The Stroop effect is an increase in reaction time for a given task, when the brain simultaneously deals with conflicting information. The Stroop test, in which subjects need to name the color of the ink of the given word regardless of the word’s actual meaning, studies this phenomenon.
According to PBS, the phenomenon was named after psychologist Ridley Stroop, who investigated it in the 1930s. According to his findings, word processing is much faster and harder to suppress than color processing; words written in a conflicting color to their meaning, such as "red" written in blue ink, cause delays and errors in the response.
For the correct response, the brain needs to inhibit the stronger word-recognition process with selective attention. The test produces results associated with the subject's mental vitality and flexibility, making it a widely used diagnostic tool; errors in recognizing the colors are associated with impulsivity and insufficient inhibition in the prefrontal cortex, common in patients with ADHD and other dopamine-dependent disorders.