The Stroop Effect: Can Your Brain Glitch?

The Stroop effect is one of the most fascinating discoveries of experimental psychology that uncovers how our brain processes information. Named after psychologist John Ridley Stroop, it reveals how cognitive interferences can make seemingly simple cognitive tasks surprisingly difficult. Don’t take Stroop’s words for it, test it out yourself!

The Stroop test studies how our brain’s automatic cognitive processes interfere with our conscious and intentional cognition. Building on a body of existing research dating back to the nineteenth century, psychologist John Ridley Stroop designed a series of experiments measuring the impact of cognitive interferences on our ability to perform simple cognitive tasks. In 1935, he published the results of three experiments in a paper titled Studies of Interference In Serial Verbal Reactions. The experiments consisted of three different tasks. 

Firstly, participants were asked to read the names of colors written in black ink. Secondly, they were asked to identify the colors of certain shapes. Thirdly, participants were asked to identify the font colors of words denoting different colors. For example, if the word “red” was written in a blue font, the correct answer would be blue, not red. 

While there are numerous variations of the stimuli given in the Stroop test, they can be divided into three main categories: neutral, congruent, and incongruent. Neutral stimuli are when only the text or color needs to be processed to execute the task, such as in the case of the first and second tasks. Congruent stimuli are when the text and the color are the same (e.g. the word “red” written in red font). Incongruent stimuli are when the intelligible meanings of the words conflict with the perceptual colors of the fonts with which they are written, such as in the case of task three. 

What Did Stroop Discover in the Word-Color Test?

In the word-color test, Stroop discovered that semantic interferences delay our cognition of incongruent stimuli. He found that participants took significantly more time to complete tasks involving incongruent stimuli than tasks involving neutral or congruent ones. The cognitive interference was identified as a semantic interference, as our brain processes intelligible meanings faster and more automatically than it recognizes sensory colors. 

Saying the correct answer in cognitive tasks involving incongruent stimuli requires conscious effort to inhibit and override the cognitive interference of our automatic semantic information processing, which results in a momentary glitch and delay in our cognition, known as the Stroop effect. Most interestingly, Stroop discovered that when the words matched the font color (i.e. congruent stimuli), participants were able to name the font color much faster than in the case of neutral or incongruent stimuli. He explained that the increased speed was due to semantic facilitation – our brain’s ability to automatically and effortlessly process intelligible words facilitates the recognition of congruent font colors. 

You can test the Stroop effect yourself by setting a simple cognitive task involving incongruent stimuli. You can replicate a simplified version of Stroop’s study by measuring the difference between the time you take to identify the font colors of words referring to the same color (i.e. congruent stimuli) versus the time you take to identify the font colors of words referring to different colors (i.e. incongruent stimuli). The delay you will experience in performing the second task will give you a first-hand experience of the momentary glitch caused by cognitive semantic interference. You can also try the test online through the numerous versions available. 

Why Is the Stroop Effect Important?

The Stroop effect is important because it reveals how our brain processes information, and assesses our capacity for attention, cognitive control, and processing speed.  The accuracy and speed with which we can perform cognitive tasks involving incongruent stimuli depend on the prowess of our selective attention (i.e. paying attention to the font color and not the word) and our ability to override the initial impulse of the cognitive interference to read the word rather than identify the color. 

The results of the Stroop test hence reveal not only our brain’s information processes, but also our selective attention, executive function, processing speed, and cognitive flexibility. Psychologists have used the test in neurological experiments studying the various brain regions responsible for decision-making and as a clinical test used in assessing various psychological conditions, such as ADHD, schizophrenia, addiction, and depression.