356 H. M. JOHNSON 



did not sometimes react to the sound component instead of the 

 flash-component in the (Fs) series. In the case of reactor W 

 only thirty reactions in each of the two series in the check- 

 experiment are compared. These indicate nothing contrary to 

 Dunlap's hypothesis, the only ground for criticism being that the 

 number is small. In the case of reactor J (the present writer) 

 sixty reactions are presented under each of the two conditions. 

 In the course of accumulating the sixty under condition (Fs-ds) 

 which are presented, eleven reactions were made to the sound 

 alone, to which reaction was to be inhibited. In the absence of 

 conflicting evidence, one would suspect that approximately eleven 

 reactions to the sound component were made when the stimulus 

 was the flash accompanied by the sound; and 1 that these reactions, 

 being shorter than the ones made to the flash-component, tended 

 to reduce the average for the series. Under condition (F-ds) 

 only five errors were recorded. 



In the circumstances I am inclined to suspension of judgment 

 as to whether the second component in Dunlap's stimuli tended 

 to reinforce, inhibit or usurp the place of the first component. 



THE PRESENT PROBLEM 



The specific problem attacked in the present study is whether 

 tactile discrimination is increased, diminished or unaffected by 

 uniform and continuous stimulation of the retina by light, under 

 conditions which preclude the use of vision as a direct aid. 5 



PROCEDURE 



Tactile discrimination can be indirectly measured by the speed 

 and accuracy of performance in which it is an essential factor. 

 This method was adopted for our present purpose. The task 

 chosen was that of sorting a pack of 100 shuffled playing-cards of 

 standard size into four " suits" of 25 cards each, according to 

 patterns perforated in them, to be distinguished by the senses of 

 touch alone. 



5 1 am indebted to Professor Dunlap for suggesting the use of a card-sorting 

 test in this problem. The patterns to be discriminated, and the procedure fol- 

 lowed, are of my selection. 



