The Stroop effect is a simple phenomenon that reveals a lot about how the how the brain processes information. First described in the 1930s by psychologist John Ridley Stroop, the Stroop effect is our tendency to experience difficulty naming a physical color when it is used to spell the name of a different color. This simple finding plays a huge role in psychological research and clinical psychology.
The Original Stroop Experiments
In Stroop’s original study, he used three elements: names of colors printed in black ink, names of colors printed in different ink than the color named, and squares of each given color. He then conducted his experiment in two parts:
- In his first experiment, he asked participants to simply read the color printed in black ink. He then asked them to read the words printed, regardless of the color they were printed in.
- For his second experiment, he asked participants to name the ink color instead of the word written. For example, “red” might have been printed in green and participants were asked to identify the color green instead of reading the word “red.” In this segment, participants were also asked to identify the color of the squares.
Stroop found that subjects took longer to complete the task of naming the ink colors of words in experiment two than they took to identify the color of the squares. Subjects also took significantly longer to identify ink colors in experiment two than they had to simply read the printed word in experiment one. He identified this effect as an interference causing a delay in identifying a color when it is incongruent with the word printed.
The Stroop Test
The discovery of the Stroop effect led to the development of the Stroop test. According to an article in Frontiers in Psychology, the Stroop test is used in both experimental and clinical psychology to “assess the ability to inhibit cognitive interference that occurs when processing of a specific stimulus feature impedes the simultaneous processing of a second stimulus attribute.”
In short, the Stroop test, a simplified version of the original experiment, presents incongruent information to subjects by having the color of a word differ from the word printed. The Stroop test can be used to measure a person’s selective attention capacity and skills, processing speed, and alongside other tests to evaluate overall executive processing abilities.
Explanations for the Stroop Effect
A few theories have emerged about why the Stroop effect exists, though there is not widespread agreement about the cause of the phenomenon. Some reasons proposed for the Stroop effect include:
- Selective Attention Theory: According to the second edition of the “Handbook of Psychology,” selective attention chooses “which information will be granted access to further processing and awareness and which will be ignored.” In relation to the Stroop effect, identifying the color of the words takes more attention than simply reading the text. Therefore, this theory suggests that our brains process the written information instead of the colors themselves.
- Automaticity Theory: Our two types of cognitive processing include automatic and controlled thinking. In relation to the Stroop effect, the brain likely reads the word because reading is more of an automated process than recognizing colors.
- Speed of Processing Theory: Simply stated, this theory for the cause of the Stroop effect posits we can process written words faster than we can process colors. Thus, it is difficult to identify the color once we’ve already read the word.
- Parallel Distributed Processing: This theory suggests the brain creates different pathways for different tasks. Therefore, it’s the strength of the pathway that plays an important role in which is easier to name, the color or the text.
Psychologists continue to research the Stroop effect to find the underlying cause for the phenomenon, although many factors have been identified that affect results. For example, some variations in the severity of the Stroop effect are found in women and men. Stroop himself first noted that women experience shorter interruptions than men. Studies have also typically found that older people show longer delays than younger people.
The Impact of the Stroop Effect
It may seem as though the Stroop effect is just a fascinating experiment with no real effect on human psychology. In truth, it illustrates a lot about the way we process information and helps us assess our ability to override our instinctual fast thinking. A study published in the Psychological Review stated, “The effects observed in the Stroop task provide a clear illustration of people’s capacity for selective attention and the ability of some stimuli to escape attentional control.”
The Journal of Experimental Psychology reported that Stroop’s article introducing this phenomenon was among the most cited of the articles they’ve published in their first 100 years. In 2002 as part of its centennial issue, it stated “More than 700 studies have sought to explain some nuance of the Stroop effect; thousands of others have been directly or indirectly influenced by Stroop’s article.”
While the Stroop test is interesting, it also has incredible uses in the world of psychology and the study of the brain. According to a study published on the National Center for Biotechnology Information, the Stroop test is valuable when assessing interference control and task-set coordinating in adults with ADHD. Also, a study published in 1976 found that it was 88.9 percent accurate in distinguishing between clients who had suffered brain damage and those who had not. Later studies confirmed these findings, and the Stroop test is often used to assess selective attention in traumatic brain injury patients.
Multiple studies, including the original experiments by Stroop, suggest that practice can decrease Stroop inference. This has implications for our learning skills, ability to multitask, and how we form habits. Psychologist and economist, Daniel Kahneman explored this concept in his book “Thinking, Fast and Slow.” Our fast thinking, what he refers to as System 1, is our initial, automatic reaction to things we encounter.
Kahneman wrote, “When System 1 runs into difficulty, it calls on System 2 to support more detailed and specific processing that may solve the problem of the moment.” When it comes to the Stroop effect, System 1 (our automatic, fast thinking) seeks to find the quickest pattern available. Kahneman believes by understanding how our brains make connections, we can overcome them to reach more logical conclusions by calling on System 2, our controlled thinking, quicker.
Exploring the Stroop effect continues to play a role in studies and experiments involving automatic and controlled thinking, selective attention, our cognitive processing, and more. Even though the Stroop effect has never been definitively explained, it provides a tried and true benchmark for psychologists and scientists that has been referred to for many years.
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