Monroe Institute Research Files: Binaural Beats

Physiology & Behavior, Vol. 63, No. 2, pp. 249 –252, 1998 © 1998 Elsevier Science Inc. All rights reserved. Printed in the U.S.A. 0031-9384/98 $19.00 1 .00 PII S0031-9384(97)00436-8 Binaural Auditory Beats Affect Vigilance Performance and Mood JAMES D. LANE,1* STEFAN J. KASIAN,* JUSTINE E. OWENS† AND GAIL R. MARSH* *Departments of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, North Carolina; and †Center for the Study of Complementary and Alternative Therapies, School of Nursing, University of Virginia, Charlottesville, Virginia Received 18 July 1997; Accepted 29 August 1997 LANE, J. D., S. J. KASIAN, J. E. OWENS AND G. R. MARSH. Binaural auditory beats affect vigilance performance and mood. PHYSIOL BEHAV 63(2) 249 –252, 1998.—When two tones of slightly different frequency are presented separately to the left and right ears the listener perceives a single tone that varies in amplitude at a frequency equal to the frequency difference between the two tones, a perceptual phenomenon known as the binaural auditory beat. Anecdotal reports suggest that binaural auditory beats within the electroencephalograph frequency range can entrain EEG activity and may affect states of consciousness, although few scientific studies have been published. This study compared the effects of binaural auditory beats in the EEG beta and EEG theta/delta frequency ranges on mood and on performance of a vigilance task to investigate their effects on subjective and objective measures of arousal. Participants (n 5 29) performed a 30-min visual vigilance task on three different days while listening to pink noise containing simple tones or binaural beats either in the beta range (16 and 24 Hz) or the theta/delta range (1.5 and 4 Hz). However, participants were kept blind to the presence of binaural beats to control expectation effects. Presentation of beta-frequency binaural beats yielded more correct target detections and fewer false alarms than presentation of theta/delta frequency binaural beats. In addition, the beta-frequency beats were associated with less negative mood. Results suggest that the presentation of binaural auditory beats can affect psychomotor performance and mood. This technology may have applications for the control of attention and arousal and the enhancement of human performance. © 1998 Elsevier Science Inc. binaural auditory beats vigilance performance mood frequency-following response WHEN two pure auditory signals of similar frequency are might be capable of eliciting an entrainment of EEG frequencies, mixed together, the phase interference between their waveforms similar to that known to occur during low frequency photic stim- produces a composite signal with a frequency midway between ulation (photic-driving). Anecdotal evidence does suggest that the upper and lower frequencies and an amplitude modulation presentation of low-frequency binaural auditory beats can elicit a that occurs with a frequency equal to the difference between the variety of changes in the listener’s state of consciousness that two original frequencies. For example, mixing tones of 100 Hz might have a broad range of practical applications (5,7). For and 110 Hz yields a signal with a perceived frequency of 105 example, the presentation of binaural auditory beats in the delta Hz that rises and falls in amplitude with a frequency of 10 Hz. and theta frequency ranges is said to be associated with enhanced The amplitude-modulated composite signal is called an auditory creativity and improved sleep. Preliminary experimental studies beat. suggest that binaural auditory beats in the EEG beta frequency A similar phenomenon occurs when auditory signals of similar range can enhance attention and memory task performance (3), and frequency are presented separately to the left and right ear through that those in the alpha frequency range may increase alpha EEG stereo headphones. Although each ear hears only one of the fre- production and subjective relaxation (2). quencies, the listener perceives the middle frequency and the A recent study2 examined the effects of delta and theta fre- amplitude modulation, even though the auditory beat does not exist quency binaural auditory beats on EEG spectral patterns in healthy in physical space. This phenomenon, called a ‘‘binaural auditory volunteers. EEG spectra were compared between a period of beat,’’ and described more than 25 years ago (6), is created by the wakeful rest and a period in which participants listened through brain’s processing of the two separate auditory signals at the level stereo headphones to pure tones designed to produce binaural beats of the olivary nuclei of the brainstem. in the theta and delta range. During the stimulus period participants Binaural auditory beats provide a mechanism for stimulating produced significantly less spectral power in the alpha and beta the auditory system at very low frequencies, below the frequency EEG bands and significantly more power in the theta and delta threshold of hearing. Such very low frequency auditory stimuli bands, evidence of possible EEG entrainment by the binaural beat 1 To whom correspondence and reprint requests should be addressed. E-mail: jdlane@acpub.duke.edu 2 Owens, J. E; Atwater, F. H. EEG correlates of an induced altered state of consciousness: ‘‘mind awake/body asleep.’’ Submitted for publication. 249 250 LANE ET AL. stimuli. During stimulation participants reported subjective expe- Thus, this tape included binaural beats at 1.5 and 4 Hz. For the beta riences similar to meditative, trance, or hypnagogic states. condition the 200-Hz tone was presented with a 16-Hz binaural beat Taken together, the anecdotal, clinical, and preliminary exper- and the 300-Hz tone was presented with a 24-Hz binaural beat. The imental evidence suggests that the presentation of binaural audi- 100 and 250-Hz tones were presented with no binaural beat. The tape tory beats may produce controllable changes in EEG and/or sub- for the beta condition contained binaural beats at 16 and 24 Hz. jective states of consciousness. Only the most recent studies Subjectively the three tape recordings sounded exactly alike, de- include sufficient experimental controls and can be considered as scribed by subjects as similar to the constant monotonous roar of a scientific investigations. Even so, the value of potential applica- waterfall or the sound inside a large propeller-driven airplane. The tions of a technology for self-control of EEG patterns and states of presence of binaural beats was very difficult to detect when the tapes consciousness argues for continued investigation of the binaural were listened to by the experimenters, and none of the participants beat phenomenon and its psychophysiological effects. reported noticing them. The tapes were played to subjects through The present study was designed to investigate whether different stereo headphones, and volume was set to a comfortable listening patterns of binaural-beat stimulation could produce changes in level. level of arousal and alertness manifested in behavior and mood. A Vigilance task. A continuous performance vigilance task was double-blind cross-over design was used to compare two distinct administered using a personal computer (Compaq 386 SX), which patterns of binaural-beat signals, one containing binaural beats in contained a multifunction data acquisition and timing card the EEG-beta frequency range and the other binaural beats in the (ADA1100; Real Time Devices, State College, PA) configured to EEG-delta/theta range. These patterns were selected because these measure response times with a precision of 1 ms. The vigilance EEG frequency bands are typically associated with states of alert- task was administered using a special-purpose computer program ness versus drowsiness, and entrainment of these frequencies written by J. D. L. It can be summarized as follows. might thus enhance or impair alertness. The binaural-beat signals The participant watched the VGA video monitor as individual were presented continuously during the performance of a 30-min stimuli of 5-cm height were displayed at a rate of 1/s and a vigilance task that required continuous video monitoring and re- duration of 100 ms. The stimuli were capital letters that were sponses to infrequent targets. We predicted that presentation of selected at random from a list of 20 capitals that excluded those binaural-beat signals in the EEG beta frequency range would elicit with similar shapes (e.g. O and Q). On 10% of stimulus presen- better task performance in this monotonous task (more correct tations, the previous letter was repeated. This repetition of a detection of targets and fewer false alarms) than presentation of stimulus was the target for the participant to detect. The computer binaural beat signals that entrained EEG frequencies in the theta/ program presented 1 target in each block of 10 stimuli (every 10-s delta range. We also expected that differential stimulation would interval) to insure that 6 targets were presented each minute, affect the mood changes associated with the monotonous task, although the position of the target within the block was random. especially those related to subjective alertness and fatigue. The intervals between targets ranged from 0 to 18 stimuli. The participant pressed the spacebar of the keyboard as quickly as MATERIALS AND METHODS possible each time a target was detected. The total duration of the vigilance task was 30 min. Instructions emphasized the importance