knowledge of psychology

Stroop Effect


Our knowledge of psychology is continually updated by scientific observations, experiments, and research conducted in the lab and elsewhere. The measurement of reaction time—how long it takes for psychological processes to occur in our brains—has been an important aspect of these inquiries since the emergence of the first laboratories devoted to psychology in the late 1800s.

In this ZAPS lab your reaction times will be measured. In the Experience section you will take a form of the Stroop test—a task designed to measure conflicts between two sensory inputs that is perhaps the mostly widely used and important of all cognitive tests. Cognitive tests examine cognition, which is the mental activity that includes thinking and the understanding gained from thinking, such as memory and intelligence. The Stroop cognitive test is based on the Stroop effect, which you will learn more about after taking the test. But before that, try this quick challenge.

Can you look at the word in the middle of the following screen without thinking about its meaning?


It is impossible, right? No matter how hard you try, you cannot help but process the meaning of familiar words. When you learned how to read as a child, you probably needed to devote a considerable amount of attention to sounding out new words and learning their meanings. But with time and practice, reading became automatic and no longer required conscious attention to perform. Learning to read and understand language is one example of a cognitive function.

How about color? While you might have some recollections of learning how to read, it isn’t likely that you can remember seeing a color without recognizing what it was. For example, when you see the following

you recognize that it is red. How did you know that? Was it through the same process by which you recognized the meaning of the word midterm?

You will find out more about how you are able to recognize word meanings and colors—as well as about how measuring mental reaction time helps us better understand psychological processes—as you move through this lab. Click on the Experience tab (at the top of the page) to proceed to the next section.


In each trial of this ZAPS lab, a single word will appear on the screen. Your task is to indicate as quickly as possible the color of the text used to “print” the word on the screen, by clicking or tapping one of the numbered buttons you’ll see below the word, using the following key:

Button 1BLUE       Button 2RED       Button 3BLACK

For example, if you saw pig, you would click or tap the button labeled “2” as quickly as possible, to indicate that the color of the word is RED.

This won’t be as easy as it sounds. The words you will be identifying the color of will be the names of colors themselves: BLUE, RED, and BLACK. To make the task even harder, the words and the colors will not always match. For example, you might see the word BLACK, in which case you should click or tap the button labeled “1” to indicate that the word appears in blue. Take a moment now to memorize what color each button number refers to, as the buttons will not be labeled during the experimental trials.

Before we begin the actual experiment, let’s try 5 practice trials. For each trial, remember to click or tap one of the buttons to indicate the printed color of the word:

Button 1BLUE       Button 2RED       Button 3BLACK

On each trial, what should you indicate as quickly as possible?

the number of letters in the word your favorite color

the meaning of the word the text color of the word



Okay, we’re ready to begin the experiment. Remember that your task is to identify the text color of the word you see in each trial, ignoring the meaningof the word. Here’s the color key one more time:

Button 1BLUE       Button 2RED       Button 3BLACK

Your responses are being timed, so click or tap a button as quickly as possible in each trial! Trials in which you incorrectly identify the color or have taken more than 4 seconds, will be repeated.


Data Introduction

In Stroop effect experiments, trials where the color named by the word is the same as the color of the text used for the word (e.g., BLUE) are called congruent trials. In contrast, trials where the color named by the word differs from the color of the text (e.g., BLUE) are called incongruent trials.

The key question, is, does it take people longer to respond to incongruent trials than it does to congruent trials? In the graph you will see next, we average all of the different combinations of words and text colors to determine the mean response time for both congruent trials (BLUERED, and BLACK) and incongruent trials (BLUEBLACKRED, etc.).

In the table, we also show error rates for congruent and incongruent trials. To calculate error rate, we divide the number of incorrect trials for a condition by the total number of trials for the condition. For example, if you saw 20 incongruent trials and got two of them incorrect, your error rate would be 2 / 20 = 10%.

Based on your experience in the experiment, do you think your data will show quicker responses to the congruent or the incongruent trials? Why?

You will initially receive full credit for any answer, but your instructor may review your response later.


· Graph

· Table

Raw Data


Congruent trials: words and colors match.

Incongruent trials: words and colors do not match.

The typical result of this Stroop test—as the reference results showed and as you most likely saw in your results in Your Data section of this ZAPS lab—is that reaction times in the incongruent trials are higher than reaction times in the congruent trials. Several theories have been proposed to explain why this Stroop effect occurs.

Most of these theories involve the concept of semantic interference. This basically means being distracted by the meaning of words. Your brain automatically recognizes the meaning of the words you see even when the chief task you are given is to recognize the color of the text of the word. Your mind recognizes the word meaning and the color of the text using different processes. During incongruent trials, processing word meaning conflicts with the color recognition process, causing you to respond more slowly.

Description of image Brain imaging evidence for the Stroop effect

Reaction time is an indirect gauge of how the brain processes information, but because it is easily measured, it is still widely studied. However, researchers are now also able to directly visualize the processing of information by specific parts of the brain through techniques that are collectively called neuroimaging. We now know much more about the Stroop effect and other cognitive functions than we did in the past because of advances in neuroimaging.

Studies using neuroimaging have provided evidence that during a Stroop test the meaning of words is determined in a part of the brain’s temporal lobe called the Wernicke’s area, while the color of the text is, at least initially, processed by the visual areas of the occipital lobe. Studies provide evidence that a third area of the brain, the dorsolateral prefrontal cortex, is crucial in evaluating the two sources of information, ignoring the irrelevant one, and making a decision.

Applications of the Stroop effect

Understanding the Stroop effect should help you understand the broader psychological concept of mental conflict. You are probably familiar with many examples of conflict, such as the conflict between your impulses and your goals. As mentioned earlier in this ZAPS lab, the Stroop effect and Stroop tasks also have many applications in the study and clinical practices of psychology. For example, in one study, research subjects were hypnotized and told that they would be seeing meaningless symbols on a cognitive test. When given a Stroop test, they did not show the typical results and had the same reaction times for congruent and incongruent trials. In this case, the Stroop test was used to verify the effectiveness of hypnosis.

This ZAPS lab was designed to help you better understand not just Stroop, but related topics that you will encounter as you study psychology. These include the measurement of reaction time in psychological studies, how your brain processes information, and how brain imaging has helped us understand the functioning of the brain and has expanded our psychological knowledge.

Suppose we ran another experiment using the same stimuli used here, but flipped the instructions. That is, suppose your task was to identify the meaning of the word and ignore the text color. What would you expect to find when you looked at the response times of such an experiment?

You will initially receive full credit for any answer, but your instructor may review your response later.


Answer the following questions to complete this ZAPS activity. Your performance in this section accounts for 10% of your grade.

Based on the ideas presented in this ZAPS lab, under which of the following conditions do you think participants would be able to most quickly name the color in which the stimuli are written or drawn?

colored words with incongruent color associations (e.g., grassbananasky)

incongruent color words (e.g., blueredgreen)

colored “blobs” (e.g., Blue blobGreen blobRed blob)


Since these shapes do not have established meanings, there should be nothing interfering with the process of naming their colors.

You answered the question correctly on your first attempt, so your grade for the question is 100%.

Imagine you are a web designer working on an interactive website. You need a symbol to indicate to users that they will start a timed task. Based on the ideas presented in this ZAPS lab, which of the following symbols would be most effective for this purpose?

The word GO in a green octagon

 The word GO in a green circle

The word GO in a red circle

The word GO in a red octagon


To most effectively signal users to start a task, congruent colors, words, and shapes should be used. In most of the world, green is used to indicate “GO,” while red is used to indicate “STOP.” The circle is a neutral shape that does not conflict with the concept of “GO,” unlike the octagon, which is also associated with “STOP.”

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