COLOR SENSITIVITY OF THE PERIPHERAL RETINA. 63 



DISCUSSION OF RESULTS. 



Our investigation of the changes of color-tone in indirect vision 

 has yielded results which are in harmony with the all but unanimous 

 testimony of previous investigators. The contention of Woinow and 

 Klug that yellow appears green in indirect vision has not been con- 

 firmed, nor has Hellpach's discovery upon the periphery of the absence 

 of the sensation of yellow and of the presence of a " gegenfarbige Zone." 

 Our determinations of the relative extension of the retinal zones are in 

 agreement with those of all other investigators who have worked under 

 standardized conditions of experimentation. Moreover, it has been 

 established by the present investigation that the coincidence of the zones 

 of each pair of " stable " colors which was previously found to be valid 

 for the light-adapted retina, holds also for the dark-adapted retina. 



The phenomena which we have found to attend upon the con- 

 tinuous stimulation of the peripheral retina, and those which have been 

 sho\vn to persist as an after-effect, upon the removal of the stimulus, 

 are, we believe, for the most part, here pointed out for the first time, 

 although they have, in part, been vaguely foreshadowed in the literature 

 ever since the days of Troxler, Purkinje, and Aubert. So far as we 

 have been able to discover, however, they have never been investigated 

 in satisfactory detail. And the present paper can not hope to do more 

 than to call attention to their existence, and emphasize the necessity of 

 a more detailed investigation of their characteristics. 



As to our observation of the rapid fading of color from peripheral 

 images, it is interesting to note that the same phenomenon was described 

 by Troxler, just one hundred years ago. (.See pp. 7f.) The existence 

 of successive phases in this process of chromatic adaptation is sug- 

 gested in the investigation of Landolt and Charpentier* and is discussed 

 in the more recent work of McDougall.f That the phenomena of direct 

 and of indirect vision are, at least to some extent, analogous in this 

 regard, is clear from the familiar observation that the color may wholly 

 disappear from the central image with continued fixation. 



The difficulty which we encountered in the production of after- 

 images upon the peripheral retina was also experienced by Foerster,$ 



*Landolt et Charpentier. Des sensations de lumiene et <de couleur, dans la 

 vision direote et dans la vision indirecte, Comptes Rendus, LXXXVI, 1878, 

 pp. 495 ff. 



|W. McDougall. The Sensations Excited by a Single Momentary Stimula- 

 tion of the Eye, British Journal of Psychology, i, 1904, p. 85. 



jFoerster. Ueber Hemeralopie, u. s. w. Habilitationsschrift, Hamburg, 

 1857, S. 32. 



