98 



EXPERIMENTAL PHYSIOLOGY 



Reaction time in man. The reaction time in man may be deter- 

 mined by an arrangement of electric signals, but is done more simply 

 by Waller's apparatus (fig. 79). This consists of two wooden levers 

 lying across a piece of india-rubber tube, one end of which is closed, 

 the other being connected with a tambour which writes upon a 

 drum, the speed of which should be moderate. A screen hides the 

 movements of the experimenter from the person experimented on, 

 who sits at the table with one finger resting lightly on the 

 extremitv of one of the levers. He is to respond by pressing the 



FIG. 79. WALLER'S APPARATUS FOR REACTION TIME, a, RUBBER TUBE CLOSED AT ONE END AND AT 



THE OTHER CONNECTED BY 6 WITH A TAMBOUR (NOT SHOWN) ; C, d, d, d', LEVERS (WITH COLOURED 



PATCHES) HINGED NEAR c\ d', AND RESTING ON TEE RUBBER TUBE, a ; e, WOODEN SCREEN. 



lever the instant he (1) feels a movement of that lever, his eyes 

 being shut ; (2) hears a tap on the second lever ; (3) sees a move- 

 ment which is imparted to the second lever by the experimenter, 

 who presses it down on the other side of the screen. In each case 

 two marks are recorded upon the abscissa : one being that which 

 is made by the experimenter in imparting the stimulus, and the 

 other that made by the observed person in responding. The interval 

 between the two marks, which can be accurately measured by the aid 

 of a time tracing, indicates the time between stimulus and response 

 i.e. the reaction time in the case of each of the three senses. To 

 record this with any accuracy several observations must be made 

 with each method of stimulation and the average time calculated. 



