reaction time

Your hand accidentally touches the hot plate of an oven and is withdrawn immediately. A young child runs out in front of your car and you hammer on the brakes. A lottery ball falls into its position upside down and you have to shout out the correct number as fast as you can to a colleague who is checking off the numbers for your syndicate. All three examples of reaction time are the time it takes to make a movement in response to a sensory stimulus. However, even if we try to respond as fast as possible in each situation, the reaction time is quite different.

In this context, time is measured in milliseconds (ms) — thousandths of a second. It may take only 100 ms to withdraw our hand from the stove, 200 ms to stamp on the brakes, and 500 ms to read out the number on the ball. The difference occurs because of the different amount of time it takes for the central nervous system (CNS) to process the sensory signals and to choose the appropriate course of action.

The quickest reaction times have the simplest neuronal circuitry. Tap the knee and the leg moves. This is the tendon jerk beloved of clinical neurologists. The tap excites receptors in the quadriceps muscle at the front of the thigh and these send signals back to the lumbar part of the spinal cord. There, a direct connection is made to the motor neurons that innervate the quadriceps muscle and cause it to contract, making the leg kick forwards. It takes a total of about 30 ms for this to happen. The receptors take 1-2 ms to respond, and another 1-2 ms is needed for the connections to operate in the spinal cord. The remaining 27 ms or so is taken up with the time it takes nerve impulses to travel from muscle to spine and back again. There is of course a price to pay for such a fast circuit. The circuit is so simple that the same thing happens every time the tendon is tapped; it is impossible to control what happens no matter how hard we try. Because of this we refer to this type of reaction as a reflex, and the time it takes as the reflex response time. In electronic jargon we can imagine that it is a hard-wired input-output circuit.

There are rather few examples where the circuit is so simple. The corneal reflex, which causes an eye blink when a speck of dust hits the cornea, is one of the few other familiar examples. Most other very rapid reactions turn out to be more complex. Withdrawal of a hand from a hot cooker is certainly automatic, but can, with great effort of will, be controlled. The neural circuit is more complex than that for the tendon jerk, and this gives it more adaptability at the expense of a longer response time. However, like the tendon jerk, this is a circuit that is innate, and ready for action from the moment we are born.

More complex reactions, like hitting the brakes to stop a car in an emergency, are neither innate nor hard-wired. After all, a person who had never been in a car before would have no idea how to stop the vehicle. They are learned responses that can be selected with remarkable speed in the correct conditions. In the simplest situation we may be asked to press a button as soon as possible after a light is illuminated. There is no ready-made circuit to do the job. Instead, the motor system prepares in advance the instructions for the response (move the arm), and all our attention is concentrated on the light. As soon as a change in illumination is detected, the instructions for movement are released and the button is pressed. In this situation the CNS narrows down the total possible number of movement options and sensory events to just one of each, and links them together with high security. Of the millions of possible connections between sensation and movement, one is highlighted by the preparation to respond in a particular manner. In the case of driving a car, there may be several circuits that have a particularly high probability of being called into action. One of them may link the operation to press the brakes hard with the unexpected arrival of an object in the path of the vehicle. Such very fast responses are sometimes referred to as voluntary, to indicate the necessary involvement of volition in preparing to respond in a particular way to what may well be an arbitrary event. The term ‘voluntary’, however, does not mean that we need consciously identify the sensory signal before issuing the instructions to move. Drivers will often volunteer that they pressed the brakes before knowing what it was that was in front of the car. They may well say that it was a ‘reflex’ response, presumably indicating that conscious appreciation of the action occurred only after the event.

There are some responses that require much more careful evaluation of the sensory input before an appropriate movement can be selected. These have longer reaction times, since the circuits cannot be prepared in advance with any certainty. Calling out upside-down numbers on lottery balls is probably in this category. First of all the visual field must be rotated mentally by 180 degrees, and even then, fifty possible responses are available, perhaps narrowed down to 10 if the colour of the ball is known. All of this takes the CNS a good deal of processing, and by the time the response (vocalization of the number) is selected, the sensory impression has probably reached consciousness.

In summary, reaction times span a spectrum of response types. At one end are very fast, predefined neural circuits such as the tendon jerk and the withdrawal reflex that always operate, but which can be modulated, depending on how complex their connections are, by volitional control. At the other end, sensations must first be evaluated and then assigned the correct motor response, which prolongs the response time by a factor of ten or more. In the middle, situations occur in which the CNS can accurately predict what to do when a certain simple sensation is received. In these circumstances, sensory and motor circuits are selected in advance and joined with high probability so that processing time is reduced to an absolute minimum.

— J. C. Rothwell

See also reflexes.

The delay between the presentation of a stimulus (e.g. the sound of a starting pistol) and the initiation of a response. The delay is due to all the events which have to take place before a person is able to respond. Information in the form of nerve impulses has to travel from the sense organ along nerves to the central nervous system (i.e. the brain or spinal cord) where it is processed. Then a message has to be conveyed to the muscles before they respond. It takes about 14-16 hundredths of a second to respond to an acoustic stimulus (excluding the time it takes for the sound to reach the ear), and 16-18 hundredths of a second to respond to optical stimuli. Reaction times can be improved by training, but even well-trained, elite sprinters cannot respond physiologically in less than 10 hundredths of a second without anticipating the signal; in electronically-timed competitions, any starts quicker than this are regarded as false starts.

You may assess the speed of your reactions by doing the ruler drop test (sometimes called the stick test).▪ Get a partner to hold the top of a metre rule with the thumb and index finger. The rule should be held upright between your thumb and fingers, but you must not touch the rule. Your thumb and fingers should be around the 50 cm mark. When your partner drops the rule catch it as quickly as possible between your thumb and fingers. Repeat three times and calculate the average distance the rule dropped before you caught it.Rating: <8 cm, excellent; 8-12 cm, good; 13-20 cm, fair; >20 cm, poor.

The time between any kind of change and the response it elicits in a system.

1. The time interval from presentation of a stimulus to the initiation of the response. Reaction time is a simple measure to make. It is used extensively in the chronometric approach to information-processing to study the different stages of the processing. Reaction time is the sum of all the event-durations that occur between the presentation of a stimulus and the evocation of a response. It depends on the length of the neural path between the receptor organ (e.g. eye or ear) and the responding muscles (e.g. in the leg of runner) together with delays incurred when the information is processed centrally. Reaction times of 14-16-hundredths of a second for acoustic stimuli and 16-18-hundredths of a second for optical stimuli are generally regarded as good.

2. A skill-orientated ability underlying tasks for which there is one stimulus and one response, and for which the subject must react as quickly as possible to a stimulus in a single reaction time situation: for example, a sprint start in swimming. See also choice reaction time, digit symbol substitution test, response time, simple reaction time.

(DOD) 1. The elapsed time between the initiation of an action and the required response. 2. The time required between the receipt of an order directing an operation and the arrival of the initial element of the force concerned in the designated area.

For Ian Lowe's book, see Reaction Time (book).

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. 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 increases in proportion to the logarithm of the number of response alternatives. The law is usually expressed by the formula RT = a + blog₂(n + 1), where a and b are constants representing the intercept and slope of the function, and n is the number of alternatives.^[1]

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.^[2]

Contents 1 History 2 Measurement 3 RT and cognitive ability 4 See also 5 References 6 External links 6.1 Additional information 6.2 Online tests

History

The Persian scientist, Abū Rayhān al-Bīrūnī was the first person to describe the concept of reaction time:^[3]

"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 Donders. Donders found that simple reaction time is shorter than recognition reaction time, and that choice reaction time is longer than both.^[4] Donders also devised a subtraction method to analyze the time it took for mental operations to take place. By subtracting simple reaction time from choice reaction time, for example, it is possible to calculate how much time is needed to make the choice..

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.^[5]

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).^[6] This relationship may be due to more efficient information processing or better attentional resources in more intelligent people.

See also

• CDR Computerized Assessment System
• Implicit Association Test
• Ramell

References

1. ^ Hick's Law at Encyclopedia.com Originally from Colman, A. (2001). A Dictionary of Psychology. Retrieved February 28, 2009.
2. ^ 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.
3. ^ Iqbal, Muhammad, "The Spirit of Muslim Culture", The Reconstruction of Religious Thought in Islam, http://www.allamaiqbal.com/works/prose/english/reconstruction, retrieved 2008-01-25 
4. ^ Kosinski, R. J. (2008). A literature review on reaction time, Clemson University.
5. ^ Kosinski, R. J. (2008). A literature review on reaction time, Clemson University.
6. ^ Deary, I. J., Der, G., & Ford, G. (2001). Reaction times and intelligence differences: A population-based cohort study. Intelligence, 29, 389–399.

External links

Additional information

• A Literature Review on Reaction Time by Robert J. Kosinski, Clemson University
• Historical Background by Museum of the History of Reaction Time Research
• Fingertip Reaction Time by The Physics Factbook

Online tests

• Simple visual reaction time from Human Benchmark
• Simple visual reaction time from Cognitive Fun
• Simple auditory reaction time from Cognitive Fun
• Go/No-go visual reaction time from Cognitive Fun

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