PSYCHOPHYSICAL DISCRIMINATION 



71 



from the movement of the eye from one end of the line to the other. 

 The effect of binocular cues also has been considered (Householder, 

 1940) . 



In the case of discrimination of weights (Householder, 1940), it 

 is found that it is unsatisfactory to assume a simple proportionality 

 between the weight W and the value of e at the end of the afferent 

 neuron. If a logarithmic relation is assumed together with a particu- 

 lar distribution of the thresholds, it is then possible to determine a re- 

 lationship between d and W in terms of two parameters. Experimental 

 results from discrimination of weights are shown as points in Figure 

 10, the weights being placed in the subject's hand. The theoretical 

 predictions are shown as curves. The weight of the hand is a third 

 parameter in this case and had to be estimated indirectly from the 

 data in each case since the direct measurement was not included. The 

 estimated values were 400 gms for each hand of the male subjects and 

 350 gms for each hand of the female subjects— values which are quite 

 plausible. 



ae 



.005 



.01 



.02 



.05 



e 



.10 



.20 



.50 



Figure 9. — Comparison of theory with experiment: discrimination of lengths 

 of line-segments, visually perceived. Curve, theoretical, based on equations (25)- 

 (28); points, experimental (Chodin, 1877). Abscissa, visual angle of shorter 

 segment; ordinate, just-discriminable angular difference. 



