|
MENTAL CHRONOMETRY,
ATTENTION, AND LANGUAGE PERFORMANCE some historical
threads
|
|
|
|
"Distraction
during the appearance of the stimulus is always punished with prolongation of
the process" —F.
C. Donders (1868) |
|
The term mental chronometry was coined by
Posner (1978, Chronometric explorations
of mind, Erlbaum, Hillsdale, NJ) to describe an approach to cognitive
psychology 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, p. 7). Common methods
are measurements of response times, event-related electrical brain
potentials, and eye movements. Interest in the measurement of human response
time—the time elapsing between the onset of a stimulus and the onset of a
response to that stimulus—began as a result of the work of the Dutch
physiologist F. C. Donders in the 1860s. Until that time, mental processes
had been thought to be too fast to be measurable. The ability to accurately
measure response times in milliseconds was greatly facilitated by the
invention of a device for measuring the velocity of artillery shells by the
Englishman Charles Wheatstone in 1840. In 1842, the Swiss watchmaker Mathias
Hipp improved on Wheatstone's design and began selling an instrument which
used a tuning fork-like spring which vibrated at 500 Hz to repetitively
engage the teeth of a wheel and thus regulate the speed of revolution of the
wheel (Hipp Chronoscope). In the 1870s, Wilhelm Wundt built an elaborate
laboratory and research program around measuring the time taken by various
mental processes—James McKeen Cattell (1888), a student of Wundt at Leipzig,
estimated that about 50% of the experiments in Wundt's lab involved measuring
response times. Wundt's laboratory in Leipzig became a model for dozens of
scientific psychology laboratories throughout the world. Wundt's insistence
on precision of measurement has continued to influence the design of psychological
experiments to the present.
Titchener's
Photo Album: An album of photographs of Titchener, also a student of
Wundt at Leipzig, contains rare photographs and hand written descriptions
from the earliest days of instruments made especially for psychological
research. Some of the instruments were from Cattell. In Leipzig, Titchener
began to collect trade catalogues relevant to the new, experimental
psychology. He bound these catalogues into over 40 volumes by the time of his
death in 1927. Titchener's library was sold to Rice University in Texas soon
after his death. Unfortunately, during a de-accession sweep of the Rice
University Library in the 1970s, the catalogue collection was discarded. Only
three volumes survived, having been discovered in a trash bin by a member of
the psychology faculty. One of the three surviving bound 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 traces the history of mental chronometry. It is a subdivision of the Cyber-museum of the history of psychological
instrumentation, which includes many
downloadable descriptions and pictures of a wide variety of instruments used
by early psychologists in studying the mind and behavior. The
Virtual
Laboratory of Max Planck Institute for the History of Science in
Berlin is a digitalization project devoted to the history of the
experimentalization of life. It consists of an archive and an essay section.
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 studies in mental
chronometry a decade later. Donders and Wundt (picture
below) were both pioneers of speech and language production research.
Moreover, both studied eye movements. Donders was the first person to measure
vocal naming latencies and he developed a model for eye movements (i.e., a
mechanical model demonstrating what came to be called “Donders’ Law”).
Whereas before those days the eyes used to be poetically called a window to
the soul, 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.
|
|
Franciscus Cornelis Donders was born the
27th May, 1818, in Tilburg, a manufacturing town in North Brabant, the
Netherlands (the same area where Vincent van Gogh was born 35 years later).
He had eight older sisters—to have a son was a long deferred hope of his
parents. Frans 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 next to 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 bloom month of the year O.H.
MDCCC-XVIII, Franciscus Cornelis Donders was born in this house"). |
|
Donders was one of the pioneers of
ophthalmology. His major contributions here were in the areas of refraction
and astigmatism. In 1858 Donders established the first eye hospital in the
Netherlands. In 1864, his influential work, the 635-page book "On the anomalies
of accommodation and refraction of the eye with a preliminary essay on
physiologic dioptrics" was published in English. It describes a complete
doctine, both as to theory and practice, of 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 strikingly modern. For example, he
investigated cerebral circulation, 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". 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 the two most widely used
modern functional neuroimaging techniques, PET and fMRI. Donders published on
natural selection in 1848, some ten years before Charles Darwin published
"The origin of species" (1859). Donders and Darwin were good
friends. Darwin acknowledges in a letter to Donders that "It is clear to
me that you were as near as possible in preceding me on the subject of
Natural Selection" (Darwin, 18th March, 1871). |
|
Donders was also interested in the
mechanisms underlying speech. 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, his mechanical model 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), 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 Onderzoekigen 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 oscillation (261 Hz) of a tuning-fork
recorded simultaneously (S). The latency of the response was found by
counting the number of oscillations recorded between a and b,
irrespective of their length (i.e., a constant speech 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). Donders attempted to describe the
processes going on in the mind by analyzing cognitive activity into separate,
discrete stages. Until Donders' work, many (if not most) scientists had
assumed that the mental operations involved in responding to a stimulus
occurred instantaneously. Donder was particularly interested in "timing
the mind" and designed a subtraction technique to time the different
mental processes that the brain goes through when faced with different tasks
(as mentioned, the subtraction idea forms the basis of much modern functional
brain imaging work). Together with his student De Jaager, Donders performed
experiments using reaction time tasks in the early 1860s. His was the first
attempt to analyze and measure the component processes of a simple task. He
used three methods: (Method a) A simple response time task.
For example, you are seated in front of a panel that contains a light bulb
and a response button. When the light comes on, you must press the button. (Method b) A choice response time task.
For example, you are seated in front of two light bulbs, each with its own
button. You must press the button corresponding to the appropriate light. (Method c) A go/no-go discrimination
response time task. For example, you are seated in front of a panel with two
light bulbs and one response button. When the target light goes on you must
press the button, but not if the other light comes on. Donders then predicted the kinds of
processes that might be involved in each task: 1. A simple response time task requires
perception and motor stages: the time to receive and then execute the
response. 2. A discrimination response time task
requires the above plus a discrimination stage. 3. A choice response time task requires
all of the above: the time to receive and execute the response, and the time
to discriminate plus a choice stage. As expected, Donders observed that simple tasks took the shortest amount of time, followed by discrimination tasks, with choice tasks taking the longest amount of time. Donders calculated the time required for each stage by using a subtraction technique: Perception and motor time = the time required for the simple task. Discrimination time = the time for the discrimination task minus the time for the simple task. Choice time = the time for the choice task minus the discrimination time. He demonstrated a simple principle: The time it takes to perform a task depends on the number and types of mental stages involved. With this observation, he laid the foundation of a research programme 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 colors, written syllables, or spoken syllables, and the
responses could be manual key presses or spoken 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). This S-R compatibility phenomenon was rediscovered a century later. |
|
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 president of the Academy 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, click on it for an interactive video tour through this chamber and
try to spot Donders; 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 für Anatomie und
Physiologie und wissenschaftliche Medizin, 657-681. Donders, F. C. (1868). La vitesse des
actes psychiques. Archives Néerlandaises, 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 seminal chronometric experiments in the early 1860s together
with Johan Jacob de Jaager, who wrote a dissertation on his work in 1865: 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, 1818-1889". |
|
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.
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.
|
|
|
|
As Donders investigated response time,
Wilhelm Wundt, first at Heidelberg and later at Leipzig, began to work toward
the conception of physiological psychology that was to serve as the basis for
his systematic approach to experimentation (by physiological psychology,
Wundt meant experimental psychology—using methods of
physiology). In 1867, in a new quarterly journal of psychiatry founded by Max
Leidesdorf and Theodor Meynert, Wundt published an invited article,
"Neuere Leistungen auf dem Gebiete der physiologischen
Psychologie". Under the banner of physiological psychology, he reviewed
recent literature on visual space perception and the measurement of response
times. A report on the activities at Wundt's lab in Leipzig during the 1880s
by someone who was there, James McKeen 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 response time measurements in Wundt's lab. Wundt was a pioneer of psycholinguistics, a topic that takes up the first two books of his Völkerpsychologie (in which he pioneered tree diagrams for syntax, now widely used in linguistics). Wundt saw all his response time 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 (e.g., I am a ninth generation student of Wundt and an eighth generation student of Külpe—that is, Wundt was the supervisor of Külpe, who was the supervisor of the supervisor of the … supervisor of my supervisor.) |
|
|
|
|
|
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. He grew up the eldest
child of a wealthy and prominent family. His father, William Cassady Cattell,
a Presbyterian minister, became president of Lafayette College in
Pennsylvania shortly after James' birth. William Cattell could easily provide
for his children, as he had married a rich woman, Elizabeth
"Lizzie" McKeen, in 1859. By all accounts, Cattell had a happy
childhood. He entered Lafayette College in 1876 at the age of sixteen, and
graduated in four years with the highest honors. In 1883 the faculty at
Lafayette awarded him a M.A., again with highest honors. Despite his later
renoun as a scientist, he spent most of his time devouring English
literature, although he showed a remarkable gift for mathematics as well.
Cattell did not find his calling until after he arrived in Germany for
graduate studies, where he met Wilhelm Wundt at the University of Leipzig.
Cattell left Germany in 1882 to study at Johns Hopkins University, but
returned to Leipzig the next year as Wundt's assistant. The partnership
between the men proved highly productive, as the two helped to establish the
experimental study of intelligence. Under Wundt, Cattell became the first
American to publish a dissertation in the field of psychology, “Psychometric
Investigation”. After returning from Germany with his Ph.D., Cattell began a
meteoric career in America, with the following highlights: Lecturer in
Psychology, Bryn Mawr, 1887; Professor of Psychology, University of
Pennsylvania, 1888; Department Head of Psychology, Anthropology, and
Philosophy, Columbia University, 1891-1905; President of the American
Psychological Association, 1895. 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 proposed to use color naming as one of the tests for measuring intelligence. We now know that color naming provides little indication of a person's intelligence, except when response time distributions are examined. In particular, characteristics of the tail of a distribution reflect individual differences in intelligence (known as the “worst performance rule”). In his 1890 article, Cattell coined the term "mental test". Cattell became one of the first American psychologists to stress quantification, ranking, and ratings. His work with mental tests appeared to be a good start, but his tests were proven unreliable and later Alfred Binet made much more acceptable tests. 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 bought a failing journal from Alexander
Graham Bell and turned it into 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. |
|
|
|
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 Psychology class 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. A 1921 graduate of David
Lipscomb Junior College, he later earned bachelor's, master's, and doctoral
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, after the school had become
Lipscomb University. While a student, Stroop, whose wife was a niece of David
Lipscomb, designed and built a house near the Lipscomb campus that one of his
sons, Fred Stroop, still lives in. Stroop, who died in 1973, loved to preach
every Sunday and taught Bible classes throughout his years at Lipscomb. In
fact, he was more interested in teaching the Bible than psychology.
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, e.g., ADHD).
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. Colin MacLeod's website has a biography and pictures of J. R. Stroop. 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! |
|
|
|
|
|
|
