Markdown lines 160–266 · Part 2 of 3
Subjects of continuous monitoring for targets, rapid responding, and the
importance of maintaining good performance throughout the entire
Volunteers were recruited by advertisement from the Duke task. The computer program administered all stimuli and recorded
University community. They were required to be in good health, the parameters of each stimulus trial. Response latency was mea-
have normal hearing and vision (corrected or uncorrected), and be sured for all keypresses and recorded with stimulus data for later
free from acute illness or use of medications. Thirty-two people analysis.
were recruited and 29 completed the protocol. This group had a Mood assessment. The Profile of Mood States (POMS; EdITS,
mean age (6SD) of 32 (610) years with a range from 19 to 51 San Diego, CA) was used to assess changes in mood. The POMS
years. The group contained 19 females and 10 males; 20 whites, 8 contains 65 adjective rating items (0 to 4 scale) that describe
blacks, and 1 Asian; 18 employed workers and 11 students. All feelings people experience (e.g., friendly, tense, grouchy, etc.).
volunteers were nonsmokers. Each received $30 for completion of Item ratings can be summarized on standard scales that represent
the study. six general moods: tension-anxiety; depression-dejection; anger-
hostility; vigor-activity; fatigue-inertia; and confusion-bewilder-
Materials ment (4). This inventory was administered before and after the
Binaural beat stimulation. Binaural beat signals were presented vigilance task to assess task-related changes in mood.
stereophonically by cassette tape.3 Three different tapes were
Procedure
prepared as follows. All three tapes contained a background of
‘‘pink noise’’ with uniform amplitude in the frequency spectrum Participants were kept blind to the true purpose of the study.
from 40 –320 Hz and decreasing amplitude (12 db/octave) at When volunteers were recruited, they were told that the study was
frequencies above and below these limits. Tapes also contained intended to evaluate a new computerized vigilance task and to
carrier tones at 100, 200, 250, and 300 Hz, which had amplitudes assess how stable performance was over several days. Throughout
15 db above the amplitude of the pink noise. The tape constructed the study, they were told that task conditions were identical across
for the training session contained no binaural beat stimuli, but the days and that the tape-recorded sounds were intended to provide a
tapes for the two experimental treatments did. For the delta/theta uniform monotonous auditory background that would block out
condition the 100-Hz tone was presented with a 1.5-Hz binaural any external sounds. Participants were not told about the differ-
beat, the 200 and 250 Hz tones were presented with 4-Hz binaural ences in the treatment conditions or the presence of auditory
beats, and the 300-Hz tone was presented with no binaural beat. binaural beats on the tape recordings. This deception was judged to
3
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 251
be necessary to prevent expectation bias regarding treatment ef- quency beats, a one-tailed test was used to maximize statistical
fects. Furthermore, keeping participants unaware of the presence power from our sample.
of binaural-beat stimulation prevented the distraction of actively A total of 180 targets were presented during the 30-min task.
listening to the tape recordings in order to determine their content, Participants detected a significantly larger number of targets when
which could help to maintain arousal during the task and interfere exposed to the beta-frequency binaural beats (mean 5 153.5,
with the development of a vigilance decrement. Use of this decep- SD 5 23.6) than when exposed to theta/delta-frequency binaural
tion was approved by the Medical Center Institutional Review beats (mean 5 147.6, SD 5 34.7). The difference in the number of
Board, and participants were debriefed at the conclusion of the correct detections was 5.9 6 3.4 (mean 6 SEM), which yielded
study. t(28) 5 1.7 (p , 0.05). In contrast, participants produced more
Each volunteer took part in three experimental sessions that false alarms in the theta/delta condition (mean 5 8.7, SD 5 12.2)
were identical except for the treatment condition. Sessions were than in the beta condition (mean 5 6.6, SD 5 9.4). The difference
scheduled beginning between 1300 and 1600 hours, and all ses- in false alarms was 2.0 6 0.9 (mean 6 SEM), which yielded t(28)
sions for a participant were scheduled at the same time of day. 5 2.26 (p , 0.02). Thus, the binaural beat treatments had the
Participants were asked to abstain from recreational drugs and predicted effects on vigilance task performance.
alcohol for at least 24 h prior to testing and to get a normal night’s To determine whether the treatments had differential effects on
sleep. Compliance was confirmed by self-report. The first experi- performance decrements during the vigilance task, performance
mental session was intended for training and to provide a stable scores for six 5-min periods were analyzed with a two-condition
level of performance for the two subsequent test sessions. The (beta versus theta/delta) by 6-period repeated-measures analysis of
control tape recording, which contained the same sounds but no variance, using Greenhouse-Geisser corrections. The effect of pe-
binaural beats, was presented during the training session. The beta riod was significant for correct detections (F(5, 135) 5 7.63, p ,
and theta/delta treatment conditions were presented in the second 0.0008), but the condition by period interaction was not (F(5, 135)
and third sessions. The tape cassettes were blind-coded so that 5 1.40, p , 0.24). Although there was a significant decrement in
treatments were presented double-blind, and the order of treat- correct detections over time during the task, the rate of decrement
ments was counterbalanced across subjects. did not differ significantly between the beta and theta/delta con-
Each session began with the completion of a short battery of ditions. For false alarms, neither the period effect or the interaction
questionnaires. The first session included completion of informed were significant (both p . 0.20).
consent procedures followed by completion of demographic and
health history forms. During the second and third sessions different Subjective Mood
psychological questionnaires were completed during this time. The
POMS scale scores were evaluated by two condition 3 two
POMS was completed at the end of this battery each day, imme-
period repeated-measures analysis of variance, in which the inter-
diately before the vigilance task, with instructions to describe
action tested the hypothesis that the binaural-beat stimuli would
feelings at that moment.
alter how the vigilance task affected mood. The main effect of
The computer program displayed instructions for the vigilance
period represented the effects of the vigilance task itself, regardless
task on the monitor and presented samples of the stimuli. The
of treatment. We did not propose directional hypotheses for each
experimenter reviewed the instructions with the participant, and
of the six mood scales of the POMS, and thus used this omnibus
the participant’s questions were answered. Participants then com-
approach to detect treatment effects.
pleted a 1-min practice/warm-up trial of the vigilance task, and
As demonstrated by significant interactions, the binaural-beat
performance feedback was provided upon completion. When the
condition affected scores for confusion/bewilderment (F(1, 28) 5
experimenter was convinced that the participant understood how to
7.30, p , 0.01) and fatigue/inertia (F(1, 28) 5 4.07, p , 0.05),
perform the task, the actual task was begun.
with a trend observed in scores for depression/dejection (F(1, 28)
The participant performed the task while seated at a desk in a
5 3.81, p , 0.06). Scores for confusion/bewilderment rose more
swivel chair. The room was dimly lit. The experimenter adjusted
from the beginning to the end of the vigilance task when the
the stereo headphones and started the tape playback. Auditory
participant listened to theta/delta binaural beats (mean 5 1.9,
volume was adjusted to a comfortable listening level for the
SE 5 0.4, p , 0.0001), than when beta binaural beats were
participant that would block perception of external sounds. Then
presented (mean 5 0.9, SE 5 0.4, p , 0.03). Moreover, scores for
the experimenter left the room, and the participant began the
fatigue/inertia also rose more when the participant listened to
30-min vigilance task after a brief delay. The tape-recorded bin-
theta/delta binaural beats (mean 5 3.6, SE 5 0.7, p , 0.0001),
aural-beat stimulation was presented continuously during the task.
than when beta binaural beats were presented (mean 5 2.3, SE 5
Immediately after completion of the task, the participant com-
0.8, p , 0.005). In contrast, depression/dejection scores rose
pleted a second POMS to indicate how she or he felt at that