Reaction Time Method

In psychology, the reaction time method is the process of measuring the time between a stimulus received by a subject and the subject’s response.

Reaction time (RT; also referred to as “response time”) is measured by the time elapsed between stimulus onset and an individual’s response on elementary cognitive tasks (ECTs), which are relatively simple perceptual-motor tasks typically administered in a laboratory setting. A distinction is made between simple reaction time, in which a single stimulus corresponds to a single predetermined response, and complex reaction time, in which the subject must make a choice between several stimuli and, but not necessarily, several responses. This definition was adopted in 1871 by the Austrian physiologist S. Exner, and was one of the main topics of study in the early days of scientific psychology, mainly due to W. Wundt in Leipzig.

The first person interested in measuring reaction times was Franciscus Donders, who, between 1860 and 1867, while studying volunteers exposed to certain stimuli, discovered that different individuals responded at different rates to the same stimulus. This led him to conclude that an individual’s reaction time depended on the number of mental “steps” required to process the stimulus and produce the response. And so he hypothesized that although mental processes could not be observed directly, it was possible to get around the obstacle of reaction time and reconstruct them indirectly with some accuracy.

It was not until 1871 that the physiologist Siegmund Exner coined the term “reaction time,” which had previously been called “physiological time.

Donders relied on Hermann von Helmholtz’s experiments to measure the conduction velocity of nerve fibers. Based on this, he developed the so-called “subtractive method” to be used under three conditions. The first condition (a) contained a stimulus to which a response was to be given; the second condition (b) contained several stimuli, each of which corresponded to a different response; and finally, the third condition (c) contained several stimuli, but only one of them was to be responded to, while the others were not to be responded to by the subject. Donders could thus see that times a were the shortest of all, followed by times c, and the longest were times b.

Based on this, Donders defined the following subtractions:

  • c – a : discrimination between stimuli
  • b – c : discrimination between responses

These discrimination times corresponded to the purely psychological processes of choice to which a physical measurement index was associated.

Reaction time as a function of experimental conditions

The assumption that mental operations can be measured by the time it takes to perform them is considered fundamental to modern cognitive psychology. To understand how different brain systems acquire, process, and respond to stimuli, experimental psychologists often use reaction times as a dependent variable under different experimental conditions. This approach to the study of mental chronometry is typically aimed at testing theory-driven hypotheses that seek to explain observed relationships between measured RT and some experimentally manipulated variable of interest, often making precisely formulated mathematical predictions.

The distinction between this experimental approach and the use of chronometric tools to study individual differences is more conceptual than practical, and many modern researchers integrate tools, theories, and models from both areas to study psychological phenomena. Nevertheless, it is a useful organizing principle to distinguish the two fields in terms of their research questions and the purposes for which a number of chronometric tasks have been developed. The experimental approach of mental chronometry has been used to investigate a variety of cognitive systems and functions common to all humans, including memory, language processing and production, attention, and aspects of visual and auditory perception. The following is a brief overview of some of the well-known experimental tasks of mental chronometry.

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