Conscious Production of Illusions 179
may be as many as a dozen of them. By looking to the side of the light or letter, or looking away obliquely at any angle, the images can be made to arrange themselves horizontally, or obliquely at any angle.
To see objects in the wrong location, as when the first letter of a word occupies the place of the last, requires an ingenuity of eccentric fixation and an education of the imagination which is unusual.
The black or colored spots seen after looking at the sun, and the strange colors which the sun sometimes seems to assume, are also the result of the mental strain. When one becomes able to look at the orb of day with out strain, these phenomena immediately disappear.
After-images have been attributed to fatigue of the retina, which is supposed to have been so overstimulated by a certain color that it can no longer perceive it, and therefore seeks relief in the hue which is complementary to this color. If it gets tired looking at the black C on the Snellen test card, for instance, it is supposed to seek relief by seeing the C white. This explanation of the phenomenon is very ingenious but scarcely plausible. The eyes cannot see when they are closed; and if they appear to see under these conditions, it is obvious that the subject is suffering from a mental illusion with which the retina has nothing to do. Neither can they see what does not exist; and if they appear to see a white C on a green wall where there is no such object, it is obvious again that the subject is suffering from a mental illusion. The after-image indicates, in fact, simply a loss of mental control, and occurs when there is an error of refraction, because this condition also is due to a loss of mental control. Anyone can produce an after-image at will by trying to see the big C all alike-that is, under a strain;