FLUCTUATIONS OF THE THRESHOLD 



55 



pare this result with the results of experiments by Berger and Cattell 

 (1886) cited in chapter vi, in which the mean variations of the re- 

 sponse-times were measured. We may use the same parameters ex- 

 cept for (7 which is arbitrary for this curve. Thus we have one para- 

 meter to determine this relation. The data are incomplete in the re- 

 gion of the threshold, but the comparison in Figure 1 is made for 



.040 



.030 - 





O.020 





.010 



10 100 



STIMULUS INTENSITY S— * 



1000 



Figure 1. — Comparison of theory with experiment : the variation in reaction- 

 times as a function of stimulus-intensity. Curve, theoretical predictions by equa- 

 tion (1); points, experimental (Cattell, 1886). Abscissa, intensity of stimulus; 

 ordinate, mean variation in reaction times. 



illustrative purposes primarily. Nothing has been said of the type 

 of distribution one would expect for a particular stimulus-intensity. 

 This would require a more detailed analysis. We wish only to indi- 

 cate the kind of effects due to the variations in the threshold. In the 

 next chapter we shall show how they provide a possible basis for the 

 distribution of judgments in situations that require some form of 

 discrimination. 



