. A text-book of physiology : for medical students and physicians . mCD 3 »2,S3 era g g-«.3 CD o aCJ^>—B. Br.^ CD 30-SS.^v CD _. SL « ° £°a-SE CO J^ CD * 1 o»2,. rog-£ n? PROPERTIES OF THE RETINA. 353 After-images may be used in a very instructive way to show thatour estimates of the size of a retinal image vary with the distance towhich we project it,—that is, with the distance at which we supposewe see it. Once the image is, so to speak, branded on the retina,its actual size, of course, does not vary, but our judgment of its sizemay be made to vary rapidly by projecting the image upon scr
. A text-book of physiology : for medical students and physicians . mCD 3 »2,S3 era g g-«.3 CD o aCJ^>—B. Br.^ CD 30-SS.^v CD _. SL « ° £°a-SE CO J^ CD * 1 o»2,. rog-£ n? PROPERTIES OF THE RETINA. 353 After-images may be used in a very instructive way to show thatour estimates of the size of a retinal image vary with the distance towhich we project it,—that is, with the distance at which we supposewe see it. Once the image is, so to speak, branded on the retina,its actual size, of course, does not vary, but our judgment of its sizemay be made to vary rapidly by projecting the image upon screens atdifferent distances. If, for instance, in obtaining the after-imageof the strips shown in Fig. 147 one moves the white paper usedto catch the image toward and away from the eye, the apparent sizevaries proportionally to its distance. Color Contrasts.—By color contrast is meant the influencethat one color field has upon a contiguous one. If, for instance, apiece of blue paper is laid upon a larger yellow square, the colorof each of them is heightened by contrast. A piece of bluepaper on a blue background does not appear so saturated as whenplaced
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