Assignment # 1663LA3

Running Head: CAFFEINE EFFECT ON WORKING MEMORY

Caffeine Stimulates on Working Memory to Perform The Stroop Task

Ashaby Tejada, Kizzy Rosant, Charlene Lau

CUNY Queens College

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Abstract

Caffeine is a crystalline compound that stimulates the central nervous system. The central

nervous system consists of the brain and spinal cord. It controls the function of the mind and the

body. The present experiment focused on how caffeine can boost working memory when

performing the Stroop interference test. Interference is an external distraction stimulus that alters

task performance. Caffeine stimulates the working memory to store the information and to recall

the information later at the time in performing the task. Consuming caffeine can boost your

attention level and accelerate the reaction time to a task. The studies investigate the benefits of

caffeine on working memory and how working memory can affect the rate of one’s physical

reaction when performing a task.

Keywords: Caffeine, Stroop task, working memory, stimulation, interference

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Caffeine stimulates on working memory to perform the Stroop task

Performing the Stroop test could be difficult when there is interference. The consumption

of caffeine goes to the brain and stimulates the working memory to suppress task-relevant

response tendencies. Caffeine automatically activates mental focus and alertness when learning a

new skill. Caffeine has been shown to have many positive effects on working memory. Caffeine

could benefit various information processing tasks including the Stroop interference test.

Consuming caffeine accelerates processing speed to reactions and sustains attention to

accomplish the tasks. Conversely, interference occurs when some information makes it difficult

to recall. It reduces the accuracy of what is being tested and increases the rate of responding

times. Blocking can be an external factor to learn and to accomplish the task.

The purpose of the experiment is to replicate the Stroop effect study. It is hypothesized

that consuming caffeine stimulates working memory. Caffeine will decrease the reaction time to

encode and decrease the number of errors while performing the task.

Literature Review

Chen Ke, Yanyan Ye, Jiushu Xie, Tiangsheng Xia, and Lei Mo (2017) conducted an

experiment which tested working memory in attention and if visuo-spatial information interfered

more than word information with working memory (WM) due to perceptual judgement. Twenty-

eight participants (9 males, 19 females) were recruited from South China Normal University and

were compensated for their participation. The first experiment examined if WM stroop effect

occured when there was no overlapping response between the working memory items and

intervening color judgment. To help examine this, participants were asked to look at a fixed

point

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on a screen for 250 ms. The fixation point was then replaced by a word which appeared for 350

ms, immediately after a background color (red or green) was added to the word that was initially

presented. Participants were then asked to report the color by pressing “f” for red and “j” for

green. Both congruent and incongruent trials were utilized; in the congruent trial the attentional

word-color task required participants to identify if the color related with the word “blood” was

consistent with the red patch. Participants completed 8 practice trials with feedback and 96

experimental trials without feedback. On the incongruent trial, the WM word-color task

contained a color discrimination task and a WM probe test. The participants had to report the

color of the patch in which the color related with the word “grass” and the red color of the patch

differed. Participants completed 12 practice trials with feedback and then finished the following

96 experimental trials without feedback. These two experiments reported that there was a main

effect in reaction time. Participants in the attentional color discrimination task were significantly

faster than in the WM color discrimination task. However, participants had a slower response

time in incongruent trials when asked to identify the color related with the word “grass” and the

red color of the patch differed than in the congruent trials when asked to identify the color

related with the word “blood” was consistent with the red patch.

The second experiment utilized the Simon task (attentional Simon task vs. WM Simon

task) to assess how working memory is affected by spatial location of the presented stimulus. It

is important to note the WM Simon task is similar to that of the WM word-color test, except

spatial location information was retained rather than words. The Simon effect requires the

subject to identify the color of the stimulus as quickly as possible. The reaction times are usually

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faster and more accurate when the stimulus occurs in the same location as the response even if

stimulus location is irrelevant to the task.

While Chen Ke et. al (2017) explored how visuo-spatial cues interfere with how well a

participant performs both the Simon and Stroop task, Kenemans, J., Wieleman, J. S., Zeegers,

M., & Verbaten, M. N. (1999) researched how caffeine affects performance while stroop

interference is tested. In the first experiment, subjects participated in 4 sessions that were each

separated by 1 week. During the first 2 sessions participants were administered 25mg of lactose

(placebo) and for the remaining sessions they were given 250 mg of caffeine dissolved within

decaffeinated coffee to participants. The interference was measured to see if there was a

reduction in the performance using incongruent digits, compared to neutral digits. Researchers

found that the Stroop effect was reduced and at times reversed after caffeine was administered.

Subjects response time was generally reduced post treatment compared to pretreatment data

collected. This significant reduction in error rate found after consumption of caffeine suggest that

there was a significant benefit that allows for the suppression of task-relevant response tendency.

The results showed that the interference effect was smaller than expected, so a second

experiment was done for further examination. The second experiment, utilized color-word

incongruence and a fixed rate of stimulus. This design explored the use multiple types of

Stroop’s classic word-color task, which in hopes, would show a higher interference rate. The

format of the second experiment was the same as the first the difference was in the type of

stimuli presented. Twelve neutral stimuli consisting of three possible colors for each string, 12

incongruent stimuli (four words X three noncorresponding colors = 12 stimuli) were given and

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both were randomly mixed in two functionally equivalent conditions. Results also showed that

the Stroop interference was much smaller post administration, under caffeine, than with the

placebo.

Caldas, Pinheiro, Daneyko, and Riggio (2019) used a different approach with the use of

graspable objects. In their first experiment twenty-five subjects were presented with two stroop

stimuli. Stimulus 1 was a colored cup with an intact or a broken handle oriented to the right or to

the left. Stimulus 2 was a photograph of a cup combined with a color word in a congruent color

stimuli that the words ( red, green, or blue) matched the cup color in red, green, or blue and the

incongruent color stimuli that the words (red, green, or blue) does not matched with the cup color

in blue, red, or green. Subjects were asked to press “1” using the right index finger if the color

the cup and the word are the same. If the color of the cup and the word were different, the

subjects pressed the “Z” button with the index finger on the left.

Experiment 1, post hoc analysis identified there was a difference in corresponding and

non corresponding trials in both experiments with and without stroop effect at the 10 ms

mark.Longer reaction times were noted for broken handles in relation to cups with handles intact

(approx. 14 second difference). Non-corresponding versus corresponding (626 and 620 ms) and

trials with Stroop effect conflict and without Stroop effect conflict (647 and 599 ms) and at

100ms intervals and 800ms intervals (710 and 537 ms). A significant main effect for all factors

was noted in experiment 2 (Stroop-matching task, correspondence and intervals). Stroop-

matching task and intervals were also noted as being significant. Longer reaction times were

noted in 100 ms intervals in relations in 800 ms intervals.

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Method

Participants

To investigate how caffeine affects working memory on the Stroop test, a sample of 11

undergraduate students were recruited from the advance experimental psychology class at

Queens College. The sample consisted of 1 male and 10 females. The participants ranged from

19 to 40 years old.

Setting

The experiment was conducted in a Queens College classroom, NY.

Materials

Dunkin Donuts black caffeinated coffee, cups, timer, pen, data record sheet and a quiet

well lit room. To investigate working memory, participants were administered the Stroop test

which consisted of three levels (incongruent, congruent and normal).

Variables

The IV was the black caffeine coffee and the control group without the coffee. The DV

was the recalling of the information which was measured by the Stroop test to calculate the

participant reaction time. The Stroop test was used to test if the participant is more aware of what

they have recalled after the consumption of caffeine. The participants were randomly assigned

into the experimental and control group to avoid bias. All participants were told and signed an

agreement that can not consume anything has caffeine 6 hours prior to the experiment to control

any confounding effects.

Experimental Design

The present study is a 2 x 3 mixed factorial design. The Stroop test consists of three

levels which are congruent, incongruent and normal. These levels are within-subject because all

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participants were exposed to all 3 levels. The present study is a mixed factorial design because it

consisted of both within-subjects and between-subjects designs.

Procedure

All participants signed a consent form prior to participating in the present study and was

asked to refrain from drinking any caffeinated beverages 6 hours prior to participation. Students

were randomly assigned to either the control (5 students) or experimental group (6 students).

Each participant was individually brought to a separate room to participate in the experiment to

limit the amount of distractions. In the room there was a two chairs separated by a desk in

between and 3 experimenters. One experimenter presented the word sets, one informed each

participant of the instructions and kept time, while another counted the amount of errors

observed.

Participants were instructed that they would be presented with three word sets, and for

each word set they were required to read the word, not the color of the word. Also, that their

completion time and errors for each word set would be recorded. The word set were presented in

the following order: colors of the print and the word corresponded (congruent), the word and the

color of the print were different (incongruent) and the color bar (normal).

The experiment was separated into two trials, both the experimental and control

participated in each. After completion of the first trial the students selected to be in the

experimental group were given a cup of Dunkin Donuts caffeinated black coffee (200 mg) and

told to consume the coffee as soon as possible. They were called back 20 minutes after

consumption to complete the second trial. The control group was not given any coffee but

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conducted the same trial in the same allotted time. No additional form of caffeine was allowed

during the wait period.

For the second trial, the experimental group and control group were called one at a time,

with the experimental group being brought in first. The participants were required to follow the

same rules and procedures as outlined in the first trial. Errors and completion time were

recorded for each participant, as done in the first trial.

Results

The results indicated the caffeine decreases the response time of the participants when

performing the Stroop task. As shown on the table, in trial 1 the participants with caffeine in the

congruent condition showed a decrease in reaction time response in comparison to the

participants without caffeine in the same condition. In the incongruent condition took longer

response time but made less errors for the participants with caffeine in comparing to the

participants without caffeine. In the normal condition, the participants with or without caffeine

are very close in the reaction time response and are nearly errorless when there is no interference

to their task.

REACTION TIME ERRORS

Stroop Test

Non-caffeinated Caffeinated Non-caffeinated Caffeinated

Congruent 20.89 17.89 0.00 0.17

Incongruent 22.64 29.48 10.20 6.33

Normal 19.60 19.94 0.00 0.83

Table 1: The average/ mean performance of all participants

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Discussion

This study was conducted to test the effect of caffeine on working memory by using a

version of the Stroop test. The results from the study has shown there was a significant

difference from the control group (non-caffeinated) and the experimental group (caffeinated &

non-caffeinated) in the baseline scores and the post test scores. The results concluded that

consumption of caffeine boosted working memory to decrease the reaction time and has made

fewer errors when performing the Stroop test. The findings have supported the hypothesis

because the results have decreased the reaction time to encode a task. This study, the participants

were refrain caffeine for six hours prior to the experiment.

In a previous study conducted by Chen Ke et al. (2017) had participants refrain from

caffeine 12 hours before the test. The researchers assumed that the participants will comply.

There was no test to ensure that the participants actually completed the 12 hours or not. If they

consumed caffeine and only completed 8 hours instead of 12, would that have had an effect on

how well the task was performed. The last study conducted by Caldas et al. (2019), there was

one limitation that was most noticeable, behavior. The participants coming into the experiment

demonstrated daily behavioral inconsistencies. This showed that, performing a task can be

influenced by behavior. As a researcher, there is no real way to know a person's emotional state

and their actions unless they are asked and if not, then the participants behavior may have an

effect on performance.

In comparison to another study that involves caffeine and the effects it has on performing

the stroop task. Kenemans, J., Wieleman, J. S., Zeegers, M., & Verbaten, M. N. (1999) believed

that caffeine has a negative effect on performance and used the stroop task to test this hypothesis.

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The researchers told participants to refrain from drinking anything with caffeine for 12 hours

before the test so that they have control over how much caffeine is being consumed by the

participants. To test out their hypothesis, they measured the reduction in performing the stroop

task. This resulted in a reduction in the amount of errors participants had, comparing the before

and after caffeine treatments. Caffeine consumption also resulted in a shorter reaction time.

For each experiment done, there are some common factors that were present that showed

that caffeine has an effect on working memory. The stroop task helps with making sure that a

person working memory is processing information properly even with an interference being

present. With this interference comes the ability to also identify what are the causes of these

errors and the reaction time of each participant. Along with what is found from doing the stroop

task, adding caffeine can make the working memory process work at a much faster pace, with

less amount of errors made and even help with the reaction time when performing the task.

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Reference

Caldas, Ariane & Machado-Pinheiro, Walter & Daneyko, Olga &

Riggio, Lucia. (2019). The Stroop-matching task as a tool to study the correspondence

effect using images of graspable and non-graspable objects. Psychological Research.

10.1007/s00426-019-01191-5.

Chen K, Ye Y, Xie J, Xia T, Mo L (2017) Working memory operates over the same

representations as attention. PLoS ONE 12(6): e0179382. https://doi.org/10.1371/journal.

Pone.0179382.

Kenemans, J., Wieleman, J. S., Zeegers, M., & Verbaten, M. N. (1999). Caffeine and

Stroop Interference. Pharmacology Biochemistry and Behavior, 63(4), 589–598.

Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental

Psychology, 18, 643-652.

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Figure 1.0 Overall data table of the stroop task performed Pink: the reaction time in trial 1 for

each participant Purple: the number of errors each participant made in trial one.Light Blue: the

reaction time of each participant during trial 2( participants 1- 6 consumed caffeine). Dark

Blue: the reaction time of each participant during trial 2 ( participants 7- 11 did not consume

caffeine) .

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Figure 2. Trial 1 reaction time

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Figure 2.1. Trial 1 error

Table 3.1. Trial 2 error

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Table 3.1. Trial 2 reaction time