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Page:Popular Science Monthly Volume 54.djvu/319

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The importance of the mind's eye in ordinary vision is also well illustrated in cases in which we see or seem to see what is not really

PSM V54 D319 Optical illusion 1.png

Fig. 3.—Observe the appearance of these letters at a distance of eight to twelve feet. An interesting method of testing the activity of the mind's eye with these letters is described in the text.

present, but what for one cause or another it is natural to suppose is present. A very familiar instance of this process is the constant overlooking of misprints—false letters, transposed letters, and missing letters—unless these happen to be particularly striking. We see only

PSM V54 D319 Optical illusion 2.png
Fig. 3a. Fig. 3b.

the general physiognomy of the word and the detailed features are supplied from within; in this case it is the expected that happens. Reading is done largely by the mental eye; and entire words, obviously suggested by the context, are sometimes read in, when they have been accidentally omitted. This is more apt to occur with the

PSM V54 D319 Optical illusion 3.png
Fig. 4.—For description, see text.

irregular characters used in manuscript than in the more distinct forms of the printed alphabet, and is particularly frequent in reading over what one has himself written. In reading proof, however, we are eager to detect misprints, and this change in attitude helps to