56 COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



A survey of these results reveals the presence in indirect vision of 

 two general directions of change of sensation during the period of 

 stimulation. One of these is a change of saturation ; the other has to do 

 with color-tone. Changes of brightness were reported in only a few 

 instances. However well saturated the color may appear at the first 

 instant of exposure, it tends to fade out as the exposure continues, and 

 finally to become gray. In the above results it will be seen that the 

 persistence of color was much greater upon paracentral than upon peri- 

 pheral regions. In the latter case, the saturation is much less deep in 

 the initial phase, and the color frequently fades so rapidly that it appears 

 but as a momentary flash. On the paracentral regions, however, the 

 color frequently persisted in sufficient saturation to be recognized, dur- 

 ing the whole period of exposure. Besides the degree of eccentricity 

 the color-tone of the stimulus seems to have an influence upon the per- 

 sistence of the saturation. It will be noticed that yellow and blue paled 

 out much less rapidly than did the other colors ; while, under the con- 

 ditions of our experiments at least, violet and purple changed most 

 rapidly. Still another point is to be noted in this connection. The series 

 did not always terminate when the gray phase was reached, but fre- 

 quently passed over into the complementary of the ante-gray phase. 

 The variety of colors apearing in the complementary phase is therefore 

 limited to two blue and yellow. 



The variations of color-tone are no less pronounced than are those 

 of saturation. Here the tendency is to change in the direction of yellow 

 or blue ; thus colors of the red-end of the spectrum, including our purple 

 and our green stimulus, successively pass through those tones which 

 separate them in the spectrum from the yellow and finally appear yellow, 

 while the violet passes over into blue. From that point on, their sole 

 change is, as described above, a more or less gradual loss of satura- 

 tion and a subsequent passage into the complementary blue or yellow. 



There is reason to believe that the whole chromatic series described 

 above may be preceded, at the first instant of stimulation, by a phase of 

 gray. This phase was occasionally reported in our experiments, but it 

 was never present for more than the briefest period of time. It was 

 more frequently seen with blue than with any other stimulus. In 

 nearly all other cases it was either wholly lacking or it was so brief 

 and fleeting that its presence could not be affirmed with any degree of 

 assurance. 



After-images in the ordinary sense of the term were almost in- 

 variably absent from our experiments. They were reported in less than 

 one per cent of our exposures ; and when they did occur, they were 



