Some historical and personal threads




"Distraction during the appearance of the stimulus is always punished with prolongation of the process"—Donders (1868)


The phrase mental chronometry refers to an experimental approach that examines the time required by mental operations to obtain insights into human attention, perception, cognition, and action. "Mental chronometry can be defined as the study of the time course of information processing in the human nervous system" (Posner, 1978, Chronometric Explorations of Mind, p. 7). Common methods are measurements of response time (RT), event-related electrical brain potentials, and eye movements. The measurement of RTs (i.e., the time elapsing between the onset of a stimulus and the onset of a response to that stimulus) began with the work of the Dutchman F.C. Donders in the 1860s. Before that time, mental processes had been thought, following Johannes Müller, to happen too fast to be measurable. The precise measurement of RTs was made possible by a number of inventions in the 1840s, including those of the Englishman Charles Wheatstone and the Swiss watchmaker Mathias Hipp. From the 1870s onwards, Wilhelm Wundt engaged in an elaborate research program that aimed to understand human mental processes by measuring RTs. James McKeen Cattell, a student of Wundt at Leipzig, estimated that about half of the experiments in Wundt's laboratory involved RT measurements. Wundt's laboratory in Leipzig became a model for scientific psychology laboratories throughout the world. Wundt's insistence on precision of measurement has influenced the design of psychological experiments up to the present.

Titchener's Photo Album: Photographs and handwritten descriptions of instruments that were especially made for psychological research (some of the instruments were from Cattell) can be found in an album of photographs of Titchener, also a student of Wundt at Leipzig. Several of the instruments were designed for RT research. From his time in Leipzig onward, Titchener collected trade catalogues, which he bound into over 40 volumes. These catalogues were sold to Rice University soon after Titchener's death in 1927. Unfortunately, the catalogue collection was discarded in the 1970s, but three volumes survived. One of the three surviving volumes was the album of photographs. Titchener put the album together sometime between 1894 and 1899.


The Museum of the history of reaction time research documents many aspects of the history of mental chronometry. It provides many downloadable descriptions and pictures of a wide variety of instruments used by psychologists in the early days of experimental psychology.


The Virtual Laboratory of Max Planck Institute for the History of Science in Berlin is devoted to the history of the experimentation in the life sciences. It provides detailed information on Helmholtz's physiological time experiments on frogs and humans in the 1850s, which inspired F.C. Donders to conduct his seminal RT studies fifteen years later.


In addition to measuring RTs, chronometric research may examine eye movements. Donders was not only the first person to measure naming RTs, but he also developed models for eye movements. Wundt took gazes to be a window into the operation of the attention system. As Wundt (1897) reasoned in his Outlines of Psychology, visual acuity is best at the center of eye fixation (by 5 degrees from the center, acuity has diminished about 50 percent). Therefore, to bring aspects of the visual world in the focus of attention, eye fixations are directed to those visual aspects that are of interest. This makes a shift of gaze between two visual stimuli an overt sign of the orienting of attention, although attention and eye movements can sometimes be dissociated in simple signal detection and identification tasks.


Wundt, W. (1897). Outlines of psychology (C. H. Judd, Trans.). Engelmann. (Original work published 1896)




From the second of the six editions of his Grundzüge der physiologischen Psychologie (Principles of Physiological Psychology) onward, Wundt described a detailed processing model for the attentional control (Apperception) of naming and reading (the first edition of the Grundzüge appeared in 1874, the second in 1880, and the sixth in 1908–1911). Wundt presented his model as an alternative for the models of normal and impaired naming and reading of his contemporaries Wernicke (1874) and Lichtheim (1885) that lack topdown control mechanisms (already in 1880, Wundt applied the model to aphasia and acquired dyslexia, with reference to Kussmaul, 1877).


I have made a possible computational implementation of Wundt’s attentional control model, called Wundt 2.0, and have applied it to the Stroop effect (see below) and its time course. For more information about the Wundt 2.0 model, click on the icon above.

Roelofs, A. (2021). How attention controls naming: Lessons from Wundt 2.0. Journal of Experimental Psychology: General, 150, 1927-1955. Article (PDF 2577K)

Wundt, W. (1904). Principles of physiological psychology (E. B. Titchener, Trans.). Swan Sonnenschein. (Original work published 1902)



F. C. Donders

Franciscus ("Frans") Cornelis Donders was born on May 27, 1818, in Tilburg, North Brabant, the Netherlands (the same area where Vincent van Gogh was born 35 years later). Donders went to seminaries in Tilburg and Boxmeer (some 35 km south of Nijmegen) and to Medical School in Utrecht. The rest of his academic career (from the age of 29 on), he was professor of physiology at the University of Utrecht.



The house in which Donders was born, Nieuwlandstraat 44 in Tilburg. A plate above the door by the Dutch poet Nicolaas Beets says "Op den 27sten van bloeimaand des jaar O.H. MDCCC-XVIII werd Franciscus Cornelis Donders in deze woning geboren" ("On the 27th of the blooming month of the year O.H. MDCCC-XVIII, Franciscus Cornelis Donders was born in this house").




Donders was one of the pioneers of ophthalmology. In 1858, Donders established the first eye hospital in the Netherlands. In 1864, his influential 635-page book On the Anomalies of Accommodation and Refraction of the Eye was published in English. It describes the employment and prescription of corrective glasses.




Donders' ophtalmomicroscope (left), isoscope for the determination of the apparent vertical and horizontal meridians in downward gaze and convergence (middle), and demonstration model for eye movements (right).



Donders' interests included not only ocular physiology, eye movements (he discovered what came to be called the Law of Donders), color vision and color blindness, but also general physiology, evolution, and mental processes. His views are often strikingly modern. For example, he investigated cerebral circulation in 1849, and was excited about the discovery of the metabolism of the brain: "As in all organs, the blood undergoes a change as a consequence of the nurishment of the brain" (Donders, 1868). One "discovers in comparing the incoming and outflowing blood that oxygen has been consumed" (Donders, 1868). This insight, together with a subtractive method designed by Donders, constitutes the basis of two widely used modern functional neuroimaging techniques, PET and fMRI.



Donders was also interested in speech. In 1864, he published an article on his finding that vowels are characterized by their fixed overtones (now called formants), independent of the fundamental tone of the voice (i.e., the fundamental frequency). In his monograph De Physiologie der Spraakklanken, in het Bijzonder van die der Nederlandsche Taal [The Physiology of Speech Sounds, in Particular those of the Dutch Language] (Donders, 1870), he gave a detailed account of the acoustic and phonetic properties of (Dutch) speech sounds and how they are articulated.





Clockwise from above: Donders at the time of his inauguration at Utrecht, one of his mechanical models of eye movements, his lab from the outside, and from the inside. The photograph of the room in Donders' lab was made shortly after his death. In the back corner to the left, there is a kymograph, which Donders used for his phonetic research; a modified version of the kymograph was used in his chronometric work (i.e., to measure speech production latencies).



Donders realized that the mind is not the brain, but what the brain does. As concerns mental phenomena, one should investigate "the relation between these phenomena and the action of the brain", trying "to locate the various mental faculties as much as possible" (Donders, 1868). However, "a complete knowledge of the functioning of the brain, with which each mental process is connected, does not carry us a step further in the understanding of the nature of their relation" (Donders, 1868). Donders lacked the theoretical apparatus to precisely specify mental processes (the computational theory of mind and its modeling tools he would have needed took the full first half of the 20th century to develop), but he discovered another handle on mental processes, the response time: "But will all quantitative treatment of mental processes be out of the question then? By no means! An important factor seemed to be susceptible to measurement: I refer to the time required for simple mental processes" (Donders, 1868).




Instruments designed by F. C. Donders to "determine the duration of actions of the mind" (top figure: the "noematachograph and phonautograph", as he called them) and "to determine the shortest possible time for a simple thought" (bottom left: initial version of the noematachometer, which controlled the presentation of stimuli; middle: the definitive version of the noematachometer; right: its prism at a larger scale).



To measure the speed of mental processes, Donders designed a number of instruments (shown above), some of which were made in a special department of his laboratory by the mechanician Kagenaar (see photo below), a pupil and friend of Donders. The working of the instruments is described in "Twee werktuigen tot bepaling van den tijd, voor psychische processen benoodigd" (Two instruments for determining the time required for mental processes), which appeared in Onderzoekingen gedaan in het Physiologisch Laboratorium Utrecht, 1867-1868, 2, 21-25.

Donders was the first person to measure the time it takes to name stimuli by spoken responses. One way he achieved this was by using the "noematachograph and phonautograph" as follows. Two participants A and B were seated before the mouth of the phonautograph. While the cylinder was rotated, A uttered a syllable and B had to repeat it as quickly as possible without making mistakes. The beginning of the oscillations caused by the two sounds was marked on paper (illustrated below) by points a and b on a line (P). The time interval between the two points was deduced from the oscillations (261 per second) of a tuning-fork recorded simultaneously (S). The RT was found by counting the number of oscillations recorded between a and b, irrespective of their length (i.e., a constant speed of rotation of the cyclinder is not required).

"The idea occurred to me to interpose into the process of physiological time some new components of mental action. If I investigated how much this would lengthen the physiological time, this would, I judged, reveal the time required for the interposed term" (Donders, 1868).

Until Donders' work, it was generally believed that the mental operations involved in responding to a stimulus occurred too fast to be measurable. Donder designed a subtraction technique to measure the duration of the different mental processes that the brain goes through when performing different tasks. Together with his students, Donders conducted experiments using RT tasks in 1865. He used three methods:

Method a: A simple RT. For example, when you hear the syllable ki, you must repeat it by saying "ki".

Method b: A choice RT. For example, you may hear the syllable ki, ka, ko, ke, or ku, and you must produce the corresponding response (e.g, when you hear ka, say "ka").

Method c: A go/no-go RT. For example, you may hear the syllable ki, ka, ko, ke, or ku, and you must only respond to one of the sylables by producing the corresponding response (e.g, when you hear ki, say "ki", but when you hear one of the other syllables, you say nothing).

Donders argued that a simple RT (method a) requires perception and motor stages, a go/no-go RT (method c) requires the same plus a discrimination stage, and a choice RT (method b) requires all these stages plus a choice stage.

The critical observation by Donders was that simple RTs (method a) were shortest, followed by go/no-go RTs (method c), and choice RTs (method b), which were longest. Donders calculated the duration of the discrimination and choice stages by subtraction. The duration of the discrimination stage equals the RT of the go/no-go task (method c) minus the RT of the simple task (method a). The duration of the choice stage equals the RT of the choice task (method b) minus the RT of the go/no-go task (method c). With these subtractions, Donders provided evidence for an important principle: The time it takes to perform a task depends on the number and types of mental stages involved. With this principle, he laid the foundation of a research program that is still extremely productive today: the componential processing analysis of human task performance.







Donders used a large variety of tasks. The stimuli could be spoken syllables (as in the example above), colors, or written syllables, and the responses could be spoken responses (as in the example above) or manual key responses.

In passing, he made a number of other seminal observations. "We made the subjects respond with the right hand to the stimulus on the right side, and with the left hand to the stimulus on the left side. When movement of the right hand was required with stimulation on the left side or the other way around, then the time lapse was longer and errors common" (Donders, 1868).



Donders first reported his findings on a meeting of the Dutch Koninklijke Akademie van Wetenschappen (Royal Netherlands Academy of Sciences), on June 14, 1865, in Amsterdam. The meeting was chaired by Donders himself. He was the chairman of one of the Academy departments for 17 years. A report of the meeting can be found in "Proces Verbaal van de gewone vergadering der Koninlijke Akademie van Wetenschappen. Afdeeling Natuurkunde op saturdag 24 Junij 1865".



Top left: Portrait of Donders painted by his second wife, Bramine Hubrecht, to celebrate his seventieth birthday in 1888, one year before his death (24th March, 1889). Bottom left: Portrait of him in the Senate Chamber of the University of Utrecht; Bottom right: sculpture of Donders by Paul de Swaaf at the Max Planck Institute for Psycholinguistics, Nijmegen.



At the end of his seminal article on the measurement of mental processing times, Donders reports that "distraction during the appearance of the stimulus is always punished with prolongation of the process" (1868). This observation is interesting in the light of later research developments exploiting distraction, in particular, the work of J. Ridley Stroop in the 1930s, described below.



F. C. Donders on a Dutch stamp, 1935, the year in which J. Ridley Stroop published his classic article on color-word interference.




Donders, F. C. (1868). Over de snelheid van psychische processen. Onderzoekingen gedaan in het Physiologisch Laboratorium der Utrechtsche Hoogeschool, 1868-1869, Tweede reeks, II, 92-120.

Donders, F. C. (1868). Die Schnelligkeit psychischer Prozesse. Archiv fuer Anatomie und Physiologie und wissenschaftliche Medizin, 657-681.

Donders, F. C. (1868). La vitesse des actes psychiques. Archives Neerlandaises, III, 269-317.

Donders' seminal report in Dutch, German, and French respectively, has been translated into English and reprinted as "On the speed of mental processes" in the journal Acta Psychologica (1969) and in the volume Attention and Performance II (W. G. Koster, Ed.) in 1969.

Donders performed his first chronometric experiments in 1865 together with Johan Jacob de Jaager, who wrote a dissertation on this work: Jaager, J. J. de. (1865). De physiologische tijd bij psychische processen. Utrecht: P. W. van de Weijer.





A large set of photos of the Donders' physiological laboratory in Utrecht can be found in a photo album that was compiled to celebrate Kagenaar's 40 years of work as laboratory attendent at the physiological lab in 1900: Kagenaar, D. B. (1900). Ter Herinnering van de veertig jarige amtsvervulling van D. B. Kagenaar Sr., 1860-1 Mei-1900 [photo album]. Utrecht. For a description of the lab, see Physiological Laboratory, Utrecht University, 1872.




Painting of Donders in the townhall of Tilburg, his place of birth (left), and his grave in Oud-Zuilen (right). The text on the stone says "F.C. Donders, Hoogleeraar te Utrecht 1848-1888".




A description of the historical context of Donders' work can be found in: Draaisma, D. (2002). The Age of Precision: F. C. Donders and the Measurement of Mind. This essay was written for and published on the occasion of the opening of the F. C. Donders Centre for Cognitive Neuroimaging (now called the Centre for Cognitive Neuroimaging of the Donders Institute for Brain, Cognition and Behaviour) at Radboud University Nijmegen in 2002. The booklet was reprinted when celebrating the 200th anniversary of the birth of Donders in 2018.

A classic on mental chronometry is Posner, M. I. (1978). Chronometric explorations of mind. Hillsdale, New Jersey: Erlbaum.

Another classic (describing Donders' work, problems with it, and the most important subsequent developments on mental chronometry) is Luce, R. D. (1986). Response times: Their role in inferring elementary mental organization. New York: Oxford University Press.



The classic instrument (i.e., the noematachograph and phonautograph) that Donders used to measure, for the first time ever, speech production times was on display in the Anatomical Museum of Radboud University, on temporary loan (from April till June 2018) from the Utrecht University Museum. VOX magazine made a video clip (3 min) on this instrument and the connection with modern neuroimaging, in which I did the explaining. The video also shows how we replicated Donders' classic ki-ki speech repetition experiment, the participants being my daughter Sterre and myself, while I was in the MRI scanner. We used Donders' original stimulus lists.


Click here for the article and video in Vox magazine (in Dutch) and here for the video on Donders' noematachograph and neuroimaging on YouTube (in Dutch, but with English subtitles). Errata for the video: Donders' instrument is called 'noematachograph' (not 'noemotachograph') and the counting of tuning fork waves is done from speech onset of person A to speech onset of person B (and not from offset to onset, as the animation suggests).

Early 2018, I discovered in a handwritten laboratory notebook of Donders (kept in 1865) a full record of all the RT experiments that he had performed in the 1860s. The notebook is in the archives of the University Museum Utrecht (Archive Do 07.77). Donders' notebook not only contains the raw data and laboratory notes of his classic published experiments, but also unpublished raw data of experiments that Donders had conducted together with his daughter Marie, his good friend William Bowman, and a number of students. Moreover, the notebook contains all the original stimulus lists of the famous "ki-ki" experiments.

I decided to replicate the "ki-ki" experiments together with my daughter Sterre using all the original stimulus lists of Donders. A report of the replication can be found in an article that appeared in Acta Psychologica that same year. The replication allowed me to resolve a disagreement between Donders and Wundt on the go/no-go method that Donders had used.

Roelofs, A. (2018). One hundred fifty years after Donders: Insights from unpublished data, a replication, and modeling of his reaction times. Acta Psychologica, 191, 228-233. Article (PDF 666K)






James McKeen Cattell



Inspired by the work by Donders in the 1860s, Wundt engaged in an elaborate research program that aimed to understand human mental processes by measuring RTs. James McKeen Cattell, one of the first PhD students of Wundt at Leipzig and his first student assistant, estimated that about half of the experiments in Wundt's laboratory involved RT measurements. A report on the activities at Wundt's lab in Leipzig during the 1880s by Cattell can be found in

Cattell, J. M. (1888). The psychological laboratory at Leipsic, Mind, 13, 37-51.

The second section of this article by Cattell ("The duration of mental processes") is on the RT measurements in Wundt's lab. Wundt was also a pioneer of psycholinguistics, a topic that takes up the first two books titled Die Sprache of his ten-volume Völkerpsychologie (in which he used tree diagrams for syntax, now widely employed in linguistics). As concerns RTs, Wundt saw all his experiments as studies of volition: acts of will, decision, and choice.

Wundt's influence has been enormous and lasts till today, both in terms of his ideas and his students. Wundt’s 188 doctoral students, Külpe, Cattell, Titchener, and Spearman among them, and their students such as Woodworth and Thorndike, shaped psychological research and theorizing according to his example. Wundt’s descendants not only performed important experimental and theoretical work (Cattell, Titchener, Thorndike), but also initiated clinical psychology (Witmer) and intelligence tests (Cattell, Spearman). Most contemporary psychologist are only a few handshakes away from Wundt. For example, three academic steps or handshakes separate me from Wundt: I was a PhD student of Willem J. M. Levelt (Max Planck Institute for Psycholinguistics), who was a research assistant for Albert E. Michotte van den Berck (Catholic University of Louvain, Belgium), who was a postdoc of Wundt at the University of Leipzig.



Cattell (above) and Wundt surrounded by collaborators and students at Leipzig (below), the site of the first experimental laboratory devoted to psychological research.


Cattell was born in Easton, Pennsylvania, on May 25, 1860. In 1883 he went to Leipzig to become Wundt's assistant. Under Wundt, Cattell became the first American to publish a dissertation in the field of psychology, Psychometric Investigation. After returning from Germany with his PhD, Cattell began a career in America. Cattell died on January 20, 1944.



At Leipzig, Cattell applied chronometric methods to simple psycholinguistic tasks, such as object naming, color naming, and reading. He was the first to report that reading is faster than object and color naming. In 1885, Cattell discovered that the naming of 100 line drawings of objects took about twice as long as naming a list of the corresponding printed object names.




Drawings of the instruments used by Cattell to measure speech production latencies.



In an article published in 1890 in the journal Mind, called Mental tests and measurements, Cattell coined the term "mental test" and he proposed to use color naming RT as one of the tests to measure intelligence. It has now become clear that color naming RT tells little about a person's intelligence, except when RT distributions are examined. In particular, the tail of a distribution may reflect individual differences in intelligence (known as the "worst performance rule"). Cattell is one of the first American psychologists to stress quantification, ranking, and ratings. In later years, Cattell's organization The Psychological Corporation published the Wechsler Intelligence Test. Soon after Cattell developed the first mental tests, another student of Wundt at Leipzig, Charles E. Spearman, would become a leader in the psychometric approach to intelligence by the publication of an article called "General intelligence", objectively determined and measured (1904).



Cattell's laboratory at the University of Pennsylvania showing a Hipp Chronoscope and a gravity chronometer.



Cattell was among the first persons in the world to be officially called "Professor of Psychology", at the University of Pennsylvania (1888-91), where he was appointed soon after he obtained his PhD from Wundt in Leipzig. Cattell was one of the founding members of the American Psychological Association (APA) and he was its fourth President. With James Mark Baldwin, Cattell founded the journal Psychological Review in 1897, and in 1894 he began a journal that has become one of the world's leading science magazines, Science. Cattell was editor and owner of Science for half a century (from 1894 till 1944). He was the first psychologist to be admitted to the National Academy of Sciences (1901).




Cattell, J. M. (1886). The time it takes to see and name objects. Mind, 11, 63-65.

Cattell, J. M. (1886). The time taken up by cerebral operations, Parts 1 & 2. Mind, 11, 220-242.

Cattell, J. M. (1886). The time taken up by cerebral operations, Part 3. Mind, 11, 377-392.

Cattell, J. M. (1887). The time taken up by cerebral operations, Part 4. Mind, 11, 524-538.





J. Ridley Stroop



Cattell's observation of a difference in time for naming colors and reading their names constitutes the starting point for the work of J. Ridley Stroop (1897-1973) in the early 1930s. To examine the ground of this difference, Stroop designed a new chronometric color-word task as part of his dissertation work. This color-word task has become one of the most widely employed tasks in academic and applied psychology. Stroop's 1935 article in the Journal of Experimental Psychology, which first introduced the task and reported the basic finding, is among the most cited publications, if not the most cited one, in the history of experimental psychology. The finding that Stroop reported seems to be discussed in every introductory textbooks and it is known to many nonexperts, bridging the gap between specialist research and something everyone should know. The Stroop task has become one of the "gold standards" of attentional measures.

John Ridley Stroop was born in Hall's Hill, a farming community near Murfreesboro in Rutherford County, Tennessee, USA, in 1897. He earned BA, MA, and PhD degrees from George Peabody College for Teachers in Nashville, Tennessee, between 1924 and 1933 (Peabody College is now part of Vanderbilt University). During most of that time, he taught at Lipscomb, and he returned to teach there from 1936 until his retirement in 1967. While a student, Stroop designed and built a house near the Lipscomb campus. One of his sons, Fred, still lives in this house. Stroop loved to preach every Sunday and taught Bible classes throughout his years at Lipscomb. In fact, he appeared to be more interested in teaching the Bible than in psychology. Stroop died in 1973.



In the basic version of the color-word Stroop task, a speaker is presented with color words written in colored ink. The task is to name the color of the ink and to try to ignore the word. For example, speakers have to say "red" to the red ink of the word green, the incongruent condition, to say "red" to the red ink of the word red, the congruent condition, or to say "red" to the red ink of a series of Xs, the control condition. In another basic version of the task, speakers are asked to read aloud the words and to ignore the ink colors.





J. Ridley Stroop, around the time of his dissertation at George Peabody College, circa 1933.



The original 1935 experiments of Stroop measured the time it takes to complete cards of 10 x 10 stimuli. Presentation of Stroop stimuli on cards is still characteristic of psychometric applications of the task (when it is used as a diagnostic for determining an attention problem). In the original form, speakers are presented with four cards. One card has color words on it printed in black ink, with the words to be read aloud. A second card has color words on it, now each printed in a conflicting ink color, and again the words have to be read aloud. The third card has colored Xs on it and the ink colors have to be named. Finally, the fourth card has color words on it each printed in a conflicting ink color, and again the ink colors have to be named. Note that in Stroop's original study, there was no congruent condition (i.e., there was no card where the ink colors and the color words agreed). The critical measure is the time it takes to complete each card. Using cards with stimuli generally gives the same pattern of results as those obtained from measuring the time to name or read individual Stroop stimuli, which is the standard in modern experimental studies.




J. Ridley Stroop when he was Chair of the Psychology Department of David Lipscomb College in 1948.



Stroop's classic article is: Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology, 18, 643-662. It has been reprinted in 1992 in the Journal of Experimental Psychology: General, 121, 15-23.

A classic review of the Stroop literature, covering over 400 articles, is: MacLeod, C. M. (1991). Half a century of research on the Stroop effect: An integrative review. Psychological Bulletin, 109, 163-203.

The website of the American Psychological Association also contains a brief description of the Stroop task.

Enough read about the task? Test yourself in the following interactive demo!





Interactive demo of the Stroop task


As indicated, the color-word Stroop task has become one of the gold standards of attentional measures. This interactive demo is designed to help you experience the Stroop phenomenon by means of a computerized, scaled-down version of Stroop's original study (i.e., his Experiments 1 and 2; Stroop's Experiment 3 studied the effect of practice, and is not included in the demo). In the two demo experiments, you are presented with cards of 5 x 5 stimuli. Stroop used the colors red, green, blue, brown, purple, and the corresponding color words (he had first considered using yellow instead of brown, but found that yellow did not have sufficient contrast with the white card background). The demo uses the same colors and color words. Stroop presented the stimuli on white cards in 14-point Franklin lower-case type. This is also done in the demo. In the first experiment, you are required to read color words printed in black ink (Card #1) or color words printed in a conflicting ink color (Card #2). For example, to green or green, you should say "green". In the second experiment, you are required to name the ink color of strings of Xs (Card #3) or the ink color of conflicting color words (Card #4). For example, to xxxxx or to green, you should say "red".

As soon as a card of 5 x 5 stimuli appears on your screen, read the words (Cards #1 and #2) or name the ink colors (Cards #3 and #4), aloud or silently, as fast as you can while trying to make no mistakes. The colors are red, green, blue, brown, and purple. When you have finished a card, click immediately on the "Finish" button. The time it took you to name or read all of the items on the card will be shown. If you want to try the same card, click on the "reload" button of your browser (no problem, the Stroop phenomenon persists even after thousands of repetitions). If you want to continue with the experiment, click on "Continue experiment".

Go to the first stimulus card