Stroop Effect

STROOP EFFECT 1

INTRODUCTION

Background of the study

The color-word naming originated way back almost to the beginning of experimental

psychology, in the first psychological laboratory, in Leipzig, Germany. In 1883, Wilhelm Wundt

recounted his student, James Mckeen Cattel, to investigate in his doctoral research on the time

required to name objects and colors and read corresponding words. The research focused on

the duration of naming such objects. Cattell, in 1886, recognized that color naming required

more time than word naming and these finding was noted in William James’ book in 1908.

In spite of the fact that there were several first experimental studies regarding with color-

word naming, the test had not yet achieved its identity until 1929 when an American

psychologist, named John Ridley Stroop, devised a test in the laboratory of Erick Rudolf

Jaensch (as cited in Killian, 1935). The test shows that people cannot help but process word

meanings, and that this processing interferes with the color-naming task. This test was then

named as the “Stroop test”.

The most intriguing feature of the Stroop test is the conflict or interference situation in

which the subject must name the color of the ink of color-words when the color and the word are

incongruous. The effect of such test was already noted as the “Stroop Effect”.

The “Stroop Effect”, as defined, is the state of color confusion; it is the difficulty in

identifying the colors in which names of colors are written (Encarta, 2010). For example, if the

word "red" is printed in green ink, people are likely to say "red" when asked the color of the

printed word. In March 21, 1929 the identified color-word test, the true “Stroop test”, was first

introduced into American psychology.

Why has the Stroop effect continued to fascinate psychologists? Part of the answer is

that the Stroop effect appears to tap into essential operations of cognition, thereby offering clues

to fundamental cognitive processes.

STROOP EFFECT 2

In two classic experiments, Stroop first compared reading a list of words printed in black

(verbal condition) with reading the same list of words printed in incongruent colors (Stroop-

verbal condition). Stroop found that there was little difference in reading time for the two lists.

Subsequent to the first, Stroop then compared the naming of colors for a list of solid color

squares (intrinsic condition) with the naming of colors for a list of words printed in incongruent

colors (Stroop-intrinsic condition). Subjects averaged 74% longer to name ink colors of

incongruent words (Mangun, 2012). The results of these two studies led Stroop to conclude that

since people are more practiced at word reading than naming colors, there is less interference

with word reading than with color naming.

The theory of visual selective attention proposes a special status for spatial location in

visual processing (Naatanen, 1992). According to Naatanen (1992), selective attention was

viewed as selecting between messages arriving on different “channels”. Selecting one “channel”

is usually defined on the basis of spatial origin or some other distinctive feature. According to

the zoom-lens model, attention is directed to a given region of the visual field. The area of focal

attention can be increased or decreased in line with task demands (Eysenck, 2004). Selective

attention also has obvious advantages because it allows us to maximize information gained

from the object of our focus while reducing sensory interference from other irrelevant sources

(Baron & Kashler, 2005).

The automaticity model may also explain the concept of the Stroop effect. According to

this theory, reading is an automatic process, which cannot be turned off. Automatic processing

must occur without intention, without involving conscious awareness and must not interfere with

other mental activity (Galotti et al., 2010). In other words, people see the words without much

effort or consciousness. On the other hand, naming colors is not automatic. It requires more

effort than reading, thus creating interference in the Stroop task. The Stroop effect has often

been regarded as involving unavoidable and automatic processing of the color words (Eysenck,

STROOP EFFECT 3

2004). This explanation derives more from Cattell’s theory, with automaticity viewed as a

continuum that develops with practice (MacLeod & Dunbar, 1988).

In processing stimuli, mainly visual stimuli it was widely recognized that gender is a

causable factor. Strickland et. Al. (1997) concluded that there are significant sex differences on

time taken to complete the color-naming and word-naming cards. (Baroun & Alansari, 2006)

According to Golden and Sarmany there is a widespread agreement among researchers that

females tend to have shorter latency on naming color card, while males and females perform

almost equally on the word card. Merkarski, et. al (1996) also supports, linked to their findings

which indicates that women perform in shorter times on the Stroop test latencies than men.

The focus of the experiment; therefore, is on Stroop effect as determined by duration -

the length of time it will take for the subject to finish the given task. By conducting one

experimental setting, the experiment aims to find out if there is a significant difference among

the four conditions in terms of duration, this is to prove whether Stroop findings was applicable.

Second, the experiment aims to find out whether gender is a causable factor on Stroop effect

and to prove whether the findings stated by Baroun and Alansari (2006) is likewise applicable.

STATEMENT OF THE PROBLEM AND HYPOTHESES

1. What is the significant difference between males and females in the four conditions

namely: a.) Verbal b.) Intrinsic c.) Stroop Verbal and d.) Stroop Intrinsic in terms of

duration of response?

There is a significant difference between males and females in the four

conditions namely; a. Verbal, b.) Intrinsic, c.) Stroop Verbal and d.) Stroop Intrinsic, in

terms of duration of response. Females have shorter duration than males, in completing

the four conditions.

2. What is the significant difference among the four conditions namely; a.) Verbal, b.)

Intrinsic, c.) Stroop Verbal and d.) Stroop Intrinsic, in terms of duration of response?

STROOP EFFECT 4

There is a significant difference among the four conditions namely; a.) Verbal, b.)

Intrinsic, c.) Stroop Verbal and d.) Stroop Intrinsic, in terms of duration of response.

Verbal condition has the shortest duration among the four conditions and Stroop-intrinsic

condition has the longest duration among the four conditions.

METHODSubjects

Twenty-four undergraduate students of Saint Louis University, Navy Base Campus acted

as subjects as a part of the experiment. Of the 24 subjects, 12 were males and 12 were

females. The subjects were selected randomly based on their availability during the time of the

experiment.

Apparatus

Two sets of stimulus boards were used in the experiment. The first set of stimulus

boards were the “trial boards”. The experimenter used three trial boards with white background.

Each trial board consisted of three conditions, namely: verbal (with written words red, blue,

yellow, green and black that are printed in black ink) with a size of 5.5x20 inches, intrinsic (each

rectangle is colored with red, blue, yellow, green and black) with a size of 9x20 inches and

Stroop, which can be verbal or intrinsic as well (written name of colors with different font colors)

with a size of 7.6x17.5 inches. For each trial board, five words (verbal) and five rectangles

(intrinsic) are printed on it to be read or recognized.

The second set of stimulus boards were the “actual boards”. The experimenter used

three actual boards with white background and with a size of 30x20 inches each. Each actual

board has the same conditions applied to it as the trial boards. The only difference between the

two boards is that the actual boards consisted of 20 words, arranged in a 4x5 matrix of evenly

spaced rows and columns and the intrinsic board consists of rectangles with a size of 5x2

inches.

STROOP EFFECT 5

For this experiment, a stopwatch (cellular phone) was also used to record the time

duration the subjects are able to read or recognize all the words or colors in the actual board. As

for the applicable standard unit of measurement, seconds and milliseconds were used.

Procedure

First, the experimenter prepared the boards to be used in the experiment. Subsequently,

the recorders prepared the record sheets and the timers to be used. The recruiters dispersed

themselves around the GD building to look for subjects. They politely asked each person they

meet if they were willing to participate in the experiment. An available and willing subject was

brought to the cubicle in the 7th floor where the experiment is performed.

Each subject who entered the cubicle was greeted by the experimenter and the

recorders. The subject was asked to sit and relax on the chair provided, facing the south wall of

the cubicle. When the subject was ready, the experimenter gave instructions and further

explained how the experiment will take place.

They began the experiment with a trial. The experimenter showed the subject 3 trial

boards — each with different a different condition or stimuli (verbal, intrinsic, Stroop verbal,

Stroop intrinsic). For the first board, the experimenter asked the subject to read the words

placed on the board. For the second board, the experimenter asked the subject to name the

color of the rectangles on the board. And lastly, for the third board, two instructions were given:

first, to read the words on the board and second, to tell the font color of the words. When the

subject finally finished the trial boards and understood the instructions, they moved on to the

actual experiment. In the middle of the experiment, the subject was entertained in order for

him/her not to be bored. This was done before proceeding to the actual experiment.

In the actual experiment, the experimenter used the actual boards. For each board, 4

columns with 5 words were present. The subject was asked to read the words column to

column, from top to bottom.

STROOP EFFECT 6

The instructions given for the actual boards were the same with the instructions given for

the trial boards. In the first actual board, the experimenter instructed the subject to just read the

word he would see. For the second actual board, the subject was asked to tell the experimenter

the color he/she saw on each rectangle on the board. Lastly, the third board was used twice for

two different conditions. For the first instruction of the last board, the subject was asked to read

the word he sees, but now with a twist — the words were written in colors different to its name.

For the second instruction given, the subject was asked to tell the color of the word in which it

has been written or the font color.

The subject only started reading when the experimenter gave the go signal. The go

signal was also the cue for the recorders to start recording. After the subject was finish with the

first board, the recorder stopped the timer. The recorder then wrote on the record sheet how

long the subject took for him/her to read all the words on the board. Once done, everyone in the

cubicle thanked the subject and escorted him/her outside the cubicle. The same procedures

were followed for all 30 subjects.

Treatment of Data

The data in problem no. 1 were analyzed using t-Test for uncorrelated sample means (t-

Test: Two-Sample Assuming Equal Variances) with gender (male and female) as the parameter

factor and the mean time duration for each of the four conditions as the real factor.

The data in problem no. 2 were analyzed using analysis of variance (ANOVA): single

factor design for correlated sample means (ANOVA: two-factor without replication) with the time

duration as the within subject factor and the four conditions as the between subject factor. The

statistical analyses for both problems were carried out by means of manual computation and

were verified using statistical package for social science (SPSS) for Windows Version XP, both

computations standardized at significance level 0.05.

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RESULTS AND INTERPRETATION

The following results obtained through application of the appropriate statistical treatment

for each problem:

Problem no. 1: t-Test: Two-Sample Assuming Equal Variances

T-TEST SUMMARY TABLES:

VERBAL CONDITION Females Males

Mean9.519 9.694

Variance3.823 9.364

Observations15 15

Pooled Variance6.594

Hypothesized Mean Difference0

Df28

t Stat - 0.186NS

t Critical two-tail 2.048

The table above shows the full summary of the t-test done for verbal condition. The

results clearly presented that the t-value of - 0.186 falls within the critical region of 2.048 at

0.05 and is therefore, not significant. Hence, we can conclude that there is no significant

difference between males and females in their time duration for the verbal condition.

INTRINSIC CONDITION Females Males

Mean 10.290 11.201

Variance 2.035 5.194

Observations 15 15

Pooled Variance 3.614

Hypothesized Mean Difference 0

Df 28

STROOP EFFECT 8

t Stat - 1.312NS


The table above shows the full summary of the t-test done for intrinsic condition. The

results clearly presented that the t-value of -1.312 falls within the critical region of 2.048 at


difference between males and females in their time duration for the intrinsic condition.

STROOP-VERBAL CONDITION Females Males

Mean 9.759 10.743

Variance 4.659 13.848

Observations 15 15



Df 28

t Stat - 0.886NS


The table above shows the full summary of the t-test done for Stroop-verbal condition.

The results clearly presented that the t-value of 0.886 falls within the critical region of 2.048 at


difference between males and females in their time duration for the stroop-verbal condition.

STROOP-INTRINSIC CONDITION Females Males

Mean 14.874 16.304

Variance 13.710 15.336

Observations 15 15


STROOP EFFECT 9


Df 28

t Stat - 1.028NS


The table above shows the full summary of the t-test done for Stroop-intrinsic condition.

The results clearly presented that the t-value of -1.028 falls within the critical region of 2.048 at


difference between males and females in their time duration for the Stroop-intrinsic condition.

The general results of the statistical analyses in problem no. 1 evidently presents that all

of the t-value for each of the condition (verbal, intrinsic, Stroop-verbal, Stroop-intrinsic) are

insignificant at 0.05. Therefore; the alternative hypothesis which states that there is a

significant difference between males and females in the four conditions, in terms of time

duration is REJECTED. Thus; this evidently shows that males and females have significantly

performed the same in terms of the length time it took them to complete (duration) the tasks

(four conditions). Gender is not a causable factor in to prove “Stroop-effect” as determined by

time duration.

Problem no. 2: ANOVA: Two-Factor Without Replication

DATA SUMMARY TABLE:

Groups Count Sum Average S2

Verbal 30 288.20 9.61 6.37

Intrinsic 30 322.36 10.75 3.70

Stroop-verbal 30 307.53 10.25 9.19

Stroop-intrinsic 30 467.67 15.59 14.55

ANOVA TABLE:

Source of Variation SS df MS F P-value F crit

STROOP EFFECT 10

Columns 522.00 2 261.00 36.20* 0.00 3.16

Error 418.20 58 7.21

Total 1317.77 89

Shown above is the summary table of the statistical treatment ANOVA. The data clearly

shows that the F-value of 0.535 falls beyond the critical value 3.16 at = 0.05. Therefore; the

alternative hypothesis which states there is a significant difference among the four conditions,

namely: a) verbal b) intrinsic c) Stroop-verbal d) Stroop-intrinsic in time duration is ACCEPTED.

Hence, we proceed to the Tukey Method.

CLUSTERING:

There is a significant difference among the four conditions in terms of time duration.

Verbal, Stroop-verbal, and intrinsic conditions do not significantly differ from one another in

terms of time duration. The three having the shortest time duration, means that they were

equally performed faster. On the other hand, the Stroop-intrinsic condition having the longest

duration means that it was the task performed the slowest. This implies that verbal, Stroop-

verbal and intrinsic conditions have the least “Stroop effect” or none at all, compared to Stroop-

intrinsic who has the highest manifested “Stroop-effect”.

DISCUSSION

The purpose of this experiment is to explore more about the Stroop effect. More

specifically to find out if there is a significant difference between males and females in terms of

VERBAL = 9.61

STROOP-VERBAL = 10.25

INTRINSIC = 10.75

STROOP-INTRINSIC = 15.59

STROOP EFFECT 11

duration for each of the conditions and to find out if there is a significant difference among the

four conditions (verbal, intrinsic, Stroop-verbal and Stroop-intrinsic) in terms of time duration.

For the first problem, the researchers found out that gender is not a causable factor to

prove the Stroop effect as determined by time duration (Baroun & Alansari, 2006). According to

Golden and Sarmany, there is a widespread agreement among researchers that females tend to

have shorter latency on naming color card, while males and females perform almost equally on

the word card. Merkarski, et. al (1996) also supports, linked to their findings which indicates that

women perform in shorter times on the Stroop test latencies than men.

According to Ligon (1932), women tend to perform better on color naming while men and

women tend to perform equally on word naming. In addition, Peretti (1971) reported the

difference favoring females on color-word naming. A study was conducted by Barbara Dozier

which confirmed the findings that states there is gender difference between males and females.

On the same research, Alansari & Baroun (2003) investigated performance differences related

to gender and culture using Stroop color and word test. However, it was found out that there is

no difference.

Though there were a lot of studies that reported there is a significant difference between

males and females in terms of “Stroop effect”, there were also valid studies and evidences that

reported there is no difference in gender when it comes to word or color naming. A study that

was done by Insua (2002), conducted on 2000 English and Spanish subjects in the United

States, showed no gender difference in performance across all Stroop test.

Proving such studies, Galer et. al, (2014) stated gender has significantly lower effect in

processing visual stimuli, compared to age gaps, educational attainment and prior training and

experiences. He said that, time related differences between individuals have greater effect on

the speed in processing stimuli. Other than organic variables (biological factors), environmental

variables have a more or less higher influence on results of experimental-based researches.

This was proven to be true by (Flaudias & Llorca, 2014).

STROOP EFFECT 12

Huguet, et al., who conducted an experiment, found that another person’s presence

during the test significantly reduced the Stroop effect. They showed that in the presence of a co-

actor or simply a presence, the Stroop effect decreased in comparison with a situation where

the participant was alone in the room. Conty, et al., (2014) further elaborated this, claiming that

in an experimental setting, results were influenced more by the feeling of being watched than by

the presence of others. In this case, emotional states caused by individual differences might be

triggered (Baron & Kalsher, 2008).

For example, if a male subject who has inferiority complex and who has a high anxiety

tendencies, is introduced to a time pressured task with the presence of strangers, his

performance will be poorer compared to a female who don’t have confidence and trust issues

(Baron & Klasher, 2008). Another reason as to why gender is a weak basis is the fact that the

reduction of Stroop interference may be the result of the task-specific nature of the effort

procedure used (MacKinnon, et al. 1985). This means that the prior training might affect the

speed of performance of a certain person if the actual task is already introduced. Thus, effort is

an important mediating variable to be considered in all strop studies.

Since the subjects were exposed to trials, they were already given clues as to how the

actual task would take place, and according to Galer, et.al (2014), if a set of people is equally

introduced to a certain task, this may reduce their ability to exhibit differences among them.

Prior training may directly lessen the typical performance of a person.

For the second problem the researchers have found out that there is a significant

difference among the four conditions. It was proved that verbal, intrinsic, and Stroop-verbal

conditions have the least “Stroop effect” or none at all. According to the findings of Hubel and

Wiesel, many brain cells respond only to lines of a certain width or orientation (Coon, 1995).

These same cells didn’t get the least bit ‘excited’ over a dot of light or overall illumination. Other

cells responded only to lines at certain angles, or lines at certain lengths, or lines moving in a

particular direction. The upshot of these findings is that cells in the brain seem to first analyze

STROOP EFFECT 13

incoming information into such sequence: lines-angles-shading-movement-and other basic

features. These findings explain why we process written words and shapes faster than colors,

since words and shapes have more definite lines and angles we tend to recognize them more

quickly than colors.

On the other hand, it was also proved that the Stroop-intrinsic condition having the

longest time duration has the highest established “Stroop effect”. What could be an explanation

to this? According to Banich & Compton (2011), in processing of stimuli, if the stimuli are of the

same sensory modality, you must try to divide your attention between the two sources of

information. Although we control the focus of our attention, at least to some extent, certain

characteristics of stimuli can cause our attention to shift suddenly. Features such as contrast,

novelty, stimulus intensity, color and sudden change tend to attract our attention (Baron &

Kalsher, 2005). Hence, most of the time, the Selective Attention Theory is applied. In this

theory, it states that if there are competing stimuli, the attention mechanism focuses on one

stimulus (the attended message) and blocks out the other stimulus (unattended message). But

on the other hand, the unattended message is not fully blocked out. There is a certain degree of

registration because when the special information is included, it cannot be overlooked.

This explains why the Stroop-intrinsic condition elicits a longer duration. Since there are

two competing stimuli: the word (unattended message) and the color (attended message), the

subject had some trouble in recognizing the right stimulus to process and the right response.

Furthermore, the findings of Hubel and Wiesel stated above added as to why Stroop-intrinsic

condition elicits the longest duration. Since the words become the unattended message, it was

harder to block out because as said earlier our brain tends to recognize words quickly than

colors. That is why subjects had a longer time in processing the Stroop-intrinsic condition

because the unattended message is a very strong distractor.

CONCLUSION

STROOP EFFECT 14

The researchers conclude that there is no significant difference between males and females, in

terms of time duration among the four conditions, namely: a) verbal b) intrinsic c) Stroop-verbal

d) Stroop-intrinsic, where females is said to have a shorter time duration compared to males.

Therefore the alternative hypothesis is REJECTED. These results claim that gender is not a

causable factor in to prove “Stroop-effect” as determined by time duration.

The researchers also concluded that there is a significant difference in terms of time

duration, among the four conditions, namely: a) verbal b) intrinsic c) Stroop-verbal d) Stroop-

intrinsic; therefore the alternative hypothesis is ACCEPTED. Verbal-condition having the

shortest time duration and Stroop-intrinsic having the longest time duration is proven to be true.

These results claims that, verbal conditions have the least “Stroop effect” or none at all,

compared to Stroop-intrinsic condition which has the highest manifested “Stroop-effect”.

RECOMMENDATIONS

When driving, it is advisable most especially for the males, given that they are more

inclined to such activity, to be more careful and attentive in observing traffic signs, to avoid

accidents and penalties. People should also avoid the male driver stereotype. The findings in

this research proved that females may also be as capable as male in the driving department.

When visiting the grocery stores or markets, most especially for the females since they

are much inclined to such task, colors can help them better to distinguish the condition of the

goods they are buying. For example when buying fruits and vegetables, color is good

determinant whether the fruit or the vegetable is fresh and ripe or rotten. This way they can

avoid to be fooled by foolish vendors.

For those storeowners or businessmen who are planning to build commercial buildings

along the road, it is advisable for them to create signage/posters/billboards that are easily

readable - with readable font, font size, and font color. Also avoid using font colors that will

make the letters troublesome to read for easy location of the place, and avoid using colors that

are too distracting for the motorists to avoid causing unwanted accidents.

STROOP EFFECT 15

It is advisable for writers, teachers, students and others who are planning or obliged to

make illustrative reading devices, visual aids and flashcards, to see to it that the colors they are

going to use in making their visual devices must blend appropriately with the words written, for

easy and quick comprehension of words or the concept of the written material.

REFERENCES

Baron, R.A. & Kalsher, M.J. (2005). Introductory Psychology (taken from Psychology: From

Science to Practice). (custom ed.). (pp. 54 - 55). Boston, MA: Allyn and Bacon.

Baroun, K. & Alansari, B. (2006). Gender Differences in Performance on the stroop test. Social

Behavior and Personality, 34(3). 309-318. Kuwait University, Kuwait.

Banich, M.T. & Compton, R. (2011). Cognitive Neuroscience (3rd ed.). (p. 317). Belmont, CA:

Wadsworth.

Coon, D. (1995). Introduction to Psychology: Exploration and Application (7th ed.). NY: West

Publishing Company.

Eysenck, M.W. (2004). Psychology: An International Perspective. (pp. 193 – 217). NY:

Psychology Press.

Flaudias, V & Llorca, P.M. (2014). A brief review of the three manipulations of the stroop

taskfocusing on the automaticity of semantic access. Psychologica Belgica, 54(2), 1991-

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Galotti, K.M. et. Al. (2010). Cognitive Psychology: In and Out of the Laboratory. (pp. 110 – 113).

Toronto: Nelson Education.

Insua, M. C. (2002). Performance on the Stroop colour and word test as a function of language

in bilinguals. Dissertation Abstracts International: Section B: The Sciences &

Engineering, 63(1-B), 559.

James, W. (1908). The Principles of Psychology (Vol 1). (p. 559). London: Macmillan.

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STROOP EFFECT 16

Killian, G. (1985). The Stroop Color-Word Interference Test. In Keyser, D., & Sweetland, R.

(Eds.), Test Critiques (Vol 2). (pp. 751 – 758). Kansas City, MO: Test Corporation of

America.

Ligon, E.M. (1932). A genetic study of color naming and word reading. American Journal of

Psychology, 44, 103 – 121.

MacKinnon, D. & Geiselman, E. et. al. (1985). The Effects of Effort on stroop Interference. Acta

Psychologica, 58. 225-235. University of California, Los Angeles, USA.

Macleod, C.M. (1991). Haifa Century of Research on the Stroop Effect: An Integrative Review.

American Psychological Association, 109(2), 163 – 203.

Mangun, G.R. (ed.). (2012). The Neuroscience of Attention: Attentional Control and Selection.

(p. 230). New York, NY: Oxford University Press.

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Stroop Effect