Reaction time
From Exampleproblems
For a reflex, reaction time is the time from the onset of a stimulus until the organism responds.
Contents |
Types
- Simple reaction time is the latency between a fixed stimulus and a fixed response.
- Complex reaction time is the latency between a variable stimulus and a respectively variable response.
Extended reaction times as a possible contributing factor in falls of elderly humans has been studied extensively at the University of New South Wales. Refer to the author, Stephen Lord, pertaining to a book on reducing falls, which was published after the study of 80,000 older Australian citizens.
Factors
The major factors affecting reaction time are:
- Recognition;
- Choice;
- Number of stimuli;
- Type of stimulus;
- Stimulus intensity;
There are many other factors that can also affect reaction time:
History of the Field
- Ancient Times;
Physical scientists such as Archimedes and philosophers such as Aristotle conducted many observations involving aspects of chronometric measurement; however the tools or impetus to measure cognitive reaction time apparently was not developed, or simply has not left a significant traceable thread in the literature. The literature in other fields, e.g., epigraphical evidence, remnants of papyri, sherds, and other source material is uncertain and warrants additional investigation. An understanding of physical reaction time is critical for fields such as ballistics, archery, and the physical sciences in order to estimate and measure.
- Modern Times;
Modern interest in the measurement of human reaction time (the time elapsing between the onset of a stimulus and the onset of a response to that stimulus) apparently began as a result of the work of a Dutch physiologist named F. C. Donders. Beginning in 1865, Donders became interested in the question of whether the time taken to perform basic mental processes could be measured. Until that time, mental processes had been thought to be too fast to be measurable. In his early experiments, Donders applied electric shocks to the right and left feet of his subjects. The subject's task was to respond by pressing a telegraph key with his right or left hand to indicate whether his right or left foot had received the shock. In one experimental condition the subject knew 'in advance' which foot was to receive the electric shock and in the other condition the subject did not know 'in advance' which foot was to receive the shock. Donders found that the difference between the two conditions was 1/15 second. This measurement represented the very first time that the human mind had been measured. Donders was apparantly aware of the importance of his discovery because he wrote: "This was the first determination of the duration of a well-defined mental process. It concerned the decision in a choice and an action of the will in response to that decision."
Donders' ability to accurately measure such a short time interval was greatly facilitated by the solution of an earlier military problem. In 1840, the Englishman Charles Wheatstone invented a device for measuring the velocity of artillery shells. The device, which was based on his early electric telegraph system, was started electrically when the projectile left the muzzle of a gun and stopped electrically when it struck the target.
By 1842, a Swiss watchmaker named Mathias Hipp had 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. Later models of his 'Hipp Chronoscope' had vibrating regulators which vibrated at 1000 Hz. This improved their accuracy.
The clockwork mechanism of the Hipp Chronoscope was caused to rotate continuously by a motor powered by a heavy weight. At the start of a reaction-time measuring trial, the mechanism was set in motion but prevented from moving the indicating hands on its dial by a clutch which was held in the disengaged position by an electrically-energized solenoid. When the electrical current through the solenoid was interrupted, the clutch engaged and the dial rotated rapidly. When the current was reestablished, the clutch disengaged and the dial stopped at a reading which showed the elapsed time in thousandths of a second.
Although Donders did not continue to pursue his interest in the reaction time, Willhelm Wundt built an elaborate laboratory and research program around measuring the time taken by various mental processes. A student of the eminent and meticulous researchers, Hermann von Helmholtz and Emil Du Bois-Reymond, Wundt designed a psychology laboratory in Leipzig which was to become the model for dozens of scientific psychology laboratories throughout the world. His focus on the precise measurement of psychological processes or "MENTAL CHRONOMETRY" became the central issue in psychological research from the 1870's certainly into the 1950's. His insistence on precision of measurement has continued to influence the design of psychological experiments to the present.
Although the date 1879 is often given as the date of establishment of Wundt's first laboratory in Leipzig, it is clear that he was busy designing and performing precise measurements of human reaction times far earlier. His book: 'Grundzuge der physiologischen Psychologie' appeared in 1873 and contained a great deal of information about this new kind of psychological research.
