In psychology

Psychology

Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...

, the Stroop effect is a demonstration of the reaction time of a task. When the name of a color (e.g., "blue," "green," or "red") is printed in a color not denoted by the name (e.g., the word "red" printed in blue ink instead of red ink), naming the color of the word takes longer and is more prone to errors than when the color of the ink matches the name of the color. The effect is named after John Ridley Stroop

John Ridley Stroop

John Ridley Stroop was an American psychologist.Stroop was born in Rutherford County, Tennessee, USA. He developed a color-word task in 1935, named after him , to demonstrate interference in attention....

 who first published the effect in English in 1935. The effect had previously been published in Germany in 1929. The original paper has been one of the most cited papers in the history of experimental psychology

Experimental psychology

Experimental psychology is a methodological approach, rather than a subject, and encompasses varied fields within psychology. Experimental psychologists have traditionally conducted research, published articles, and taught classes on neuroscience, developmental psychology, sensation, perception,...

, leading to more than 700 replications. The effect has been used to create a psychological test (Stroop Test) that is widely used in clinical practice and investigation.

Original experiment

The effect is named after John Ridley Stroop

John Ridley Stroop

John Ridley Stroop was an American psychologist.Stroop was born in Rutherford County, Tennessee, USA. He developed a color-word task in 1935, named after him , to demonstrate interference in attention....

, who published the effect in English in 1935 in an article entitled Studies of interference in serial verbal reactions that includes three different experiments. However, the effect was first published in 1929 in German, and its roots can be followed back to works of James McKeen Cattell

James McKeen Cattell

James McKeen Cattell , American psychologist, was the first professor of psychology in the United States at the University of Pennsylvania and long-time editor and publisher of scientific journals and publications, most notably the journal Science...

 and Wilhelm Wundt

Wilhelm Wundt

Wilhelm Maximilian Wundt was a German physician, psychologist, physiologist, philosopher, and professor, known today as one of the founding figures of modern psychology. He is widely regarded as the "father of experimental psychology"...

 in the nineteenth century.

In his experiments, J. R. Stroop administered several variations of the same test for which three different kinds of stimuli were created. In the first one, names of colors appeared in black ink. In the second, names of colors appeared in a different ink than the color named. Finally in the third one, there were squares of a given color.

In the first experiment, 1 and 2 were used. The task required the participants to read the written color names of the words independently of the color of the ink (for example, they would have to read "purple" no matter what the color of its ink was). In the second experiment, stimulus 2 and 3 were used, and participants were required to say the color of the letters independently of the written word with the second kind of stimulus and also name the color of the dot squares. If the word "purple" was written in red, they would have to say "red", but not "purple"; when the squares were shown, the participant would have to say its color. Stroop, in the third experiment, tested his participants at different stages of practice at the tasks and stimulus used in the first and second experiments, to account for the effects of association.

Stroop identified a large increase in the time taken by participants to complete the color reading in the second task compared to the naming of the color of the squares in experiment 2 while this delay did not appear in the first experiment. Such interference was explained by the automation of reading, where the mind automatically determines the semantic meaning of the word (it reads the word "red" and thinks of the color "red"), and then must override this first impression with the identification of the color of the word (the ink is a color other than red), a process that is not automatized.

Unlike researchers performing the Stroop test that is most commonly used in psychological evaluation, J.R Stroop never compares the time used for reading black words and the time needed for naming colors that conflicted with the written word.

Experimental findings

Stimuli in Stroop paradigms can be divided into 3 groups: neutral, congruent and incongruent. Neutral stimuli comprise those in which only the text (similarly to stimuli 1 of Stroop's experiment), or color (similarly to stimuli 3 of Stroop's experiment) are displayed. Congruent stimuli are those in which the ink color and color name refer to the same concept (for example the "red" word written in red). Incongruent stimuli are those in which ink color and concept differ. Three experimental findings are recurrently found in stroop experiments. A first finding is semantic interference, consisting of the fact that naming the ink of neutral stimuli is faster than in incongruent conditions. It is called semantic interference since it is usually accepted that the relationship in meaning between ink color and word is at the origin of the interference. Semantic facilitation defines the finding that naming the ink of congruent stimuli is faster than with neutral stimuli. The third finding is that both semantic interference and facilitation disappear when the task consists in reading the word instead of naming the ink. It has been sometimes called Stroop asyncrony, and has been explained by a reduced automaticitation when naming colors compared to reading.

In the study of interference theory

Interference theory

-History:Bergström, a German psychologist, is credited as conducting the first study regarding interference in 1892. His experiment was similar to the Stroop task and required subjects to sort two decks of card with words into two piles. When the location was changed for the second pile, sorting...

, the most commonly used procedure has been similar to Stroop's second experiment in which subjects are tested on naming colors of incompatible words and of control patches; however the first experiment (reading words in black versus incongruent colors) has received less interest. In both cases, the interference score is expressed as the difference between the times needed to read each of the two types of cards. Usually lists of stimuli are used, but time measures for individual words permit more control on research variables. Rather than naming or reading stimuli aloud, subjects have also been asked to sort stimuli into categories. Different characteristics of the stimulus such as ink colors or direction of words have also been systematically varied. None of all these modifications eliminates the effect of interference.

Modifications

As one of the most referenced papers in experimental psychology, the test has also been further modified to investigate very different phenomena.

The Stroop task has been employed to study frontal function and attention

Attention

Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....

 in brain imaging studies. Speaking is not possible in the scanner because it moves the head, so a number theme is often used instead. For instance, three words may be displayed that read "two" and the participant must press three on their button box. Other examples of derived tasks which show interference effects may include a drawing with an incongruent caption (e.g. a drawing of a bird with the name of another animal as caption, the task being naming the drawing), or the word left in the right of the image (the task being saying where the word is located).

The test has additionally been modified to include other sensory modalities

Modality (semiotics)

In semiotics, a modality is a particular way in which the information is to be encoded for presentation to humans, i.e. to the type of sign and to the status of reality ascribed to or claimed by a sign, text or genre. It is more closely associated with the semiotics of Charles Peirce than Saussure...

 and variables, to study the effect of bilingualism

Multilingualism

Multilingualism is the act of using, or promoting the use of, multiple languages, either by an individual speaker or by a community of speakers. Multilingual speakers outnumber monolingual speakers in the world's population. Multilingualism is becoming a social phenomenon governed by the needs of...

, or to investigate the effect of emotions on interference. A similar effect has also been observed in individuals with grapheme–color synesthesia, people who perceive colors when seeing certain numbers and letters. If a number or letter is presented to such an individual in a color other than what they would perceive, there is a delay in determining what color the character actually is.

In the neo-Piagetian theories of cognitive development

Neo-Piagetian theories of cognitive development

Jean Piaget's theory of cognitive development has been criticized on many grounds. One criticism is concerned with the very nature of development itself. It is suggested that Piaget's theory does not explain why development from stage to stage occurs. The theory is also criticized for ignoring...

, several variations of the Stroop task have been used to study the relations between speed of processing and executive functions

Executive functions

The executive system is a theorized cognitive system in psychology that controls and manages other cognitive processes. It is responsible for processes that are sometimes referred to as the executive function, executive functions, supervisory attentional system, or cognitive control...

 with working memory

Working memory

Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...

 and cognitive development

Cognitive development

Cognitive development is a field of study in neuroscience and psychology focusing on a child's development in terms of information processing, conceptual resources, perceptual skill, language learning, and other aspects of brain development and cognitive psychology compared to an adult's point of...

 in various domains. This research shows that reaction time to Stroop tasks decreases systematically from early childhood through early adulthood. These changes suggest that speed of processing increases with age and that cognitive control becomes increasingly efficient. Moreover, this research strongly suggests that changes in these processes with age are very closely associated with development in working memory and various aspects of thought.

Stroop test

The Stroop effect has been used to investigate the psychological capacities of a person since its discovery during the twentieth century it has became a popular neuropsychological test

Neuropsychological test

Neuropsychological tests are specifically designed tasks used to measure a psychological function known to be linked to a particular brain structure or pathway. Tests are used for research into brain function and in a clinical setting for the diagnosis of deficits. They usually involve the...

.

There are different test variants commonly used in clinical settings

Clinical neuropsychology

Clinical neuropsychology is a sub-field of psychology concerned with the cognitive function of individuals with neurological and psychiatric disorders. Neuropsychological assessment examines cognitive function in the broadest sense, including the behavioural, emotional, social and functional status...

, with differences between them in the number of subtasks, type and number of stimulus, times for the task, or scoring procedures. Regarding the number of subtasks, all versions have at least two: there are written color names differing from the ink used and in the first trial the participant has to say the written word and the ink in the second. However, there can be up to four different subtasks adding in some cases stimulus consisting of groups of letters "X" or dots printed in a given color with the participant having to say the color of the ink, or names of colors printed in black ink that have to be read. The number of stimuli varies between less than twenty items to more than 150, being closely related to the scoring system used. While in some variants the score is the number of items from a subtask read in a given time, in others it is the time that it took to complete each of the trials. The number of errors and different derived punctuations are also taken into account in some versions.

This test is considered to measure selective attention

Attention

Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....

, cognitive flexibility and processing speed, and it is used as a tool in the evaluation of executive functions

Executive functions

The executive system is a theorized cognitive system in psychology that controls and manages other cognitive processes. It is responsible for processes that are sometimes referred to as the executive function, executive functions, supervisory attentional system, or cognitive control...

. An increased interference effect is found in disorders such as brain damage

Brain damage

"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...

, dementia

Dementia

Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...

s and other neurodegenerative diseases, attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder

Attention deficit hyperactivity disorder is a developmental disorder. It is primarily characterized by "the co-existence of attentional problems and hyperactivity, with each behavior occurring infrequently alone" and symptoms starting before seven years of age.ADHD is the most commonly studied and...

, or a variety of mental disorders such as schizophrenia

Schizophrenia

Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...

, addictions

Substance dependence

The section about substance dependence in the Diagnostic and Statistical Manual of Mental Disorders does not use the word addiction at all. It explains:...

, and depression.

Anatomical basis

EEG

EEG

EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...

 and functional neuroimaging

Functional neuroimaging

Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions...

 studies of the Stroop effect have consistently revealed activation in the frontal lobe

Frontal lobe

The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...

 and more specifically in the anterior cingulate cortex

Cingulate cortex

The cingulate cortex is a part of the brain situated in the medial aspect of the cortex. It includes the cortex of the cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the cingulate sulcus...

 and dorsolateral prefrontal cortex

Dorsolateral prefrontal cortex

The dorsolateral prefrontal cortex , according to a more restricted definition, is roughly equivalent to Brodmann areas 9 and 46. According to a broader definition DL-PFC consists of the lateral portions of Brodmann areas 9 – 12, of areas 45, 46, and the superior part of area 47. These regions...

, two structures hypothesized to be responsible for conflict monitoring and resolution. Accordingly patients with frontal lesions

Acquired brain injury

An acquired brain injury is brain damage caused by events after birth, rather than as part of a genetic or congenital disorder such as fetal alcohol syndrome, perinatal illness or perinatal hypoxia. ABI can result in cognitive, physical, emotional, or behavioural impairments that lead to permanent...

 obtain lower punctuations in the Stroop test when compared to those with more posterior lesions. However, these frontal regions are not the only ones implicated in the effect. Stroop performance has also been associated with the correct functioning of the hippocampus

Hippocampus

The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

 or posterior brain areas.

Popular culture

The Brain Age: Train Your Brain in Minutes a Day!

Brain Age: Train Your Brain in Minutes a Day!

Brain Age: Train Your Brain in Minutes a Day!, also known as Dr. Kawashima's Brain Training: How Old Is Your Brain? in PAL regions, is an entertainment video game that employs puzzles. It was developed and published by the video gaming company Nintendo for the Nintendo DS handheld video game console...

software program, produced by Ryūta Kawashima

Ryuta Kawashima

is a Japanese neuroscientist known in PAL regions for his appearance in the Brain Training series of video games for the Nintendo DS -Biography:Kawashima was born...

 for the Nintendo DS

Nintendo DS

The is a portable game console produced by Nintendo, first released on November 21, 2004. A distinctive feature of the system is the presence of two separate LCD screens, the lower of which is a touchscreen, encompassed within a clamshell design, similar to the Game Boy Advance SP...

 portable video game system, contains an automated Stroop Test administrator module, translated into game form. A Nova

NOVA (TV series)

Nova is a popular science television series from the U.S. produced by WGBH Boston. It can be seen on the Public Broadcasting Service in the United States, and in more than 100 other countries...

episode used the Stroop Effect to illustrate the subtle changes of the mental flexibility of Mount Everest

Mount Everest

Mount Everest is the world's highest mountain, with a peak at above sea level. It is located in the Mahalangur section of the Himalayas. The international boundary runs across the precise summit point...

climbers in relation to altitude.

External links

• Video of Stroop Effect: Try Yourself
• A flash implementation