THE EFFECT OF CAFFEINE ON PSYCHOMOTOR PERFORMANCE
Maria Cuevas and Catalina Munoz
Dept. of Biological Sciences, Saddleback College, Mission Viejo, CA 92692
Abstract
Caffeine is known to be central nervous system (CNS) stimulant that can improve
alertness and treat drowsiness. In this study, three products one containing caffeine, one
with non-caffeine, and water are tested to see if caffeine has a positive effect on reducing
reaction time. The products included a Coca-Cola can with caffeine, a Coca-Cola can
without caffeine, and water. Both Coca-Cola cans contain the same ingredients with the
exception of caffeine. Since caffeine is known to be a stimulant it was expected that the
Coca-Cola with caffeine would have a decrease in reaction time. Each product was tested
by having a participant in the study drink Coca-Cola, non-caffeine Coca-Cola, and water
over a course of three days. The participant took a reaction test prior to consuming the
specific drink. Then from the time the drink was finished and waiting 10 minutes they
took the reaction test again. The p-value for the average difference among the 3 groups
was 0.057 which is greater than 0.05. Thus this meant that there was no significant
difference between the groups, so the results do not support the hypothesis that caffeine
decreased reaction time.
Introduction
. Caffeine is mainly consumed to help enhance alertness and also used to help
with physical activity because it acts as a stimulant to the central nervous system.
Caffeine has been shown to improve sprint time, anaerobic power, and reaction time, all
integral aspects of agility (Lorino, 2006). Many people consume caffeine when they are
suffering from drowsiness and are un-alert throughout the day. In 2007–2010, average
daily reported caffeine intake was just under 150 mg for the 18–29 year age group
(Wesensten, 2014). Caffeine is a naturally occurring alkaloid found in the seeds, leaves,
and fruit of coffee, tea, cocoa, maté, guarana, kola nuts, yerba maté, and more than 60
other plants.1,2 Caffeine is also added to a number of products for its known stimulant
effects (Bailey et al, 2014). Since caffeine is a stimulant it is added to energy drinks,
capsules, tablets, and energy shots for an energy boost. It is also found in soda, chocolate,
coffee, and tea because leaves that are used in the products naturally contain caffeine.
Specifically in caffeine drinks such as colas are known to offer not only caffeine but also
a hefty dose of sugar (Clark, 2014). The expectation of people on the product also has an
impact on an increase in cognitive performance. (Irmak et al, 2005). Since participants
know that they are drinking caffeine their reaction time may slightly decrease.
The objective of the experiment will determine if caffeine helps decrease reaction time.
Coca-Cola will be consumed by volunteer participants and then they will take a reaction
time test to see if time decreases or increases. Then on another day the same group of
volunteers will drink non-caffeine Coca-Cola and take the reaction test. On the final day
they will drink water and take the reaction test. The groups will then be compared see if
caffeine has an effect on reaction time or if the other ingredients also contributed to the
effect of reaction time. The results will help the investigators determine if caffeine has an
impact on the psychomotor performance of people.
Materials and Methods
The experiment took place over a period of 5 weeks (October 26, 2015 to
November 27, 2015) in the Biology lab and Learning Resource Center at Saddleback
College (Mission Viejo, CA). Two 12 pack of 12 ounces of Coca-Cola cans and two 12
pack of 12 ounces of Coca-Cola caffeine-free were purchased at the Target on
Jeronimo in Mission Viejo, on October 25, 2015 the day prior to experiment. The
ingredients in the 12 ounces of Coca-Cola are carbonated water, high fructose corn
syrup, caramel color, phosphoric acid, natural flavors, and caffeine. The caffeine-free
Coca-Cola contained the same ingredients except for the caffeine.
The 30 volunteers were asked to consume a specific drink. They were asked
to drink either 8 ounces of Coca-Cola, Coca-Cola caffeine-free, or water. After
choosing what drink they would consume that day the other two drinks would be
consumed on a later day. Before participating in the experiment each participant
was asked to sign a consent form. At the beginning of the experiment each volunteer
was asked not to drink any sort of caffeine and be on a non-fasting diet. The
participants would then take an online reaction test provided by the University of
Washington between the hours of 8:00am-11:00am. The online reaction test
consists of a stoplight that starts on red and then randomly changes to green. Each
participant was asked to take the test and when he or she saw the color change hit
the button to record their reaction time. The participants took the reaction test 10
times in order to record the average. After completing the drink they did for that
day they would consume the other two drinks later on separate days and repeat the
process as they did for the first drink.
When the volunteer arrived to participate in the experiment they were first
asked to take the test without drinking any of the specified drinks first and the
average reaction time was recorded. Once they were finished taking the test they
were then given 8 ounces of a specified drink to consume and would have 10
minutes to finish it. Once they had finished their drink they would wait and
additional 10 minutes from the time they had finished consuming the drink. After
the 10 minutes was finished they took the online reaction test again and the average
reaction time was recorded.
Results
The average reaction time for the experimental group and the control group was
used to obtain the result in Figure 1. There were 3 different time groups for with and
without the specified drink As indicated in figure 1, each group reaction time slightly
decreased after drinking specified drink with the exception of water staying relatively the
same. The three group times without the drink were compared to each other. ANOVA
test was run on the three without the drink and the p value was 0.935. ). The Bonferroni
Correction test indicated since p>0.05 that there is significant difference between the
data. The three with drink were also compared using. ANOVA test and the p value was
0.119). The Bonferroni Correction test indicated that p-value is greater than 0.05 that
there is no significant difference between the data.
To determine if there was a decrease in reaction time the groups with the drink
were subtracted by the groups without the drink. For example the reaction time with
Coca-Cola was subtracted from the reaction time of without Coca-Cola. The difference
for each group was then averaged to find the results in Figure 2. ANOVA test was run
and the resulting p-value 0.057 which is greater than 0.05 and indicates that there is no
significant different between the groups.
Average Time (seconds)
0.38
0.37
0.36
0.35
0.34
0.33
0.32
0.31
0.3
0.29
0.28
Without
Caffeine
With
Caffeine
Without
With NonNon-Caffeine Caffeine
Without
Water
With Water
Product
Figure 1. This graph shows the average reaction time of the six different groups for with
and without the drink. The average reaction time was faster with the Coca-Cola, CocaCola caffeine-free, and water than without. Error bars are mean + SEM.
Average Difference in Time (s)
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0.
caffeine
non caffeine
water
Product
Figure 2. The graph shows the average difference of the reaction time between without
and with the specified drink. Error bars are mean + SEM.
Discussion
The purpose of this experiment, reaction time was measured as the average
difference between without and with (experimental) for Coca-Cola to see if reaction time
decreased with caffeine. Caffeine enhanced physical performance (faster tapping speed
and faster simpler and choice reaction times) in both medium-high and non-low
consumers (Rogers et al, 2013). In some cases it did increase reaction time while others it
did not affect. This could be caused by the fact that some of the participants consume
caffeine on a daily basis. Frequent consumption fails to enhance mental alertness and
mental performance (Rogers et al, 2013). This seemed to be the case for some of the
participants.
The water acted as a control to see if there would be a significant difference
between the Coca-Cola and Coca-Cola caffeine-free. However in some the reaction time
had decreased when participants were given water to drink. This could be due to the fact
of the learners curve. The learners curve theory is that individuals get better with practice.
Personal experience tells them that the more derivatives they work, the easier it is to do
—that changing a tire is easier the second time than the first time (Neely et al, 2010).
Since the participants took the test a second time after consuming their drink they knew
what to expect rather than the first time.
The statistical test run on the groups without the drink and the three with the drink
indicated that there was no significant difference between the products. Both of the pvalues of the ANOVA test had a greater value than 0.05. The ANOVA test that was run
on the average difference between the groups of without and with the drink also showed
that there was no significant difference (p=0.057, Figure 2). Since there was no difference
between the groups the results did no support the hypothesis that caffeine would decrease
reaction time.
Further research on the effect of caffeine on decreased reaction time could expand
on the result of the current study. This study was limited to the number of participants
and the participants aware that they are consuming caffeine. Also the intake of caffeine
on a daily basis of each participant limited the effect caffeine had on the individual. By
making them unaware of which product has caffeine and having more participants that do
not consume caffeine as often as others may lead to more consistency.
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