|
JAMES
D. LANE,'* STEFAN J. KASIAN,* JUSTINE E. OWENSt 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 perJbrmance 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 = 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 mixed together,
the phase interference between their waveforms produces a composite
signal with a frequency midway between the upper and lower
frequencies and an amplitude modulation that occurs with a frequency
equal to the difference between the two original frequencies. For
example, mixing tones of 100 Hz and 110 Hz yields a signal with a
perceived frequency of 105 Hz that rises and falls in amplitude with
a frequency of 10 Hz. The amplitude-modulated composite signal is
called an auditory beat.
A
similar phenomenon occurs when auditory signals of similar frequency
are presented separately to the left and right ear through stereo
headphones. Although each ear hears only one of the frequencies, the
listener perceives the middle frequency and the amplitude
modulation, even though the auditory beat does not exist in physical
space. This phenomenon, called a "binaural auditory beat," and
described more than 25 years ago (6), is created by the brain's
processing of the two separate auditory signals at the level of the
olivary nuclei of the brainstem.
Binaural auditory beats provide a mechanism for stimulating the
auditory system at very low frequencies, below the frequency
threshold of hearing. Such very low frequency auditory stimuli
frequency-following response might be capable of eliciting an
entrainment of EEG frequencies, similar to that known to occur
during low frequency photic stimulation (photic-driving). Anecdotal
evidence does suggest that presentation of low-frequency binaural
auditory beats can elicit a variety of changes in the listener's
state of consciousness that might have a broad range of practical
applications (5,7). For example, the presentation of binaural
auditory beats in the delta and theta frequency ranges is said to be
associated with enhanced creativity and improved sleep. Preliminary
experimental studies suggest that binaural auditory beats in the EEG
beta frequency range can enhance attention and memory task
performance (3), and that those in the alpha frequency range may
increase alpha EEG production and subjective relaxation (2).
A
recent study- examined the effects of delta and theta frequency
binaural auditory beats on EEG spectral patterns in healthy
volunteers. EEG spectra were compared between a period of wakeful
rest and a period in which participants listened through stereo
headphones to pure tones designed to produce binaural beats in the
theta and delta range. During the stimulus period participants
produced significantly less spectral power in the alpha and beta EEG
bands and significantly more power in the theta and delta bands,
evidence of possible EEG entrainment by the binaural beat stimuli.
During stimulation participants reported subjective experiences
similar to meditative, trance, or hypnagogic states.
Taken
together, the anecdotal, clinical, and preliminary experimental
evidence suggests that the presentation of binaural auditory beats
may produce controllable changes in EEG and/or subjective states of
consciousness. Only the most recent studies include sufficient
experimental controls and can be considered as scientific
investigations. Even so, the value of potential applications of a
technology for selfcontrol of EEG patterns and states of
consciousness argues for continued investigation of the binaural
beat phenomenon and its psychophysiological effects.
The
present study was designed to investigate whether different patterns
of binaural-beat stimulation could produce changes in level of
arousal and alertness manifested in behavior and mood. A
double-blind cross-over design was used to compare two distinct
patterns of binaural-beat signals, one containing binaural beats in
the EEG-beta frequency range and the other binaural beats in the
EEGdelta/theta range. These patterns were selected because these EEG
frequency bands are typically associated with states of alertness
versus drowsiness, and entrainment of these frequencies might thus
enhance or impair alertness. The binaural-beat signals were
presented continuously during the performance of a 30-min vigilance
task that required continuous video monitoring and responses to
infrequent targets. We predicted that presentation of binaural-beat
signals in the EEG beta frequency range would elicit better task
performance in this monotonous task (more correct detection of
targets and fewer false alarms) than presentation of binaural beat
signals that entrained EEG frequencies in the theta/ delta range. We
also expected that differential stimulation would affect the mood
changes associated with the monotonous task, especially those
related to subjective alertness and fatigue.
MATERIALS AND METHODS
Subjects
Volunteers were recruited by advertisement from the Duke University
community. They were required to be in good health, have normal
hearing and vision (corrected or uncorrected), and be free from
acute illness or use of medications. Thirtytwo people were recruited
and 29 completed the protocol. This group had a mean age (± SD) of
32 (± 10) years with a range from 19 to 51 years. The group
contained 19 females and 10 males; 20 whites, 8 hlacks. and I Asian;
18 employed workers and I I students. All volunteers were
nonsmokers. Each received $30 for completion of the study.
Materials
Buuwural beat .stimulation. Binaural beat signals were presented
stereophonically by cassette tape.; Three different tapes were
prepared as follows. All three tapes contained a background of "pink
noise" with uniform amplitude in the frequency spectrum from 40-320
Hz and decreasing amplitude (12 db/octave) at frequencies above and
below these limits. Tapes also contained carrier tones at 100, 200,
250, and 300 Hz, which had amplitudes 15 db above the amplitude of
the pink noise. The tape constructed for the training session
contained no binaural beat stimuli, but the tapes for the two
experimental treatments did. For the delta/theta condition the
100-Hz tone was presented with a 1.5-Hz binaural beat, the 200 and
250 Hz tones were presented with 4-Hz binaural beats. and the 300-Hz
tone was presented with no binaural beat.
Thus,
this tape included binaural beats at 1.5 and 4 Hz. For the beta
condition the 200-Hz tone was presented with a 16-Hz binaural beat
and the 300-Hz tone was presented with a 24-Hz binaural beat. The
100 and 250-Hz tones were presented with no binaural beat. The tape
for the beta condition contained binaural beats at 16 and 24 Hz.
Subjectively the three tape recordings sounded exactly alike,
described by subjects as similar to the constant monotonous roar of
a waterfall or the sound inside a large propeller-driven airplane.
The presence of binaural beats was very difficult to detect when the
tapes were listened to by the experimenters, and none of the
participants reported noticing them. The tapes were played to
subjects through stereo headphones, and volume was set to-a
comfortable listening level.
Vigilance task. A continuous performance vigilance task was
administered using a personal computer (Compaq 386 SX), which
contained a multifunction data acquisition and timing card (ADAI
100; Real Time Devices, State College, PA) configured to measure
response times with a precision of 1 ms. The vigilance task was
administered using a special-purpose computer program written by J.
D. L. It can be summarized as follows.
The
participant watched the VGA video monitor as individual stimuli of
5-cm height were displayed at a rate of I/s and a duration of 100
ms. The stimuli were capital letters that were selected at random
from a list of 20 capitals that excluded those with similar shapes
(e.g. O and Q). On 10% of stimulus presentations, the previous
letter was repeated. This repetition of a stimulus was the target
for the participant to detect. The computer program presented 1
target in each block of 10 stimuli (every 10-s interval) to insure
that 6 targets were presented each minute, although the position of
the target within the block was random. The intervals between
targets ranged from 0 to 18 stimuli. The participant pressed the
spacebar of the keyboard as quickly as possible each time a target
was detected. The total duration of the vigilance task was 30 min.
Instructions emphasized the importance of continuous monitoring for
targets, rapid responding, and the importance of maintaining good
performance throughout the entire task. The computer program
administered all stimuli and recorded the parameters of each
stimulus trial. Response latency was measured for all keypresses and
recorded with stimulus data for later analysis.
Mood
assessment. The Profile of Mood States (POMS; EdITS, San Diego, CA)
was used to assess changes in mood. The POMS contains 65 adjective
rating items (0 to 4 scale) that describe feelings people experience
(e.g., friendly, tense, grouchy, etc.). Item ratings can be
summarized on standard scales that represent six general moods:
tension-anxiety; depression-dejection; angerhostility;
vigor-activity; fatigue-inertia; and confusion-bewilderment (4).
This inventory was administered before and after the vigilance task
to assess task-related changes in mood.
Procedure
Participants were kept blind to the true purpose of the study. When
volunteers were recruited, they were told that the study was
intended to evaluate a new computerized vigilance task and to assess
how stable performance was over several days. Throughout the study,
they were told that task conditions were identical across days and
that the tape-recorded sounds were intended to provide a uniform
monotonous auditory background that would block out any external
sounds. Participants were not told about the differences in the
treatment conditions or the presence of auditory binaural beats on
the tape recordings. This deception was judged to
Cassette tapes were prepared specifically for this project by F.
Holmes Atwater of The Monroe Institute, Faber, VA, and we are
grateful for his assistance. Further details of their content and
construction are available from J. D. L.
BINAURAL BEATS AFFECT VIGILANCE AND MOOD
be
necessary to prevent expectation bias regarding treatment effects.
Furthermore, keeping participants unaware of the presence of
binaural-beat stimulation prevented the distraction of actively
listening to the tape recordings in order to determine their
content, which could help to maintain arousal during the task and
interfere with the development of a vigilance decrement. Use of this
deception was approved by the Medical Center Institutional Review
Board, and participants were debriefed at the conclusion of the
study.
Each
volunteer took part in three experimental sessions that were
identical except for the treatment condition. Sessions were
scheduled beginning between 1300 and 1600 hours, and all sessions
for a participant were scheduled at the same time of day.
Participants were asked to abstain from recreational drugs and
alcohol for at least 24 h prior to testing and to get a normal
night's sleep. Compliance was confirmed by self-report. The first
experimental session was intended for training and to provide a
stable le%el of performance for the two subsequent test sessions.
The control tape recording, which contained the same sounds but no
binaural beats, was presented during the training session. The beta
and theta/delta treatment conditions were presented in the second
and third sessions. The tape cassettes were blindcoded so that
treatments were presented double-blind, and the order of treatments
was counterbalanced across subjects.
Each
session began with the completion of a short battery of
questionnaires. The first session included completion of informed
consent procedures followed by completion of demographic and health
history forms. During the second and third sessions different
psychological questionnaires were completed during this time. The
POMS was completed at the end of this battery each day, immediately
before the vigilance task, with instructions to describe feelings at
that moment.
The
computer program displayed instructions for the vigilance task on
the monitor and presented samples of the stimuli. The experimenter
reviewed the instructions with the participant, and the
participant's questions were answered. Participants then completed a
I-min practice/warm-up trial of the vigilance task, and performance
feedback was provided upon completion. When the experimenter was
convinced that the participant understood how to perform the task,
the actual task was begun.
The
participant performed the task while seated at a desk in a swivel
chair. The room was dimly lit. The experimenter adjusted the stereo
headphones and started the tape playback. Auditory volume was
adjusted to a comfortable listening level for the participant that
would block perception of external sounds. Then the experimenter
left the room, and the participant began the 30-min vigilance task
after a brief delay. The tape-recorded binaural-beat stimulation was
presented continuously during the task. Immediately after completion
of the task, the participant completed a second POMS to indicate how
she or he felt at that moment. The experimenter reviewed a summary
of performance to insure that instructions had been followed and
reasonable levels of success obtained. However, participants
received only general positive feedback each day.
RESULTS
Vigilance Performance
Task
performance was scored as the number of correct target detections
(out of a possible 180 targets) and the number of false alarms (when
a key press response was made to a nontarget stimulus). The number
of hits and false alarms in the beta and theta/ delta binaural beat
conditions were compared by paired t-test. Because we proposed a
directional hypothesis, that beta frequency beats would improve
performance compared to the W delta frequency beats, a one-tailed
test was used to maximize statistical power from our sample.
A total
of 180 targets were presented during the 30-min task. Participants
detected a significantly larger number of targets when exposed to
the beta frequency binaural beats (mean = 153.5, SD = 23.6) than
when exposed to theta/delta-frequency binaural beats (mean = 147.6,
SD = 34.7). The difference in the number of correct detections was
5.9 ± 3.4 (mean ± SEM), which yielded t(28) = 1.7 (p < 0.05). In
contrast, participants produced more false alarms in the theta/delta
condition (mean = 8.7, SD = 12.2) than in the beta condition (mean =
6.6, SD = 9.4). The difference in false alarms was 2.0 -"-_ 0.9
(mean -!- SEM), which yielded t(28) = 2.26 (p < 0.02). Thus, the
binaural beat treatments had the predicted effects on vigilance task
performance.
To
determine whether the treatments had differential effects on
performance decrements during the vigilance task, performance scores
for six 5-min periods were analyzed with a two-condition (beta
versus theta/delta) by 6-period repeated measures analysis of
variance, using Green house-Geisser corrections. The effect of
period was significant for correct detections (F(5, 135) = 7.63, p <
0.0008), but the condition by period interaction was not (F(5, 135)
= 1.40, p < 0.24). Although there was a significant decrement in
correct detections over time during the task, the rate of decrement
did not differ significantly between the beta and theta/delta
conditions. For false alarms, neither the period effect or the
interaction were significant (both p > 0.20).
Subjective Mood
POMS
scale scores were evaluated by two condition x two period repeated
measures analysis of variance, in which the interaction tested the
hypothesis that the binaural-beat stimuli would alter how the
vigilance task affected mood. The main effect of period represented
the effects of the vigilance task itself, regardless of treatment.
We did not propose directional hypotheses for each of the six mood
scales of the POMS, and thus used this omnibus approach to detect
treatment effects.
As
demonstrated by significant interactions, the binaural-beat
condition affected scores for confusion/bewilderment (F(1, 28) =
7.30, p < 0.01) and fatigue/inertia (F(l, 28) = 4.07, p < 0.05),
with a trend observed in scores for depression/dejection (F(1, 28) =
3.81, p < 0.06). Scores for confusion/bewilderment rose more from
the beginning to the end of the vigilance task when the participant
listened to theta/delta binaural beats (mean = 1.9, SE = 0.4, p <
0.0001), than when beta binaural beats were presented (mean = 0.9,
SE = 0.4, p < 0.03). Moreover, scores for fatigue/inertia also rose
more when the participant listened to theta/delta binaural beats
(mean = 3.6, SE = 0.7, p < 0.0001), than when beta binaural beats
were presented (mean = 2.3, SE = 0.8, p < 0.005). In contrast,
depression/dejection scores rose slightly (mean = 0.3, SE = 0.2)
when participants listened to the theta/delta binaural beats during
the vigilance task and dropped slightly (mean = -0.4, SE = 0.4) when
they listened to beta binaural beats.
Scores
for vigor/activity did not contain a significant condition by period
interaction, although there was a significant period effect (F(l,
28) = 25.02, p < 0.0001). Scores dropped from the beginning to the
end of the task (mean = -2.9).
DISCUSSION
The
results of this study provide evidence that presentation of simple
binaural auditory beat stimuli during a 30-min vigilance task can
affect both the task performance and the changes in mood associated
with the task. The observed effects were consistent with our
predictions regarding differential effects on alertness and
LANE ET
AL.
mood.
Binaural beats in the beta EEG frequency range were associated with
relative improvements in target detection and reduction in the
number of false alarms compared to binaural beats in the theta/delta
EEG frequency range. Moreover, beta binaural beats were associated
with smaller increases in task-related confusion and fatigue
compared to theta/delta beats, and the two conditions had different
effects on scores for depression/dejection.
Scores
on the confusion/bewilderment scale increased under both conditions,
but rose significantly more during theta/delta frequency
stimulation. This scale includes the items "confused,'
. .
unable to concentrate," "muddled," "bewildered," "efficient" (scored
in reverse). "forgetful," and "uncertain about things." It appears
to represent "a self-report of cognitive efficiency" (4). Changes
observed in this study suggest that the theta/delta binaural beats
produced a subjective impairment in the ability to think clearly.
Performance of the vigilance task also increased scores for
fatigue/inertia in both conditions, but more so for the theta/delta
condition. This scale describes "a mood of weariness, inertia, and
low energy level" (4) and includes "worn-out," "listless,"
"fatigued," "exhausted," "sluggish," "weary," and "bushed" as its
items. The depression/dejection scale represents depressed mood
accompanied by a sense of inadequacy, and includes "unhappy."
"sorry," "sad." "miserable," "hopeless," "unworthy." "discouraged,"
"desperate," and "worthless" among its items. Together these scales
suggest that the negative changes in mood produced by a monotonous
task may have been partially ameliorated by the presentation of
beta-frequency binaural beats.
These
effects on behavior and mood were observed in the absence of
participant expectations, and experimental controls ruled out other
"placebo" effects. Not only were participants unaware of their
treatment condition, they were unaware that different binaural-beat
treatments were being presented during the three days of testing.
Although experimenters knew the true nature of the .study, they were
careful to maintain the cover story throughout the study. Moreover,
they were also blind to the order in which the experimental
treatments were administered and thus could not systematically bias
the results.
We
presume that the behavioral and mood effects were mediated by
changes in level of central nervous system arousal induced by
binaural-beat stimulation. It is plausible that these signals
entrained corresponding EEG frequencies and increased relative
I.
Bean, J.: Greenberg, A.: Deibler, W. P.; O' Hanlon, J. F. Operant
control
of occipital theta rhythm affects performance in a radar moni
toring
task. Science 183:871-873; 1974.
?.
Foster, D. S.. EEG and subjective correlates of alpha-frequency
binau-
ral-beat
stimulation combined with alpha biofeedback. 1996:http://www.Monroelnstitute.org/research/alpha-binaural-beat.html
3. Kennerly, R. C.. An empirical investigation into the effect of
beta
frequency binaural-beat audio signals on four measures of human
EEG
spectral power in the beta or theta/delta bands. Such an
interpretation is consistent with earlier studies that suggest
apparent EEG changes in response to binaural beat stimulation (2),
although the evidence of such effects remains preliminary. The
present study lacked EEG measurements that could confirm this
interpretation, but future studies can test this hypothesis
directly.
It is
interesting to note that similar changes in performance of a
vigilance task were observed when normal volunteers were trained
using biofeedback to increase or suppress EEG theta activity (1).
Those trained experimental groups did differ both in theta activity
and in vigilance performance during testing, and suppression of
theta activity during the task was associated with relatively better
vigilance performance. Perhaps binaural-beat stimulation provides an
alternative means of suppressing theta activity, or enhancing beta
activity, to enhance performance. If so, it has the distinct
advantage that it requires neither extensive training or intent to
self-control EEG for its successful application.
The
observations in the present study have interesting implications. If
binaural beat auditory stimulation can influence behavior and mood,
then such stimulation may have useful applications for the
self-control of arousal, attention, and performance. There may be
potential applications of these performance enhancing signals in
situations that demand high levels of continuous sustained attention
and performance, such as commercial highway driving or air traffic
control. Performance enhancing stimulation may prove useful in other
occupational tasks as well. Conversely, binaural-beat stimulation
that decreases arousal may have applications in the treatment of
insomnia or stress.
The
phenomenon of binaural auditory beat stimulation and its
psychophysiological consequences deserves further study. Additional
controlled studies will be required to determine what behavioral,
affective, and cognitive effects different patterns of binaural
beats might have and how any associated changes in physiology,
behavior, or subjective experience might be used. Little is known
about the mechanisms that may be involved in the transduction of
simple auditory signals into changes in mood and performance
demonstrated here. However, the results of this study demonstrate
clearly that simple binaural-beat auditory stimulation can influence
psychomotor and affective processes, even when people are unaware
that such signals are being presented.
REFERENCES
memory.
1994:http://www.Monroelnstitute.org/research/humanmemorykennerly.html
4. McNair, D. M.; Lorr, M.; Droppleman, L. F. EdITS manual for the
profile of mood states. San Diego: EdITS;1992.
5. Monroe, R. A. Far journeys. New York: Doubleday; 1985.
6. Oster, G. Auditory beats in the brain. Sci. Am. 229:94-102; 1973.
7. Russell, R., ed. Using the whole brain. Hampton Roads Publishing
Co.:
Norfolk, VA; 1993.
e-mail:
RemembranceMusic@aol.com
©2004 Remembrance Music All Rights
Reserved |