, and enhancement of cognitive performance while others have reported negative effects or largely mixed and confusing results. (Physiol Beh 1998;63:249; J Altern Complement Med 2007;13:199; J Pediatr Nurs 2010;25:3).
Binaural Beats as a Digital Drug
Binaural beat technology was once limited to acoustics or music laboratories, but Internet access and the portability of music files have resulted in audio file accessibility that contains the technology. A simple Internet search with the keywords “binaural beats dosing” will yield more than 118,000 hits of commercial websites, smartphone and tablet apps, articles, videos, music files, and product-related links. Some of these websites market audio files that claim various health benefits ranging from smoking cessation to lucid dreams. The titles of some audio files contain words such as peyote, marijuana, and opium, and these companies have been accused by the media of marketing to minors.
While binaural beats form the fundamental basis of all these audio files to induce brainwave synchronization, different binaural beat frequencies and types of sounds have been mixed in for variety. Sometimes the beats are unaccompanied, but they are often embedded in ambient sounds or different genres of music. Techno music is a particularly popular genre to use in binaural beat audio files. Anyone with normal hearing can attempt to experience the effects of binaural beats. All you do is close your eyes in a quiet room for 30 minutes wearing a pair of headphones plugged into your favorite media player.
Dangerous or Beneficial?
Patients and consumers may ask about binaural beats and request audio file and headphone recommendations, and about binaural beat technology for tinnitus relief, auditory processing deficits, and post-traumatic brain injury therapies. The perceived benefits may be in the eye of the beholder but could possibly be nothing more than a placebo effect. The principle issue of concern to hearing healthcare professionals is the intensity at which some individuals are listening to binaural beat and other audio files to produce the desired effect. The current generation of personal listening devices is capable of putting people at risk for noise-induced hearing loss, and adolescents in particular may be irresponsible when it comes to picking appropriate listening levels. (Ear Hear 2004;25:513; J Am Acad Audiol 2010;21:663.)
Some YouTube videos show teenagers lying on their beds, eyes covered, playing these sounds at potentially dangerous levels. Auditory stimulation and vestibular stimulation are likely occurring at high-intensity levels. This stimulation may lead listeners to believe they are achieving a high from the binaural beats while they are damaging their auditory systems.
* Read past Pathways columns in a special collection at http://bit.ly/PathwaysCollection.
* Visit HJ's Student Blog at http://bit.ly/HJStudentBlog.
* Check out HJ's R&D Blog at http://bit.ly/RDBlog.
* Click and Connect! Access the links in The Hearing Journal by reading this issue on our website or in our new iPad app, both available at thehearingjournal.com.
* Follow us on Twitter at twitter.com/hearingjournal and like us on Facebook at www.facebook.com/HearingJournal.