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Page:Popular Science Monthly Volume 54.djvu/328

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—does the mind's eye eke out the imperfections of physical vision. The vague conformations of drapery and make-up that are identified and recognized in spiritualistic séances illustrate extreme instances

PSM V54 D328 Optical illusion image used in psychological tests.png
Fig. 18. Fig. 19.

of this process. The whitewashed tree or post that momentarily startles us in a dark country lane takes on the guise that expectancy gives it. The mental predisposition here becomes the dominant factor, and the timid see as ghosts what their more sturdy companions recognize as whitewashed posts. Such experiences we ascribe to the action of suggestion and the imagination—the cloud "that's almost in shape like a camel," or "like a weasel," or "like a whale." But throughout our visual experiences there runs this

PSM V54 D328 Optical illusion of a duck or a rabbit head.png
Fig. 20.—Do you see a duck or a rabbit, or either? (From Harper's Weekly, originally in Fliegende Blätter.)

double strain, now mainly outward and now mainly inward, from the simplest excitements of the retina up to the realms where fancy soars freed from the confines of sense, and the objective finds its occupation gone.