PSYCHOLOGICAL MEASUREMENTS. 



601 



15 



20 



25 



enough fluctuation to be particularly noteworthy. Near the end of the 

 experiment the eye reaction time decreased, and the variability was also 

 smaller. The curves for the general averages are at the bottom of 

 the figure. Squad B shows a rather consistent practice effect from the 

 beginning to end, with the exception of a slight decrease in the third 

 experiment, which corresponds with what has been noted above for 

 the variabiUty. There was no lengthening of reaction time asso- 

 ciated with the period of food reduction for this squad. Squad A 

 shows no significant change in the second experiment over their 

 first one. The data for the second experiment are very fragmentary; 

 indeed, they might have been omitted, since on account of the faulty 

 action of the shutter (see S 

 in figure 30), many of the squadA oct28 nov.h nov.25 Dec 9 jan.13 Jan. 27 



, , '. r -1 J J. Squad B Nov. 4 Nov. 18 Dec. 16 Jan. 14 Jan.20 



shorter reactions tailed to 

 appear on the records. There 

 was improvement up to Dec- 

 ember 9 and slightly length- 

 ened reactions during Jan- 

 uary. The increase following 

 the shortest reaction -time 

 average of December 9 was 

 approximately 5 per cent. 



For comparison with the 

 general averages, we may give 

 attention to the short reac- 

 tions made by the various 

 subjects. Short reactions, 

 which are at the same time 

 true reactions, would seem 

 theoretically to measure the 

 real process involved better 

 than the average of all reac- 

 tions, many of which are 

 unavoidably complicated by 

 fluctuations in attention and 

 other disturbing conditions, 

 objective as well as subjective 



160 



180 



200 



220 



240 



Fig. 112. — Eye-reaction time and its variability. 



Solid lines represent Squad A and broken lines Squad 

 B. The two curves at the bottom represent 

 average reaction time; the two in the middle 

 are for the five shortest reactions made by each 

 subject at each experiment; the two curves at 

 the top show the coefficients of variability. 



The 5 shortest reactions made by each 

 subject at each experiment were averaged (see tables 169 and 170) and 

 the averages of these figures for the 10 men of Squads A and B used to 

 plot the curves shown in the middle of figure 1 12. The initial values are 

 172 c and 182 o- for Squads A and B, respectively. The similar value 

 for the normal series of 1917 previously referred to was 193 a. The 

 curve for Squad B shows a gradual and uninterrupted practice effect 

 from the value 182 o" to the final value of 160 <t. Squad A shows a 

 practice effect approximately equal or parallel to that of Squad B, up 



