472 H. M. JOHNSON 



is not as important as it might seem to the novice. The bright- 

 ness-difference created by cutting out one of the supplementary 

 lamps is several times as large as a threshold value, and it cer- 

 tainly appeared to be no smaller under one condition than under 

 another. It had been pretty well established that when the 

 absolute intensities of the stimuli are well above the threshold, 

 differences of this magnitude do not appreciably affect the time 

 required for reaction; and none of the subjects used in the present 

 work gave differences in reaction-time under the several con- 

 ditions corresponding to the direction of the differences given 

 above. 



THE SUBJECTS USED 



Certain information regarding the subjects is of interest in 

 connection with the results which they yielded. 



Subject C was an unmarried woman, twenty years old, a 

 junior in the college for women of Western Reserve University. 

 She is exceptionally intelligent, and prior to this work had served 

 as a laboratory subject for several months. Her reactions which 

 are presented below were preceded by only 400, distributed over 

 four days, but she made few errors in the regular work. She 

 showed considerable improvement with practice, however, and 

 this tends to increase the dispersion of the averaged reaction- 

 times, and thus to reduce the apparent reliability of the differences 

 among the several sets. The differences, however, are for the 

 most part quite definite. Her academic schedule and vacation- 

 plans prevented the allowance of more training and the accumu- 

 lation of as many reactions as were desired. A fact of consider- 

 able interest is that in some earlier work she showed a definitely 

 higher tactile sensitivity in "total" darkness than in an illumi- 

 nated room, most of the other subjects used in that experiment 

 showing a contrary effect. In the present experiment she "pre- 

 ferred to work in the dark," asserting that she found it "easier 

 to pay attention" in the dark than in the light. She maintained 

 this preference throughout the work, and expressed herself as 

 being certain that her reactions under condition DI were shorter 



