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J Camosun Psyc Res. (2019). Vol. 1, pp. 7-11.
Submitted April 2019; accepted 12 July 2019.

The effect of caffeine on performance.
Author: Milton Cabrera*, Shannon Firman, and Elsa Parsons
Supervising Instructor: Judy Caldwell, Psyc 201 (“Research Methods”)
Department of Psychology, Camosun College, 3100 Foul Bay Road, Victoria, BC, Canada V8P 5J2
*Corresponding author email: milton.s.cabrera@gmail.com

ABSTRACT
The purpose of this study was to investigate the effects of caffeine on reaction time, as
measured by PEBL2 software. To test this relationship, participants were measured across three
tests within the PEBL2 software, with one group of participants receiving a 300 mL dose of
caffeinated coffee before testing, and another receiving a 300 mL dose of a decaffeinated coffee.
It was hypothesized that the participants who received a dose of caffeinated coffee would
perform better and thus have faster reaction times than those who received the decaffeinated
control. The results did not support the hypothesis: the mean response time was the same across
the caffeinated and decaffeinated conditions. The results of this study are discussed in relation to
other findings on the effects of caffeine on performance, specifically the relationship between
caffeine and reaction time.
1. Introduction
A substantial percentage of the world’s
population consumes coffee, or other
caffeinated beverages, daily to increase their
ability to maintain their level of vigilance
(Mitchell, Knight, Hockenberry, Teplanky,
& Hartman, 2014). There are other supposed
benefits of caffeine, but stimulation is the
typical reason for its consumption. When
tired, a person can drink caffeine and
achieve an enhanced ability to maintain
concentration. But does caffeine actually
have the intended effects we think it does? It
is this question that has, over the course of
time, spurred researchers to investigate the
effects of caffeine on vigilance, mood, and
arousal. Many of these studies explored the
impact of caffeinated beverages versus
decaffeinated beverages on cognitive
vigilance tasks. The findings of such studies

typically show reaction times that are
numerically faster, but not statistically so, in
the caffeinated conditions (e.g., Amir et al,
2001; Durlac, Edmunds, Howard, & Tipper,
2002; Schneider et al., 2006; Smith,
Whitney, Thomas, Perry, & Brockman,
1997).
Smith et al. (1997) investigated the
impact that stress has on reaction time after
ingesting caffeine and demonstrated that
caffeine did help maintain alertness and
performance efficiency. Specifically, the
researchers investigated the effects of
caffeine on psychomotor tasks using a
between-subject design that measured
participant reaction time. Examples of
psychomotor tasks used included simple
reaction time tasks, five-choice serial
response tasks, and pegboard tests. These
tests operated by requiring a participant to
maintain a high level of focus while waiting
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for a specific stimulus to appear or change
before responding in a previously
determined manner. In one of the reaction
time tasks, computer software was used to
display a box on a screen. When a square
was presented inside the box, the participant
was instructed to press a key as soon as it
was detected. While the results showed that
there were no significant effects of caffeine
on performance, the trend of caffeine
improving performance was consistent with
previous findings (Smith et al., 1997).
In contrast to experiments that investigate
the vigilance task performance of
randomized groups of participants, a study
conducted by Amir et al. (2001) investigated
the effects of caffeine on vigilance in
introverted and extraverted non-coffee
drinkers. The researchers used a withinsubjects design; they tested participants once
with a caffeinated coffee and on another
occasion with a decaffeinated beverage.
Contrary to their hypothesis, they found that
caffeine influenced the performance of both
groups. Specifically, the results showed that
caffeine had a positive effect on vigilance
performance, however there did not appear
to be a significant effect on personality type
or an interaction between caffeine and
personality type.
Another study by Schneider et al. (2006)
was conducted to determine the impact of
the expectation of consuming caffeine on
reaction time. One part of the experiment
involved telling half of the participants they
were going to be given a caffeinated
beverage but instead they were provided
with decaffeinated coffee. The other half of
the participants were given decaffeinated
coffee and were not mislead about the
contents of their beverage. The results
demonstrated an increase in awareness in the
misinformed group. In a second experiment,
the researchers provided two groups with
caffeinated orange juice, but only one group

was told about the true contents of the drink.
It was hypothesized that participants given
the true information would show a greater
effect on reaction time when compared to
participants given false information. The
results demonstrated a very small effect that
was not significant. The researchers
concluded that future studies should be
conducted in order to allow for a broader
assessment of these effects (Schneider et al.,
2006).
The present experiment employed a
between-subjects design to compare the
reaction times of participants given either
caffeinated coffee or decaffeinated coffee
before being asked to complete a series of
three computer tests using the program
called PEBL2. The first two of these tests
(called Oddball and Path Memory) were
employed as distractors in order to avoid
expectancy effects in participants. The third
test was a psychomotor vigilance test, called
PPVT. This test measured the speed and
accuracy with which participants reacted to
a specific stimulus (hitting the spacebar
when the X symbol appeared, as opposed to
another symbol) during a boring task. The
purpose was to measure the ability to
maintain vigilance during a reaction time
task. Given previous research demonstrating
that placebo effects can occur with caffeine
(e.g., Schneider et al., 2006) a double-blind
procedure was used in the present
experiment. With previous studies showing
either significant effects of caffeine on
reaction time (e.g., Amir et al., 2001) or
trends in that direction, it was expected that
the ingestion of caffeinated beverages would
result in participants having faster reaction
times in comparison to those in the
noncaffeinated group.
2. Methods
2.1 Participants
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The participants’ ages range from 19 to
70 years with a median age of 30.5 years.
Participants were friends and family of the
experimenters who agreed to participate in
the study. There were 11 females and 9
males.
2.2 Materials and Apparatus
The materials used for this experiment
were fairly simple. PEBL2 software was
used to administer the tests. PEBL is an
open source software program that allows
researchers to design and run psychological
experiments. From the program three
psychological tests were selected: Oddball,
Path Memory and Psychomotor Vigilance
Task (PPVT). Oddball is a continuous
performance test thought to involve
prefrontal strategy updating. For Path
Memory, a random design is drawn across a
grid, after which it disappears, and the
participant is asked to redraw the path as
closely as possible. PPVT a simple reaction
time test in which a circle stimulus appears
at delays between 2 and 12 seconds at which
time the participant must press the space bar
as quickly as possible. The coffee was
Starbucks coffee and the cups used were
disposable Starbucks cups. A timer was
employed to ensure that the tests did not run
past the 5-minute mark.
2.3 Procedure
Participants were required to sign consent
forms, which explained what was required
(the experiment involved partial-disclosure
to minimize reactivity). Participants were
then tested either individually or in pairs. All
participants were questioned before testing
to ensure they had not yet consumed any
caffeine before commencing the experiment.

Any participant that had already consumed
caffeine that day was not tested.
Each cup was filled with 300 mL of
either caffeinated or decaffeinated coffee.
The researcher provided two cups, identical
in appearance, to the participant. Each cup
was marked on the bottom to indicate which
was coffee and which was decaf. The
researcher placed both beverages in front of
the participant and turned around while the
participant moved the cups around. In this
way, neither the researcher nor the
participant knew which coffee cup contained
the caffeine; which allowed for a doubleblind study.
After consuming their beverages,
participants were immediately asked to
complete three tasks. Each task was
administered for 5-minutes using the PEBL2
computer software. Participants were told
that the total number of correct responses
was being measured when in fact reaction
time/vigilance was being tested. The first
two tasks were included to reduce reactivity
as well as provide a 15-minute waiting
period in which the caffeine could fully take
effect. Oddball and Path Memory were
conducted for 5-minute periods. Five
minutes were allowed between tests so that
there was a delay of 15 minutes before
starting the third test, PPVT; by this time the
participants that consumed caffeine should
have been feeling the effects of the
stimulant. The PPVT test was the only test
for which results were recorded.
After completing the three tasks, the
participants were debriefed. A detailed
review of the partial disclosure used in this
experiment was provided, as well as a
description of what the research was actually
testing. Each participant was given an
opportunity to ask questions or voice any
concerns. They were reminded that all
results would be anonymous, and their data
could be removed from the findings if they
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so wished. Participants who were given
decaffeinated coffee and wanted a cup of
caffeinated coffee were provided with a
caffeinated beverage at that time.
3. Results
The level of significance set in this
experiment was 0.05. The mean response
time for the Caffeinated Group was 388.83
milliseconds (SD = 43.78) and the mean
response time for the Decaffeinated Group
was 422.33 milliseconds (SD = 81.01). See
Figure 1 for a summary of the descriptive
statistics. These data were analyzed using a
two-tail t-test and the results were not
statistically significant, t(18) = 1.15, p =
0.27, suggesting that there was no difference
between the reaction time across the two
conditions.

4. Discussion
The hypothesis investigated in the current
report was that participants who received a
300 mL dose of caffeinated coffee would
have faster reaction times than those who
received a 300 mL decaffeinated control.
The findings did not support this hypothesis.
These findings are inconsistent with the
past studies demonstrating statistically
significant effects of caffeine on reaction
time (Amir et al., 2001). Given the results
obtained from past studies, it was expected
that participants who belonged to the
Caffeinated Group would have faster
reaction times than those who belonged to
the Decaffeinated Group. Despite observing
a slight difference between groups, the effect
was not sufficient to yield statistical
significance.
In conducting this experiment, several
factors may have affected the outcome. For
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Cabrera, Firman, Parsons - J Camosun Psyc Res. (2019). Vol. 1, pp. 7-11.

example, some participants opted to add
milk and/or sugar to their coffee while
others did not and participants may have had
varied levels of alertness at the beginning of
the experimental session. To combat these
factors and improve upon this experiment,
researchers could have disallowed the
addition of milk and sugar to the
participants’ coffee and could have tested all
participants at the same time of day in
anticipation that all participants would have
the same relative alertness.
Concerning external validity, a larger
sample size may have generated results
more reflective of the general population,
with the potential of obtaining statistical
significance. A larger sample size is
therefore recommended for any future
research on this topic.

Behavioural Medicine, 13(4), 330-339.
doi: 10.1207/s15327558ijbm1304_8
Smith, A., Whitney, H., Thomas, M., Perry,
K., & Brockman, P. (1997). Effects of
caffeine and noise on mood, performance
and cardiovascular functioning. Human
Psychopharmacology: Clinical and
Experimental, 12(1), 27–33. doi:
10.1002/(sici)10991077(199701/02)12:1<27::aidhup827>3.0.co;2-y

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