The Stroop effect has been used toinvestigatea person's psychological capacities; since its discoveryduring thetwentieth century, it has become a popularneuropsychologicaltest.
There are different test variants commonly used inclinicalsettings, with differences between them in the number ofsubtasks,type and number of stimulus, times for the task, orscoringprocedures. All versions have at least two numbers ofsubtasks. Inthe first trial, the written color name differs fromthe color inkit is printed in, and the participant must say thewritten word. Inthe second trial, the participant must name the inkcolor instead.However, there can be up to four different subtasks,adding in somecases stimuli consisting of groups of letters "X" ordots printedin a given color with the participant having to say thecolor ofthe ink; or names of colors printed in black ink that haveto beread. The number of stimuli varies between less than twentyitemsto more than 150, being closely related to the scoring systemused.While in some test variants the score is the number of itemsfrom asubtask read in a given time, in others it is the time thatit tookto complete each of the trials. The number of errors anddifferentderived punctuations are also taken into account insomeversions.
This test is considered to measure selective attention,cognitiveflexibility and processing speed, and it is used as a toolin theevaluation of executive functions. An increased interferenceeffectis found in disorders such as brain damage, dementias andotherneurodegenerative diseases, attention-deficithyperactivitydisorder, or a variety of mental disorders such asschizophrenia,addictions, and depression.