Although the literature dealing with reaction time is enormous, no studies seem to have appeared of the relationship between reaction time and chronological age in a large group of individuals having a wide span of age limits. It seemed desirable that this relationship be studied.We employed 150 individuals, sampled at random and ranging from the ages of 4 years to 60 years, grouped, for convenience, as shown in Table I.Our purpose being to determine the reaction times to light and sound, 2 simple arrangements were constructed. For light, an ordinary 50 watt electric light was placed in series with one of the poles of a double throw switch, the other pole being in series with a signal magnet, recording on a moving drum, the operator's key, and the subject's tap key, the response recorded by tapping the key and breaking the circuit, The apparatus for sound consisted of a signal magnet in series with the operator's and subject's tap key placed in the primary circuit of an induction coil, with a set of head ...