Experiment in Cognition: Stroop Effect

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Table of Contents

Abstract
Introduction
Method
Results
Discussion
References

Abstract

The current research paper is aimed at investigating the effect of interference in cognitive processes, which is known under the title of the Stroop effect. The study introduces the overview of the research conducted on the topic within a century of scientific work in the field of psychology. A variety of modifications of the experiment are discussed, and the theoretical explanations behind the investigated cognitive effect are explicitly articulated. The method section depicts the specifics of the experimental design, including the characteristics of the participants, the materials used, and the procedure. The results are demonstrated in the form of a table that demonstrates the descriptive statistics of the experiment. Finally, the findings are discussed to validate the hypothesis and explain the theory behind the identified cognitive effect.

Introduction

The human cognitive processes have long been the focus of psychological research. The way the brain processes different kinds of information affects the psychological and emotional spheres of individuals’ lives and constitutes a relevant research topic. The issues of people’s abilities to multitask and manage some physical or cognitive processes automatically present a number of research cases for psychologists. The patterns and specific features of brain work in general, and the functions of attention in particular, are at the center of scientists’ attention. One such pattern is the Stroop effect named after an American psychologist of the first half of the twentieth century who introduced the phenomenon of cognitive interference to the field of neuropsychology. In this research paper, the fundamentals of the Stroop effect, as they are presented by Stroop (1935), will be used as a basis for an experiment investigating the impact of cognitive interference on the time of response to stimuli.

The experiment conducted within the realm of this research study is a modification of the original experiment presented by Stroop (1935) in his article “Studies of interference in serial verbal reactions.” The work by Stroop (1935) was comprised of three similar experiments. The first one required reading the names of the colors when the ink color was different from the one named in the card. The second one asked the participants to name the color of the ink in which the words were typed under the circumstances where the colors named and the inked used for typing the same card were different. The third experiment investigated how practice influenced the time of response to interfering stimuli. Consequently, the results showed that the time spent on naming colors of the ink was 74 percent longer than that spent on reading the names (Stroop, 1935, p. 651). However, practice showed to have a positive effect on decreasing the time of reaction, implying the training implications of the cognitive processes.

The experiment discussed above became a significant benchmark in cognitive psychology that brought light onto the very important issues of cognition particularities. It incepted the phenomenon called the Stroop effect, meaning the delay in response to incongruent stimuli that explains the basic principles of how the human brain disseminates attention and processes information. Many researchers in the fields of neuropsychology, emotional psychology, and other branches of science continue to refer to the Stroop effect. Several variations have entered the scholarly circles since the first publication of Stroop’s (1935) article. Much investigation has been made to expand the clinical, theoretical, and scientific implications of the issue. Indeed, according to MacLeod (1991), such psychologists as McCown and Arnoult, Regan, Kipnis and Glickman, Golden, and others have significantly modified the original experiment by changing the conditions of the process, the stimuli, or the presentation of the word. In such a manner, they attempted to measure more complex issues related to interference. The Stroop effect contributes to the studying of individual differences in cognition, mental conditions, the flexibility of attention, and other psychological particularities.

Today, the Stroop task is very well-known and is applied in both clinical settings and for educational or training purposes. Mainly it is used to test “the ability to inhibit cognitive interference, which occurs when the processing of a stimulus feature affects the simultaneous processing of another attribute of the same stimulus” (Scarpina & Tagini, 2017, p. 1). More variations continue to appear, where the semantics of the stimuli is altered to test emotional spheres, or the words are substituted with pictures, which allows obtaining more substantial results (MacLeod, 1991). However, the original test, which is the serial color-word test, remains highly relevant for testing cognitive abilities and the particularities of attention in individuals. Therefore, the standard version of the experiment is going to be carried out within this research study.

The experimental procedure allows for retrieving the exact information about the time spent by a participant in responding to the colors of the letter strings under different conditions. The difference in conditions is defined by either the absence or presence of interfering stimuli. As the academic literature on the issues suggests, the reason why participants spend more time naming the colors of letter strings under incongruent conditions is due to the automaticity of the reading process. Indeed, Stroop (1935), in his third experiment, came to the conclusion that practice influences performance in a positive way. The researcher stated that the differences in response delay when the subjects’ “habitual reaction pattern is interfering with reactions to a stimulus for which the subjects do not have a habitual reaction pattern” (Stroop, 1935, p. 658). In other words, people have an automatic habit of reading and understanding the meaning of the words but have to make an effort to name the colors since this process is not automatic.

This explanation refers to the reading habits and might be presented in a modified form. Indeed, the issues of the reading process automaticity are claimed by Megherbi, Elbro, Oakhill, Segui, and New (2017). The scholars investigated the Stroop effect in children whose reading skills are very low. The absence of the effect in such conditions proves the complexity of the cognitive processes that deal with decoding interfering stimuli when participating in the experiment. The researchers argue that this process contains two effects, including “the obligatory decoding of the distracting words” and the ability to “block out, to suppress, or inhibit the potential distraction” (Megherbi et al., 2017, p.657). Therefore, the delay in response to incongruent cards represents the multi-staged cognitive processes.

However, the neuropsychological perspective on the nature of the Stroop effect provides a more detailed explanation of the processes taking place in the human brain when completing the Stroop task. According to Banich (2019), there is a cascade-of-control model that includes four processes behind the Stroop effect. Each of them is processed in separate brain regions and deals with different goals necessary for task completion. Firstly, prefrontal and posterior brain regions come in conflict when processing the information that is either relevant or irrelevant for the task. Secondly, the mid regions of the brain process the working memory to include the information necessary for the task. Thirdly, separate areas of the brain are involved in giving responses in the later stages. Fourthly, “rostral dorsal regions of the anterior cingulate cortex … evaluate the appropriateness of the response selected and send feedback to lateral prefrontal regions to make adjustments in control as needed” (Banich, 2019, p. 2). Thus the inclusion of various loci of the brain to respond to inconsistent stimuli explains the existence of the Stroop effect.

All the above-mentioned theoretical explanations of the Stroop task implications allow for anticipating the results of the current research. Since the experiment will involve three different conditions, including neutral, consistent, and inconsistent, the response time will be different for each of them due to the level of interference between stimuli. The hypothesis for the current research is based on the literature review and helps to assume that the time spent on responding to inconsistent stimuli would be longer than the time spent on responding to consistent stimuli or neutral stimuli. Also, the response time under consistent conditions will be shorter than under neutral one due to the facilitating effect of color-word congruence. It is anticipated that the results of the study will be compatible with those obtained in the classical serial color-word experiment.

Method

Participant

For the experiment held in a digital setting, it is sufficient to engage one participant to investigate the particularities of his or her cognition and attention. The participant in the current study is a healthy 24-year-old student at Athabasca University. The participant is a healthy individual without any physical or mental issues that might affect the results of the procedure. Before the beginning of the task, the student was instructed as per the conditions and rules relevant to the successful completion of the experiment. Also, the individual was informed that no personal information would be disclosed upon the procedure; only the results in the form of response time and errors will be collected. The participant has signed the informed consent form, thus agreeing to cooperate.

Materials

The experiment is conducted digitally with the utilization of electronic cards. Therefore, the materials used for the procedure include a computer and software that presents the experiment. The program contains three types of cards representing each of the three task conditions. The four colors used either as the ink color or as the words naming the colors are red, green, blue, and yellow. The first set of cards is aimed at testing responses in a neutral condition and contains colored letter strings in the form of Xs. The second type of cards includes those measuring interference and consists of the words the meanings of which do not match the ink color in which they are typed. The third set of cards is used to test a facilitating condition and presents the cards with words, meanings, and the ink color of which are consistent. Overall, there are 36 cards of each type, which are displayed twice; ultimately, a participant is asked to respond to 216 cards.

Procedure

The procedure of the experiment is estimated to last for a maximum of thirty minutes. In the beginning, the participant is instructed according to the specifications of the experiment and its features. The informed consent is signed to retrieve the agreement for processing the information collected during the experiment. The task that is necessary to complete during the procedure is to name the color of the letter strings on the screen regardless of the meaning of the words typed in those colors. The colors used for the experiments are limited to four (red, green, blue, and yellow), each attributed to a particular button on the computer keyboard. More specifically, the red color is represented by ‘z’s, the green color is represented by ‘x’s, the blue color is represented by ‘.’, and the yellow color is represented by ‘/’. The symbols synchronized with the colors are displayed at the top of the screen throughout the whole experiment; however, it is advised to mark the respective buttons with colored patches for better recognition.

The participant is explained that it is required to respond to the color of the letters displayed on the screen by pressing a respective button as quickly as possible. Prior to the beginning of the test, a training session is run. Each card is shown on the screen for 1500 milliseconds, the pause between consecutive cards is represented by a white ‘x’s on the black screen and lasts for 500 milliseconds, after which the next card is shown. If the participant does not respond within the designated time or makes a mistake, a short sound is played, and the next card appears on the screen. Each set of cards (two sets containing 36 cards per one of the three conditions) is displayed randomly with pauses between them. The participant is obliged to press any button to start a new set of cards.

Upon the completion of the experiment, the results table is displayed that demonstrates the data retrieved during the procedure. Descriptive data portraying the time spent on each response, the code of the color, the text of a stimulus, and the type of conditions are available to review. Also, the summarized data showing the meantime of delay in response, standards deviation, and the number of trials (indicating errors) is presented. Finally, the group results collected from all participants taking part in the experiment and saved on a server are available for a researcher to compare the results of the participant with the average.

Results

The participant has followed the instructions thoroughly and responded to each card attentively. The color patches were attached to the buttons of the keyboard for convenience. The pauses between different sets of cards were minimal. The summarized data is demonstrated in the form of descriptive statistics in Table 1 and shows the exact results of the task completion under three different conditions. The mean time of response is indicated in milliseconds spent per card. The standard deviation depicts the difference between the longest and the shortest reaction within the specific condition. The number of trials shows if there were errors made during the procedure.

Table 1.
Summarized Data on the Stroop Effect Experiment
Condition	Mean	SD	n
Condition 1 – Neutral	734.03	156.51	72
Condition 2 – Interference	986.63	180.33	70
Condition 3 – Facilitation	675.86	148.54	70
Note. SD=standard deviation, n=number of trials.

As it is seen from the table, the neutral condition required more time to respond than the facilitation condition and let time than the interference condition. The interference condition or the one with the inconsistent representation of words and colors took the longest time of reaction. Finally, the facilitation condition or the one with the consistent representation of colors and words was the easiest task and took the least time to react. The number of errors (two) is insignificant and does not affect the results of the study. Overall, the results retrieved during the experiment on the Stroop effect are consistent with those demonstrating the average summarized data collected from 1476 participants. The group means time in condition 1 is 744.23, 809.65 in condition two, and 679.88 in condition three.

Discussion

The current research hypothesized that the time spent on the responses under an inconsistent condition would be longer than that for responding under neutral or consistent conditions. The hypothesis was proved and showed that the dependent variable (the time of reaction) changed depending on the change in independent variables (colors of the words). The mean time for reacting to the stimuli where words and colors are different is 986.63. The time of reaction on the stimuli where the word meanings and the ink color match is 675.86. Therefore, the reaction to incongruent stimuli is delayed by 68.5 percent in comparison to the reaction to congruent word-color representation. These results match the initial findings made by Stroop (1935). As for the neutral condition where the participant had to name the color of letters X strings, the delay in the reaction was longer than in a facilitating condition.

To explain the Stroop effect identified within the conducted experiment, it is relevant to refer to the theory of automatic reading reaction and the complexity of the brain processes related to selective attention. In accordance with the claims made by Megherbi et al. (2017), reading is an automatic and uncontrolled reaction to words that occurs effortlessly and provokes an immediate reaction. However, the naming of the colors is not an automatic process; it requires a more complex analysis of information than involves blocking the data retrieved upon reading to respond according to the task requirements. Moreover, the fact that the reaction needs to be demonstrated not verbally, but by pressing a respective button, the brain takes time to validate the choice of the button. Therefore, the delay in the reaction under the inconsistent condition represents the Stroop effect. On the contrary, when the word is written in the color it names (for example, when the word ‘red’ is typed in red ink), which complies with the facilitating condition, the reaction is significantly faster since it is based solely on automatic reading.

The results of the experiment are valid and consistent with those obtained within the original study conducted by Stroop (1935). The indicators of reaction time might be used to interpret the individual cognitive characteristics of the participant. Nonetheless, the limitations of the research might include the engagement of only one participant, whose results were compared to those of a group. Also, the possible confusion when pressing a button representing a particular color might have biased the speed of reaction. However, the overall findings prove the validity of the Stroop effect and might be used for further research in cognitive psychology.

References

Banich, M. T. (2019). The Stroop effect occurs at multiple points along a cascade of control: Evidence from cognitive neuroscience approaches. Frontiers in Psychology, 10, 1-12. Web.

MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109, 163-203.

Megherbi, H., Elbro, C., Oakhill, J., Segui, J., & New, B. (2017). The emergence of automaticity in reading: Effects of orthographic depth and word decoding ability on an adjusted Stroop measure. Journal of Experimental Child Psychology, 166, 652-663.

Scarpina, F., & Tagini, S. (2017). The Stroop color and word test. Frontiers in Psychology, 8, 1-8. Web.

Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18, 643-662.

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