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Effects and after-effects of chewing gum on vigilance, heart rate, EEG
and mood
Andrew P. Allen
a
, Tim J.C. Jacob
b
, Andrew P. Smith
a,
⁎
a
Centre for Occupational and Health Psychology, School of Psychology, Cardiff University, 63 Park Place, CF10 3AS, United Kingdom
b
School of Biosciences, Cardiff University, Life Sciences Building, Museum Avenue, CF10 3AX, United Kingdom
HIGHLIGHTS
•Chewing gum shortens vigilance reaction time.
•Vigilance accuracy increases during chewing.
•Heart rate increases during chewing.
•Chewing gum increases temporal and frontal beta power.
abstractarticle info
Article history:
Received 10 October 2013
Received in revised form 3 April 2014
Accepted 14 May 2014
Available online 21 May 2014
Keywords:
Vigilance
Sustained a ttention
Chewing gum
Heart rate
EEG
Research has shown that chewing gum improves attention, although the mechanism for this effect remains
unclear. This study investigated the effects and after-effects of chewing gum on vigilance, mood, heart rate and
EEG. Participants completed a vigilance task four times; at baseline, with or without chewing gum, and twice
post-chewing. EEG alpha and beta power at left frontal and temporal lobes, subjective mood and heart rate
were assessed. Chewing gum shortened reaction time and increased the rate of hits, although hits fell during
the secondpost-chewing task.Chewing gum heightened heart rate, butonly during chewing.Gum also increased
beta power at F7 and T3 immediately post-chewing, but not following the post-chewingtasks. The findings show
that chewing gum affects several different indicators of alertness.
© 2014 Elsevier Inc. All rights reserved.
1. Introduction
The ability to sustain attention is crucial, and determines higher at-
tention function [25]. Vigilance, defined as sustained attention requiring
the production of a target response to an occasionally occurring stimu-
lus [37], is characterised by a vigilance decrement [15]; as attention is
sustained over time, performance worsens. The role of arousal in the
vigilance decrement is controversial: although vigilance performance
may decline due to reduced arousal [8], vigilance tasks can also be
stressful [40], which would imply that the decline in vigilance is due
to heightened arousal instead. Research on sustained attention has indi-
cated a fall in heart rate over time [23], and participants reported engag-
ing in other mental activities during the task, whichrefutes the idea that
attention resources are engaged but become overstretched during
vigilance.
Chewing gum could act as a relatively inexpensive and safe means of
enhancing sustained attention. Following conflicting findings on the ef-
fect of chewing gum on global performance measures from attention
tasks (e.g. [29,41]), studies have investigated the possibility that gum
chewing may affect sustained attention after a certain amount of time,
attenuating the vigilance decrement. Chewing gum has shortened reac-
tion time towards the end of a vigilance task [2,18,34],aswellas
improving accuracy ([29], secondary analysis) and schoolchildren com-
pleted a greater number of items towards the end of a concentration
task when chewing gum [33]. The fact that a beneficial effect of chewing
is not immediately evident may be in part due to a distracting effect of
chewing gum during performance; however, such distraction may be
specific to people who have habituated to consuming chewing gum.
Consequently, habitual gum consumption should also be taken into
account. Despite numerous studies indicating a positive effect of gum
later in testing, a negative effect of gum was observed towards the
end of a vigilance task [1]; this might be due to a shorter testing period
being used than in research which showed a positive effect over time.
Physiology & Behavior 133 (2014) 244–251
⁎Corresponding author at:Room 5.35, Alimentary PharmabioticCentre/Department of
Psychiatry, Bio sciences Institute, University College Cork, Cork, Ireland. Tel.: + 44
2920874757.
E-mail addresses: andrewallen@ucc.ie (A.P. Allen), Jacob@cardiff.ac.uk (T.J.C. Jacob),
SmithAP@cardiff.ac.uk (A.P. Smith).
http://dx.doi.org/10.1016/j.physbeh.2014.05.009
0031-9384/© 2014 Elsevier Inc. All rights reserved.
Contents lists available at ScienceDirect
Physiology & Behavior
journal homepage: www.elsevier.com/locate/phb
Author's personal copy
Another study did not find an interaction between gum condition and
first versus second half of a vigilance task [35]. In another study,
chewing gum improved performance not simply towards the end, but
throughout a continuous performance test which involved producing
frequent responses and withholding a response occasionally [13],sug-
gesting that the time-on-task effect of chewing gum may be more evi-
dent in sustained attention tasks where the production of a response
is relatively rare. The effects of chewing gum on cognitive performance
have also been shown to persist after chewing has ceased [22]. The au-
thors suggest that this persistent change in performance is due to an on-
going effect of chewing on arousal. Consequently, it may be the case that
chewing gum for a short period at the beginning of a lengthy task can
attenuate a decline in vigilance, even if gum is no longer being chewed.
Our first hypothesis was thus as follows:
Hypothesis 1. A decline in vigilance performance (evident in reduced
hits and lengthened reaction time on the vigilance task) will be attenu-
ated by chewing gum, compared to a no-chewing control.
Similar to competing theories of the role of arousal in the vigilance
decrement, it is also still unclear if chewing gum leads to increased or
reduced arousal; chewing gum has been found to increase subjective
alertness (e.g. [11,26,29]), but there is also evidence that chewing
gum can reduce anxiety, both over a period of two weeks (e.g. [43])
and under conditions of acute stress [28], and there is mixed evidence
regarding the effect of chewing on heart rate [27,36,39,41].Consequently,
a positive effect of chewing gum on vigilance may be due to either:
(1). Chewing gum restoring arousal after a vigilance task reduces arousal
to a sub-optimal level, or: (2). Chewing gum reducing arousal after a
vigilance task heightens arousal to an excessive level. By examining
physiological arousal, this study may help to elucidate which account of
vigilance and which putative mechanism of chewing gum are accurate.
A state of arousal is associated with increased beta activity and re-
duced alpha activity, while the opposite trends are associated with re-
laxation [16], although heightened beta activity was associated with
lower skin conductance levels in children with ADHD [5], suggesting
that indices of central nervous system and sympathetic nervous system
arousal may not correspond directly. EEG measures show differential
effects during sustained attention; beta power is associated with ten-
dency to respond [3], suggesting that a state of vigilance is associated
with heightened beta power. Beta power reductions in elderly adults
have been associated with poorer attentional performance [6], provid-
ing further evidence of an association between higher beta power
and higher attentional performance. Spearmint gum has heightened
alpha frequencies at T3, F3 and F4 during a post-chewing recording
[17]. Beta ratios of activity at T3 increased following the chewing of
flavourless gum, suggesting that a more alert state was induced. How-
ever, beta ratios of activity fell at F4, and alpha rose at T3, following
chewing of gum with sucrose [16]. Chewing gumbase with sucrose led
to an increase in the ratio of alpha activity at T3 and F3 [19]. However,
following chewing of flavoured gum this did not occur, although the
ratio of alpha activity increased at F4, and beta increased at T3. The
fact that chewing gum can increase both alpha and beta activity led to
the description of chewing gum as inducing a mental state of “relaxed
concentration”[16]. Studies of chewing gum and EEG examine the
EEG after chewing in order to eliminate movement artefacts.
EEG studies concerning chewing have generally examined brain
activity in the absence of a cognitive performance task. However, fMRI
research has indicated that chewing gum during performance of an
attention task is associated with activation in the left frontal gyrus and
anterior cingulate cortex (ACC) [10]. Furthermore, connectivity be-
tween the dorsal ACC and the left anterior insula has been found to be
attenuated when chewing gum under conditions of noise stress [42],
suggesting that a stress-reducing effect of gum on ACC function could
potentially explain positive effects on vigilance performance. More
generally, frontal and temporal activities have been associated with
sustained attention (e.g. [38]). Frontal and temporal areas are thus
promising candidate areas for chewing gum effects in the central
nervous system during attention performance. Our second hypothesis
was as follows:
Hypothesis 2. Consistent with a low-arousal model of vigilance, heart
rate, beta activity and subjective alertness will fall during vigilance per-
formance, and chewing gum's attenuation of the vigilance decrement
will be evident in higher heart rate, increased beta activity, and higher
subjective alertness.
The present research investigated the effects and after-effects of
chewing standard gumbase with sweeteners on vigilance performance
during and after chewing, as well as the effects of chewing on the activ-
ity of both the sympathetic nervous system (heart rate—during and
after chewing) and the central nervous system (EEG—after chewing).
This study also assessed changes in mood over the test session. Partici-
pants alternated between performing blocks of a vigilance task and
receiving brief EEG recordings. We hypothesised that chewing gum
would attenuate a reduction in vigilance performance, as well as associ-
ated changes in physiology (reduced heart rate and EEG beta power) and
subjective mood (reduced alertness).
2. Method
The research described in this paper received approval from Cardiff
University's School of Psychology Ethics Committee.
2.1. Design
Participants were divided into two groups by random assignment
to either a chewing or control condition. Participants in the chewing
condition chewed during the gum/control vigilance task that followed
baseline EEG (see Fig. 1).
2.2. Participants
Forty-eight right-handed participants were initially recruited, but
eight participants' EEG data had to be excluded due to movement arte-
facts. Forty participants were included in the final study. Age, gender
and occupational status of participants in each group are summarised
in Table 1. Participants were recruited through an online university no-
tice board. Participants had normal or corrected-to-normal vision. They
were paid £10 forparticipation. Exclusion criteria were: medication use,
any self-reported medical problems, consumption ofmore than 40 units
of alcohol per week or smoking more than 10 cigarettes in the daytime
and evening.
2.3. Materials
2.3.1. Electroencephalography
Participants were seated in a comfortable chair in a quiet room. Ac-
cording to the international 10/20 system, silver electrodes were placed
in specific regions on the scalp (T3 and F7). Additionally, a reference elec-
trode was placed on the mastoid behind the left ear while the two earth
electrodes were positioned on the forehead and right arm. All the elec-
trodes were connected to an electrode adaptor box (Cambridge Electron-
ic Design CED1902, Cambridge, UK) followed by a pre-amplifier/amplifier
(CED1902, Cambridge, UK) before the signal was digitised (CED1401
laboratory interface) and stored on a computer for subsequent analysis.
2.3.2. Heart rate
ARBO ECG electrodes were used for the reference and earth
electrodes. A piezo-electric pulse transducer (UFI, CA, USA) was used
in conjunction with a CED 1401-plus laboratory interface to monitor
245A.P. Allen et al. / Physiology & Behavior 133 (2014) 244–251
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heart rate. The monitor was attached to the finger of the participant's
non-dominant hand.
2.3.3. Gum
Wrigley's standard gumbase was used: this consisted of gum base,
glycerine, lecithin, sorbitol, sweeteners (aspartame and acesulfame K)
and emulsifier.
2.3.4. Psychological tasks
2.3.4.1. Repeated digits vigilance task [31].Three-digit numbers were
shown on the screen of a laptop at the rate of 100 per minute. Each
was normally different from the preceding one but on 8 trials per min-
ute the number presented was the same as that presented on the previ-
ous trial. Participants had to detect these repetitions and respond as
quickly aspossible bypressingthe central button on a purpose-built re-
sponse box. Digits were presented in white on a black background. Each
session of this task lasted 5 min 30 s. Previous research has shown that
performance on the task declines even when the task lasts for only 3
min. Correct detections of target repetitions (hits), incorrect button
presses when no repetition was presented (false alarms) and reaction
time were assessed.
2.3.4.2. Mood (visual analogue scale). Self-reported alertness (range =
0–400), hedonic tone (range = 0–300) and anxiety (range = 0–150)
were measured using visual analogue scales (previously used at our
laboratory, e.g. [2]) at baseline and at the end of testing. Using the same
response box used for the vigilance task, participants moved the cursor
left or right to describe the extent to which they felt a certain mood.
There was no time limit for this task.
2.4. Procedure
Testing took place either in the late morning (start time at 10:00,
11:00 or 12:00) or the afternoon (start time 15:00 or 16:00), so that
participants were not tested during periods of low circadian alertness.
Participants were requested not to eat for 1 h before entering the lab,
in order to avoid post-meal effects.
Participants signed a consent form and filled in a demographic ques-
tionnaire. Participants sat approximately 85 cm from the laptop screen.
A reference electrode was attached at the left mastoid. Test electrodes
were then placed at F7 and T3, followed by an earth on the right
forehead. An extra earth was attached to the left wrist. The heart rate
monitor was attached to the index finger of the left hand.
The stages of testing are summarised in Fig. 1. Following a
familiarisation with the computer tasks, participants performed a base-
line measure of mood and vigilance. The next vigilance task was
performed with or without chewing gum, and was followed by two
more vigilance tasks without chewing gum. EEG recording followed
each performance of the vigilance task. A post-test assessment of
mood followed the last EEG recording.
Heart rate was measured continuously from the beginning of the
baseline vigilance test until the end of the final EEG measurement.
Participants in the chewing gum condition expectorated their gum im-
mediately after finishing the vigilance task with chewing. During EEG
readings, participants were instructed to rest their heads back in the
seat with their eyes closed, and to remain as still as possible, in order
to minimise muscle movement.
2.5. Analysis
Heart rate and EEG data were analysed using Spike 2, version 7.07.
Heart rate and EEG were visually inspected for artefacts, which were re-
moved from the analysis. EEG was analysedin 30 second epochs, which
were then averaged to give each 60 second post-vigilance EEG measure.
The two EEG frequency bands analysed werealpha, 8 to 13 Hz, and beta,
13 to 30 Hz.
Change-from-baseline data were analysed using ANOVA. The inde-
pendent variables were chewing gum condition and time-on-task, and
habitual gum consumption was also entered to test for interactions be-
tween experimental gum condition and habitual level of consumption.
For vigilance performance and EEG, a 2-factor (2 X 3) mixed design
was used, with the between-participants variables being gum condition
(2 levels: whether participants chewed or not during the second vigi-
lance task) and the within-participants variable being stage of testing
(3 levels: with/without chewing, post-chewing 1 and post-chewing
2). The dependent variables were hits, false alarms and reaction time
for vigilance performance, alpha power and beta power at F7 and T3
for EEG, and heart rate. For mood, a 2-factor (2 X 2) mixed design
was used, with gum condition as the between participants variable,
and the within-participants variable being stage of testing (2 levels:
pre-vigilance tasks and post-vigilance tasks). For heart rate, a 2-factor
(2 X 6) mixed design was used, with gum condition as the between
participants variable, and the within-participants variable being
stage of testing (6 levels: vigilance with/without chewing, EEG1, post-
chewing vigilance 1, EEG2, post-chewing 2 and EEG3). Furthermore,
the potential moderating effects of habitual gum consumption were
analysed using 2-factor (2 X 3) ANOVA with the additional between-
participants predictor of habitual gum consumption (3 levels: regular,
infrequent and never; see Section 3.4.). The dependent mood variables
were alertness, hedonic tone and anxiety. Scores that were three inter-
quartile ranges above the median were excluded from analysis.
3. Results
3.1. Effect of gum and time on reported mood
For mood, a 2 (gum condition: gum or control) × 2 (stage of testing:
pre-test and post-test) mixed ANOVA was conducted.
The main effect of gum condition was examined to determine the
overall effect of chewing gum; there was not a main effect on alertness,
F
(1, 38)
= .32, pN.05, partial η
2
= .01, hedonic tone, F
(1, 38)
= .26, pN.05,
partial η
2
= .01, or anxiety, F
(1, 38)
= .18, pN.05, partial η
2
= .01. The
main effect of time was investigated to determine if the vigilance task
itself altered mood. Regardless of gum condition, time led to a
highly significant reduction in alertness, F
(1, 38)
= 72.75, pb.001, partial
Fig. 1. Order and approximate timings of conditions.
Table 1
Participant characteristics.
Gum condition No-gum control
Age 22.33 (SD = 2.5) 24.4 (SD = 3)
Gender Female = 16 Female = 16
Male = 2 Male = 6
Occupation Student = 16 Student = 16
Administrator = 1 Administrator = 3
Researcher = 1 Researcher = 1
Interpreter = 1
246 A.P. Allen et al. / Physiology & Behavior 133 (2014) 244–251
Author's personal copy
η
2
= .66, and hedonic tone, F
(1, 38)
= 22.36, pb.001, partial η
2
=.37,
but not anxiety, F
(1, 38)
= .35, pN.05, partial η
2
= .01. The interaction
between chewing gum and time was tested to examine if gum could
moderate any time-on-task effects. There was an interaction between
gum condition and time; gum condition was associated with a signifi-
cantly smaller reduction in alertness between baseline and post-test,
F
(1, 38)
=6.27, p= .02, partial η
2
=.14(seeFig. 2), although
there was no gum × time interaction for hedonic tone, F
(1, 38)
= 2.53,
pN.05, partial η
2
= .06, or anxiety, F
(1, 38)
= 2.8, p=.1,partial
η
2
= .07. The mean anxiety and hedonic tone scores are reported in
Table 2.
3.2. Effect of gum and time on vigilance performance
For vigilance performance, a2 (gum condition: gum or control) × 3
(stage of testing: with/without chewing, post-chewing 1 and post-
chewing 2) mixed ANOVA was conducted. For testing as a whole,
reaction time was shortened in the gum condition, F
(1, 38)
=2.72,
p= .05, partial η
2
= .07, but there was not a main effect of gum
condition on hits, F
(1, 38)
= .08, pN.05, partial η
2
= .002, or false alarms,
F
(1, 37)
= 1.09, pN.05, partial η
2
= .03. Stage of testing had a main effect
on repeated digits hits, which fell significantly across sessions, F
(2, 76)
=
3.66, p= .03, partial η
2
= .09, as did false alarms, F
(2, 74)
= 2.63, p= .04,
partial η
2
= .07, indicating a lower overall response rate, although
there was no main effect of stage of testing on reaction time, F
(2, 76)
= 1.94, pN.05, partial η
2
= .05. There was an interaction between
chewing gum and stage of testing on hits, F
(2, 76)
= 2.71, p= .04, partial
η
2
=.07(seeFig. 3). Hits were higher for the gum condition during
chewing and at post 1, but slightly lower at post 2. There was no signif-
icant gum × time interaction for false alarms or reaction time.
3.3. The effect of gum and time on physiology
For heart rate data, a2 (gum condition: gum or control) × 6 (stage
of testing: vigilance with/without chewing, EEG1, post-chewing
vigilance 1, EEG2, post-chewing 2 and EEG3) mixed ANOVA was
conducted. Gum condition did not have a significant main effect on
heart rate, F
(1, 32)
= .70, pN.05, partial η
2
= .02. However, heart rate
was significantly affected by time, F
(1.84, 58.9)
= 16.77, pb.001, partial
η
2
= .34, Greenhouse-Geisser adjusted. Mean heart rate fell slightly
across the EEG testing sessions, but was substantially reduced for the
post-chewing vigilance tasks, compared to heart rate during the
vigilance task with chewing. Furthermore, there was a significant
interaction between gum condition and time of testing for heart rate,
F
(1.91, 61.12)
= 8.51, p= .001, partial η
2
= 0.21, Greenhouse–Geisser
adjusted. Gum led to a highly significant increase in heart rate during
chewing, F
(1, 32)
= 48.59, pb.001, partial η
2
= 0.72, but there was a
lack of a difference between conditions later in the experiment,
although heart rate was somewhat lower for the gum condition during
the post-chewing vigilance tasks (see Fig. 4).
For EEG data, a 2 (gum condition: gum or control) × 3 (stage of test-
ing: with/without chewing, post-chewing 1 and post-chewing2) mixed
ANOVA was conducted. Chewing led to a non-significant increase in
beta power at T3, F
(1, 28)
=1.95,pN.05, partial η
2
= .07, and at F7,
F
(1, 28)
=1.91,pN.05, partial η
2
= .06. Stage of testing did not
significantly affect beta power at T3, F
(1.41, 39.39)
= .31, pN.05, partial
η
2
= 0.01, Greenhouse–Geisser adjusted, or at F7, F
(1.22, 34.05)
=.63,
pN.05, partial η
2
= 0.02, Greenhouse–Geisser adjusted. There
was no significant interaction between gum and stage of testing at T3,
F
(1.41, 39.39)
=1.41, pN.05, partial η
2
= 0.05, Greenhouse–Geisser
adjusted, or at F7, F
(1.22, 34.05)
=.32,pN.05, partial η
2
= 0.01,
Greenhouse–Geisser adjusted.
Although the interaction between gum condition and stage of test-
ing was not significant, a speculative simple effects analysis indicated
that the effect of gum was significant immediately post-chewing
(EEG1), both for T3, F
(1, 50)
= 5.73, pb.05, partial η
2
= 0.1, as well as
for F7, F
(1, 48)
= 11.57, pb.01, partial η
2
=0.19(seeFig. 5).
With regard to alpha power, chewing condition did not
have a main effect at T3, F
(1, 23)
= .59, pN.05, partial η
2
= 0.03, or at
F7, F
(1, 23)
=.59,pN.05, partial η
2
= 0.03. Stage of testing did not
have a significant effect at T3, F
(2, 46)
=1.99,pN.05, partial η
2
=0.08,
or at F7, F
(2, 52)
= 1.43, pN.05, partial η
2
= 0.05. Gum condition did
not interact with stage of testing at T3, F
(2, 46)
= 1.05, pN.05, partial
η
2
= 0.04, or at F7, F
(2, 52)
=.13,pN.05, partial η
2
= 0.05.
3.4. Habitual gum consumption
To examine the potential moderating effects of habitual gum con-
sumption,2 (gum condition) × 3 (level of habitual consumption: regu-
lar, infrequent and never) mixed ANOVA were conducted. Consistent
with previous research [30], habitual chewing was classified as follows:
twenty-one participants chewed five or more pieces of gum a week
(“regular”: median pieces chewed per week = 10, range = 5–21),
fourteen chewed gum, but fewer than five pieces a week (“infrequent”:
median = 1.6, range = 0.25–2.5) and five never chewed. Experimental
groups did not differ significantly in the mean number of pieces chewed
per week. Habitual gum consumption did not moderate the effects of
gum on mood, vigilance performance, heart rate or EEG data.
150
170
190
210
230
250
270
290
310
330
350
Gum Control
Alertness rating (total VAS score)
Condition
Pre-test
Post-test
*
Fig. 2. Effectof gum on change in alertness. (Error bars indicate standard error. Asteriskindicates significantdifference (pb.05) in change in alertness. Maximumalertness score = 400.)
Table 2
Hedonic toneand anxiety for gum conditionsat pre- and post-test assessment. (Standard
errors in brackets.)
Gum No gum
Pre-test hedonic tone (maximum score = 300) 223.6 (8.6) 226.8 (7.2)
Post-test hedonic tone 206.7 (9.2) 192.8 (8.0)
Pre-test anxiety (maximum score = 150) 97.7 (4.3) 100.2 (4.6)
Post-test anxiety 101.0 (5.4) 93.2 (5.1)
247A.P. Allen et al. / Physiology & Behavior 133 (2014) 244–251
Author's personal copy
A
B
C
-6
-5
-4
-3
-2
-1
0
1
Chewing Post-chewing 1 Post-chewing 2
Stage
Gum
No
gum
-7
-6
-5
-4
-3
-2
-1
0
1
Chewing Post-chewing 1 Post-chewing 2
Number of false alarms
(Baseline change)
Stage
Gum
No
gum
-20
-10
0
10
20
30
40
50
60
70
80
90
Chewing Post-chewing 1 Post-chewing 2
Stage
Gum
No
gum
Number of hits
(Baseline Change)
Mean RT
(ms - Baseline change)
Fig. 3. Effect of gum across sessions on (A) hits, (B) false alarms and (C) mean reaction time for the repeated digits task. (Change scores from pre-chewing baseline are used. Error bars
indicate standard error.)
-25
-20
-15
-10
-5
0
5
10
15
20
25
Chewing EEG1 Post-chewing 1 EEG2 Post-chewing 2 EEG3
Stage
Gum
No
gum
†
HR (Beats per min - Baseline Change)
Fig. 4. Effectof gum on heart rate duringvigilance tasks andduring EEG readings. (Change scoresfrom pre-chewing baseline are used. Error bars indicatestandard error. Dagger indicates
significant difference at pb.001.)
248 A.P. Allen et al. / Physiology & Behavior 133 (2014) 244–251
Author's personal copy
4. Discussion
This study indicates that chewing gum can alter central and sympa-
thetic nervous system activity associated with vigilance performance.
The transient effect on central and sympathetic nervous system arousal
is consistent with the short-lived effect of chewing gum on hits on the
vigilance task. The enhanced beta activity at F7 and T3 is consistent
with evidence suggesting that vigilance performance is associated
with frontal and temporal lobe activity (e.g. [9,38]), as well as fMRI
research indicating increased activation in frontal areas when
chewing gum during an attention task [10]. This article offers prelimi-
nary evidence that chewing gum may lead to a transient increase
in frontal and temporal beta activity, which is associated with an alert
state [16]. However, alpha activity was not affected by chewing
gum, in contrast to previous research which indicated that chewing
gum base increased alpha activity at the frontal and temporal regions
[16,19].
Some studies concerning chewing gum and vigilance have required
participants to chew gum for longer periods of time than used here
(e.g. [29]); the effects on vigilance performance reported here may
have been stronger and more persistent if participants had chewed for
longer. A condition in which participants make chewing movements
without any gum in their mouths (“sham chewing”) could be useful
for separating effects of chewing with mouth movements per se. How-
ever, previous research has indicated that, during a vigilance-type task,
the effects of sham chewing on both physiological and subjective mea-
sures of sleepiness were more similar to those of a no gum control
condition than those of gum [12], suggesting that motion alone may
not suffice to explain alerting effects of gum. Both females and males
were included as participants, as previous research has not indicated
sex differences in chewing gum effects [32].
A vigilance decrement was evident in vigilance performance, as well
as heart rate and subjective alertness. The reduction in heart rate as well
as hits and false alarms suggests that reduced vigilance was associated
with reduced sympathetic arousal. These findings may not generalise
to all vigilance tasks; participants' self-reported mood indicated that
the current task did not heighten anxiety, but where a vigilance task in-
duces anxiety, different trends may be seen.
The recording of the EEG with eyes closed prevented trends in brain
activity during vigilance performance from being measured. This is un-
fortunate, as more complete data on central nervous system activity
could be observed, but this method was essential to remove artefacts as-
sociated with participants having their eyes open; the use of an auditory
vigilance task which can be performed with the eyes closed may allow
for recording of EEG data during vigilance performance in future
research. However, even in this case EEG cannot be measured while
chewing gum, as this will also create artefacts due to muscle movement.
Mood assessment could also be conducted at more frequent intervals to
gain greater information concerning any decline in alertness, although
longer breaks between stages of vigilance testing may result in less of
a decrement in vigilance [20], so interrupting testing stages for longer
periods to conduct mood assessments may lead to a recovery in
vigilance performance which could impair study of the vigilance
decrement.
A
B
-0.005
-0.003
-0.001
0.001
0.003
0.005
EEG1 EEG2 EEG3
Stage
Gum
No
gum
*
-0.003
-0.002
-0.001
0
0.001
0.002
0.003
0.004
EEG1 EEG2 EEG3
Stage
Gum
No
gum
*
Beta power
(µV squared: change from baseline)
Beta power
(µV squared: change from baseline)
Fig. 5. Effectof gum on beta power (A) at T3 and(B) at F7. (Change scoresfrom pre-chewingbaseline are used. Errorbars indicate standard error. Asterisk indicates significant differenceat
pb.05.)
249A.P. Allen et al. / Physiology & Behavior 133 (2014) 244–251
Author's personal copy
The smaller fall in alertness for the chewing condition is consistent
with previous research. However, baseline alertness happened to
already be lower in the gum condition, before the gum manipulation,
and it fell to a level similar to that of the control condition post-test.
Given this baseline difference, it is unclear from the current data if
chewing gum had a subjectively alerting effect. Chewing gum did not
affect anxiety, although this may be due to anxiety being close to floor
for participants, in contrast with research assessing the effect of
chewing gum under conditions of acute stress [28].
Previous research (e.g. [22]) and discussion of time-on-task trends in
chewing effects have suggested that an initial distracting effect (which
should become less evident as chewing becomes more automatic) may
be followed by enhanced arousal (which may persist after chewing has
ceased). The current findings do not suggest an impairment of vigilance
by a distracting effect of chewing gum; indeed the interaction between
stage of testing and gum condition for hits suggests that chewing led to
higher accuracy while it was being chewed rather than following
chewing. There was a slight (non-significant) trend for lower heart
rate in the gum condition at post-chewing; this may suggest that lower
sympathetic arousal could play a role in this interaction.
The major advantage of thisstudy is that it allowed for the measure-
ment of both central nervous system and sympathetic nervous system
arousal, along with the measurement of post-chewing effects which
occur after chewing has finished. Assuming a Yerkes–Dodson inverted
U-shaped curve relationship between arousal and cognition, the fact
that heart rate was increased and reaction time was shortened by
gum suggests that participants were in a sub-optimal rate of arousal
when they completed the vigilance task (although see [7], for a critique
of the “Yerkes–Dodson law”). As the reduction in response rate to the
vigilance task was associated with a fall in heart rate, our findings
support the reduced arousal account of the vigilance decrement [8],as
opposed to an account whereby heightened arousal characterises
vigilance [40]. The fact that reaction time remained shortened by gum
compared to control, while the physiological effects were more
transient, suggests that some other mechanism may explain the more
persistent effects of reaction time. The fact that performance and phys-
iological indices of vigilance differed in their time course could be due to
compensatory control [14,24]; for example, participants in the control
condition may have maintained a slower rate of response (to avoid
making errors) due to an experienced reduction in arousal compared
to baseline.
Future research should examine the role of flavour in chewing gum,
given existing evidence that it can have differing effects on EEG data
[16]. As brain activation in response to vigilance can be bilateral [9],
assessment of EEG trends on both sides of the brain will be of interest
in future research. It is also of interest if any neurochemical changes
are associated with chewing during sustained attention; noradrenaline
and acetylcholine have been suggested as playinga role in sustaining at-
tention [25], as well as dopamine, through its effects on motivation [21].
The enhancing effect of chewing gum on vigilance accuracy suggests
that it may be useful in a number of applied contexts, such as driving;
it has been suggested that this could be tested using driving simulation
techniques [29], similar to research assessing possible enhancing effects
of caffeine [4].
In conclusion, the findings show that increases in both cardiovascular
and central nervous system arousal may explain the effects of gum on
vigilance, although the after-effects of chewing gum appear to be
time-limited. These effects were not moderated by habitual chewing
gum consumption, indicating they are not dependent upon familiarity
with chewing gum, and may potentially be useful in applied contexts
such as driving.
Acknowledgements
The first author's PhD studies were supported by the Wrigley
Science Institute.
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