Visual Illusions: Their Causes, Characteristics and Applications

by Matthew Luckiesh

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. Ofttimes they appear unheralded and unexpected. The existence of visual illusions is sufficient to justify the artist’s pride in his “eye” and his dependence upon his visual judgment rather than upon what he knows to be true. However true this may be, knowledge is as useful to the artist as to anyone else. The artist, if he is to produce art, is confronted with the tremendous task of perfecting an imperfect nature and he is handicapped with tools inferior to those which nature has at her disposal. He must deal with reflected lights from earthly materials. Nature has these besides the great primary light-sources—the sun, the moon, the stars, and, we might say, the sky. She also has the advantage of overwhelming magnitudes.

These are only a few of the disadvantages under which the artist works, but they indicate that he must grasp any advantage here and there which he may. Knowledge cannot fail him; still, if he fears that it will take him out of his “dream world” and taint him with earthliness, let him ponder over da Vinci, Rembrandt, and such men. These men knew many things. They possessed much knowledge and, after all, the latter is nothing more nor less than science when its facts are arranged in an orderly manner. If the arts are to speak “a noble and expressive language” despite the handicaps of the artist, knowledge cannot be drawn upon too deeply.

Perhaps in no other art are the workmen as little acquainted with their handicaps and with the scientific facts which would aid them as in painting. Painters, of course, may not agree as to this statement, but if they wish to see how much of the science of light, color, lighting, and vision they are unacquainted with, let them invade the book-shelves. If they think they know the facts of nature let them paint a given scene and then inquire of the scientist regarding the relative values (brightnesses) in the actual scene. They will usually be amazed to learn that they cannot paint the lights and shadows of nature excepting in the feeblest manner. The range of contrast represented by their entire palette is many thousand times less than the range of values in nature. 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, for it strives to present the three-dimensional world upon plane areas of two dimensions. Through representation or imitation it creates an illusion. 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. He can find a use for facts as well as anyone. Facts as well as experience will prepare him to do his work best.

The artist may suggest brilliant sunlight by means of deep shadow. The old painters gained color at the expense of light and therefore lowered the scale of color in their representations of nature. It is interesting to see how increasing knowledge, as centuries passed, directed painters as it did others onward toward the truth. Turner was one of the first to abandon the older methods in an attempt to raise the scale of his paintings toward a brilliance more resembling nature. By doing this he was able to put color in shadows as well as in lights. Gradually paintings became more brilliant. Monet, Claude, and others worked toward this goal until the brightnesses of paintings reached the limits of pigments. The impressionists, in their desire to paint nature’s light, introduced something which was nothing more nor less than science. All this time the true creative artist was introducing science—in fact, illusions—to produce the perfect illusion which was his goal. A survey of any representative paintings’ gallery shows the result of the application of more and more knowledge, as the art of painting progressed through the centuries. Surely we cannot go back to the brown shadows and sombre landscapes of the past.

In the earliest art, in the efforts of children, in the wall-paintings of the Egyptians, and in Japanese representation of nature, the process is selective and not imitative. Certain things are chosen and everything else is discarded. In such art selection is carried to the extreme. Much of this simplicity was due to a lack of knowledge. Light and shade, or shading, was not introduced until science discovered and organized its facts. Quite in the same manner linear and aerial perspective made their appearances until in our present art the process of selection is complex. In our paintings of today objects are modeled by light and shade; they are related by perspective; backgrounds and surroundings are carefully considered; the proper emphasis of light, shade and color are given to certain details. The present complexity provides unprecedented opportunities for the application of knowledge pertaining to illusions but it should be understood that this application tends only toward realism of external things. Idealism in art and realism of character and expression are accomplished by the same tools—pigments and brushes—as realism of objective details is attained and there is nothing mysterious in the masterpieces of this kind. Mystery in art as in other activities is merely lack of understanding due to inadequate knowledge. Mysteries of today become facts tomorrow. Science moves with certainty into the unknown, reaping and binding the facts and dropping them behind where they may be utilized by those who will.

The painter can imitate aerial perspective although many centuries elapsed before mankind was keen enough to note its presence in nature. The atmospheric haze diminishes the brightness of very bright objects and increases that of dark objects. It blurs the distant details and adds a tinge of blue or violet to the distance. In painting it is a powerful illusion which the painter has learned to employ.

The painter can accurately imitate mathematical or linear perspective but the art of early centuries does not exhibit this feature. In a painting a tremendously powerful illusion of the third dimension is obtained by diminishing the size of objects as they are represented in the distance. Converging lines and the other manifold details of perspective are aiding the artist in his efforts toward the production of the great illusion of painting.

The painter cannot imitate focal perspective or binocular perspective. He can try to imitate the definition in the central portion of the visual field and the increased blurring toward the periphery. Focal perspective is not of much importance in painting, because it is scarcely perceptible at the distances at which paintings are usually viewed. However the absence of binocular perspective in painting does decrease the effectiveness of the illusion very markedly. For this reason a painting is a more successful illusion when viewed with one eye than with two eyes. Of course, in one of nature’s scenes the converse is true because when viewing it with both eyes all the forms of perspective coöperate to the final end—the true impression of three dimensions.

The painter may imitate the light and shade of solid forms and thereby apparently model them. In this respect a remarkable illusion of solid form or of depth may be obtained. For example, a painted column may be made to appear circular in cross-section or a circle when properly shaded will appear to be a sphere. Both of these, of course, are pure illusions. Some stage paintings are remarkable illusions of depth, and their success depends chiefly upon linear perspective and shadows. However, the illusion which was so complete at a distance quite disappears at close range.