THE INFLUENCE OF THE DISTRIBUTION OF BRIGHT- 

 NESSES OVER THE VISUAL FIELD ON THE TIME 

 REQUIRED FOR DISCRIMINATIVE RESPONSES TO 

 VISUAL STIMULI 1 



H. M. JOHNSON 



Captain, Sanitary Corps, U. S. A., Air Service Medical Research Laboratory, 

 Hazelhurst Field, Mineola, Long Island, New York 



INTRODUCTION 



V 



The following pages contain a report of a study which was 

 undertaken as a methodological preliminary to an extensive 

 study of the influence on visual performance of the distribution 

 of brightnesses over the visual field. 



The primary purpose was two-fold: (1) To ascertain whether 

 the method employed is sufficiently sensitive to demonstrate the 

 effects of such moderate differences in distribution of lighting 

 as might be encountered under installations which are volun- 

 tarily used; and (2) to train the subjects so thoroughly that their 

 diurnal performance under a given condition would be free of 

 important fluctuations due to the variable effects of fatigue and 

 practice. This was to permit of their economical use in the more 

 extensive work, which was designed to include a wide range of 

 distributions of brightnesses and variable sizes of the test-field, 

 under such controls as would justify direct intercomparison of 

 the data obtained under the various external conditions. 



As the author has been prevented from carrying out the 

 complete study, the results of the preliminary investigation are 

 presented without apology, as indicating definitely the sensitivity 

 and reliability of the method employed, and the differential 

 effects of the particular environmental conditions under which 



1 This paper from the Nela Research Laboratory, National Lamp Works of 

 General Electric Company, Nela Park, Cleveland, Ohio. 



459 



