Mental chronometry

Mental chronometry is the study of reaction time (RT; also referred to as "response time") in perceptual-motor tasks to infer the content, duration, and temporal sequencing of mental operations. Mental chronometry is one of the core methodological paradigms of human experimental and cognitive psychology, but is also commonly analyzed in psychophysiology, cognitive neuroscience, and behavioral neuroscience to help elucidate the biological mechanisms underlying perception, attention, and decision-making across species.

Mental chronometry uses measurements of elapsed time between sensory stimulus onsets and subsequent behavioral responses. It is considered an index of processing speed and efficiency indicating how fast an individual can execute task-relevant mental operations.[1] Behavioral responses are typically button presses, but eye movements, vocal responses, and other observable behaviors can be used. RT is constrained by the speed of signal transmission in white matter as well as the processing efficiency of neocortical gray matter.[2] Conclusions about information processing drawn from RT are often made with consideration of task experimental design, limitations in measurement technology, and mathematical modeling.[3]


RT is the time that elapses between a person being presented with a stimulus and the person initiating a motor response to the stimulus. It is usually on the order of 200 ms. The processes that occur during this brief time enable the brain to perceive the surrounding environment, identify an object of interest, decide an action in response to the object, and issue a motor command to execute the movement. These processes span the domains of perception and movement, and involve perceptual decision making and motor planning.[4]

There are several commonly used paradigms for measuring RT:

  • Simple RT is the motion required for an observer to respond to the presence of a stimulus. For example, a subject might be asked to press a button as soon as a light or sound appears. Mean RT for college-age individuals is about 160 milliseconds to detect an auditory stimulus, and approximately 190 milliseconds to detect visual stimulus.[5][6] The mean RTs for sprinters at the Beijing Olympics were 166 ms for males and 189 ms for females, but in one out of 1,000 starts they can achieve 109 ms and 121 ms, respectively.[7] This study also concluded that longer female RTs can be an artifact of the measurement method used, suggesting that the starting block sensor system might overlook a female false-start due to insufficient pressure on the pads. The authors suggested compensating for this threshold would improve false-start detection accuracy with female runners.
  • Recognition or go/no-go RT tasks require that the subject press a button when one stimulus type appears and withhold a response when another stimulus type appears. For example, the subject may have to press the button when a green light appears and not respond when a blue light appears.
  • Choice reaction time (CRT) tasks require distinct responses for each possible class of stimulus. For example, the subject might be asked to press one button if a red light appears and a different button if a yellow light appears. The Jensen box is an example of an instrument designed to measure choice RT.
  • Discrimination RT involves comparing pairs of simultaneously presented visual displays and then pressing one of two buttons according to which display appears brighter, longer, heavier, or greater in magnitude on some dimension of interest.

Due to momentary attentional lapses, there is a considerable amount of variability in an individual's response time, which does not tend to follow a normal (Gaussian) distribution. To control for this, researchers typically require a subject to perform multiple trials, from which a measure of the 'typical' or baseline response time can be calculated. Taking the mean of the raw response time is rarely an effective method of characterizing the typical response time, and alternative approaches (such as modeling the entire response time distribution) are often more appropriate.[8]

Evolution of methodology

Car rigged with two pistols to measure a Bureau motorist’s reaction time in applying his brakes
Car rigged with two pistols to measure a driver's reaction time. The pistols fire when the brake pedal is depressed

Galton and differential psychology

Sir Francis Galton is typically credited as the founder of differential psychology, which seeks to determine and explain the mental differences between individuals. He was the first to use rigorous RT tests with the express intention of determining averages and ranges of individual differences in mental and behavioral traits in humans. Galton hypothesized that differences in intelligence would be reflected in variation of sensory discrimination and speed of response to stimuli, and he built various machines to test different measures of this, including RT to visual and auditory stimuli. His tests involved a selection of over 10,000 men, women and children from the London public.[1]

Donders' experiment

The first scientist to measure RT in the laboratory was Franciscus Donders (1869). Donders found that simple RT is shorter than recognition RT, and that choice RT is longer than both.[5]

Donders also devised a subtraction method to analyze the time it took for mental operations to take place.[9] By subtracting simple RT from choice RT, for example, it is possible to calculate how much time is needed to make the connection.

This method provides a way to investigate the cognitive processes underlying simple perceptual-motor tasks, and formed the basis of subsequent developments.[9]

Although Donders' work paved the way for future research in mental chronometry tests, it was not without its drawbacks. His insertion method, often referred to as "pure insertion", was based on the assumption that inserting a particular complicating requirement into an RT paradigm would not affect the other components of the test. This assumption—that the incremental effect on RT was strictly additive—was not able to hold up to later experimental tests, which showed that the insertions were able to interact with other portions of the RT paradigm. Despite this, Donders' theories are still of interest and his ideas are still used in certain areas of psychology, which now have the statistical tools to use them more accurately.[1]

Hick's law

W. E. Hick (1952) devised a CRT experiment which presented a series of nine tests in which there are n equally possible choices. The experiment measured the subject's RT based on the number of possible choices during any given trial. Hick showed that the individual's RT increased by a constant amount as a function of available choices, or the "uncertainty" involved in which reaction stimulus would appear next. Uncertainty is measured in "bits", which are defined as the quantity of information that reduces uncertainty by half in information theory. In Hick's experiment, the RT is found to be a function of the binary logarithm of the number of available choices (n). This phenomenon is called "Hick's law" and is said to be a measure of the "rate of gain of information". The law is usually expressed by the formula , where and are constants representing the intercept and slope of the function, and is the number of alternatives.[10] The Jensen Box is a more recent application of Hick's law.[1] Hick's law has interesting modern applications in marketing, where restaurant menus and web interfaces (among other things) take advantage of its principles in striving to achieve speed and ease of use for the consumer.[11]

Sternberg's memory-scanning task

Saul Sternberg (1966) devised an experiment wherein subjects were told to remember a set of unique digits in short-term memory. Subjects were then given a probe stimulus in the form of a digit from 0–9. The subject then answered as quickly as possible whether the probe was in the previous set of digits or not. The size of the initial set of digits determined the RT of the subject. The idea is that as the size of the set of digits increases the number of processes that need to be completed before a decision can be made increases as well. So if the subject has 4 items in short-term memory (STM), then after encoding the information from the probe stimulus the subject needs to compare the probe to each of the 4 items in memory and then make a decision. If there were only 2 items in the initial set of digits, then only 2 processes would be needed. The data from this study found that for each additional item added to the set of digits, about 38 milliseconds were added to the response time of the subject. This supported the idea that a subject did a serial exhaustive search through memory rather than a serial self-terminating search.[12] Sternberg (1969) developed a much-improved method for dividing RT into successive or serial stages, called the additive factor method.[13]

Shepard and Metzler's mental rotation task

Shepard and Metzler (1971) presented a pair of three-dimensional shapes that were identical or mirror-image versions of one another. RT to determine whether they were identical or not was a linear function of the angular difference between their orientation, whether in the picture plane or in depth. They concluded that the observers performed a constant-rate mental rotation to align the two objects so they could be compared.[14] Cooper and Shepard (1973) presented a letter or digit that was either normal or mirror-reversed, and presented either upright or at angles of rotation in units of 60 degrees. The subject had to identify whether the stimulus was normal or mirror-reversed. Response time increased roughly linearly as the orientation of the letter deviated from upright (0 degrees) to inverted (180 degrees), and then decreases again until it reaches 360 degrees. The authors concluded that the subjects mentally rotate the image the shortest distance to upright, and then judge whether it is normal or mirror-reversed.[15]

Sentence-picture verification

Mental chronometry has been used in identifying some of the processes associated with understanding a sentence. This type of research typically revolves around the differences in processing 4 types of sentences: true affirmative (TA), false affirmative (FA), false negative (FN), and true negative (TN). A picture can be presented with an associated sentence that falls into one of these 4 categories. The subject then decides if the sentence matches the picture or does not. The type of sentence determines how many processes need to be performed before a decision can be made. According to the data from Clark and Chase (1972) and Just and Carpenter (1971), the TA sentences are the simplest and take the least time, than FA, FN, and TN sentences.[16][17]

Models of memory

Hierarchical network models of memory were largely discarded due to some findings related to mental chronometry. The TLC model proposed by Collins and Quillian (1969) had a hierarchical structure indicating that recall speed in memory should be based on the number of levels in memory traversed in order to find the necessary information. But the experimental results did not agree. For example, a subject will reliably answer that a robin is a bird more quickly than he will answer that an ostrich is a bird despite these questions accessing the same two levels in memory. This led to the development of spreading activation models of memory (e.g., Collins & Loftus, 1975), wherein links in memory are not organized hierarchically but by importance instead.[18][19]

Posner's letter matching studies

Michael Posner (1978) used a series of letter-matching studies to measure the mental processing time of several tasks associated with recognition of a pair of letters. The simplest task was the physical match task, in which subjects were shown a pair of letters and had to identify whether the two letters were physically identical or not. The next task was the name match task where subjects had to identify whether two letters had the same name. The task involving the most cognitive processes was the rule match task in which subjects had to determine whether the two letters presented both were vowels or not vowels.

The physical match task was the most simple; subjects had to encode the letters, compare them to each other, and make a decision. When doing the name match task subjects were forced to add a cognitive step before making a decision: they had to search memory for the names of the letters, and then compare those before deciding. In the rule based task they had to also categorize the letters as either vowels or consonants before making their choice. The time taken to perform the rule match task was longer than the name match task which was longer than the physical match task. Using the subtraction method experimenters were able to determine the approximate amount of time that it took for subjects to perform each of the cognitive processes associated with each of these tasks.[20]

Cognitive development

There is extensive recent research using mental chronometry for the study of cognitive development. Specifically, various measures of speed of processing were used to examine changes in the speed of information processing as a function of age. Kail (1991) showed that speed of processing increases exponentially from early childhood to early adulthood.[21] Studies of RTs in young children of various ages are consistent with common observations of children engaged in activities not typically associated with chronometry.[1] This includes speed of counting, reaching for things, repeating words, and other developing vocal and motor skills that develop quickly in growing children.[22] Once reaching early maturity, there is then a long period of stability until speed of processing begins declining from middle age to senility (Salthouse, 2000).[23] In fact, cognitive slowing is considered a good index of broader changes in the functioning of the brain and intelligence. Demetriou and colleagues, using various methods of measuring speed of processing, showed that it is closely associated with changes in working memory and thought (Demetriou, Mouyi, & Spanoudis, 2009). These relations are extensively discussed in the neo-Piagetian theories of cognitive development.[24]

During senescence, RT deteriorates (as does fluid intelligence), and this deterioration is systematically associated with changes in many other cognitive processes, such as executive functions, working memory, and inferential processes.[24] In the theory of Andreas Demetriou,[25] one of the neo-Piagetian theories of cognitive development, change in speed of processing with age, as indicated by decreasing RT, is one of the pivotal factors of cognitive development.

Cognitive ability

Researchers have reported medium-sized correlations between RT and measures of intelligence: There is thus a tendency for individuals with higher IQ to be faster on RT tests.[26]

Research into this link between mental speed and general intelligence (perhaps first proposed by Charles Spearman) was re-popularised by Arthur Jensen, and the "Choice reaction Apparatus" associated with his name became a common standard tool in RT-IQ research.

The strength of the RT-IQ association is a subject of research. Several studies have reported association between simple RT and intelligence of around (r=−.31), with a tendency for larger associations between choice RT and intelligence (r=−.49).[27] Much of the theoretical interest in RT was driven by Hick's Law, relating the slope of RT increases to the complexity of decision required (measured in units of uncertainty popularized by Claude Shannon as the basis of information theory). This promised to link intelligence directly to the resolution of information even in very basic information tasks. There is some support for a link between the slope of the RT curve and intelligence, as long as reaction time is tightly controlled.[28]

Standard deviations of RTs have been found to be more strongly correlated with measures of general intelligence (g) than mean RTs. The RTs of low-g individuals are more spread-out than those of high-g individuals.[29]

The cause of the relationship is unclear. It may reflect more efficient information processing, better attentional control, or the integrity of neuronal processes.

Application in biological psychology/cognitive neuroscience

Regions of the Brain Involved in a Number Comparison Task Derived from EEG and fMRI Studies. The regions represented correspond to those showing effects of notation used for the numbers (pink and hatched), distance from the test number (orange), choice of hand (red), and errors (purple). Picture from the article: 'Timing the Brain: Mental Chronometry as a Tool in Neuroscience'.

With the advent of the functional neuroimaging techniques of PET and fMRI, psychologists started to modify their mental chronometry paradigms for functional imaging (Posner, 2005). Although psycho(physio)logists have been using electroencephalographic measurements for decades, the images obtained with PET have attracted great interest from other branches of neuroscience, popularizing mental chronometry among a wider range of scientists in recent years. The way that mental chronometry is utilized is by performing RT based tasks which show through neuroimaging the parts of the brain which are involved in the cognitive process.[30]

With the invention of functional magnetic resonance imaging (fMRI), techniques were used to measure activity through electrical event-related potentials in a study when subjects were asked to identify if a digit that was presented was above or below five. According to Sternberg's additive theory, each of the stages involved in performing this task includes: encoding, comparing against the stored representation for five, selecting a response, and then checking for error in the response.[31] The fMRI image presents the specific locations where these stages are occurring in the brain while performing this simple mental chronometry task.

In the 1980s, neuroimaging experiments allowed researchers to detect the activity in localized brain areas by injecting radionuclides and using positron emission tomography (PET) to detect them. Also, fMRI was used which have detected the precise brain areas that are active during mental chronometry tasks. Many studies have shown that there is a small number of brain areas which are widely spread out which are involved in performing these cognitive tasks.

Current medical reviews indicate that signaling through the dopamine pathways originating in the ventral tegmental area is strongly positively correlated with improved (shortened) RT;[32] e.g., dopaminergic pharmaceuticals like amphetamine have been shown to expedite responses during interval timing, while dopamine antagonists (specifically, for D2-type receptors) produce the opposite effect.[32] Similarly, age-related loss of dopamine from the striatum, as measured by SPECT imaging of the dopamine transporter, strongly correlates with slowed RT.[33]

See also


  1. ^ a b c d e Jensen, A. R. (2006). Clocking the mind: Mental chronometry and individual differences. Amsterdam: Elsevier. (ISBN 978-0-08-044939-5)
  2. ^ Kuang, S. (2017). "Is reaction time an index of white matter connectivity during training?". Cognitive Neuroscience. 8: 126–128. doi:10.1080/17588928.2016.1205575.
  3. ^ Luce, R.D. (1986). Response times: Their role in inferring elementary mental organization. New York: Oxford University Press. ISBN 0-19-503642-5.
  4. ^ Wong, Aaron L.; Haith, Adrian M.; Krakauer, John W. (August 2015). "Motor Planning". The Neuroscientist: A Review Journal Bringing Neurobiology, Neurology and Psychiatry. 21 (4): 385–398. doi:10.1177/1073858414541484. ISSN 1089-4098. PMID 24981338.
  5. ^ a b Kosinski, R. J. (2008). A literature review on reaction time, Clemson University. Archived 11 June 2010 at the Wayback Machine
  6. ^ Taoka, George T. (March 1989). "Brake Reaction Times of Unalerted Drivers" (PDF). ITE Journal. 59 (3): 19–21.
  7. ^ Lipps, D.B.; Galecki, A.T.; Ashton-Miller, J.A. "On the Implications of a Sex Difference in the Reaction Times of Sprinters at the Beijing Olympics". PLoS ONE. 6 (10): e26141. Bibcode:2011PLoSO...626141L. doi:10.1371/journal.pone.0026141. PMC 3198384. PMID 22039438. open access
  8. ^ [1] Whelan, R. (2008). Effective analysis of reaction time data. The Psychological Record, 58, 475–482.
  9. ^ a b Donders, F.C. (1869). On the speed of mental processes. In W. G. Koster (Ed.), Attention and Performance II. Acta Psychologica, 30, 412–431. (Original work published in 1868.)
  10. ^ Hick's Law at Originally from Colman, A. (2001). A Dictionary of Psychology. Retrieved 28 February 2009.
  11. ^ W. Lidwell, K. Holden and J. Butler: Universal. Principles of Design. Rockport, Gloucester, MA, 2003.
  12. ^ Sternberg, S. (1966). "High speed scanning in human memory". Science. 153 (3736): 652–654. Bibcode:1966Sci...153..652S. doi:10.1126/science.153.3736.652. PMID 5939936.
  13. ^ Sternberg, S. (1969). "The discovery of processing stages: Extensions of Donders' method". Acta Psychologica. 30: 276–315. doi:10.1016/0001-6918(69)90055-9.
  14. ^ Shepard, R.N.; Metzler, J. (1971). "Mental rotation of three-dimensional objects". Science. 171 (3972): 701–703. Bibcode:1971Sci...171..701S. doi:10.1126/science.171.3972.701. PMID 5540314.
  15. ^ Cooper, L. A., & Shepard, R. N. (1973). Chronometric studies of the rotation of mental images. New York: Academic Press.
  16. ^ Clark, H. H.; Chase, W. G. (1972). "On the process of comparing sentences against pictures". Cognitive Psychology. 3 (3): 472–517. doi:10.1016/0010-0285(72)90019-9.
  17. ^ Just, M. A.; Carpenter, P. A. (1971). "Comprehension of negation with quantification". Journal of Verbal Learning and Verbal Behavior. 10 (3): 244–253. doi:10.1016/S0022-5371(71)80051-8.
  18. ^ Collins, A. M.; Loftus, E. F. (1975). "A spreading activation theory of semantic processing". Psychological Review. 82 (6): 407–428. doi:10.1037/0033-295X.82.6.407.
  19. ^ Collins, A. M.; Quillian, M. R. (1969). "Retrieval time from semantic memory". Journal of Verbal Learning and Verbal Behavior. 8 (2): 240–247. doi:10.1016/S0022-5371(69)80069-1.
  20. ^ Posner, M. I. (1978). Chronometric explorations of mind. Hillsdale, NJ: Erlbaum, 1978.
  21. ^ Kail, R. (1991). "Developmental functions for speed of processing during childhood and adolescence". Psychological Bulletin. 109 (3): 490–501. doi:10.1037/0033-2909.109.3.490. PMID 2062981.
  22. ^ Case, Robbie (1985). Intellectual development: birth to adulthood. Boston: Academic Press. ISBN 0-12-162880-9.
  23. ^ Salthouse, T. A. (2000). "Aging and measures of processing speed". Biological Psychology. 54 (1–3): 35–54. doi:10.1016/S0301-0511(00)00052-1. PMID 11035219.
  24. ^ a b Demetriou, A.; Mouyi, A.; Spanoudis, G. (2008). "Modeling the structure and development of g". Intelligence. 36 (5): 437–454. doi:10.1016/j.intell.2007.10.002.
  25. ^ Demetriou, A., Mouyi, A., & Spanoudis, G. (2010). The development of mental processing. Nesselroade, J. R. (2010). Methods in the study of life-span human development: Issues and answers. In W. F. Overton (Ed.), Biology, cognition and methods across the life-span. Volume 1 of the Handbook of life-span development (pp. 36–55), Editor-in-chief: R. M. Lerner. Hoboken, NJ: Wiley.
  26. ^ Sheppard, Leah D.; Vernon, Philip A. (February 2008). "Intelligence and speed of information-processing: A review of 50 years of research". Personality and Individual Differences. 44 (3): 535–551. doi:10.1016/j.paid.2007.09.015. ISSN 0191-8869.
  27. ^ Deary, I. J.; Der, G.; Ford, G. (2001). "Reaction times and intelligence differences: A population-based cohort study". Intelligence. 29 (5): 389–399. doi:10.1016/S0160-2896(01)00062-9.
  28. ^ Bates, T. C.; Stough, C. (1998). "Improved Reaction Time Method, Information Processing Speed, and Intelligence". Intelligence. 26 (1): 53–62. doi:10.1016/S0160-2896(99)80052-X.
  29. ^ van Ravenzwaaij, Don; Brown, Scott; Wagenmakers, Eric-Jan (2011). "An integrated perspective on the relation between response speed and intelligence" (PDF). Cognition. 119 (3): 381–93. doi:10.1016/j.cognition.2011.02.002. PMID 21420077.
  30. ^ Posner, Michael I. (2005). "Timing the Brain: Mental Chronometry as a Tool in Neuroscience". PLoS Biology. 3 (2): e51. doi:10.1371/journal.pbio.0030051. PMC 548951. PMID 15719059. open access
  31. ^ Sternberg, S. (1975). "Memory scanning: New findings and current controversies". Quarterly Journal of Experimental Psychology. 27: 1–32. doi:10.1080/14640747508400459.
  32. ^ a b Parker KL, Lamichhane D, Caetano MS, Narayanan NS (October 2013). "Executive dysfunction in Parkinson's disease and timing deficits". Front. Integr. Neurosci. 7: 75. doi:10.3389/fnint.2013.00075. PMC 3813949. PMID 24198770. The neurotransmitter dopamine is released from projections originating in the midbrain. Manipulations of dopaminergic signaling profoundly influence interval timing, leading to the hypothesis that dopamine influences internal pacemaker, or "clock," activity (Maricq and Church, 1983; Buhusi and Meck, 2005, 2009; Lake and Meck, 2013). For instance, amphetamine, which increases concentrations of dopamine at the synaptic cleft (Maricq and Church, 1983; Zetterström et al., 1983) advances the start of responding during interval timing (Taylor et al., 2007), whereas antagonists of D2 type dopamine receptors typically slow timing (Drew et al., 2003; Lake and Meck, 2013). ... Depletion of dopamine in healthy volunteers impairs timing (Coull et al., 2012), while amphetamine releases synaptic dopamine and speeds up timing (Taylor et al., 2007).
  33. ^ van Dyck, Christopher H.; et al. (2008). "Striatal dopamine transporters correlate with simple reaction time in elderly subjects". Neurobiol Aging. 29 (8): 1237–46. doi:10.1016/j.neurobiolaging.2007.02.012. PMC 3523216. PMID 17363113.

Further reading

External links

Arthur Jensen

Arthur Robert Jensen (August 24, 1923 – October 22, 2012) was an American psychologist and author. He was a professor of educational psychology at the University of California, Berkeley. Jensen was known for his work in psychometrics and differential psychology, the study of how and why individuals differ behaviorally from one another.

He was a major proponent of the hereditarian position in the nature and nurture debate, the position that genetics play a significant role in behavioral traits, such as intelligence and personality. He was the author of over 400 scientific papers published in refereed journals and sat on the editorial boards of the scientific journals Intelligence and Personality and Individual Differences.Jensen was controversial, largely for his conclusions regarding the causes of race-based differences in intelligence.


An astrarium, also called a planetarium, is the mechanical representation of the cyclic nature of astronomical objects in one timepiece. It is an astronomical clock.

BPL (time service)

BPL is the call sign of the official long-wave time signal service of the People's Republic of China, operated by the Chinese Academy of Sciences, broadcasting on 100 kHz from CAS's National Time Service Center in Pucheng County, Shaanxi at 34°56′54″N 109°32′34″E, roughly 70 km northeast of Lintong, along with NTSC's short-wave time signal BPM on 2.5, 5.0, 10.0, and 15.0 MHz.

BPL broadcasts LORAN-C compatible format signal from 5:30 to 13:30 UTC, using an 800 kW transmitter covering a radius up to 3000 km.


Chronometry (from Greek χρόνος chronos, "time" and μέτρον metron, "measure") is the science of the measurement of time, or timekeeping. Chronometry applies to electronic devices, while horology refers to mechanical devices.

It should not to be confused with chronology, the science of locating events in time, which often relies upon it.

Clock position

A clock position is the relative direction of an object described using the analogy of a 12-hour clock to describe angles and directions. One imagines a clock face lying either upright or flat in front of oneself, and identifies the twelve hour markings with the directions in which they point.

Using this analogy, 12 o'clock means ahead or above, 3 o'clock means to the right, 6 o'clock means behind or below, and 9 o'clock means to the left. The other eight hours refer to directions that are not directly in line with the four cardinal directions.

In aviation, a clock position refers to a horizontal direction; it may be supplemented with the word high or low to describe the vertical direction which is pointed towards your feet. 6 o'clock high means behind and above the horizon, while 12 o'clock low means ahead and below the horizon.

Common year

A common year is a calendar year with 365 days, as distinguished from a leap year, which has 366. More generally, a common year is one without intercalation. The Gregorian calendar, (like the earlier Julian calendar), employs both common years and leap years to keep the calendar aligned with the tropical year, which does not contain an exact number of days.

The common year of 365 days has 52 weeks and one day, hence a common year always begins and ends on the same day of the week (for example, January 1 and December 31 fell on a Sunday in 2017) and the year following a common year will start on the subsequent day of the week. In common years, February has four weeks, so March will begin on the same day of the week. November will also begin on this day.

In the Gregorian calendar, 303 of every 400 years are common years. By comparison, in the Julian calendar, 300 out of every 400 years are common years, and in the Revised Julian calendar (used by Greece) 682 out of every 900 years are common years.

Elementary cognitive task

An elementary cognitive task (ECT) is any of a range of basic tasks which require only a small number of mental processes and which have easily specified correct outcomes. Although ECTs may be cognitively simple there is evidence that performance on such tasks correlates well with other measures of general intelligence such as Raven's Progressive Matrices. For example, corrected for attenuation (random measurement error), the correlation between IQ test scores and inspection time (how long the subject needs to discriminate between 2 stimuli at a specified level of accuracy) is about 0.5. It has been found that when a battery of ECTs is factor analyzed, the general factor that emerges from this is strongly correlated with general intelligence extracted from traditional IQ batteries, and relates similarly to other variables.Arthur Jensen invented a simple measurement tool for easily collecting reaction time data, subsequently called a Jensen box. Using this, he restarted research on the link between general intelligence and ECTs in the 1970s which had previously been considered a dead end. This earlier conclusion was based on research conducted around 1901-1911 by Clark Wissler with methodology considered very problematic by today's standards. Today, mental chronometry is a significant research topic with about 3800 papers published per year in the period 2005-2015.The term was proposed by John Bissell Carroll in 1980, who posited that all test performance could be analyzed and broken down to building blocks called ECTs. Test batteries such as Microtox were developed based on this theory and have shown utility in the evaluation of test subjects under the influence of carbon monoxide or alcohol.


Endurantism or endurance theory is a philosophical theory of persistence and identity. According to the endurantist view, material objects are persisting three-dimensional individuals wholly present at every moment of their existence, which goes with an A-theory of time. This conception of an individual as always present is opposed to perdurantism or four dimensionalism, which maintains that an object is a series of temporal parts or stages, requiring a B-theory of time. The use of "endure" and "perdure" to distinguish two ways in which an object can be thought to persist can be traced to David Lewis.


HD2IOA is the callsign of a time signal radio station operated by the Navy of Ecuador. The station is located at Guayaquil, Ecuador and transmits in the HF band on 3.81 and 7.6 MHz.The transmission is in AM mode with only the lower sideband (part of the time H3E and the rest H2B/H2D) and consists of 780 Hz tone pulses repeated every ten seconds and voice announcements in Spanish.

While sometimes this station is described as defunct, reception reports of this station on 3.81 MHz appear regularly at the Utility DX Forum.

Hexadecimal time

Hexadecimal time is the representation of the time of day as a hexadecimal number in the interval [0,1).

The day is divided into 1016 (1610) hexadecimal hours, each hour into 10016 (25610) hexadecimal minutes, and each minute into 1016 (1610) hexadecimal seconds.

Intercalation (timekeeping)

Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months.


The minute is a unit of time or angle. As a unit of time, the minute is most of times equal to ​1⁄60 (the first sexagesimal fraction) of an hour, or 60 seconds. In the UTC time standard, a minute on rare occasions has 61 seconds, a consequence of leap seconds (there is a provision to insert a negative leap second, which would result in a 59-second minute, but this has never happened in more than 40 years under this system). As a unit of angle, the minute of arc is equal to ​1⁄60 of a degree, or 60 seconds (of arc). Although not an SI unit for either time or angle, the minute is accepted for use with SI units for both. The SI symbols for minute or minutes are min for time measurement, and the prime symbol after a number, e.g. 5′, for angle measurement. The prime is also sometimes used informally to denote minutes of time.


OLB5 was the callsign of a Czech time signal radio station. The station was located at Poděbrady and transmitted time signals which originated from the OMA (time signal) clock at Liblice.

The station transmitted in the HF band, on 3.17 MHz with 1 kW.

OMA (time signal)

OMA was the callsign of a Czech time signal station. The station was operated by the Astronomical Institute of Prague and the transmitters were located at RKS Liblice 1.

The station transmitted in the LF band on 50 kHz with a power of 7 kW and in the HF band on 2500 kHz with 1 kW. A reserve LF transmitter was located at Poděbrady.

OMA, which could be also used for synchronizing radio controlled clocks, was shut down in 1995.

Tempus fugit

Tempus fugit is a Latin phrase, usually translated into English as "time flies". The expression comes from line 284 of book 3 of Virgil's Georgics, where it appears as fugit inreparabile tempus: "it escapes, irretrievable time". The phrase is used in both its Latin and English forms as a proverb that "time's a-wasting". Tempus fugit, however, is typically employed as an admonition against sloth and procrastination (cf. carpe diem) rather than a motto in favor of licentiousness (cf. "gather ye rosebuds while ye may"); the English form is often merely descriptive: "time flies like the wind", "time flies when you're having fun".

The phrase's full appearance in the Georgics is:

The phrase is a common motto, particularly on sundials and clocks.

Term (time)

A term is a period of duration, time or occurrence, in relation to an event. To differentiate an interval or duration, common phrases are used to distinguish the observance of length are near-term or short-term, medium-term or mid-term and long-term.

It is also used as part of a calendar year, especially one of the three parts of an academic term and working year in the United Kingdom: Michaelmas term, Hilary term / Lent term or Trinity term / Easter term, the equivalent to the American semester. In America there is a midterm election held in the middle of the four-year presidential term, there are also academic midterm exams.

In economics, it is the period required for economic agents to reallocate resources, and generally reestablish equilibrium. The actual length of this period, usually numbered in years or decades, varies widely depending on circumstantial context. During the long term, all factors are variable.

In finance or financial operations of borrowing and investing, what is considered long-term is usually above 3 years, with medium-term usually between 1 and 3 years and short-term usually under 1 year. It is also used in some countries to indicate a fixed term investment such as a term deposit.

In law, the term of a contract is the duration for which it is to remain in effect (not to be confused with the meaning of "term" that denotes any provision of a contract). A fixed-term contract is one concluded for a pre-defined time, although it may also include provision for it to be extended. A contractor required to deliver against a term contract is often referred to as a "term contractor".

Tomorrow (time)

Tomorrow is a temporal construct of the relative future; literally of the day after the current day (today), or figuratively of future periods or times. Tomorrow is usually considered just beyond the present and counter to yesterday. It is important in time perception because it is the first direction the arrow of time takes humans on Earth.


YVTO is the callsign of the official time signal from the Juan Manuel Cagigal Naval Observatory in Caracas, Venezuela. The content of YVTO's signal, which is a continuous 1 kW amplitude modulated carrier wave at 5.000 MHz, is much simpler than that broadcast by some of the other time signal stations around the world, such as WWV.

The methods of time transmission from YVTO are very limited. The broadcast employs no form of digital time code. The time of day is given in Venezuelan Standard Time (VET), and is only sent using Spanish language voice announcements. YVTO also transmits 100 ms-long beeps of 1000 Hz every second, except for thirty seconds past the minute. The top of the minute is marked by a 0.5 second 800 Hz tone.The station previously broadcast on 6,100 MHz but appears to have changed to the current frequency by 1990.

Yesterday (time)

Yesterday is a temporal construct of the relative past; literally of the day before the current day (today), or figuratively of earlier periods or times, often but not always within living memory.

Key concepts
Measurement and
  • Religion
  • Mythology
Philosophy of time
Human experience
and use of time
Time in
Related topics
International standards
Obsolete standards
Time in physics
Archaeology and geology
Astronomical chronology
Other units of time
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