Although it might sound simple, the Stroop effect refers to the delayed reaction times when the color of the word doesn't match the name of the word. It's easier to say the color of a word if it matches the semantic meaning of the word.
Full Answer
Other experimental setups utilize the lessons of the Stroop Effect – that incongruent information will require more mental resources to resolve correctly – with numbers, rather than words.
For students of psychology looking for a relatively easy and interesting experiment to try on their own, replicating the Stroop effect can be a great option. The words themselves interfere with your ability to quickly say the correct color of the word. Two different theories have been proposed to explain this phenomenon: 2
The test is also used in a variety of different ways to the original, in an effort to exploit the experimental setup to reveal more about a clinical population, for example. Even neurodevelopmental disorders such as schizophrenia and autism have been examined with the Stroop test.
An interesting feature with the Numerical Stroop is that the interference is found for both types of incongruence – when the numbers are incongruent with size, then a delay is shown for reporting the size, as well as for reporting the numbers.