SINGLE SYNAPSE: SEVERAL NEURONS 



51 



t' = --log 



a, 



h 



, fa(S 2 ) 



^ ( e -w, 



-a 2 1 



fa(S x ) 0i (50 



■) 



(3) 



Finally if we set £ r = t + £', where t is a constant as in equation (2) 

 of chapter vi, we can determine the total reaction time t r as a function 

 of S 2 through fa , Si through fa , and of t w , which differs by t from 

 the time by which S 2 precedes the initiation of the response. As S 2 is 

 a stimulus which precedes S x and affects the response time to Si , but 

 is itself incapable of producing the response, it may be considered a 

 warning stimulus. Hence we may take equation (3) to predict the 

 kind of results to be obtained in an experiment in which a particular 

 stimulus of intensity Si has been preceded by a warning stimulus S 2 

 and produces a response in a time t r (S 1} S 2 , t w ) depending on the 

 strength of the warning stimulus as well as upon the manner in which 

 S x and S 2 are spaced in time. 



For the particular case in which a fixed Si and S 2 are used and 

 for t l0 > > t r , we may write equation (3) as 



t r = t ' log [1 + D(e- 6 *<- - e-°»'»)] 



a, 



(4) 



in which 



U' = t log (1-h/fa) > D = fa/ (fa - h) 



12 16 20 2* 



PREPARATORY INTERVAL IN SECONDS t w — * 



Figure 2. — Comparison of theory with experiment: effect of time of occur- 

 rence of warning stimulus upon the reaction-time. Curve, theoretical predictions 

 by equation (4); points, experimental (Woodrow, 1914). Abscissa, interval be- 

 tween presentation of warning and effective stimuli; ordinate, interval between 

 presentation of effective stimulus and occurrence of response. 



