Psychology
2011. Vol.2, No.8, 834-840
Copyright © 2011 SciRes. doi:10.4236/psych.2011.28127
Do Individual Differences Moderate the Cognitive Benefits of
Chewing Gum?
Richard Stephens*, Nicola M. J. Edelstyn
School of Psychology, Keele University, Keele, Staffordshire, UK.
Received May 26th, 2011; revised July 29th, 2011; accepted September 8th, 2011.
Recent experiments investigating whether chewing gum enhances cognitive performance have shown mixed re-
sults and a recent replication failed to reproduce earlier findings. The present experiment aimed to investigate
whether participant individual differences underlie the discrepant findings. Therefore, in addition to examining
differences in Digit Span and Spatial Span performance across gum and control groups, chronotype, extraver-
sion, habitual tiredness, current stress, current arousal and current thirst were assessed using questionnaires.
Task difficulty was also manipulated. While there were no chewing gum effects under standard testing condi-
tions, chewing gum enhanced Digit Span performance in the more difficult dual task condition. Furthermore,
Spatial Span performance was improved by chewing gum in introverts but not extraverts and chewing gum was
shown to eliminate the negative relationship between thirst and Digit Span performance. In explaining these data
it is proposed that chewing gum may act both to reduce stress and to alleviate thirst.
Keywords: Chewing Gum, Cognitive Performance, Individual Differences, Introversion, Thirst, Stress
Introduction
Around 90 years ago, when chewing gum sales began to
take-off in North America, there were a variety of views per-
taining to whether gum was an altogether suitable mass-con-
sumer product. Detractors considered chewing gum to be so-
cially distasteful, even plebian, and unsightly. On the other
hand it was claimed in advertisements that chewing gum re-
lieved tension, relaxed the nerves and muscles, aided fatigue,
quenched thirst, benefited digestion and slowed tooth decay
(Robinson, 2004; see Figure 1 for an example). Nevertheless,
the 20th Century saw only one attempt to substantiate the
claimed psychological benefits of chewing gum; a study carried
out at Columbia University noted a positive correlation between
gum chewing and mental task performance (Hollingworth,
1939). More recently, positron emission tomography imaging
data has shown a possible mechanism by which chewing could
lead to enhanced cognitive performance: increased blood flow
in brain regions associated with motor function during chewing
(Momose, Nishikawa, Watanabe, Sasaki et al., 1997). Follow-
ing this discovery, the early part of the 21st Century saw a re-
surgence of interest in the cognitive performance effects of
chewing gum.
Since 2002 there have been 13 published experiments inves-
tigating whether chewing gum benefits young adults’ cognitive
performance (Wilkinson, Scholey, & Wesnes, 2002; Baker et
al., 2004, experiment 1; Tucha, Mecklinger, Maier, Hammerl,
& Lange, 2004, experiments 1 and 2; Stephens & Tunney, 2004;
Miles & Johnson, 2007, experiments 1 and 2; Johnson & Miles,
2007; Johnson & Miles, 2008 experiment 1; Allen, Norman, &
Katz, 2008; Smith, 2009a; Smith, 2009b; Smith, 2010). These
experiments have shown mixed results. So, for example, on the
one hand Wilkinson et al. (2002) found that chewing gum en-
hanced immediate word recall, delayed word recall, spatial
working memory and numeric working memory, with some
results replicated by Stephens & Tunney (2004), and Smith
(2010) showed improved focused attention and faster reaction
time. In the meantime Baker et al. (2004) reported context de-
Figure 1.
A 1919 newspaper advertisement for Wrigley’s Chewing Gum. Source:
London Free Press, 6 January 1919, p. 6. Reproduced from Robinson
(2004).
pendent memory effects where the context was set by whether
or not participants chewed gum. On the other hand, Tucha et al.
(2004) found chewing gum did not enhance participants’ im-
mediate and delayed word recall and differentially affected
aspects of attention, enhancing sustained attention, showing no
effect for divided attention, selective attention, visual scanning

R. STEPHENS ET AL.
835
and vigilance, and showing decrements in tonic alertness, pha-
sic alertness and flexibility. In addition, recent studies have
found no memory enhancement from chewing gum (Smith,
2009a; Smith, 2010), no enhanced learning (Allen, Norman, &
Katz, 2008), no improvement in attentional performance (Smith,
2009b) and have not reproduced the context-dependent memory
effects that had been observed earlier (Johnson & Miles, 2007;
Miles & Johnson, 2007; Johnson & Miles, 2008).
There is no clear pattern to elucidate why findings have been
discrepant across experiments. Glucose is known to improve
cognitive performance (Sünram-Lea, Foster, Durlach, & Perez,
2002) and many chewing gum brands include glucose as an
ingredient. However, with the exception of Smith (2010), all
the above experiments used sugar-free gum, so ruling out glu-
cose as an explanatory factor. While all the experiments em-
ployed young adult participants there was some variation in
gender distribution across experiments. However, analysis re-
veals no link between gender distribution and cognitive per-
formance. Of seven experiments with approximately similar
numbers of males and females (proportion of males = 40%
-50%) three experiments showed enhanced performance (Tucha
et al., 2004, experiment 2; Stephens & Tunney, 2004; Smith,
2010) and four showed no enhancement (Tucha et al., 2004,
experiment 1; Johnson & Miles, 2007; Allen, Norman, & Katz,
2008; Smith, 2009b). Of the four experiments in which females
more obviously outnumbered males (proportion of males =
13% - 31%) one experiment showed enhanced performance
(Baker et al., 2004, experiment 1) and the others showed no
enhancement (Miles & Johnson, 2007, experiments 1 and 2;
Johnson & Miles, 2008 experiment 1). The gender distribution
was not stated in two experiments (Wilkinson et al., 2002;
Smith, 2009b).
Analytic power also does not explain the pattern of effects in
these experiments. Assuming constant effect sizes across stud-
ies (which seems reasonable since all the studies are concerned
with chewing gum effects on cognition), and ignoring the study
that used sugared gum (Smith, 2010), the most highly powered
experiments were those conducted by Tucha et al. (experiments
1 and 2; n = 58 in a within-subjects design). However, only
experiment 2 showed a performance enhancing effect of chew-
ing gum, and that was in only one of several measures of atten-
tion employed. On the other hand, Baker et al. experiment 1
appears to have the weakest power (n = 23 in a between-sub-
jects design) and yet showed clear context memory effects of
gum. It is particularly troubling that in an exact replication
Johnson and Miles (2007) were unable to demonstrate im-
proved recall following chewing gum at first presentation and
retrieval as reported by Baker et al (2004; experiment 1).
The absence of any clear methodological reason why some
studies showed effects while others did not together with the
failures to replicate described above lead us to consider whether
the different experimental findings reflect something about the
condition of the participants employed across studies. For ex-
ample, perhaps in some of the previous studies participants
were experiencing mild sleep deprivation and chewing gum
helped reverse the deficit associated with this. This is analogous
with research designs aiming to assess the extent to which caf-
feine and other drugs offset cognitive deficits arising due to
sleep deprivation (e.g. Wesensten, Belenky, Kautz, Thorne,
Reichardt, & Balkin, 2002). Indeed, Hodoba (1999) found that
participants who stayed up all night chewing gum reported
feeling less tired than controls who stayed up all night without
chewing gum. It is not routine in laboratory-based psychology
experiments for data concerning background factors such as
fatigue to be collected and reported, and indeed such data were
not reported in the chewing gum studies reviewed above. In the
majority of the chewing gum experiments to date the partici-
pants were drawn from the undergraduate student population.
Gill (2002) reports that up to half of male students may exceed
sensible weekly alcohol guidelines and take part in binge
drinking. Therefore, there is undoubtedly scope within this
group for participants to attend the laboratory inadequately
rested, or in some otherwise sub-optimal state.
Therefore, in the present study in addition to examining dif-
ferences in cognitive performance across gum and control
groups, we also used several questionnaires to assess dimen-
sions relating to individual differences in participants. This is a
novel approach in the research on chewing-gum effects on cog-
nitive performance. Three variables pertinent to tiredness were
assessed―chronotype (whether a person is most productive in
the morning or the evening hours) was assessed using the Mor-
ningness-Eveningness Scale (Horne & Ostberg, 1976); habitual
tiredness (as opposed to current level of tiredness) was assessed
using the Epworth Sleepiness Scale (Johns, 1991); and current
arousal level was assessed using the Stress and Arousal Check-
list (Cox & Mackay, 1985). This was on the basis that chewing
gum-mediated cognitive enhancement would be more likely to
be present in participants who were tired or fatigued relative to
those that were not so affected. In addition extraversion was
assessed using the Eysenck Personality Inventory (Eysenck &
Eysenck, 1967) as there is a body of work suggesting that in-
troverts (individuals scoring at the low end of the extraversion
scale) are chronically more highly aroused compared with ex-
traverts (Matthews, Davies, Westerman, & Stammers, 2004).
Two additional factors known to affect cognitive performance
were also assessed. These were current stress level, assessed
using the Stress and Arousal Checklist (Cox & Mackay, 1985),
and current thirst level assessed using a single 9-response
Likert scale following the method reported by Rogers, Kainth
& Smit (2001). The latter variable was included following a
suggestion made during the 2007 British and Feeding Drinking
Society symposium on chewing gum effects on cognition
(Stephens & Tunney, 2008) that gum may exert its cognitive
enhancement effects by alleviating thirst. Certainly, data exist
linking thirst with cognitive decrement (e.g. Rogers, Kainth, &
Smit, 2001).
A further manipulation was to vary task difficulty. In their
null-effect study of chewing gum effects on learning in dental
students, Allen et al. (2008) questioned whether chewing gum
may be more likely to benefit “less academically accom-
plished” individuals (p. 106) compared with high-performing
students. What they are implying here is that a law of dimin-
ishing returns acts in relation to the potential for enhancement
of cognitive performance such that enhancement is less likely
to occur the higher the performance baseline. Such a concept
seems similar to Wilder’s law of initial value, defined as “the
higher the initial value, the smaller the response of function-
raising, the larger the response to function-depressing stimuli”
(as cited in Jin, 1992, p. 176). Although usually applied in psy-
chophysiological research, Wilder’s law of initial value cap-
tures the concept that it becomes more difficult to improve
performance the higher the performance baseline. If this as-
sumption is correct, then any performance benefit of chewing
gum would be relatively smaller in individuals performing near
optimal level compared with those performing less well. There-
fore, to create conditions under which the level of performance
would be more likely to dip below optimal, we increased cogni-
tive task difficulty by adding the secondary task of concurrently

R. STEPHENS ET AL.
836
counting the incidence of specified events occurring during cer-
tain trials.
The cognitive tests employed assessed verbal and spatial
working memory. These tests were selected on the basis that
they were quick and easy to administer, and because working
memory has been shown to be enhanced by chewing gum
(Wilkinson, Scholey, & Wesnes, 2002; Stephens & Tunney,
2004). We did not expect to see cognitive enhancement effects
in participants chewing gum compared with those not chewing
under the standard testing condition. However, cognitive en-
hancement with chewing gum was hypothesised in the dual task
(difficult) condition. Furthermore, cognitive enhancement with
chewing gum was hypothesised regardless of task difficulty for
individuals reporting any of: higher levels of evening typeness,
higher levels of tiredness, lower levels of arousal, higher levels
of extraversion, higher levels of stress and/or higher levels of
thirst.
Methods
Participants
Participants, 29 females and 17 males, of mean age 21.04
years (SD 1.49), were recruited through an opportunity sample
of Keele University students.
Materials
A tape-recorded version of the Digit Span test was used to as-
sess verbal working memory (Wechsler, 1981) and the Spatial
Span test was used to assess visuospatial working memory
(Wechsler, 1999). In addition to the standard test forms the tests
were also performed under a dual-task condition with the aim
of increasing task difficulty. For Digit Span participants were
required to report the number of occurrences of a brief tone that
sounded occasionally during the number sequence presentation
(0 - 3 occasions per trial). Participants had to report accurately
both the number of tones sounded and the digit sequence in
order to “pass” each trial. For Spatial Span the investigator
occasionally used two fingers to point at the board rather than
one (0 - 3 occasions per trial). Participants were asked to report
the number of occurrences of two fingered pointing in each trial
as well as the correct sequence of blocks; both had to be accu-
rate to “pass” each trial.
Several questionnaires were used. The Morningness-Even-
ingness Scale (Horne & Ostberg, 1976) was used to assess
chronotype; lower scores are indicative of morning-typeness.
The Eysenck Personality Inventory (Eysenck & Eysenck, 1967)
was used to assess the personality dimension extraversion;
scores on this questionnaire form a continuum with lower
scores indicating introversion and higher scores indicating ex-
traversion. The Epworth Sleepiness Scale (Johns, 1991) was
employed to assess habitual tiredness; higher scores are indica-
tive of greater habitual tiredness. The Stress and Arousal Check
List (Cox & Mackay, 1985) was used to assess the extent to
which participants were feeling i) stressed and ii) aroused at the
time of questionnaire completion; higher scores are indicative
of higher current levels for each variable. Finally a single item
9-point Likert scale was used to assess participants’ current
thirst (Rogers et al., 2001); a higher score is indicative of
greater thirst. The chewing gum employed was Wrigley’s Ext ra
Sugar-free Cool BreezeTM.
Design
A mixed measures general linear design was employed, with
one between-subjects categorical predictor variable, gum (gum
vs. no gum); one within-subjects categorical predictor variable,
task difficulty (standard vs. dual task); and one continuous be-
tween-subjects predictor variable, questionnaire score (one of:
chronotype; extraversion; habitual tiredness; current stress;
current arousal; and current thirst). The dependent variables
were the Digit Span and Spatial Span scores. Participants were
randomly assigned to the gum and no gum conditions. The
order in which participants encountered the standard and dual
task conditions was randomised. Two alternative forms of the
standard and dual task Digit Span and Spatial Span tests were
employed; test form was randomised across conditions.
Procedure
Keele University School of Psychology Research Ethics
Committee approved the study. Participant consent was a prereq-
uisite for participation. For participant recruitment purposes the
research was described as a cognitive performance study. Testing
occurred between 9.00 am and 2.00 pm. All participants com-
pleted the questionnaires first and the tests of working memory
next. Participants in the “gum” condition commenced chewing a
single piece of gum immediately prior to the cognitive testing and
continued chewing throughout testing. After completing the cog-
nitive tests the participants were thanked, debriefed and offered a
free pack of chewing gum or sweets.
Results
Participants’ questionnaire and working memory test scores
in each of the experimental conditions are shown in (Table 1),
below.
There were four analytic stages. In the first stage only data
from the standard Digit Span and Spatial Span tests were ana-
lysed using one-way ANOVAs comparing performance of the
Table 1.
Means and standard deviations of the questionnaire and cognitive test
scores in the gum and control conditions.
Gum (n = 23) Control (n = 23)
Mean SD Mean SD
Age 20.78 0.85 21.30 1.92
Chronotype
(Maximum Score = 30) 14.00 4.36 18.22 4.94
Extraversion
(Maximum Score = 24) 13.48 4.44 12.48 4.89
Habitual Tiredness
(Maximum Score = 24) 8.70 3.83 7.22 2.59
Current Stress
(Maximum Score = 18) 4.52 4.14 2.52 2.27
Current Arousal
(Maximum Score = 12) 8.00 2.98 9.04 2.18
Current Thirst
(Maximum Score = 9) 6.22 1.81 6.09 2.00
Standard WAIS-R Digit Span
(Maximum Score = 28) 14.91 3.26 14.65 4.28
Dual Task Digit Span
(Maximum Score = 28) 14.26 3.31 12.57 4.52
Standard WMS-III Spatial Span
(Maximum Score = 28) 15.57 3.09 14.70 2.90
Dual Task Spatial Span
(Maximum Score = 28) 14.13 3.43 12.65 2.69

R. STEPHENS ET AL.
837
chewing group with the control group. In the second stage
mixed 2 × 2 ANOVAs were computed examining the effects on
Digit Span and Spatial Span test performance of the between
subjects factor gum (gum vs. no gum), the within subjects fac-
tor task difficulty (standard vs. dual task) and the interaction of
these factors. In the third analytic stage a series of mixed meas-
ures general linear models were applied. These included the
between-subjects categorical predictor variable, gum (gum vs.
no gum), the within-subjects categorical predictor variable, task
difficulty (standard vs. dual task), and a continuous between-
subjects predictor variable, questionnaire score. Two sets of
these analyses were applied. In the first set the dependent vari-
able was Digit Span test score, while in the second set the de-
pendent variable was Spatial Span test score. Within each set
six general linear models were computed. Each general linear
model included the categorical predictors described above, but
each general linear model included one of the following six
questionnaire-derived continuous predictor variables: chrono-
type; extraversion; habitual tiredness; current stress; current
arousal; and current thirst. Each general linear model included
the three-way interaction (gum by task difficulty by question-
naire score), the three two-way interactions (gum by task diffi-
culty; gum by questionnaire score; and task difficulty by ques-
tionnaire score) and the three main effects (gum; task difficulty;
and questionnaire score). In the fourth analytic stage bivariate
correlations among the six questionnaire-derived continuous
predictor variables were computed, in order to facilitate the
interpretation of the third phase analyses. All analyses were
carried using SPSS v16.
First Stage Analyses―Gum vs. Control on the
Standard Cognitive Tests
There was no significant difference in Digit Span perform-
ance between the gum and control groups, F(1,44) < 1, partial
eta squared = 0.001, and nor was there a significant difference
in Spatial Span performance between the gum and control
groups, F(1,44) < 1, partial eta squared = 0.022.
Second Stage Analyses―Gum vs. Control on the
Standard and Dual Task Cognitive Tests
For Digit Span, there was a significant gum by difficulty in-
teraction, F(1,44) = 4.844, p = 0.033, partial eta squared =
0.099. This interaction is depicted in Figure 2. Analytic com-
parisons showed that performance in the more difficult dual
task condition was improved in the gum group compared with
controls, F(1,44) = 13.535, p = 0.001, but there was no per-
formance difference between the gum and control groups on the
standard test, F (1,44) < 1.
For Spatial Span, the gum by difficulty interaction was not
significant, F(1,44) < 1, partial eta squared = 0.018, and neither
was the main effect of gum, F(1,44) = 2.009, p = 0.163, partial
eta squared = 0.044. However there was a significant main
effect of difficulty, F(1,44) = 25.873, p < 0.001, partial eta
squared = 0.370, such that scores in the more difficult dual task
condition were reduced compared with the standard Spatial
Span test.
Third Stage Analysis―Gum vs. Control on the
Standard and Dual Task Cognitive Tests Taking into
Account Individual Differences
There were no significant three-way interaction effects. A
significant gum by extraversion interaction predicted Spatial
Span performance, F(1, 42) = 6.578, p = 0.014, partial eta
Figure 2.
Digit span performance as a function of task difficulty (standard vs.
dual task condition) in t h e c h e w i n g g um a n d c o n tr o l c o nditions.
squared = 0.135. This interaction is illustrated in Figure 3. Un-
derlying this interaction was a non-significant regression of ex-
traversion on Spatial Span in the controls, r = 0.107, F (1,22) < 1,
partial eta squared = 0.041, whereas the regression of extraver-
sion on Spatial Span in the chewing gum group was significant, r
= –0.333, F(1,22) = 6.519, p = 0.019, partial eta squared = 0.237.
A significant gum by current thirst interaction predicted Digit
Span performance, F(1,42) = 4.642, p = 0.037, partial eta squared =
0.100. This interaction is illustrated in (Figure 4). Underlying this
interaction was a significant regression of current thirst on Digit
Span in the controls, r = –1.135, F(1,21) = 7.998, p = 0.010, partial
eta squared = 0.276, whereas the regression of current thirst on
Digit Span in the chewing gum group was not significant, r = 0.043,
F (1,21) < 1, partial eta squared = 0.001.
There were no other significant two-way interaction effects.
The only significant main effect of chewing gum, which oc-
curred on Spatial Span performance in the general linear model
including extraversion, is superseded by the interaction of gum
and extraversion described above. In the general linear models
predicting Spatial Span performance including the continuous
variable predictors, chronotype, habitual tiredness, and current
stress, there were main effects of task difficulty, F(1,42) ≥
4.285, p ≤ 0.045, partial eta-squared ≥ 0.093. In all cases per-
formance was reduced in the dual task condition. There was a
single main effect of task difficulty on Digit Span performance
Figure 3.
Spatial span performance as a function of extraversion in the chewing
gum and control conditions.

R. STEPHENS ET AL.
838
Figure 4.
Digit span performance as a function of thirst in the chewing gum and
control conditions.
such that performance was reduced in the dual task condition in
Underlying this interaction was a non-significant regression of
the general linear model including current stress as a predictor,
F(1,42) = 6.593, p = 0.014, partial eta-squared = 0.136.
Fourth Stage Analysis―Bivariate Correlations
among the Six Questionnaire-Derived Continuous
Predictor Variables
Pearson product-moment correlation coefficients were com-
puted for all bivariate combinations of the six questionnaire-
derived continuous predictor variables: chronotype; extraver-
sion; habitual tiredness; current stress; current arousal; and
current thirst. The results are summarised in Table 2. The only
significant correlation was the negative relationship between
current stress and current arousal.
Discussion
Chewing gum did not enhance working memory perform-
ance in the analyses including only the standard Digit Span and
Spatial Span tests. In this sense the present study has failed to
replicate our earlier findings (Stephens & Tunney, 2004) and
those of other researchers (Wilkinson et al., 2002; Baker et al.,
2004, experiment 1; Tucha et al., 2004, experiment 2). However,
the absence of enhanced cognitive performance brought about by
chewing gum is consistent with other research (Tucha et al., 2004,
experiment 1; Miles & Johnson, 2007; Johnson & Miles, 2007;
Allen, Norman, & Katz, 2008; Johnson & Miles, 2008; Smith,
2009a; Smith, 2009b). Nevertheless, chewing gum was shown
to be beneficial to performance compared with not chewing on
the Digit Span test when a secondary task of counting sounded
tones was concurrently performed. We employed this more
difficult dual task condition to induce sub-optimal performance
on the assumption that a law of initial value (Jin, 1992) was in
operation such that chewing gum would be more likely to im-
prove cognitive performance when it was initially sub-optimal.
These data are consistent with the interpretation that chewing
gum is most likely to improve cognitive performance in indi-
viduals who are performing at a sub-optimal level.
The most intriguing findings reported here occurred in the
analyses incorporating questionnaire-derived variables reflect-
ing individual differences. For thirst, the controls showed de-
creased Digit Span performance with increasing levels of thirst,
as predicted by some of the literature on effects of hydration
and dehydration on cognitive performance (e.g. Rogers, Kainth,
& Smit, 2001). However, in the chewing gum condition no
such decline in performance was present. It has been suggested
that chewing gum may be of benefit to cognitive performance
via reducing feelings of thirst, and indeed some of the earliest
recorded chewing gum marketing materials (see Figure 1) al-
luded to the thirst-quenching properties of chewing gum (Rob-
inson, 2004). Previous research found that using sugar-free
chewing gum six times daily for 2 weeks reduced self-reported
thirst in 137 haemodialysis patients, mediated by stimulation of
saliva flow (Bots, Brand, Veerman, Korevaar et al., 2005). The
findings of the present study are consistent with a role for
chewing gum in alleviating thirst.
Furthermore, extraversion was a significant predictor of Spa-
tial Span test performance in the chewing gum group, such that
better performance was observed in more introverted individu-
als. However, extraversion did not predict Spatial Span test
performance in the control group. This runs counter to our ini-
tial hypothesis. Previous research has found that extraverts tend
to perform well under more arousing conditions, and that in-
troverts perform better under less arousing conditions (Mat-
thews, Davies, Westerman, & Stammers, 2004) and on this
basis we predicted that chewing gum would be likely to over-
arouse introverts leading to reduced cognitive performance. On
the other hand, we had predicted that chewing gum would be
more likely to optimally arouse extraverts, leading to perform-
ance benefits in extraverts. Recent research suggests that stress
theory may be a parsimonious way to explain these findings. A
modest correlation (r = 0.44) was found between anxiety and
introversion in a survey of 441 adults in Finland (Jylhä &
Isometsä, 2006). Furthermore, chewing gum was shown to
reduce self-rated stress and salivary cortisol in 40 young adults
during completion of a stressful cognitive test battery (Scholey,
Table 2.
Pearson product-moment correlation coefficients for all bivariate combinations of the six questionnaire-derived continuous predictor variables. N =
46 in all cases; p > 0.05 in all cases except for stress-arousal.
Chronotype Extraversion Habitual tiredness Current Stress Current Arousal
Extraversion –0.014
Habitual Tiredness –0.121 0.252
Current Stress –0.211 0.064 0.039
Current Arousal 0.007 –0.119 –0.150 –0.496*
Current Thirst 0.238 –0.253 0.125 0.247 –0.123
*p < 0.001.

R. STEPHENS ET AL.
839
Haskell, Robertson, Kennedy, Milne, & Wetherell, 2009). Per-
haps introverts experienced more stress during the cognitive
testing procedure than extraverts and this stress was alleviated
by chewing gum. Further research should examine links be-
tween introversion, cognitive testing and stress.
In 2004 when we published our first experiment on chewing
gum and cognitive performance (Stephens & Tunney, 2004)
several studies including our own showed beneficial effects
while only one study pointed to the absence of cognitive bene-
fits (Tucha et al., 2004), which we interpreted as anomalous.
Consequently, our suggested mechanistic models for chewing
gum effects on cognition were somewhat simplistic. At that
time we proposed that gum chewing exerted cognitive benefits
either via activity-induced adrenergic arousal, or via increased
cerebral blood flow as a by-product of mastication. However,
given the absence of any link between chewing gum mediated
cognitive benefits and initial low arousal in the present study,
the former mechanism appears less feasible, although Smith
(2009a) argues that chewing gum has a robust alerting effect,
and so perhaps our study lacked sufficient sensitivity to prop-
erly assess arousal. Furthermore, an effect mediated solely by
cerebral blood flow seems unlikely given that the present data
indicate that chewing only produces cognitive benefits under
certain circumstances. However, a mechanism whereby en-
hanced cognition occurs due to a reduction in stress brought
about by cardiovascular changes consequent to chewing is a
possibility, and follows the suggestion of a link between stress
relief and cardiovascular changes brought about by chewing
made by Scholey et al. (2009).
Allied to this it possible that the repetitive nature of chewing,
producing stereotypical movement acts to soothe in the same
way that a baby is soothed by rocking. Indeed, a central tenet of
the first investigation of the psychological effects of chewing
gum was the idea that the “collateral motor automitism” in-
volved in sustained mastication results in a lowering of tension
(Hollingworth, 1939). Given the individual differences noted in
the present study, stress alleviation may be one of two key fac-
tors in determining when chewing gum will lead to cognitive
benefits. The other key factor is that chewing gum appears to
alleviate thirst, and consequently may attenuate the negative
cognitive performance effects of thirst.
In conclusion, the present research has replicated the null
cognitive effects observed in several recent chewing gum ex-
periments. However, the study also moves chewing gum-cog-
nition research forward by identifying conditions and partici-
pant characteristics (individual differences) where chewing
gum is more likely to confer cognitive benefits. Our findings
indicate that chewing may benefit cognitive performance where
people feel thirsty, in introverts (but not extraverts) and where
mental performance is sub-optimal. While the precise mecha-
nism for the effect remains unknown, cognitive benefits may
occur as a consequence of chewing gum-mediated alleviation of
stress and of thirst.
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