What is the Stroop Effect?
The Stroop effect is the phenomenon where people are asked to read some text and say aloud the colors in which it’s written, and if the text consists of color names like “red” and “green”, people find it very difficult to say the colors of the text rather than reading out the words that are written. Trying to say the names of the colors takes longer and is more prone to errors than reading out the words that are written.
Example of the Stroop Task
Red – Green – Yellow – Blue
In the example above, the task is to read the colors of the text: green, red, blue, yellow. Your brain probably finds it much easier to read the words: red, green, yellow, blue!
The effect was first discovered in Germany in 1929, and was more widely publicized in 1935 by John Ridley Stroop, who wrote the first paper describing the phenomenon in English.
The Stroop effect is an example of the effect of interference on reaction time. Observing and naming colors is a straightforward task which most adults can perform quickly and accurately. However, the task can be interfered with by reading words which refer to conflicting colors.
Semantic Interference and Semantic Facilitation
The Stroop task measures the delay in naming colors while reading names of conflicting colors. This is called semantic interference, because the meaning of the word you’re reading involuntarily comes to mind and interferes with the task of identifying the color you can see.
The delay would be measured relative to a neutral control task where you name the colors of text in which neutral words, unrelated to color, are written, or even where you name the colors of colored squares, with no text.
It is possible to measure the opposite effect, when the words written actually match the colors of the text they’re written in, like this:
Red – Green – Yellow – Blue
In this case, reading the name of the color helps you name it more quickly than if you were looking at a neutral word or a colored square in that color. This is called semantic facilitation, because the meaning of the word you’re reading serves to help you in your task of identifying the color.
Automation of Reading
Reading conflicting words interferes with naming colors (and reading congruent words helps with naming colors) in the Stroop task because reading is automatic: if you read the word “red”, you do not have to make a further conscious effort to think of the color red. The concept automatically and involuntarily comes to mind, and this interferes with the otherwise straightforward task of observing and naming a different color.
Literate people find it difficult to deliberately avoid reading and understanding text that’s in front of them. This is related to the phenomenon of spoiler warnings. In text-based online communities it is considered polite not to give away the ending of a book or movie that people might not have read or seen yet. If you’re going to refer to key plot points, you should post a spoiler warning well in advance, so that people can choose not to read on, or you should obscure the text, by writing it in black on black (so people have to copy and paste it elsewhere if they want to read it) or by encoding it with a simple cipher such as rot13 (a->m, b->n, c->o, etc.). This is because people generally cannot consciously choose to avoid reading text that’s in front of them, even if they don’t want to know what it says.
On a more serious note, it is also related to the phenomenon of trigger warnings, or content warnings. Like spoiler warnings, these warn people about text they may prefer not to read; but in this case, rather than spoiling the end of a movie, the text discusses topics that they are likely to find distressing. The exact nature of the content being warned about will depend on the context; a post in a general-interest community might warn about graphic violence, whereas one in a community for people recovering from alcoholism or eating disorders might warn for posts about drinking or eating. Again, people can wish – even very strongly – not to read text that’s in front of them, but are often unable to avoid doing so. Therefore, content warnings can be helpful, so that if a person feels emotionally unprepared to read the text, they can click away before it appears in their field of vision.
Uses of the Stroop Effect
Because the Stroop task measures processing speed, it is used as an assessment tool to help diagnose brain damage, dementia and problems with executive function. People suffering from these conditions demonstrate more interference in mental processing, which means they show longer reaction times and higher frequencies of errors in the Stroop task.
Variants on the Stroop Task
The Emotional Stroop Task
In the emotional Stroop task, just as in the original task, participants are asked to name the colors in which words are written. In this variant, none of the words are color names, but some of them are emotionally neutral words, such as “table”, and others are emotionally negative words, such as “pain”. People suffering from depression show a greater delay in their reaction times when naming the text color of the negative words than when naming the text color of the neutral words. This suggests they are spending more time processing, and perhaps thinking about, the meaning of the negative words, which interferes with their ability to name the colors.
The Numerical Stroop Task
In this variant, participants are asked which of two numbers is written in a physically larger font size. People answer the question more quickly and accurately if the physical sizes of the digits matches, or is congruent to, the magnitude of the numbers (for example, 5 7), and they are slower and make more errors when the sizes are incongruent, or the wrong way around (for example, 5 7).
This suggests that reading numbers, like reading words, is automatic, and people cannot see numbers without involuntarily getting an idea of their magnitude, which interferes with being asked to judge the physical font size of the digits.