The Stroop effect (Stroop, 1935) is a phenomenon that demonstrates how one's reaction time slows down when it has to deal with conflicting stimuli. The reaction time is slowed, and this occurs because of interference, or there is a delay in processing information caused by competing and opposite functions in the brain. This is an experiment that involves the control of an independent variable, which is the colour stimulus, or the colour of the ink, to see what effect it has on the dependent variable, which is the reaction time. When a noun is presented as a colour name, which is visually printed using a different colour, the interference (the Stroop Interference Effect) is plainly evident (Pardo et al., 1990). It attempts to control the influence of all other extraneous variables – such as other cognitive processes or skills. It also allows for a correlation to be established between task and mental process.
The focus of this experiment is to investigate if conflicting stimuli is responsible for a delay in the reaction time taken to name colours. A modified version of Stroop’s original experiment was conducted with high school students, to measure the reaction time with each of the two tasks. The present experiment was designed combining the incongruent word-colour combination of Stroop’s first experiment, and modifying the control of the same experiment so that they are not just colour names in black ink, however, they are colour words in the ink of the same colour (e.g., “red” in red ink). In the original experiment, there was a mean difference of 75% between both the control and the experimental experiments, the presence of which is known as the Stroop effect.
Method
Design
The experimental design was a laboratory experiment, in which the idea was to establish a relationship between the independent and dependent variables. The independent variable was the stimulus of the colour of the word provided, and the dependent variable was the reaction time of the participants when naming the colour of the word.
The participants were, at first, briefed about the experiment, and its proceedings. Then, once they agreed, they signed the consent form which explained their rights throughout this experiment, and then were asked whether they had any questions, or not before proceeding. Then, the experiment was conducted, after which the participants were debriefed. They were told that they could contact the e-mail address provided at the end of the consent form, in case the participants had any concerns. Care was taken to ensure that the participants were not caused any psychological and/or physiological harm. The briefing/debriefing notes were standardised, to act as a control variable.
Participants:
The target population was students of a Northern Virginia high school, who were willing to participate in this experiment. They were required to be over 16 years old, so as to not require paternal consent, and available during the time of the experiment (i.e. given consent to take part in the experiment by their teacher). Opportunity sampling procedure was used to pick an even number of students, which ended up giving seven males, and seven females (n=14). The reason for opportunity sampling was because they were the participants willing, and available, to take part in the experiment. Since the experiment required two measures, the same participants were used for the control and the experimental groups, making it a repeated measure study,
Materials
Informed consent form
Standardised briefing note
Standardised debriefing note
Letter-size (8.5”x 11”) sheet of paper for TestC
Letter-size (8.5”x 11”)sheet of paper for TestE
Stopwatch
Procedure
The experiment was conducted in an area where the lighting was adequate, and the chances of interference were low. Participants are first briefed about the experiment, and then asked to sign the consent form, if they agreed to participate. The participants were read to the standardised briefing, and then shown the chart for TestC.
The participants were asked to name the colour the ink of each word, from left to right, top to bottom. The times taken to name all the colours correctly were noted down. Then, the participants were shown the chart for TestE, and the time taken to name all the colours, from left to right, top to bottom were noted down as well.
After the timings were taken down, the participants were then debriefed, which explained to them the purpose of this experiment.
Results
The score was recorded after each test was conducted in one table, after being confirmed by both experimenters.
The range of the TestC was from ≈ 10, with the numbers ranging from ≈ 6 to ≈ 16. The range for TestE was ≈ 6, with the numbers ranging from ≈ 15 to ≈ 21. The mean of each data set was used for the calculations, as it helps to understand an overall trend, and the standard deviation scores were considered as well, as they measure the distribution of the data around the mean.
“Table 1: Results of the Statistical Calculations”
These calculations indicate a clear casual relation between the independent and dependent variables. The percentage m difference between both means was calculated to be ≈ 78%. The chart below indicates the difference between both means.
The difference indicated in the chart between the two tests, TestC and TestE is the Stroop Effect – the attention interference due to the change in stimulus.
“Graph 1: Means for Both Tests, Demonstrating the Stroop Effect”
Discussion
The results from this experiment did correspond with those of Stroop’s experiments. In the second trial, when asked to name the colour of the ink, and not the word itself, the stimulus of the word conflicts with that of the stimulus of the colour of the ink, demanding the attention to work harder and therefore, it takes the participants longer to name the colour of the ink. The Stroop effect is definitely present, and the mean difference is quite close to Stroop’s own experiment – 75% in his experiment, in comparison to 78% in this experiment. This slight difference could be attributed to bilingualism - bilinguals tend to take longer to name the colour of the ink than monolinguals (Rosselli et al, 2002). The participants were not chosen based on their linguistic skills, and these skills could play a role in the level of interference. Therefore, linguistic skills may need to consider this cultural aspect in future replications of this study.
Also, it was assumed that English is the first language of all the participants; however this may have not been the case. The participants were asked to read the words from left to right, top to bottom, as the reading pattern is in English. However, other languages such as Arabic and Chinese are read in a different pattern, for example from right to left and up and down, respectively. These could increase the level of interference for the participants, as then they would have been forced to read in an order different than that of their natural inclination. It is recommended that the next time this experiment is conducted, most of the participants should at least have English, or another language that reads in the same pattern as English as their first language, to prevent discrepancy in the results.
References
Pardo, J. V., Pardo, P. J., Janer, K. W., & Raichle, M. E. (1990). The Anterior Cingulate Cortex Mediates Processing Selection in the Stroop Attentional Conflict Paradigm. Proceedings of the National Academy of Sciences of the United States of America, 87(1), 256 - 259.
Rosselli, M. , Ardila, A. , Santisi, M. N. , Del Rosario Arecco, M. , Salvatierra, J. , Conde, A. and Lenis, B. (2002). Stroop effect in Spanish–English bilinguals. Journal of the International Neuropsychological Society, 8, 819-827. doi:10.1017/S1355617702860106
Stroop, J. R. (1935). Studies of interference in serial verbal reactions. . Journal of Experimental Psychology, 18, 643-662.
Appendices:
Appendix 1:
Consent Form (required for participation)
Teacher Consent form (required for [participation of the students):
Appendix 2:
Standardised Briefing Instructions:
This is an experiment for our IB Psychology SL class that you have agreed to participate in. This experiment deals with color recognition and reaction time. Please know that all your information will remain private and that you are free to withdraw from this experiment at any time. Also know that the experiment in its entirety will be fully explained to you at the end of the experiment. If you have any concerns please state them now before the experiment begins. In the first trial please read the list from left to right stating the names of each color you see. In the second trial please name the color of the ink not the name of the color written in said ink. You will be timed for each trial. When you are ready to begin please signal us and the experiment will start.
Appendix 3:
Standardised Debriefing:
The purpose of this experiment was to examine how one perceives colors using the Stroop Phenomenon. We measured your reaction time to colors that matched the color of the word they spelled versus reaction time to colors that did not match the words they spelled. The time differences, if present, between trials one and two have been recorded. Please do not repeat what occurred during this experiment to any other participants. Thank you for the time you took to help us.
Appendix 4:
Chart used for TestC.
Appendix 4:
Chart used for TestE
Appendix 6:
Raw Data for TestC and TestE:
Appendix 7:
Statistics Calculations
Mean:
TestC: ∑ x = 142.91, n = 14
= 10.21 seconds.
TestE: ∑ x = 254.83, n = 14
= 18.20 seconds
Mean percentage difference:
= 78.26%
Appendix 8:
Standard Deviations Calculations:
Standard deviation for TestC: 2.72 seconds
Standard deviation for TestE: 1.99 seconds