BJMB
Brazilian Journal of Motor Behavior
Research Article
!
Thompson et al.
2020
VOL.14
N.1
Understanding the influence of a cognitively demanding task on motor response times
and subjective mental fatigue/boredom
CHRIS THOMPSON
1,2
| JOB FRANSEN
2
| ADAM BEAVAN
1,2,3
| SABRINA SKORSKI
1
| AARON COUTTS
2
| TIM MEYER
1
1
Institute of Sport and Preventive Medicine, Saarland University, Saarbrücken, Germany.
2
Sport and Exercise Discipline Group, Faculty of Health, University of Technology Sydney, Moore Park, Australia.
3
German Football Association (Deutscher Fußball-Bund; DFB), Frankfurt, Germany.
Correspondence to: Chris Thompson. Saarland University – Institute of Sports and Preventive Medicine, Saarland University, Building 8.2, 66123 Saarbrücken, Germany.
University of Technology, Sydney – Moore Park Rd & Driver Ave, Moore Park NSW 2021, Australia. +49 (0) 681 302 70413.
email: chris.thompson@uni.saarland.de
https://doi.org/10.20338/bjmb.v14i01.167
HIGHLIGHTS
• The modified Stroop task is the most common
method of inducing mental fatigue, yet may not
be ecologically valid.
• The aim of the study was to investigate the
influence of the modified Stroop task on mental
fatigue, boredom and motor response times.
• This study has demonstrated that exposure to
the modified Stroop task results in increased
subjective mental fatigue and boredom;
however there were no significant differences in
motor task performance.
• The study also found that a short rest period
(5-min) did not elicit a full subjective recovery
from either parameter.
ABBREVIATIONS
AIC Akaike’s Information Criterion
AU arbitrary units
CRTT choice reaction time task
POST post-task
POST-5 five minute rest period
PRE pre-task
VAS visual analogue scale
PUBLICATION DATA
Received 18 02 2020
Accepted 20 03 2020
Published 01 04 2020
BACKGROUND: Several methods are used to induce mental fatigue; predominantly the modified Stroop task, which
arguably has little relation to daily lifestyle tasks.
AIM: To investigate the influence of the modified Stroop task on mental fatigue, boredom and motor response
times.
METHOD: 15 subjects (24.3 ± 2.3 years) completed a 30-min modified Stroop task (control condition: 30-min
reading) and completed PRE, POST and POST 5-min subjective ratings of mental fatigue, mental effort and
boredom. Participants' ability to use congruent and inhibit incongruent precues in a choice reaction time task
(CRTT) was measured pre- and post- Stroop and control.
RESULTS: Significantly higher subjective ratings of pre-post condition mental fatigue (pre: 2.43±1.31 AU, post:
6.42±2.08 AU, p<0.01) and boredom (PRE: 1.65±1.49 AU, POST: 5.03±2.92 AU, p<0.01) were reported following
the modified Stroop task condition compared to the control condition mental fatigue (PRE: 1.62±1.17 AU, POST:
2.10±0.92 AU, p>0.05) and boredom (PRE: 1.94±1.52 AU, POST: 3.32 ± 1.66 AU, p>0.05). No significant
differences were found between conditions for the extent to which participants’ response times were affected by
congruent (p=0.481) or incongruent (p=0.225) precues.
CONCLUSION: Future research must adopt cognitive activities with higher contextual interference for greater
ecological validity, and elucidate the impact of rest on recovery from mental fatigue.
KEYWORDS: Mental Fatigue | Boredom | Stroop
INTRODUCTION
Mental fatigue is a psychobiological state, characterised by feelings of tiredness, a lack of
energy and reduced motivation that is induced by prolonged periods of demanding cognitive
activity
1,2
. To induce mental fatigue, previous studies have used a range of cognitively
demanding tasks. These include (but are not limited to) a 90-min AX-Continuous Performance
Task
3,4,5
a 60-min Go/NoGo Task
6
, a 2-hour Eriksen Flanker test
7,8
, a blocked 4 x 10-min
Sustained Attention to Response Task
9
, and in many recent studies, a 30-min modified Stroop
task
2,10
. The modified Stroop task is a response inhibition/sustained attention task that elevates
the activation of the anterior cingulate cortex, which appears to play a significant role in the
onset of mental fatigue
11
. It has been theorised that following prolonged exposure to a
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cognitively demanding task such as the modified Stroop task, mental fatigue results from a
reduction in the transmission of dopamine to the striatum and anterior cingulate cortex
8,12
.
Based on the current evidence, the use of the modified Stroop task can be regarded as a
feasible activity to generally induce mental fatigue.
However, a limitation of the modified Stroop task is that it may not be representative of how
mental fatigue is experienced in real life settings
13
. Indeed, this task is relevant in a laboratory
setting to create a transient state of mental fatigue, but a driver would not complete a modified
Stroop task before entering a car, nor would an athlete before a competition, making the
practical validity of using a modified Stroop task questionable in high contextual situations. The
repetitive nature of continually solving the same task problem may become monotonous and
evoke lower levels of contextual interference than real life tasks such as driving, military activity
and sport. Lelis-Torres et al. (2017)
14
recently compared the task engagement associated with
high and low contextual interference practice schedules (a key-pressing task with two goals:
learning the relative timing dimension and learning the absolute timing dimension) and found
that greater cognitive effort was more closely associated with high contextual interference than
with low contextual interference practice. It has also been proposed that if a task is perceived
to be repetitive, meaningless and does not challenge the subject, it may result in boredom
15
.
Pattyn et al. (2008)
15
explain an “underload” and “overload” performance hypothesis, where a
cognitive task with an “underload” (i.e. low cognitive demand) is subjectively associated with
mind wandering (boredom), whilst an “overload” task consists of a subjectively high cognitive
demand when completing the NASA Task Load Index test (mental fatigue). It is plausible that
the modified Stroop task may be regarded as boring by participants, but it remains unknown if
impaired performance levels are partly caused by boredom due to low intrinsic motivation to
engage in the task, rather than the demands of the task itself
13,16
. Despite the widespread use
of a modified Stroop task as a means of inducing mental fatigue in the literature
2,10
, its difference
or independence to boredom is yet to be investigated.
Furthermore, recent literature has suggested the need to supplement subjective perceptions
of mental fatigue with more objectively quantifiable assessments
13
. One solution could be to
assess the effect of mental fatigue on motor response times. Motor response times represent
the ability of an individual to detect relevant information sources, process that information and
use it to generate an appropriate movement response. Indeed, mental fatigue has been shown
to impair attention
17
and reaction times
1
. Moreover, response times represent the difference
between the moment a stimulus appears and the subsequent execution of a motor response
18
.
It is suggested that response time paradigms may be able to detect inefficiencies of the motor
control system as a result of fatigue, including mental fatigue
6,19
. However, simple or even
choice response time tasks also bear little relevance to performance in cognitively demanding
activities such as driving or sport. Alongside being able to respond rapidly to a single stimulus
(i.e. simple reaction time) or deciding between different responses based on a variety of stimuli
(i.e. choice reaction time), such populations need to demonstrate fast and accurate decision
making that includes the ability to use advanced information or suppress irrelevant stimuli. For
example, a soccer player may decide to pass the ball to an available teammate but choose not
to when observing their teammate is suddenly covered by a defender or another teammate is
in a better position to receive the ball.
Limited evidence is also available on the amount of rest required to overcome subjective
feelings of mental fatigue. A break (and not necessarily sleep) from a mentally fatiguing task will
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result in some recovery
20
, but the duration of that break is unknown. In many sporting (e.g. time-
outs and half-time periods) and occupational (rest periods from driving or factory duties) tasks,
rest periods may be brief, and the amount of mental recovery (i.e. change in mental fatigue)
sustained from these periods are unknown. Understanding the timing and duration of a break
required to diminish the effects of mental fatigue is a crucial step to further understand the
relationship between mental fatigue and motor performance, as it may help mitigate the
potentially negative effects of mental fatigue on performance. Therefore, the aim of the current
study was threefold. First, to investigate the effects of a modified Stroop task on participants’
ability to use precued information in a choice response time task in which participants execute
or suppress a motor response based on a congruent or incongruent precue preceding the
stimulus. The secondary aim of the study was to understand the relationship between measures
of mental fatigue, mental effort and boredom to understand whether the modified Stroop task
represents an appropriate method to induce mental fatigue. The third aim of the study was to
measure the impact of rest on recovery from mental fatigue and boredom. It was hypothesised
that 1) a 30-min modified Stroop task would negatively affect the ability for participants to inhibit
a motor response, 2) a 30-min modified Stroop task would significantly increase subjective
ratings of mental fatigue, mental effort and boredom, and 3) an acute rest period (5-min) from
cognitive activity would be sufficient to elicit significant reductions in subjective ratings of mental
fatigue and boredom.
METHODS
Participants
Fifteen healthy adults (24.3 ± 2.3 years) with normal or corrected to normal vision
volunteered to participate in the study. Ethical approval for all procedures was attained from the
Saarland University Ethics Committee under the Declaration of Helsinki.
Procedures
The study outline consisted of two separate protocols completed in a randomised counter-
balanced order. Participants were informed that they would be completing a computer task and
a reading task on two separate occasions, four weeks apart, in the same location at the same
time of day. Participants were also told to refrain from consumption of caffeine for 24-hours
before the study. Following this, participants provided their informed consent to participate. In
both conditions, participants were placed in a rigid chair facing a desktop table containing a
laptop computer and a customised four button controller. The controller was placed `between
the computer and the participant, precisely 8 cm from the edge of the computer. The dominant
hand of the participant was placed flat on the table 3 cm away from the controller system, and
the non-dominant hand was situated either on their thigh or the table. The familiarisation
protocol consisted of a brief (12 trials) congruent version of the choice reaction time task (CRTT),
a 60s trial of the modified Stroop and a description of the reading task.
A pre-task (PRE) visual analogue scale (VAS) for mental fatigue and boredom were then
completed, followed by the first CRTT trial. Next, participants were exposed to 30-min of either
the modified Stroop task or the magazine reading condition. The test was completed with the
researcher seated two metres behind the participant to ensure study compliance. Immediately
post-task (POST), participants again completed VAS for mental fatigue, boredom and mental
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effort, which corresponded to the amount of perceived mental effort that was required to
complete the preceding task. The CRTT was then immediately completed for a second time,
followed by a five minute rest period where the participant sat alone in the testing room with the
instructions to relax and avoid any task engagement. To facilitate this, personal items (i.e.
mobile phones, laptops, mobile phones) were securely stored outside of the testing room during
the test. Finally, participants completed a final VAS for mental fatigue and boredom immediately
following the five minute rest period (POST-5).
Response Inhibition
The response inhibition task (Unity, Version 5.4.0f3, 2016) consisted of 24 trials grouped
into 12 congruent and 12 incongruent trials on a 14.3” laptop screen, lasting a total of three
minutes. Across all trials, a three second countdown was followed by the appearance of four
white circles with a black outline (all of which consist of a diameter of 512 pixels and an edge
width of 5 pixels) presented in a horizontal position. Following a randomised two – four second
delay, one of the four circles turned yellow. The participant was required to accurately press the
button on the controller (Lioncast, Berlin, Germany) which corresponded to the yellow circle as
quickly as possible. The precue in the congruent trials was a small black dot (26 pixels) which
appeared in a white circle (512 pixels) 86 ms before it turned yellow. Conversely in the
incongruent trials, the same black dot acted as a decoy by appearing in a white circle 86 ms
before an opposing circle turned yellow. In both trials, the precue was presented on the screen
for a duration of 43 ms according to the procedures outlined in one of the experimental
conditions of an implicit precue paradigm used by Fransen et al. (in press)
21
, but adapted to
include a measure of response inhibition.
Modified Stroop task
In the modified Stroop task, four words (“blue”, “yellow”, “red”, “green”) repeatedly appeared
on a Windows Powerpoint Presentation document screen in a randomised fashion. The correct
answer in the trial will be the colour of the ink (blue, yellow, red, green), and not the word.
However, to increase task difficulty, any word presented in red ink the correct response
corresponds to the meaning of the word. The test was translated into German, the first language
of the participants. Each participant completed 900 trials, each separated by 2000 ms. All trials
required a verbal response to the researcher, who was seated two metres behind the participant
to avoid acting as a visual distraction during the test.
Control Condition
In the control condition, participants were presented with a selection of four magazines of
varying topics to read (sport, cars, fashion and lifestyle). They were instructed to read any of
the chosen magazines for a period of 30-min whilst seated in front of the lead researcher. The
choice of magazines was influenced by previous pilot testing.
Visual analogue scale
A visual analogue scale (VAS) was used to measure three subjective parameters; 1)
boredom (“Please state your current level of boredom”), 2) mental fatigue (“Please state your
current level of mental fatigue”) and 3) mental effort (“Please state the mental effort of the task
you have just completed”). On a 100 mm horizontal line scale, the answer selection ranged from
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“none at all” to “maximal”. Using an independent paper version for each time point (to avoid
participants comparing subjective measures to previous time points), participants were
instructed to draw a vertical line over a selected area of the scale to select their subjective rating
of each parameter, which was later measured by the lead researcher to create arbitrary units
(AU).
Statistical analysis
To investigate the effect of the experimental condition (i.e. the reading task (control) or the
modified Stroop task and timing of the measurement (PRE, POST & POST-5) on both cognitive
(mental fatigue, mental effort and boredom) and response times (congruent and incongruent
task performance), a series of linear mixed models was developed. A stepwise approach was
used in which additional predictors were added to the model with each step, and model fit was
evaluated using the Akaike’s Information Criterion (AIC), observation of increases in degrees of
freedom, a -2 log-likelihood ratio test and the normal distribution of the models’ residuals. The
cognitive variables and response times were entered as response variables in each of the four
linear mixed models. The experimental condition and the time of measurements (fixed factors)
were entered as predictor variables in addition to each participant’s unique identifier (random
factor) to account for the random variance associated with the clustering of participants’
repeated measures within each participant. Prior to the analysis, pre-modelling assumption
checks (i.e. linearity of relationships, homogeneity of variance) were carried out. Following the
analysis, the appropriateness of each model was analysed through the normality of the
distribution of model residuals using visual inspection through boxplots and a Shapiro-Wilk test.
The significance level for the -2 log-likelihood ratio tests was set at p < 0.05, and an estimate
precision was provided using Wald-based 95% confidence intervals. In order to understand if
an association existed between the various outcomes due to the Stroop test, Pearson
correlations were conducted on the delta change between each variable.
RESULTS
The best fit was achieved using a random intercepts model (participant ID) and through
the introduction of a time*experimental condition interaction effect to explain the variance in
mental fatigue and boredom. However, no significant predictors of congruent and incongruent
response times were observed in this study (p>0.05). As mental effort was only recorded during
the post-test, a random intercept model with the experimental condition as the only fixed effect
best explained the variance in mental effort (AIC = 112.42, df = 1-,4, p = <0.001, conditional
explained variance = 75%). A random intercepts model that incorporated both the condition and
time main effects as well as the condition*time interaction effect best explained the variance in
subjective ratings of mental fatigue and boredom (mental fatigue: AIC = 326.39, df = 2,8, p =
<0.001, conditional explained variance = 66%; boredom: AIC = 371.14, df = 3,8, p = <0.021,
conditional explained variance = 54%). All model parameters organised by dependent variable
can be found in Table 1.
As shown in Figure 1, a significant condition*time interaction effect (p<0.001) was
observed in ratings of mental fatigue. Mental fatigue values increased from PRE (2.43 ± 1.31
AU) to POST (6.42 ± 2.08 AU; p<0.01) in the modified Stroop task condition. Furthermore,
despite the POST-5 mental fatigue values decreasing (5.26 ± 1.49 AU; p<0.01) from the POST
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test values, they still remained higher (p<0.01) compared to the PRE test values within the
Stroop task condition. Contrastingly no observable differences (p>0.05) were recorded in the
control condition across the PRE, POST or POST-5 time points (see Table 1). Pearson
correlations were conducted between the delta change from pre to post Stroop test between
the variables response inhibition, mental fatigue and boredom. The results demonstrated that a
moderate positive correlation between increases in mental fatigue and boredom ratings (r =
0.46, p = 0.09) existed although failed to reach significance. Furthermore, very low correlations
existed between the delta change of response inhibition and ratings of mental fatigue (r = 0.08,
p = 0.80) or ratings of boredom (r = -0.17, p = 0.55).
Subjective rating of boredom followed a similar trend to mental fatigue for both
conditions, and a significant condition*time interaction effect (p=0.021) was also observed. In
the modified Stroop condition, ratings of boredom increased from PRE (1.65 ± 1.49 AU) to
POST (5.03 ± 2.92 AU; p<0.01). Aligned with the trends of mental fatigue ratings, POST-5
boredom values (3.85 ± 2.07 AU) also decrease from POST values, but remained higher
(p<0.01) from the initial PRE test values. Ratings of boredom were also similar to the ratings of
mental fatigue in the control condition, where no significant differences (p>0.05) were observed
across PRE, POST, and POST-5 time points.
Furthermore, a conditional main effect (p<0.001) was observed for mental effort scores
recorded at POST, as participants reported higher ratings of mental effort in the modified Stroop
condition (6.67 ± 1.72 AU) compared to the control condition (1.87 ± 1.05 AU). Lastly, there
were no differences in congruent or incongruent response times between the modified Stroop
task and control conditions (see Table 1). The estimated marginal means, standard errors and
associated 95% confidence intervals derived from the best fitting models for each dependent
variable are presented in Table 2.
Figure 1. Pre and post VAS ratings of subjective mental fatigue and boredom.
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Table 1 – Models that explain the effect of condition and time of measurement on participants’ cognitive and physical variables.
Note: * indicates the best fitting model based on AIC value and -2log-likelihood ratio test. ID = individual participant identification number, Time = time of measurement (i.e. pre-test, post-
test or post-test + 5 minutes break), ExpCond = experimental condition (i.e. Control or Stroop).
AIC
p (-2 log likelihood ratio test)
Chi
2
df
R
2
fixed only (%)
Conditional R
2
random + fixed (%)
Congruent
Final Model: Congruent ~ 1 + (1|ID)
Condition main effect
-210.18
0.733
0.116
1,4
< 0.1
64
Time main effect
-210.48
0.519
0.416
1,4
0.2
64
Time + Condition main effect
-208.59
0.766
0.533
2,5
0.3
64
Interaction effect
-208.53
0.481
2.468
3,6
1.4
65
Incongruent
Final Model: Incongruent ~ 1 + (1|ID)
Condition main effect
-220.48
0.611
0.259
1,4
0.1
78
Time main effect
-220.26
0.848
0.037
1,4
< 0.1
78
Time + Condition main effect
-218.52
0.862
0.296
2,5
0.1
77
Interaction effect
-220.28
0.225
4.061
3,6
1.4
78
Mental fatigue
Final Model: Mental fatigue ~ Time*ExpCond + (1|ID)
Condition main effect
370.31
<0.001
43.663
1,4
38
38
Time + Condition main effect
346.80
<0.001
27.514
2,6
54
54
Interaction effect*
326.39
<0.001
24.412
2,8
64
66
Mental effort
Final Model: Mental effort ~ ExpCond + (1|ID)
Conditional main effect*
112.42
<0.001
41.801
1,4
75
75
Boredom
Final Model: Boredom ~ Time*ExpCond + (1|ID)
Condition main effect
399.52
0.134
2.248
1,4
2
29
Time main effect
374.87
<0.001
28.891
2,5
19
50
Time + Condition main effect
373.54
0.068
3.328
1,6
21
51
Interaction effect*
371.14
0.021
9.7301
3,8
24
54
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Table 2 - Least square means, 95% confidence intervals (CI), standard error (Std. Error), t-values and random effect parameters from four linear mixed models
investigating the effects of condition and time of measurement on participants’ cognitive and physical variables.
Note: *VAS = Visual Analogue Scale.
Experimental Condition
Time of Measurement
Estimate
Std. Error
Lower CI
Upper CI
t value
Congruent (sec)
Reading
Pre-test
0.618
0.0132
0.591
0.645
46.750
Reading
Post-test
0.612
0.0132
0.585
0.632
-0.509
Stroop
Pre-test
0.604
0.0132
0.577
0.632
-1.200
Stroop
Post-test
0.620
0.0132
0.593
0.647
1.358
Incongruent (sec)
Reading
Pre-test
0.635
0.0143
0.605
0.664
44.531
Reading
Post-test
0.621
0.0143
0.591
0.650
-1.491
Stroop
Pre-test
0.625
0.0143
0.596
0.655
-0.990
Stroop
Post-test
0.637
0.0143
0.607
0.666
1.914
Mental Fatigue VAS (au)
Reading
Pre-test
1.627
0.364
0.903
2.351
4.470
Reading
Post-test
2.100
0.364
1.376
2.824
0.946
Reading
Post-test + 5 min
1.793
0.364
1.069
2.517
0.333
Stroop
Pre-test
2.427
0.364
1.703
3.151
1.599
Stroop
Post-test
6.420
0.364
5.696
7.144
4.973
Stroop
Post-test + 5 min
5.260
0.364
4.536
5.984
3.768
Mental Effort VAS (au)
Reading
Post-test
1.873
0.369
1.118
2.628
5.083
Stroop
Post-test
6.673
0.369
5.918
7.428
9.209
Boredom VAS (au)
Reading
Pre-test
1.947
0.525
0.890
3.003
3.708
Reading
Post-test
3.320
0.525
2.264
4.376
2.387
Reading
Post-test + 5 min
3.413
0.525
2.357
4.470
2.549
Stroop
Pre-test
1.653
0.525
0.597
2.710
-0.510
Stroop
Post-test
5.033
0.525
3.977
6.090
2.466
Stroop
Post-test + 5 min
3.847
0.525
2.790
4.903
0.893
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DISCUSSION
For a number of years, many different cognitive tasks have been used to induce mental
fatigue
3-9
, with the 30-min modified Stroop task being the predominant method
2,10
. This has
recently been challenged for its low contextual interference and irrelevance to daily tasks
13
,
which may lead to low intrinsic motivation to engage in the activity and ultimately subjective
boredom. Furthermore, the amount of time required to rest from mentally fatiguing tasks is yet
to be investigated in the literature. Our study has demonstrated that in comparison to a control
condition (reading magazines), 30-min exposure to the modified Stroop resulted in significantly
greater subjective mental fatigue, mental effort and boredom, but did not significantly impair
motor task performance. Moreover, a 5-min rest period was not enough to provide a full
subjective recovery of mental fatigue and boredom. The results of the current study support the
applicability of the modified Stroop task in inducing mental fatigue in laboratory settings, but
also provides new evidence to support the presence of subjective boredom during the task.
Furthermore, evidence has been presented for the impact of acute rest from mentally fatiguing
activity, which provides future suggestions for inducing mental fatigue in subsequent research.
The primary finding in the current study was the greater subjective boredom reported
following the 30-min modified Stroop task condition in comparison to the control task. These
findings support the argument that the modified Stroop task is boring, and this boredom may
subsequently influence the perception of mental fatigue. Ultimately the modified Stroop task
may not be a relevant task to induce mental fatigue due to its irrelevance to many real-world
tasks
13
. It has been suggested that boredom is linked to monotony
22
, and that impaired task
performance is associated with low intrinsic attractiveness of the task
16
. In the present study,
the 30-min modified Stroop task is likely to have been met with low intrinsic motivation and task
engagement due to its irrelevance to daily activities and no perceived reward. The nature of the
task is highly repetitive with little variation and low contextual interference. Indeed, low
contextual interference tasks provide a lesser cognitive engagement than high contextual
interference tasks
14
, and likely provides a cognitive “underload”
15
. Here it was theorised that
compared to “overload” tasks (i.e. high cognitive engagement), an “underload” task provides a
reduced cognitive challenge and is associated with mind wandering (i.e. boredom)
15
. This
evidence suggests that whilst the modified Stroop task may bear a resemblance to some real-
world tasks with prolonged vigilance and low cognitive engagement (i.e. repetitive factory or
office based tasks), more dynamic tasks (e.g. sport, military activity) require a more ecologically
valid protocol to induce mental fatigue in future studies. To develop such protocols, future
research must further understand real-world (such as lifestyle or task specific) cognitive
demands experienced by individuals in dynamic task performers.
Despite significant increases in subjective mental fatigue and boredom, congruent and
incongruent response times were unaffected by exposure to a 30-min modified Stroop task. The
results are contrary to the hypothesis and somewhat surprising given the available literature. It
has previously been reported that participants performing a 60-min Go/NoGo recorded
significantly greater reaction times, number of errors, and mental fatigue scores with time spent
on the task
6
. These results demonstrate a decrement in response inhibition performance, along
with an impairment of the intensity of response execution. In similar work, participants
performing a 2-hour Eriksen Flanker test showed a significantly greater decline in reaction times
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during the final 30-min period in comparison to the initial 90-min of the task. Additionally, when
exposed to a 30-min modified Stroop task, Smith et al. (2016)
23
demonstrated very likely lower
decision making accuracy and likely higher response times in a soccer specific soccer decision
making test in comparison to a control condition (reading magazines). There may be multiple
explanations as to why these results differed to the current study. Firstly, the 60-min Go/NoGo
task and 2-hour Eriksen Flanker test used by Kato et al. (2009)
6
and Lorist, Boksem &
Ridderinkhof (2005)
8
were significantly greater in the duration than the 30-min modified Stroop
task used in the current study, which suggests that time on task correlates with decrement in
cognitive function. In addition, Smith et al. (2016)
23
used a soccer-specific task in a sample of
soccer players, thus using a sport-specific stimulus may complicate the comparison of the
results of these two studies. However, the fact that congruent and incongruent response times
remained unaffected in the current study, increases in subjective ratings of mental fatigue and
boredom may be due to the 30-min modified Stroop task’s inability to elicit true mental fatigue
or the ability to use implicit information to inform action is unaffected by mental fatigue.
The present findings show that a five minute rest period following the 30-min modified
Stroop task significantly reduced subjective ratings of mental fatigue and boredom but did not
fully dissipate to baseline levels after the rest period. Despite the inability to fully recover, the
study shows that even a five minute period was enough to significantly reduce subjective mental
fatigue. This suggests that mental fatigue is transient and stimulus dependent, which conflicts
the severity of mental fatigue on task performance as theorised in previous research
24,25
.
However, a limitation of the study is that each subject participated in the protocol at varying
times (but consistent within each subject) of the day (morning to early evening).Indeed, the
ability to subjectively recover from the 30-min modified Stroop may have been influenced by
this variability and future study designs interested in the acute effects of mental fatigue on
performance should aim to assess each participant at the same time of the day. Other
considerations in relation to this are the present workload experienced by the participants, as
well as sleep duration, which was not measured in the study. Additionally, whilst periods of rest
or time away from cognitive tasks have been previously advocated as methods to reduce
feelings of mental fatigue
19,26
, the timing and dosing of recovery following mentally fatiguing
tasks remains unknown. However, it must be emphasised that clearly interpreting post task
subjective measurements of mental fatigue and boredom is challenging. Participants in the
current study were required to sit alone with no stimulation (i.e. in silence with no mobile
phone/laptop access), which in longer periods may even further exacerbate subjective feelings
of mental fatigue and boredom, which has been likened to a high level of frustration
21
.
CONCLUSION
In summary, this study demonstrated that despite greater subjective mental fatigue,
boredom and mental effort in the modified Stroop condition, participants’ ability to use congruent
and suppress incongruent precues was maintained in comparison to a control condition.
Moreover, a five minute break reduced subjective mental fatigue and boredom in the 30-min
modified Stroop condition, but not significantly. The authors suggest that the modified Stroop
task may not be a “one size fits all” approach to inducing mental fatigue when considering the
level of contextual interference of a particular task. To allow for further understanding of how
such complex cognitive tasks are influenced by mental fatigue, it is recommended that future
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research understands real-life activities experienced by complex task performers. This will in
turn create more ecologically valid protocols which bear a greater resemblance than the
modified Stroop task.
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Citation: Thompson C, Fransen J, Beavan A, Skorski S, Coutts A, Meyer T. Understanding the influence of a
cognitively demanding task on motor response times and subjective mental fatigue/boredom. BJMB. 2020: 14(1): 33-
45.
Editors: Dr Fabio Augusto Barbieri - São Paulo State University (UNESP), Bauru, SP, Brazil; Dr José Angelo Barela -
São Paulo State University (UNESP), Rio Claro, SP, Brazil; Dr Natalia Madalena Rinaldi - Federal University of
Espírito Santo (UFES), Vitória, ES, Brazil.
Copyright:© 2020 Thompson, Fransen, Beavan, Skorski, Coutts and Meyer and BJMB. This is an open-access article
distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International
License which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Funding: There was no funding for this study.
Competing interests: The authors have declared that no competing interests exist.
DOI:$https://doi.org/10.20338/bjmb.v14i01.167
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