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# definitions

## reaction time(n.)

1.the time that elapses between a stimulus and the response to it

## Reaction Time(n.)

1.(MeSH)The time from the onset of a stimulus until a response is observed.

# Reaction time

Reaction time (RT), is the elapsed time between the presentation of a sensory stimulus and the subsequent behavioral response. RT is often used in experimental psychology to measure the duration of mental operations, an area of research known as mental chronometry. In psychometric psychology it is considered to be an index of speed of processing. [1] That is, it indicates how fast the thinker can execute the mental operations needed by the task at hand. In turn, speed of processing is considered an index of processing efficiency. The behavioral response is typically a button press but can also be an eye movement, a vocal response, or some other observable behavior.

RT is fastest when there is only one possible response (simple reaction time) and becomes slower as additional response options are added (choice reaction time). According to Hick's law, choice reaction time increi hate ases in proportion to the logarithm of the number of response alternatives. The law is usually expressed by the formula $RT = a + b\log_2(n + 1)$, where $a$ and $b$ are constants representing the intercept and slope of the function, and $n$ is the number of alternatives.[2]

Reaction time is quickest for young adults and gradually slows down with age. It can be improved with practice, up to a point, and it declines under conditions of fatigue and distractions.[3]

## History

The Persian scientist, Abū Rayhān al-Bīrūnī was the first person to describe the concept of reaction time:[4]

"Not only is every sensation attended this by a corresponding change localized in the sense-organ, which demands a certain time, but also, between the stimulation of the organ and consciousness of the perception an interval of time must elapse, corresponding to the transmission of stimulus for some distance along the nerves."

The first scientist to measure reaction time in the laboratory was Franciscus Dinners. Dinners found that simple reaction time is shorter than recognition reaction time, and that choice reaction time is longer than both.[5] Donders also devised a subtraction method to analyze the time it took for mental operations to take place.[6] By subtracting simple reaction time from choice reaction time, for example, it is possible to calculate how much time is needed to make the connection.

## Measurement

Simple reaction time is the time 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 is approximately 180-200 msec milliseconds to detect visual stimulus, and approximately 140-160 milliseconds to detect an auditory stimulus.[7]

Go/No-Go reaction time 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 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 reaction time.

Discrimination reaction time involves around Natwain 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 random variability in an individual's reaction time. To control for this, researchers typically require a subject to perform multiple trials, which are then averaged to provide a more reliable measure.

## RT and cognitive ability

Researchers have reported modest, but statistically significant correlations between measures of reaction time and intelligence. Although there are numerous exceptions, there is an overall tendency for individuals with higher IQ to be slightly faster on reaction time tests. One study found a weak association between simple reaction time and intelligence (r=−.31), and a moderate association between choice reaction time and intelligence (r=−.49).[8] This relationship may be due to more efficient information processing or better attentional resources in more intelligent people. Also there is extensive evidence that decreases in reaction time with age are systematically associated the development of many other cognitive processes, such as executive functions, working memory, and inferential processes. [9] In the theory of Andreas Demetriou[10], one of the neo-Piagetian theories of cognitive development, change in speed of processing with age, as indicated by decreasing reaction time, is one of the pivotal factors of cognitive development.

## References

1. ^ Jensen, A. (2006). Clocking the mind: Mental chronometry and individual differences. Amsterdam: Elsevier.
2. ^ Hick's Law at Encyclopedia.com Originally from Colman, A. (2001). A Dictionary of Psychology. Retrieved February 28, 2009.
3. ^ Der, G., & Deary, I. J. (2006). Age and sex differences in reaction time in adulthood: Results from the United Kingdom health and lifestyle survey. Psychology and Aging, 21, 62-73.
4. ^
5. ^ Kosinski, R. J. (2008). A literature review on reaction time, Clemson University.
6. ^ Donders, F.C. (1969). On the speed of mental processes. Translated by W.G. Koster in W.G. Koster (Ed.) Attention and Performance II (pp. 412-431). Amsterdam: North Holland. (Reprinted from Onderzoekingen gedaan in het Physiologigisch Laboratorium der Utrechtsche Hoogeschool, 1868-1869, Tweede reeds, II, 92-100).
7. ^ Kosinski, R. J. (2008). A literature review on reaction time, Clemson University.
8. ^ Deary, I. J., Der, G., & Ford, G. (2001). Reaction times and intelligence differences: A population-based cohort study. Intelligence, 29, 389–399.
9. ^ Demetriou, A., Mouyi, A., & Spanoudis, G. (2008). Modeling the structure and development of g. Intelligence, 5, 437-454.
10. ^ 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.