LXX.] 



REACTION-TIME. 



325 



and responds when he hears in the telephone the click of the 

 induction shock due to closure of the primary circuit. Of course, a 

 chronograph records time. 



3. Reaction-Time for Touch in Man. Two persons and the 

 following apparatus are required : coil, batteries, wires, two Du 

 Bois keys, two electro-magnets to record, and tuning-fork vibrating 

 100 D.V. per second. 



(a.) Arrange the experiment as in fig. 246, i.e., in the primary 

 circuit (single shocks), two keys arranged in the course of one 

 wire, and a recording electro- 

 magnet. Under the latter is 

 placed a chronograph recording 

 T tjV' the point of the one 

 exactly under the other, the 

 cylinder moving at a rapid 

 rate. 



(b.) Of the two persons, A 

 and B, suppose B to be experi- 

 mented on. The electrodes 

 are placed say on the back of 

 the hand or cheek of B, and 

 he has control of key marked 

 P, while A controls 0. Begin 

 with open, and P closed. 

 The observer closes O, this 

 completes the primary circuit, 

 the style of the chronograph is 

 attracted, descends and makes 

 a slightly oblique mark on the 

 paper, which indicates the 

 moment of stimulation. As 



soon as B feels this he opens key P, the primary current is broken 

 and the recording lever rises. 



(<:.) Measure the time value between the down and up movements 

 of the recording lever. In this case the individual operated on 

 knows the spot to be stimulated, but even with all his attention 

 the results may not be constant. The time varies with the 

 individual, his state of attention, fatigue, part stimulated, and many 

 other factors. 



4. The Dilemma. When the individual has to make a deliberate 

 choice between what parts of the body are stimulated, then the 

 reaction-time is considerably longer. 



The experiment is arranged as in fig. 246, save that the wires 



FIG. 245 Arrangement for Simple Reaction- 

 Time (Rutherford). 



