MOMENTARY CHARACTER OF VISUAL STIMULI 239 







the comparison appear to be of physiological importance, but 

 the method could not be proposed as a device for the technical 

 appraisal of lighting installations. 



Right here I wish to indulge in a small amount of discussion 

 by way of criticism on the work just referred to. In it, the 

 method of constant stimuli was used and the time of exposure 

 was invariably three seconds, automatically controlled by the 

 swing of a pendulum, and the observer was to consume all of that 

 time, if necessary, in order to make his judgment. 



If we reflect upon the performance of the eyes in ordinary 

 use we will find that the instances in which the eyes remain in 

 one position for a period such as three seconds, or even as much 

 as a considerable fraction of one second, of time are either unusual, 

 or they do not pertain to such situations as are implied in the 

 phrase "use of the eyes" or both. Instances in which the eyes 

 remain stationary or nearly so for gross periods of time are : 



1. Sleep, narcosis, coma and other states, medically known 

 as states of unconsciousness. 



2. The condition known as "brown study" periods of ab- 

 straction in which one is caught, perhaps, "gazing into space," 

 and in which, although the eyes appear to be in fixation, the 

 object (if any) upon which they are fixed is, to say the least, 

 remote from the center of attention. 



3. The case of the observer in the laboratory where certain 

 experiments in psychology and physiological optics are in progress 

 which call for prolonged fixation. In such cases it is noteworthy 

 that the brightness and color differences in objects tend to dis- 

 appear, and that troublesome after-images are apt to take place 

 on change of fixation. 



4. Also, the somewhat unusual case of ordinary vision, in- 

 cluding perhaps phases of certain special pursuits, when the 

 object viewed is close to the threshold for the fovea and the 

 observer gazes at it fixedly to arrive at a judgment. 



The outstanding fact is, that in the "use of the eyes," in 

 sewing, reading, checking and copying, and in "taking in" a 

 drawing or a picture or the lay of a set of objects in space the 



