|
Reprint from Physiology & Behavior, Vol. 63,
No. 2, pp. 249-252, 1998
©1998 Elsevier Science Inc.
Binaural Auditory Beats Affect Vigilance
Performance and Mood
JAMES D. LANE,* 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 electro-encephalograph 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.
Keywords: 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
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 hypnogogic 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 self-control 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 EEG-delta/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. Thirty-two
people were recruited and 29 completed the protocol. This
group had a mean age (±SD) of 32 (± IO) years with a range
from 19 to 51 years. The group contained 19 females and 10
males; 20 whites, 8 blacks, and 1 Asian; 18 employed workers
and 11 students. All volunteers were nonsmokers. Each received
$30 for completion of the study.
Materials
Binaural 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 it 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 I 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 1/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. 0 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 (O 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; anger-hostility;
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 blackout 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 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 level 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 blind-coded 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 ]-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 keypress 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 theta/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 Greenhouse-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(l,
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(l, 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 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,"
I 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
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 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 nor 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
Beatty, J.; Greenberg, A.; Deibler, W. P.; O' Hanlon, J.
F. Operant control of occipital theta rhythm affects performance
in a radar monitoring task. Science 183:871-873; 1974.
Foster, D. S., EEG and subjective correlates of alpha-frequency
binaural-beat stimulation combined with alpha biofeedback.
1996: http://www.Monroelnstitute.org/research/alpha-binaural-beat.html
Kennerly, R. C., An empirical investigation into the effect
of beta frequency binaural-beat audio signals on four measures
of human memory. 1994: http://www.monroeinstitute.com/research/humanmemory-kennerly.html
McNair, D. M.; Lorr, M.; Droppleman, L. F. EdITS manual for
the profile of mood states. San Diego: EdITS;1992.
Monroe, R. A. Far journeys. New York: Doubleday; 1985.
Oster, G. Auditory beats in the brain. Sci. Am. 229:94-102;
1973.
Russell, R., ed. Using the whole brain. Hampton Roads Publishing
Co.: Norfolk, VA; 1993. |
