382 TITCHENER AND PYLE— ON THE AFTER-IMAGES [July 23, 



work in Y-adaptation," the first, blue after-image would naturally 

 follow. If the second observation was taken at too short an interval 

 of time, the resulting B-adaptation would show itself as a yellow 

 after-image. The two final observations suggest a shift of condi- 

 tions. G is seen at 65° as greenish yellow, and as colorless; at 60° 

 as indefinite greenish gray. It is possible that, in the case in which 

 " no color " is reported, the G simply escaped notice ; peripheral 

 colors at the limit of vision often appear as momentary flashes. 

 Again, R is reported at 65° as " no color," although " reddish yel- 

 low " had been seen as far out as 75°. It is possible that the flash 

 of red escaped notice ; it is also possible that R-adaptation, from the 

 preceding after-image, brought out the blue. 



The puzzling thing is that the positive outcome should be thus 

 definite in the Mount Holyoke and Bryn Mawr laboratories, while 

 neither Professor Baird nor ourselves — though working with full 

 knowledge of conditions, and though trying various possibilities 

 which have not been reported in detail-" — are able in a single case 

 to obtain the colored after-image. We can only guess at an expla- 

 nation ; and we ofifer the following guesses in what seems to vis to 

 be the order of their likelihood: (i) chromatic adaptation;-^ (2) 

 the momentary and flash-like appearance of colors at the limit of 

 vision; (3) the phenomenon of "fluctuation of attention"; (4) de- 

 fective method and unsystematic procedure in the determination 



" These observations were taken " after the limits had been roughly de- 

 termined in previous experiments." If the determination of limits was made 

 at the same sitting, and if the last test-color employed was O, there would 

 be additional reason for an initial Y-adaptation. 



^° Thus, Mr. Ferree wrote to us : " After-images seem to occur most in- 

 tensively when the stimulus is removed while adaptation is still going on. 

 If one carries the stimulation to a stationary point in adaptation, the after- 

 image will weaken in proportion to the length of time during which the 

 stimulus is regarded before the after-image is evoked. This is true whether 

 one uses intensive or slightly supraliminal stimuli." We thought that it 

 might possibly be true of subliminal stimuli, and accordingly made brief 

 observations both in light and in dark adaptation. But we never saw the 

 after-image. 



^ On chromatic adaptation, see Baird, op. cit., 57 ff., 64 ff., 7^ f. ; Journ. 

 Philos., Psychol. & Sci. Meth., II., 1905, 21. 



