Visual illusion

“ In fact exclusive of nature’s primary light-sources, such as the sun, she sometimes exhibits a range of brightness in a landscape a million times greater than the painter can produce with black and white pigments. This suggests that the artist is justified in using any available means for overcoming the handicap and among his tools, visual illusions are perhaps the most powerful.
A painting in the broadest sense is an illusion, [Pg 181] for it strives to present the three-dimensional world upon plane areas of two dimensions. Through representation or imitation it creates an illusion. ”

“ According to Carr’s investigation internal conditions alone are responsible for the illusion with more persons than those due to external conditions alone. With some persons a combination of internal and external conditions seem to be a necessity. Fixation of vision appears to be an essential objective condition for many observers. That is, the illusion appeared while fixating a speaker or singer in a church or a theater. With others the illusion occurs while reading. ”

“ That is, for some reason through being confronted with this difference so many times, the intellect has become adapted to it and, therefore, has grown to ignore it. Regardless of the explanation, the illusion exists and this is the point of chief interest. For the same reason the curvature of the retina does not appear to account for illusion through distortion of the image, because the training due to experience has caused greater difficulties than this to disappear. We must not overlook the tremendous “corrective” influence of experience upon which visual perception for the adult is founded. ”

“ Perhaps the reader has often witnessed the striking illusion of some portraits which were made of subjects looking directly at the camera or painter. Regardless of the position of the observer the eyes of the portrait appear to be directed toward him. In fact, as the observer moves, the eyes in the picture follow him so relentlessly as to provoke even a feeling of uncanniness. This fact is accounted for by the absence of a third dimension, for a sculptured model of a head does not exhibit this feature. Perspective plays a part in some manner, but no attempt toward explanation will be made. ”

“ Many illusions of brightness-contrast are visible on every hand. For example, the point at which the mullions of a window cross will be seen to appear brighter than the remaining portions of them when viewed against a bright sky. Conversely, in Fig. 64, dark spots appear where the white bars cross. This is purely an illusion and the same type may be witnessed by the observant many times a day. In Fig. 64 it is of interest to note that the illusion is weak for the crossing upon which the point of sight rests, but by averted vision the illusion is prominent for the [Pg 119] other crossings. ”

“ For example, a tree appears longer when standing than after it has been felled for the same reason that we overestimate vertical lines in comparison with horizontal ones. The apparent movement of the sun, moon, and stars, when clouds are floating past, is a powerful, though commonplace, illusion but we are more specifically interested in static illusions. However, it is of interest to recall the effect of involuntary eye-movements or of fluctuation in fixation because this factor in vision is important in many illusions. ”

“ Gray velvet is better, when the appearance of the room is taken into consideration, as it must be. However, the influence of dark surroundings toward enhancing the illusion is well worth recognizing. In the case of a special picture or a special occasion, a painting may [Pg 190] be exhibited in a booth—a huge shadow-box not unlike a show-window in which the light-sources are concealed. Such experiments yield many interesting data pertaining to the illusions which the painter strives to obtain.
Larger Image Fig. ”

“ PAINTING AND DECORATION In the arts where colors, brightnesses, contrasts, lines, forms, and perspectives mean so much, it is obvious that visual illusions are important. Sometimes they are evils which must be suppressed; in some cases they are boons to the artist if he is equal to the task of harnessing them. ”

“ If I do not wholly lapse into the error, it is because my experience has made me vaguely aware that double images under these circumstances answer to one object, and that if there were really two pencils present I should have four visual impressions.
Once more, it is a law of sensory stimulation that an impression persists for an appreciable time after the cessation of the action of the stimulus. This "after sensation" will clearly lead to illusion, in so far as we tend to think of the stimulus as still at work. ”

“ LIGHTING It should be obvious by this time that the lighting of objects or of a scene can alone produce an illusion, and that it can in still more cases contribute toward an illusion. Furthermore, there are many cases of illusions in lighting due to brightness and color. ”

“ If the artist’s sensibility has been capable of adequate selection, his art will transmit, by means of and through the truths of science, from the region of perception to the region of emotion. Science consists of knowing; art consists of doing. If the artist is familiar with the facts of light, color, lighting, and vision, he will possess knowledge that can aid him in overcoming the great obstacles which are ever-present. A glimpse of visual illusions should strengthen him in his resolution to depend upon visual perception, but he can utilize these very illusions. ”

“ MIRROR MAGIC Strictly speaking there are fewer illusions found in the practice of the magician than is generally supposed; that is, the eye usually delivers correctly to the intellect, but the judgment errs for various reasons. The “illusion” is due to false assumptions, to the distracting words, to unduly accented superfluous movements of the magician ”

“ A lady whose sight was failing her had long visions every day of rows of buildings, houses, and parks, and such like. The subjects of visual illusions are generally perfectly trivial, like the events of a common dream. ”

“ The majority of dreams are composed of visual images. The dreamer looks upon a picture which changes silently before his eyes, without appealing to any other sense than that of sight. But in certain cases any other sense may become excited, producing illusions or hallucinations as perfect as the images of healthy vision. They may be suggested by external impressions, as in my dream of a ring at the door bell, which proved to be an auditory illusion excited by the sound of passing carriage wheels ”

“ To keep the mental eye, like the bodily eye, for any time intently fixed on one object is apt to produce a feeling of giddiness. And in the case of a subject like illusion, the effect is enormously increased by the disturbing character of the object looked at. ”

“ We may not be distinctly anticipating any one kind [Pg 103] of object, but are nevertheless in a condition of sub-expectation with reference to a large number of objects. Accordingly, when an impression occurs which answers only very roughly to one of the associated images, there is a tendency to superimpose the image on the impression. In this way illusion arises. Thus, a man, when strolling in a cathedral, will be apt to take any kind of faint hollow sound for the soft tones of an organ. ”

“ THE MAGIC LANTERN.
The illusions of which we have spoken in the first part of this work depended principally on the nature of man's vision, who, we found, was the constant and heed-*less victim of his own powers of sight. We shall now examine a series of illusions that are still more extraordinary, but which have nothing to do with the deceptions practised on us by our visual organs. ”

“ Only a part of what is perceived comes through the senses from the object; the remainder always comes from within. In fact, it is the visual sense or the intellect which is responsible for illusions of the various types to be discussed in the following chapters. Our past experiences, associations, desires, demands, imaginings, and other more or less obscure influences create illusions. ”

“ The thought that darts into the fancy and is gone as soon, the illusion that crosses the brain of the lunatic, the vision that frightens the ghost-seer, the spectrum which the camera paints on the screen, the reddened landscape seen through a colored lens, the yellow objects which the jaundiced eye cannot avoid beholding, each as really exists as does the matter of the solid earth, or the eternal forces of the cosmical system. ”

“ If the work is a picture, the figures represented seem to speak and walk; the shade is shadow, the light is day; the flesh lives, eyes move, blood flows in their veins, and stuffs have a changing sheen. Imagination helps the realism of every detail, and only sees the beauties of the work. At that hour illusion reigns despotically ”

“ Optical delusion adds still more to the effect. Every proportion changes. The eye is deceived and deceives itself, at the same time, with these sublime lights and deepening shades, all calculated to increase the illusion. ”

“ Yet it manages to produce a pretty strong illusion. It illustrates in a striking manner the ease with which the eye conceives relations of depth or relief and solidity. If, for example, on a carpet, wall-paper, or dress, bright lines are laid on a dark colour as ground, we easily imagine that they are advancing. The reason of this seems to be that in our daily experience advancing surfaces catch and reflect the light, whereas retiring surfaces are in shadow. ”

“ Among the more innocent illusions of art, I may remind you of concave and cylindrical mirrors and lenses, the magic lanthorn, “les ombres chinoises,”and the phantasmagoria of Cagliastro, by which daggers appear to strike the breast of the spectator, and images of objects in other rooms are thrown on the walls of that in which we are sitting. A mirror, thus accidentally placed, has afforded the evidence of murder within our own time.
The duration of impressions on the eye, is another source of illusion. An image remains on the retina, I believe, about the eighth of a second ”

“ In its lowest stages illusion closely counterfeits correct perception in the balance of the direct factor, sensation, and the indirect factor, mental reproduction or imagination. The degree of illusion increases in proportion as the imaginative element gains [Pg 121] in force relatively to the present impression; till, in the wild illusions of the insane, the amount of actual impression becomes evanescent. When this point is reached, the act of imagination shows itself as a purely creative process, or an hallucination. ”

“ If we look closely into this variety of illusion, we shall see that it is very similar in its structure and origin to that kind of erroneous perception which arises from inattention to the actual impression of the moment under the influence of a strong expectation of something different. The representation of ourselves as entertained dislodges from our internal field of vision our actual condition, relegating this to the region of obscure consciousness. ”

“ This is illustrated in what I have called Active Illusions, whether the excited perceptions and the hallucinations of sense, or the fanciful projections of memory or of expectation. Here we have a force directly opposed to that of experience. Active illusion arises, not through the imperfections of the intellectual mechanism, but through a palpable interference with this mechanism. It is a regrouping of elements which simulates the form of a suggestion by experience, but is, in reality, the outcome of the individual mind's extra-intellectual impulses. ”

“ We set out with an account of perfectly normal perception, and found, even here, in the projection of our sensations of colour, sound, etc., into the environment or to the extremities of the organism, something which, from the point of view of physical science, easily wears the appearance of an ingredient of illusion. ”

“ This kind of explanation is quite in line with the peculiarity of the onlooker-consciousness, noted earlier, to attribute an optical illusion to the eye's way of working, while charging the mind with the task of clearing up the illusion. In reality it is just the reverse. Since the intellect can form no other idea of the act of seeing than that this is a passive process taking place solely within the eye, it falls, itself, into illusion. ”

“ Enough has been said, perhaps, about those errors of perception which have their root in the initial process of sensation. We may now pass to the far more important class of illusions which are related to the later stages of perception, that is to say, the process of interpreting the sense-impression. Speaking generally, one may describe an illusion of perception as a misinterpretation. ”

“ Thus, whether we are dealing with sensations that fall below the ordinary limits of our mental experience, or with those which arise in some exceptional state of the organism, we carry the habits formed in the much wider region of average every-day perception with us. In a word, illusion in these cases always arises through what may, figuratively at least, be described as the application of a rule, valid for the majority of cases, to an exceptional case. ”

“ Turning to presentative, and more particularly sense-illusions, we find that the detection of an illusion takes place now by an appeal from one sense to another, for example, from sight to touch, by way of verification; [156] now (as in Myer's experiment) by a reference from sense and presentation altogether to representation or remembered experience and a process of reasoning; and now, (as in the illusions of art) conversely, by a transition of mind from what is suggested to the actual sense-impression of the moment. ”