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j. Soc. Cosmet. Chem., 42, 199-210 (May/June 1991)
Effects of olfactory stimulation on performance and stress
in a visual sustained attention task
JOEL S. WARM, WILLIAM N. DEMBER, and
RAJA PARASURAMAN, Department of Psychology, University of
Cincinnati, Cincinnati, OH 45221 (J.S.W., W.N.D.), and
Department of Psychology, The Catholic University of America,
Washington, DC 20064 (R.P. ).
Received December 5, 1990. Presented at the Annual Meeting of the
Society of Cosmetic Chemists, San Francisco, May 1990.
Synopsis
Subjects performed a visual sustained attention (vigilance) task for 40 minutes during which they received
periodic 30-second whiffs of pure air or a hedonically positive fragrance, Muguet or Peppermint, through
a modified oxygen mask. The former fragrance had been independently judged as relaxing, the latter as
alerting. Subjects receiving either fragrance detected significantly more signals during the vigil than
unscented air controls. Subjective reports of mood and workload indicated that the subjects experienced the
vigilance task as stressful and demanding. However, the fragrances had no impact on the latter measures.
These results provide the initial experimental evidence to indicate that fragrances can enhance signal
detectability in a task demanding sustained attention, though the exact characteristics of effective fragrances
have yet to be determined.
INTRODUCTION
Vigilance, or sustained attention, tasks require observers to remain alert and to detect
infrequent and unpredictable stimulus events over prolonged periods of time (1-2).
Although subjects engaged in such tasks are required only to dedicate themselves to
looking or listening for the specified events that constitute signals for detection, their
performance on these tasks is remarkably fragile, and the tasks tend to induce consid-
erable stress.
The brittle character of vigilant behavior is revealed through the decrement function, a
decline in the frequency and/or speed of signal detections over time. This decline is often
complete from 20 to 35 minutes after the initiation of the vigil (1-2); in some cases, it
can even be observed as early as the first five minutes of watch (3). Along with the
decrement function, vigilance performance is accompanied by increased catecholamine
and cortisol output, indicating physiological stress (4-5), and by subjective reports
indicating that monitors feel less energetic, more strained, bored, irritated, drowsy, and
199
200 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
headachy at the end of a vigil than at the beginning (6-7). Moreover, measures of
subjective workload show that what may appear to be a simple assignment is in fact
quite demanding (8-9).
For obvious practical reasons, it would prove very useful to develop techniques for
improving the overall level of vigilance performance, for moderating the vigilance
decrement, and for alleviating the feelings of stress attendant on engaging in vigilance
tasks. Such tasks can be found in many work settings, including those confronting radar
and sonar operators, quality control inspectors, system monitors in power plants, med-
ical personnel in intensive care units, long distance drivers, and so on. Failure to detect
and respond to critical signals in these settings can sometimes have disastrous conse-
quences (2). Efforts to moderate the vigilance decrement and combat the feelings of
stress induced by vigilance tasks have utilized exercise (10), added stimulation such as
music in a visual vigilance task or visual stimulation in an auditory task (11-12), and
stimulant drugs (13-14) to keep monitors aroused. While somewhat successful, these
techniques have limitations. Exercise at the workstation is not always possible, added
stimulation can be distracting and impair working memory (15), and drugs can produce
unwanted side effects and addiction (16).
To our knowledge, no one, prior to the present study, has appealed to the olfactory sense
as a source of stimulation for the maintenance of sustained attention. Olfactory stimuli
can be quite salient and can play important roles in emotion and in recall and recog-
nition (17-18). There is also evidence that some fragrances can enhance alertness and
that some can reduce stress, at least on a short-term basis. While this evidence is in part
anecdotal (19), much of it comes from empirical research using both psychophysiological
and self-report techniques (20-21). If the purported alerting and stress-reducing prop-
erties of fragrances can operate over extended periods of time, fragrance administration
might serve as a benign vehicle for enhancing the quality of sustained attention and/or
reducing the stressful feelings that accompany vigilance performance.
Our hypothesis was that fragrances assessed as alerting might beneficially affect vigilance
performance and that fragrances assessed as relaxing might reduce the tension and
feelings of stress consequent on performing a vigilance task. Moreover, we were prepared
to speculate that alerting fragrances might also reduce the stress of vigilance by creating
a closer match between task demands and subjects' ability to perform those tasks; that
is, part of the stress may arise from subjects' need, but inability, to remain sufficiently
alert to do well on the vigilance task. Fragrances that help them stay alert might
therefore also help them feel better. Similarly, relaxing fragrances might affect perfor-
mance efficiency as well as feelings, since subjects who are tense and uncomfortable may
find it hard to concentrate on the task.
In short, it seemed reasonable to expect that both alerting and relaxing fragrances might
have both performance- and mood-enhancing effects, albeit for somewhat different
reasons. But our main concern, at the outset, was whether we could find any effects of
fragrance at all in comparison with an appropriate control condition.
For our initial investigation, we decided to use two hedonically positive fragrances, one
assessed as alerting and the other as relaxing. Toward that end, the initial phase of the
research involved an evaluation of the hedonic and mood-inducing qualities of seven
fragrances supplied by International Flavors and Fragrances, Inc.: Benzoin, Cashmeran,
EFFECTS OF OLFACTORY STIMULATION 201
Forest-Plus, Muguet, Peppermint, Sandiewood, and Spiced-Apple. We report below
details of that evaluation study, and we then describe the main experiment.
PILOT STUDY
Forty subjects, 20 male and 20 female students from the University of Cincinnati,
judged each of the seven candidate fragrances on two scales, a hedonic, or pleasantness
scale, and a scale of alertness/relaxation. The hedonic scale was a 16-cm line, with the
zero point labeled "very unpleasant" and the 16-cm point "very pleasant." Subjects
placed a mark on the line corresponding to their judgment of how pleasant or unpleasant
each fragrance was. The other scale, a 15-cm line, was labeled "more alerting/
stimulating" at the zero point and "more relaxing" at the 15-cm point. To aid in
making the latter judgment, subjects were asked to imagine that they were engaged in
a tedious task and to note whether each fragrance, if present during the conduct of that
task, would be more relaxing or more alerting/stimulating. For the hedonic scale, marks
above the midpoint of 8 cm were considered to designate a pleasant fragrance; for the
other scale, marks above the midpoint of 7.5 cm were considered to designate a relaxing
fragrance.
Each subject judged each fragrance once on each of the scales. The order in which
subjects experienced the fragrances as they progressed through the experiment was
varied at random for each individual, while the sequence in which they responded to the
two scales was balanced within the gender groups. Subjects sampled each fragrance once
via a squeeze bottle containing fragrance-impregnated polyethylene pellets. Preliminary
inspection of the data for both types of scales revealed that ratings were similar for the
male and female subjects. Accordingly, the data were collapsed across gender prior to
further analysis.
Overall mean hedonic and alerting/relaxing ratings are displayed in Table I.
Separate analyses of variance revealed statistically significant differences among the
fragrances on both dimensions. For hedonic ratings, F(6,234) = 21.31, p ( 0.001; for
alerting/relaxing ratings, F(6,234) = 5.08, p ( 0.001. On the basis of these ratings,
Table I
Means and Standard Errors for Hedonic and Alertness/Relaxation Ratings
Hedonic rating Alertness/relaxation rating
Fragrance M SE M SE
Benzoin 8.02 0.57 7.88 0.43
Cashmeran 5.26 0.59 5.27 0.52
Forest-Plus 6.09 0.56 6.07 0.47
Muguet ! !.40 0.59 8.34 0.56
Peppermint ! !. 02 0.56 5.63 0.56
Sandiewood 5.22 0.55 6.04 0.45
Spiced-Apple 7.6 ! 0.65 6.65 0.45
H Scale: (8, unpleasant; 8, neutral; )8, pleasant.
A/R Scale: (7.5, stimulating; 7.5, neutral; )7.5, relaxing.
202 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
we selected two fragrances, both with high mean hedonic values. One, Peppermint, had
a high alertingness rating; the other, Muguet, was rated as relaxing. In both instances,
the mean ratings were at least one standard error beyond the neutral point, as illustrated
in Table I.
MAIN EXPERIMENT
SUBJECTS
Thirty-six subjects, 18 men and an equal number of women, from the Cincinnati
metropolitan area participated in the experiment. The subjects were solicited through a
newspaper advertisement and were paid $ ! 5 for serving in the study. They ranged in age
from 18 to 30 years, with a mean of 26.6 years. The sample reflected a variety of
educational and occupational backgrounds. All subjects had normal or corrected-
to-normal vision and passed a test for anosmia, designed by International Flavors and
Fragrances, Inc., as a condition for gaining entry into the study. Six male and six female
subjects were assigned at random to one of three fragrance groups, a control group which
received unscented air and groups receiving air scented with either Muguet or Pepper-
mint.
VIGILANCE TASK
All subjects participated in a continuous 40-minute vigil divided into four consecutive
10-minute periods during which they monitored the repetitive presentation of a pair of
! X 13-mm lines with a 1-mm dot centered vertically and horizontally between them.
The distance between each line and the centering dot was normally 10 mm. Critical
signals for detection were configurations in which both lines were 2 mm farther from the
centering dot than usual. Stimuli were presented at the rate of 24 events/minute, with
an exposure time of 150 msec. In all conditions, five critical signals were presented
during each 10-minute period of watch (signal probability = 0.02). Intersignal inter-
vals ranged from 20 to 240 seconds, with a mean of 120 seconds.
An Apple IIe microcomputer was used to generate the stimuli and to control the
presentation of critical signals and neutral events in all experimental conditions. The
computer also recorded the subjects' responses. The subjects indicated their detection of
critical signals by depressing the spacebar on the computer's keyboard. In all conditions,
responses occurring within 1.25 seconds after the onset of a critical signal were recorded
automatically as correct detections. All other responses were recorded either as errors of
commission (failing to detect a signal) or false alarms (calling a neutral event a signal).
Subjects were tested individually in a 1.9 X 1.8 X 2.0-meter Industrial Acoustics
sound chamber. Each subject was seated in front of a table containing a video display
terminal (VDT). Viewing distance was approximately 43.5 cm. A glare reduction screen
was mounted on the VDT to enhance the clarity of the display and to minimize visible
phosphor decay following offset of the pixels that made up the stimulus configuration.
Ambient illumination was provided by a 40-watt bulb mounted in an aluminum
cone-shaped fixture that was positioned to diffuse light evenly within the chamber.
EFFECTS OF OLFACTORY STIMULATION 203
FRAGRANCE DELIVERY
The fragrance delivery system consisted of a pair of aquarium pumps (Hagen Optima
and Whisper 1000) that forced air through Teflon tubing into a charcoal filter and then
into a 35-ml glass reservoir housed in a refrigerator that was maintained at 70 ø F. The
reservoir contained 9 x 9-mm polyethylene pellets that incorporated the fragrance to be
used. Air from the reservoir was transmitted through additional tubing under pressure
from the pumps to a modified home oxygen mask worn by the subject while seated in
the experimental chamber.
The fragrance delivery equipment was located outside the chamber. Total travel distance
from the reservoir to the mask was 2.15 meters. Odor concentration at the mask was
controlled by the air flow (0.80 liters/minute) and by the number of pellets in the
reservoir. Five pellets were used for delivering the Peppermint fragrance and 10 for
Muguet. The concentration of Peppermint was 0.05 parts/million, while that for
Muguet was 0.13 parts/million. Fragrance concentration was determined by pilot work
that equated the fragrances for salience when delivered against an unscented back-
ground. In the control condition, unscented air was delivered to the mask by forcing the
air through an empty reservoir in the refrigerator. The duration of air flow through the
mask was controlled by a decade interval timer in conjunction with a Gerbrands tape
timer. The timing system activated the air pumps for limited intervals at specified times
during the experimental session. In the course of the experiment, subjects experienced
30-second whiffs of either scented or unscented air through the mask 4.5 minutes after
the start of the vigil and every five minutes thereafter. At other times the fragrance
delivery system was dormant.
The masks used in the study were modified by cutting triangular openings (with a base
of 6 cm and an altitude of 4 cm) in both sides, which permitted subjects to breathe room
air comfortably when the fragrance delivery system was not engaged. Fresh air was
provided to the experimental chamber through a ceiling fan. An electronic air cleaner
(Sears Model 635.830000) cleansed the air within the chamber and insured against
contamination by lingering odors. Containers of charcoal and baking soda placed within
the refrigerator offered similar protection for air entering and leaving the fragrance
reservoir. To further insure against contamination, three separate reservoirs were used
for the Muguet and Peppermint pellets and in the unscented control condition. These
reservoirs had separate tubing leading to masks reserved for them. To protect against the
possibility of infection, masks were bathed in alcohol after being used. Subjects reported
little discomfort in wearing the masks. The tubing leading to each mask was of suffi-
cient length to permit the subjects considerable freedom of movement as they sat at their
workstation. Schematic drawings of the fragrance delivery system and of the experi-
mental chamber are presented in Figures 1 and 2, respectively.
STRESS AND WORKLOAD MEASUREMENT
Stress measures were obtained from three scales. They included (a) the Thackray Mood
Scales--a nine-point rating scale measuring attentiveness, sleepiness, strain, boredom,
and irritation, in which values below five reflect negative feelings (22); (b) the Yoshitake
Symptoms of Fatigue Scale•a 30-item checklist of fatigue indicants such as headache,
dizziness, eye strain, etc. (23); and (c) the Stanford Sleepiness Scale•a seven-item rating
204 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
AIR PUMP
I
AIR PUMP
CHARCOAL AIR FILTER
VIGILANCE BOOTH
REFIRIGERATOR I I ••MODI FI ED
-- ' I OXYGEN MASK
GLASS TUBING -
FRAGRANCE PELLETS
ENLARGEMENT OF A
FRAGRANCECONTAINER
Figure 1. Schematic drawing of the fragrance delivery system.
scale ranging from "wide awake { 1}" to "almost in reverie {7}" (24). Subjective workload
assessments were obtained from the NASA TLX, which measures the degree of pro-
cessing capacity that is expended during the performance of a task on a scale from 0 to
100 (25).
PROCEDURE
Upon reporting to the laboratory, subjects were asked to complete an informed consent
form, screened for allergies, and tested for anosmia. They then completed a paper and
pencil version of the Thackray, Stanford, and Yoshitake scales. The order in which they
received these scales was counterbalanced within groups. Afterwards, subjects were
given a 10-minute training period that duplicated the first period of the vigilance task
and then assessed the workload of the training phase using a computer-generated version
of the TLX.
Prior to the start of the main part of the session, subjects were given time to become
acclimated to the oxygen mask and to experience the flow of fragrance or unscented air
through the mask. Immediately following the main session, the subjects again assessed
their workload and then responded to the Thackray, Stanford, and Yoshitake scales.
Testing was accomplished between 0730 and 1100 hours and between 1230 and 1700
hours. Half of the male and female subjects in each group were tested during these
morning and afternoon periods in order to control the possibility of circadian effects that
have been found to influence vigilance performance (26). Prior to coming to the labo-
EFFECTS OF OLFACTORY STIMULATION 205
Ceiling
Light
Fragrance
Line
Apple lie Storage
Intercom M•crocomputer Box
Bell
Figure 2. Schematic drawing of the experimental chamber.
Air
Purifier
ratory, subjects were requested not to wear cologne or perfume. All subjects complied
with this request.
RESULTS
VIGILANCE PERFORMANCE
Percentages of correct detections and false alarms were determined for each subject
during each period of watch. Preliminary inspection of the data revealed that gender and
time of day had little effect upon performance. Accordingly, the data were collapsed
across these factors for further analyses.
Mean percentages of the correct detections for the air, Muguet, and Peppermint groups
are plotted as a function of periods in Figure 3. It is evident in the figure that the
detection scores for both fragrance groups were similar and that for both groups the
percentage of detections was substantially and consistently greater than that for the
unscented air control. The figure also shows that the detection percentage in all groups
declined over time. An analysis of variance of the detection scores revealed that the
206 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
Z
O
90
80
7O
6O
5O
40
30
I I I I
I I I I
1 2 3 4
I Air
i
• Muguet
ß Peppermint
I
PERIODS OF WATCH (10MIN.)
Figure 3. Percentage of correct detections as a function of periods of watch for subjects in the air, Muguet,
and Peppermint conditions.
difference between groups reached statistical significance [F(2,33) = 3.25; p = 0.05]
and that performance efficiency deteriorated significantly over time [F(3,99) = 6.30; p
< 0.001]. The groups X periods interaction lacked significance [F(6,99) = 1.17; p >
0.05].
False alarms were generally few in all conditions. Mean percentages of false alarms for
the four periods of watch were 2.7%, 1.8%, 2.0%, and 2.3 %, respectively, for the air
group; 8.9%, 6.7%, 6.2%, and 5.9%, respectively, for the group exposed to Muguet;
and 12.4%, 7.2%, 9.3%, and 7.0%, respectively, for subjects exposed to Peppermint.
EFFECTS OF OLFACTORY STIMULATION 207
An analysis of variance of the percentage of false alarms showed that their overall
frequency declined significantly over time [F(3,99) = 7.42; p ( 0.001], a typical
finding in vigilance experiments (1). All of the remaining sources of variance in the
analysis lacked significance (p) 0.05).
STRESS AND WORKLOAD RATINGS
Mean pre-test and post-test scores on the Thackray, Stanford, and Yoshitake scales are
presented for each fragrance group in Table II.
Preliminary inspection of the data for the Thackray ratings of attention, sleepiness,
strain, boredom, and irritation indicated that the results for the five subscales were
similar. Consequently, the scores in Table II for this instrument represent summated
values (possible range is 5-45, with 25 as the midpoint) across the subscales. Increments
in negative feelings are reflected in lower post-test as compared to pre-test scores. In the
case of the Stanford and Yoshitake scales, however, increments in fatigue and sleepiness
are revealed through higher post-test as compared to pre-test scores.
Perusal of Table II will show that the subjects in this study found the vigil to be quite
stressful. Composite feelings of increased inattentiveness, sleepiness, strain, boredom,
and irritability after the vigil are evident in the Thackray ratings, along with increased
feelings of sleepiness and fatigue on the Stanford and Yoshitake scales. In the case of the
Yoshitake scale, pre-test and post-test differences were dramatic. On average, symptoms
of fatigue increased by 257% in the post-test measure. Analyses of variance performed
on the data of all three scales revealed significant phase effects [F(1,33) ) 48; p (
0.001] in each case. In no case, however, were the groups or the groups X phase
components of the analyses significant (p) 0.05), indicating that the self reports of
stress in this study were not attenuated by exposure to accessory olfactory stimulation.
Mean workload scores for the practice period and for the main task in the three fragrance
conditions are displayed in Table III.
It is evident in the table that the subjects rated the workload of both the 10-minute
practice period and the 40-minute vigil to be high. All scores are in the upper range of
the TLX scale. Moreover, there is a trend for the air group to show a greater increment
in workload from the 10-minute practice session to the 40-minute vigil than for the
Table II
Mean Pre-Test and Post-Test Scores on the Thackray, Stanford, and Yoshitake Scales for Subjects in the
Air, Muguet, and Peppermint Groups
Scales
Thackray Stanford Yoshitake
Groups Pre Post Pre Post Pre Post
Air 32.5 25.6 2.3 3.6 2.5 7.4
Muguet 33.6 25.1 2.4 3.8 3.3 7.1
Peppermint 34.2 25.7 2.2 3.3 2.7 7.2
Mean 33.4 25.5 2.3 3.6 2.8 7.2
208 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
Table III
Mean Workload Scores in Practice and the Main Watch for Subjects in the Air, Muguet,
and Peppermint Groups
Groups Practice Main watch Mean
Air 64.7 68.2 66.4
Muguet 69.4 68.0 68.7
Peppermint 63.6 62.3 63.0
Mean 65.9 66.2
Muguet or Peppermint groups. An analysis of variance of the data of Table III, however,
failed to reveal any significant differences between groups or between phases (p > 0.05).
DISCUSSION
The results of this experiment indicate that two fragrances, Peppermint and Muguet,
when delivered periodically during the course of a 40-minute vigil, can have beneficial
effects on subjects' performance in a vigilance task. Specifically, subjects exposed to
either of the two fragrances showed greater overall sensitivity to signals than those
receiving periodic whiffs of unscented air; that result cannot be attributed to a change
in subjects' willingness to emit detection responses, since the false alarm rates were
equivalent in all groups. Moreover, the result cannot be due to differences among groups
in the initial level of detectability of signals, since an analysis of variance revealed no
group differences in hit rate during the practice task [F(2,33) = 2.16; p > 0.05]. The
data did not show an effect on the vigilance decrement itself: Subjects in all three groups
performed less well as the vigil progressed than at the outset. Finally, there were no
differences between men and women in performance efficiency, no interactions between
gender and fragrance condition, and no effects involving time of day. So, we can
conclude with some confidence that the effect of the two fragrances on ability to
discriminate signals from non-signals has generality over sex and time of day.
While we had reason to expect Peppermint (characterized as alerting) to be more
effective than Muguet on performance measures, and Muguet (characterized as relaxing)
to be the more effective on subjective reports of stress and workload, it is apparent that
there was no difference between the two fragrances in their effect on performance
efficiency and that neither had any dramatic impact on subjective reports. These latter
results call into question the complicated scenario outlined earlier, that Peppermint
facilitates vigilance performance by directly raising arousal level, whereas Muguet works
through its ability to reduce the perceptually distracting effects of the symptoms of
fatigue, tension, strain, headache, and so on, that typically arise in the vigilance
situation. There are three simpler hypotheses that need to be tested: (a) given that both
Peppermint and Muguet are assessed as very pleasant, perhaps any pleasant fragrance
will suffice, and there is nothing physiologically/chemically special about these two
fragrances; (b) given that Peppermint and Muguet are both fragrances, perhaps any
fragrance will suffice, pleasant, neutral or unpleasant, so long as it is judged either
alerting or relaxing; and finally, (c) it is possible that any perceptually salient fragrance
will work by temporarily increasing subjects' alertness level via connections from olfac-
tory centers to the midbrain reticular area (27), a brain region that plays an important
EFFECTS OF OLFACTORY STIMULATION 209
role in the regulation and maintenance of vigilance (28). These possibilities warrant
further investigation.
Finally, note that beyond providing the initial experimental demonstration that certain
fragrances can bolster sustained attention, our results have meaning for an even broader
issue, that of intersensory interaction. Studies of interactions among stimuli in different
sense modalities have, for the most part, been confined to combinations drawn from the
auditory, visual, and tactual modes (29). To our knowledge, the data described in this
paper are the first to show that accessory olfactory stimulation can enhance the detection
of visual stimuli.
CONCLUSIONS
The results of this study indicate that exposure to whiffs of air scented with the fragrance
of Muguet or Peppermint can enhance the rate of signal detections in a vigilance task
without a concomitant increase in errors of commission. These findings suggest that
exposure to fragrance may serve as an effective form of ancillary stimulation in tasks
demanding close attention for prolonged periods of time.
ACKNOWLEDGMENTS
This paper is based on an invited address given at the Annual Scientific Seminar of the
Society of Cosmetic Chemists, San Francisco, CA, May 11, 1990, and a talk given at
the Annual Meeting of the Psychonomic Society, New Orleans, LA, Nov. 17, 1990.
We are grateful to Marina Munteanu, Craig Warren, and Steven Warrenberg of Inter-
national Flavors and Fragrances, Inc., for suggesting that we undertake the research and
for providing extensive technical assistance; to Jonathan Gluckman, Sandy Matthews,
Judith A. Thiemann, and Mary Anne Toledo, for invaluable help with instrumentation
and data collection; and to the Fragrance Research Fund for financial support.
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