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November 1959


Author Affiliations

Doctors Building 100 N. Euclid St. Louis 8.

AMA Arch Ophthalmol. 1959;62(5):918. doi:10.1001/archopht.1959.04220050178030

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To the Editor:  —The principal conclusion of M. J. Urist in his article, "After-Images and Ocular Muscle Proprioception," A.M.A. Arch. Ophth. 61:230-232 [Feb.] 1959, was that since imagined convergence changes perceived size, after-images must be cerebral.There are several articles in the literature showing that perceived size depends not only on the retinal stimulus, but also upon real or imagined convergence (P. W. Miles, "The Relation of Perceived Size of Half-Images at the Fusion Level to Projection on the Horopter," Am. J. Ophth. 34:1543-1561 [Nov.] 1951). A simpler explanation would be that like perceived size, after-images can be altered as well as inhibited centrally.The retinal nature of after-images can be simply demonstrated. K. S. Craik (Nature, London 145:512, 1940), induced an after-image on noncorresponding areas of his two eyes from a 60 watt bulb in 2 minutes. During the induction, he pressed one eye with his finger so that

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