File:An American text-book of physiology (1897) (14596648009).jpg

Identifier: americantextbook00howe (find matches)
Title: An American text-book of physiology
Year: 1897 (1890s)
Authors: Howell, William H. (William Henry), 1860-1945 Bowditch, H. P. (Henry Pickering), 1840-1911
Subjects: Physiology
Publisher: Philadelphia : Saunders
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
other rays forwhich the eye has not been fatigued. Hence white light to an eye fatigued foryellow will appear blue. If the experiment be made with a yellow disk resting on a sheet of bluepaper, the negative after-image will be a spot on which the blue color willappear (1) more intense than on the neighboring portions of the sheet, owingto the blue-perceiving elements of that portion of the retina not being fatigued ;(2) more saturated, owing to the yellow-perceiving elements being so farexhausted that they no longer respond to the slight stimulation which is pro-duced when light of a complementary color is thrown upon them, as has beenexplained in connection with the subject of saturation. Contrast.—As the eye wanders from one part of the field of vision toanother it is evident that the sensation produced by a given portion of thefield will be modified by the amount of fatigue produced by that portion onwhich the eye has last rested, or, other words, the sensation will be the result
Text Appearing After Image:
Fig. 245.—To illustrate the phenomenon of contrast. of the stimulation by the object looked at combined with the negative after-image of the object previously observed. The effect of this combination is toproduce the phenomenon of successive contrast, the ))rinciple of which may bethus stated : Every part of the field of vision appears lighter near a darker THE SENSE OF VISION. 793 part and darker near a lighter part, and its color seen near another colorapproaches the complementary color of the latter. A contrast phenomenonsimilar in its effects to that above described may be produced under conditionsin which negative after-images can play no part. This kind of contrast isknown as simnltaneous contrast, and may perhaps be explained on the theorythat a stimulation of a given portion of the retina produces in the neighboringportions an effect to some extent antagonistic to that caused by direct stimulation.A good illustration of the phenomenon of contrast is given in Figure 245,in wh

Note About Images