PSYCHOPHYSICAL DISCRIMINATION 



59 



suits from observations made on seven subjects. The first entry in the 

 table, .012, gives the proportion P g of judgments that a weight of 84 

 gms is heavier than the standard, which is 100 gms in every case. This 

 is for the case in which judgment of "equality" is permitted, the pro- 

 portion being P e = .027. On the same line in the last column is given 

 the proportion Pi = 1 — P g — P e of times the weight of 84 gms is 



.50 



Experiment 



a 



/.CO 



Figure 2. — Comparison of theory with experiment: distribution of judgments 

 of relative weights. In 2a the abscissa of each point is the experimental value 

 (Urban, 1908) of the proportion of judgments of the indicated type and the ordi- 

 nate is the proportion theoretically predicted by equations (l)-(5). Thus perfect 

 agreement would be indicated if all points lay on the straight line. In 2b the 

 curve is theoretical, the points, experimental. The abscissa of each point is the 

 proportion of "greater than" or of "less than" judgments as the case may be, the 

 ordinate, the proportion of "doubtful" judgments when comparing the same "vari- 

 able" stimulus with the standard". 



