Investigating Interference in Response Time

Saran Singh Sound

An experiment to investigate Interference in response time

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In my investigation I have replicated the Stroop Effect, which is a test for checking interference in response time and processing. This effect has been useful as it helps us understand that brain’s reaction time slows down when there is conflicting stimuli.

In my investigation i wanted to check for the difference in the response time participants take when a colored block stimulus is compared to a conflicting stimulus.

For the collection of data for this experiment participants were conveniently chosen i.e. the students were sent into the classroom as an when they were free. In the experiment I recorded the response time of each participant until they finished the whole task. For the purpose of this investigation, standard deviation was used as a statistic measure. It was hypothesized that participants would have increased response time in the conflicting stimuli as it had interference. Our replicated study seems to match the same.

Word Count: 152


Automatic processing can be defined as processes that do not require attention; they can often be performed along with other tasks without interference.[1] The Stroop Effect tested how automatic processing works. J. Ridley Stroop (1935) aimed to demonstrate the effect of interference in the reaction time. Stroop used only five colors (red, blue, green, brown, and purple) for his stimuli and conducted three separate experiments. He tested different number of participants for each of his experiments. In his first experiment he made his seventy undergraduate college participants (14 male and 56 female) read two stimuli and call out the color name in both cases. Stimulus-one was a list of color names printed in black ink and stimulus-two was a list of colors written in conflicting/contradictory ink, i.e., blue written in red ink. For the second experiment, Stroop used 100 participants (88 college undergraduates, 29 males and 59 females, and 12 graduate students, all females) who were also made to read two stimuli. Stimulus-one was a list of colored square boxes and stimulus-two was a list of color names printed in conflicting/contradictory ink. The participants were made to call out the color the words and blocks are printed in. In his last experiment, Stroop replicated experiment two in the same manner except for two things. One he used thirty two undergraduates’ participants from the University of Arizona and second he replaced the colored blocks with colored swastikas. The results of Stroops’ experiment were:

Naming of the ink color in the neutral stimuli was faster than in the conflicting stimulus which is semantic interference.
When participants were asked to name the word instead of the ink color semantic interference disappeared.

In this study we have replicated the Stroop Effect and our aim and hypothesis is that there would be an increase in the response time for the conflicting stimuli



Repeated measures were used for this experiment. Using repeated measures helped us control any effects that might be attributed to personal characteristics of the participants, such as age and gender and if random measures were used we wouldn’t have truly known the effect of interference on response time. The independent variable for my experiment was the two-stimulus and the dependent variable was the response time taken in seconds to identify the color of the ink in both the stimuli; colored block stimuli and contradictory ink stimuli.

The instructions and procedure was kept constant for each participant. During the experiment, ethical considerations were made. Participants data was kept anonymous, were given right to withdraw and were debriefed[2] after the experiment. They were also made to sign an informed consent form[3] at their own wish and will before the experiment was conducted.


The participants in this experiment were conveniently chosen Jamnabai Narsee School IB Seniors population non psychology students. Convenience sampling was used because at the time of conducting this experiment regular classes were functioning in the School and only the students who were free at that time were chosen to participate. A total of ten participants out of 98 students in the seniors’ population were used for this experiment; 7 male and 3 female. The participants’ age ranged from sixteen to seventeen. All of the participants were fluent with English and were from the same educational and cultural background.


Standardized Instructions[4]
Informed Consent[5]
Matrix of colored blocks printed on blank sheet of paper- Colored block stimulus[6]
Matrix of color names printed in contradictory ink on blank sheet of paper-Conflicting stimulus[7]
Post task questions[8]
Digital stopwatch ±0.01s


The materials for this experiment were prepared using word processing and photo editing software. The steps for carrying out the experiment were as follows:

Participants were tested individually in a classroom in Jamnabai Narsee School.
The researcher read out the standardized instructions[10] out loud.
Then the informed consent[11] was handed out to be signed.
Instructions on performing the task – first condition (Colored block stimulus)[12]-were read aloud to the participants
The participants were then informed to begin the task on the count of 3.
After the participant finished speaking out all the color names the stopwatch was stopped and the time was noted.
The participants were then instructed on the second condition (Word stimulus)[13].
They were told to begin the new task at the count of 3.
The stopwatch was stopped immediately after they finished the task and the time was noted.
The post task questions[14] were handed over to the participants after they had finished their tasks.
Lastly, the researcher debriefed[15] the participants on the nature of the experiment.
Before the participants left they were thanked and instructed not to reveal their participation in this experiment in order to avoid revealing of the aim of this experiment.


From the mean measure on Table 1, it can be deduced that the conflicting word stimulus had higher response times than the colored block stimulus. The colored block stimulus had response times close to the mean because it has a low standard deviation. The mean was calculated for this experiment as it measures the central tendency for the response time and furthermore, mean encompasses all the data. The standard deviation shows us how far the values tend to be from the mean. Calculations[16]


Standard Deviation

Colored Block Stimulus



Conflicting Word Stimulus



Table 1: Mean response time and standard deviation of Colored Block Stimulus and Conflicting Word Stimulus

Figure 1: Comparison of the mean response time for Colored Block Stimulus and Conflicting Word Stimulus.


Colored Block Stimulus and Conflicting Word Stimulus have a mean of 17.0 and 24.8 seconds respectively. The difference in the time for both the stimulus suggests that response time was indeed greater for the conflicting word stimulus than that of the colored block stimulus which supports my hypothesis. This was because of the conflicting factors that caused interference and slowed processing speeds. This study matches the results found from the original Stroop Effect experiment[17]. The standard deviation value indicates that at some point of time there were errors in the experiment. While the execution of the experiment was simple, there were a few improvements which could have been made to ensure better results.

The font size of the text was really small which increased the difficulty in reading it. The use of a slightly bigger font size would be beneficial.
There were a few noises in the classroom which may have affected the participant’s concentration. Reassuring that there are no disturbances in the classroom during the experiment would be advantageous.
There could also be an error in time from the researcher as there is a delay in the time at which the participant finishes the task and the time at which the researcher stops the stopwatch.
The gender distribution for the experiment weren’t equal i.e. 7 male and 3 female participants.

Some of the factors mentioned above could be the reason for the high standard deviation value.

Therefore, after analyzing the data we can conclude that the hypothesis of my experiment was met even though there were some flaws in the experiment.


Stroop R, J. (n.d.), Stroop Effect, STUDIES OF INTERFERENCE IN SERIAL VERBAL REACTIONS. Journal of Experimental Psychology, 18, 643-662. Retrieved August 16, 2014 from

Gerrig, R., & Zimbardo, P. (2002, January 1). Glossary of Psychological Terms. Retrieved October 30, 2014, from

Resnik, D. (2011, May 1). National Institute of Environmental Health Sciences. Retrieved October 30, 2014, from


Appendix 1

Standardized Instructions:

Appendix 2

Informed Consent:

Appendix 3

Stimulus 1:

Appendix 4

Stimulus 2

Appendix 5

Post Task Questions:

Appendix 6


Appendix 7

Raw Data:

Participant No.

Response time for Colored Block Stimulus/s/±0.01s

Response time for Conflicting Stimulus /s/±0.01s





















Mean Calculation for colored block stimulus =

= 17.0s

Mean Calculation for conflicting stimulus =

= 24.8s

Sample Standard Deviation calculation =

= 1.7s

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