64 COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 



by Aubert, 1 and by Franz. 2 Indeed, Franz found it impossible under 

 the conditions of his experiments to arouse an after-image at a greater 

 degree of eccentricity than 30, and Foerster obtained but a very indis- 

 tinct after-image when the peripheral retina (45 from the visual axis) 

 was stimulated by a ray of direct sunlight. 



It seems, too, that the persistent after-effects which made them- 

 selves felt in our experiments upon the peripheral retina are analogous 

 in character with the after-images of direct vision. Attempts have been 

 made by Exner, 3 Hess, 4 Basevi, 5 and others to determine how the retinal 

 function is modified by local chromatic adaptation. 6 These investi- 

 gations, which were for the most part confined to direct vision, estab- 

 lish the law that fatigue by any color stimulus increases the retinal 

 sensitivity to the complementary color, and that on subsequent stimula- 

 tion a sensation of the complementary color tends to arise. Our state- 

 ment regarding the latent or subliminal character of these after-effects 

 finds confirmation in a demonstration which has recently been described 

 by McDougall. 7 'This investigator finds that when the central after- 

 image has run its course and finally disappeared from view, it still exists 

 in latent form, from which it may be revived by a restimulation of the 

 retina. An analogous phenomenon was long since pointed out by 

 Hering. 8 



It must, however, be mentioned that if we accept the testimony of 

 Aubert and of Franz as to the color of the peripheral after-image, our 

 analogy breaks down. For both these investigators report that the peri- 

 pheral after-image is of the same color as the central that, e. g., the 

 after-image of a purple stimulus is green, no matter at what part of 

 the retina the after-image be aroused. That this statement is erroneous, 

 we have succeeded in demonstrating by means of an experiment in 

 which an intensive purple stimulus and a long exposure were employed. 

 We found that the application of this stimulus to different regions of the 

 retina gave the following after-images : Green at o, blue-green at 25, 



1 H. Aubert. Ueber das Verhalten der Nachbilder auf den peripherischen 

 Th-eilen der Nethaut. Molesdiott's Untersuehungen, IV, 1858, S. 22off. 



2 S. I. Franz. After Images, Psychol. Review, Mon., Supp. Ill, 1899, p. 29. 



3 S. Exner. Ueber die Functionsweise der Netzhautperipherie und den Sitz 

 der Nadibilder, Graefe's Arohiv., XXXII, i, 1886, S. 233*1. 



4 C. Hess. Ueber die Tonanderung der Spectral farben durch Ermiidung der 

 Netzhaut mil homogenem Lichte., Graefe's Arohiv., XXXVI, i, 1890, S. I2ff. 



5 V.Basevi. Influenza dell'adattamento sulla sensibilita retinica per la luce 

 e per i colori., Annali d'Ottoknologia, XVIII, 1890, p. 480. 



6 The work of Schon, Charpentier, and Peschel need not be discussed in this 

 connection, since their results are expressed in terms of the influence of chromatic 

 adaptation upon the " light sense." Treatel and Landolt deal solely witih the 

 effects of general achromatic adaptation. 



7 W. McDougall. Some New Observations in Support of Thomas Young's 

 Theory, etc., Mind, N. S., X, 1901, p. 55. 



8 E. Hering. Zur Lehre vom Lichtsinne, Wien, 1878, S. I29f. 



