When a human subject follows instructions to make a specific response as soon as he can after the presentation of a specific signal, the latency of the response is called reaction time (RT). Average values of between 150 and 250 milliseconds (msec.) are typically found, for example, where the subject must press a telegraph key when a light is flashed; however, under some conditions, RTs even shorter than one hundred msec. and even longer than one second may occur. The term “RT,” is also applied to the continuous lag of responses to the stream of ongoing events.
Beginnings of the RT experiment are found in two sources. One is Helmholtz’ study of the speed of neural transmission. In an unsuccessful attempt, reported in 1850, to adapt the nerve muscle preparation technique to the intact human organism, he measured the latency of voluntary hand responses to light electric shocks applied to different areas of the skin. It may be supposed that Helmholtz did not appreciate what could be learned through this approach as he did not proceed with it. However, it was not long before many others were actively experimenting and theorizing on the problem.
The other source is the astronomer Friedrich Bessel’s analysis in 1822 of differences among observers in their estimates of the instant, within a series of clock ticks, in which a star passed a cross wire, the “eye and ear” method. With the interest thus aroused in the variability of human behavior, and with the concurrent development of accurate timing apparatus designed to eliminate this factor from astronomical observations, there eventually resulted the measurement of true RTs by two astronomers. One was O. M. Mitchel, an American, who used light and sound signals in 1858; the other was A. Hirsch, a Swiss, who also used electric shock in 1861–1864.
Three early programs of research on RT are of special importance. The first is that of the Dutch physiologist Frans Donders, who in 1868 introduced the experiment in...
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