Seeing Science: Exploring Perception with the Stroop Effect

Summary

Key Concepts

Psychology, reading, colors, perception, reaction time

Credits

Teisha Rowland, PhD, Science Buddies

The words 'Blue,' 'Green,' and 'Brown' each written each written twice on individual index cards, with one of each pair written in a non-matching color.

Introduction

Have you ever tried to pat your head with one hand while you rub your stomach with the other? This science activity is kind of like doing that, but it can actually give you some insight into how your mind works. The challenge of this activity is to name colors. It sounds simple enough, right? If you think it does, you should see what happens when words of colors get in the way! This is a fun activity to try out with family and/or friends while spending time together over the holidays.

This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Background

This activity is an attempt to unravel the workings of thought processes that involve attention, perception, reading and naming. How does it work? It is an investigation into a phenomenon known as the Stroop effect. In 1935, this phenomenon was first described in a now-famous experimental psychology paper by John Ridley Stroop. The Stroop effect uses words printed in different colors of ink (such as red, green or blue) and shows how when those printed words are also the words of colors, it can affect how quickly a person is able name the color of the ink. For example, if the word “red” is printed in yellow ink it will take a different amount of time for a person to name the color of the ink than if the word “red” is printed in red ink. What is the difference exactly in the time that it takes to say the ink color? Try this activity with some friends and/or family to find out!

Materials

Ten index cards that are each three inches by five inches. Alternatively, you could use fewer or more cards that are larger or smaller in size, respectively.
Scissors
Ruler (optional)
Colored markers of five different colors. The colors should be distinctly different, such as green, brown, blue, red and yellow.
Timer or stopwatch
At least three volunteers

Preparation

Hold an index card vertically and then cut across it (twice) to make three smaller cards, each about three inches by 1.6 inches. Do this to all ten index cards so you have created a total of 30 smaller cards.
On 15 of the small cards, use a colored marker to write the name the marker’s color on the card. For example, you could use a green marker to write the word “green” on one of the cards. Use all five different color markers, and use each marker on three cards. (This means that if you have a green marker, three cards should have the word “green” written on them using the green marker, and if you have a brown marker, three cards would have the word “brown” written on them using the brown marker, and so on.)
On the remaining 15 small cards, use the same colored markers but this time write a color name that is not the same as the marker’s color. For example, you could use the green marker to write the word “blue” on one of the cards. Again, use all five different color markers, and use each marker on three cards.
Keep the two sets of cards separated.

Instructions

Get your first volunteer and explain to them what they are supposed to do in this test. Tell them that they will be given a set of cards where each card contains a word written in colored ink and that the task is to call out the ink color of each word as quickly as possible without making a mistake.
When you are both ready, give one of the sets of small cards to the volunteer and time how long it takes the volunteer to name the colors in the card set. How long did it take the volunteer to get through the set?
Next, give the volunteer the other set of small cards and again time how long it takes the volunteer to name the colors in this card set. How long did it take the volunteer to get through the other set?
Repeat this process with your other volunteers. For each volunteer, switch which set you start them with.
Overall, which set did volunteers take the longest amount of time to get through, the set where the words on the cards matched the colors they’re written in, or the set where the words and ink color don’t match? Why do you think this is?

Extra: You could try this activity again but this time use cards with words written on them in matching ink compared to cards with color words written on them all in black ink. Do you find a difference in how easily people can read the color words based on the whether they’re written in matching ink or only black ink?

Extra: Repeat this activity but this time have people look at so that the words are upside-down. Is there still a Stroop effect when the cards are used upside-down?

Extra: Another way to investigate the Stroop effect would be to test it on some youngsters who know their colors but don’t yet know how to read. What do you find when testing the Stroop effect with this specific group?

Observations and Results

Did you find that people could more quickly go through the set of cards with the words written in matching ink compared to words that were written in a different colored ink?

The Stroop effect shows that when a color word is printed in the same color as the word, people can name the color of the ink used more quickly compared to when a color word is printed with an ink color that is different from the word. (For example, when blue ink is used to write the word “blue,” the ink color is named more quickly than when blue ink is used to write the word “green.”) This is what you should have also seen when doing this activity. For example, you may have seen that it took volunteers around 13-17 seconds to get through the matching set of cards, but around 20-25 seconds to get through the non-matching set.

One explanation for the Stroop effect is called interference. From the earliest years of school, reading is a task that people practice every day. We become so good at it that we read words automatically. When we are asked to name the color of the word instead of reading the word, somehow the automatic reading of the word interferes with naming the color of the word. This interference effect provides scientists with a measurable means to investigate how the brain works.