Artistic Illusions

Artists have used illusions in their works from the beginning for the simple reason that illusions reflect the way the eye and brain see the world. It is only within the past century that some of the mysteries of how the world (and the life contained therein) looks to the brain have been disclosed in the perceptual-cognitive-neurological laboratory. Sometimes artists have used perceptual illusions to make a painting look "natural," even though it might not be geometrically correct, as we will see later. Sometimes artists have used perceptual illusions to make a joke about the incongruity between what we "know" the world looks like and what the world is like—at least as validated by independent empirical measurements.

Roger Shepard, a distinguished perceptual psychologist at Stanford as well as a clever artist, has tweaked our funny cortex with dozens of delightful illustrations, two of which appear in figures 6.5 and 6.6.

The table tops in figure 6.5 are actually the same in size and shape, a sensational mind-bender. To prove this, trace one of the table tops and cut it out. Then move the tracing to the other table. Even after empirically confirming the geometric equivalence of the shapes, the mind still has difficulty accepting the evidence.

In figure 6.6, the two creatures are identical, yet, because of the contextual cues which suggest that the monster in the rear is farther away than the one in front, our brain interprets the rear one as being larger. Furthermore, there is a strong inclination to ascribe psychological values to these characters. We might

Art necessarily is illusion. In the immense history of life on earth, art is but a very recent development. Since its emergence with Homo sapiens, there has been insufficient time . . .for the evolution of extensive neural machinery adapted specifically to the interpretation of pictures. The implication is inescapable: Pictures most appeal to us, to the extent that they do, because they engage neural machinery that had previously evolved for other purposes.

6.5 Shepard turns the tables on the eye and brain by showing two tabletops that are identical in size and shape. (From Shepard 1990.)

6.6 Shepard shows two unequal-sized monsters: the big aggressive guy in the back is trying to catch the terrified little guy in the front . . . but hold on! Are the two really unequal in size? (From Shepard 1990.)

conclude that the little guy in the front is horrified at being chased by the big, angry guy in the back who is bearing down on him. In a demonstration of this illusion I made an exact cutout of the figure, superimposed it over the back figure, and moved it to the front figure. When projected, the illusion is compelling: people "see" the big guy getting smaller. When reversed, he gets bigger. There is a sensation of physical growth and motion which everyone . . . well, almost everyone . . . "knows" does not really happen. It is an illusion. But then, what is truth?

Early Illusions in Art

One can find no finer example of an artist's intuitive knowledge used in creating an aesthetic illusion than the so-called "Chinese horse" found in the Lascaux cave in France. (See figure 6.7.) The art was created about 17,000 years ago. The image of the horse is ochre on top and white on the bottom, with a characteristic M shape on its belly—common among early Magdalenian animal paintings. The hard white limestone surface provided an excellent canvas for the black charcoal outline. The illusion created is one of a moving horse with all legs attached, even though the viewer has to provide a mental link between the body and galloping hoofs and legs. We easily see that. So, too, did the cave painters, who never (we suppose) had a lesson in art, figure drawing, or perspective.

These earliest painters lived near the Vezere River, which flows through a wide valley densely covered with verdant poplars and underbrush, and surrounded by high cliffs honeycombed with dozens of caves. This was a perfect location to spend a life in the 170th century B.C. The climate was not too severe, the river was rich in seafood (which contained Omega3), the valley abundant in game and berries, and the caves were a swell place to practice art and, probably, some kinds of ritualistic ceremonies. Notice the marks above and in front of the horse, which may be symbolic. Some theorists postulate that the caves were used as chambers for puberty rituals and that the art produced was part of that rite. That may be true. However, I think they were used primarily because the caves were a superb place to draw images still alive in the heads of the artists—images made possible because humans were consciously AWARE of the world as it was and how those sensations are represented in the brain and then by the brush.

Illusions in Egyptian Art

Egyptian artists were not known for their innovations. Quite the contrary, they accepted with religious devotion the canons of proportionality set down in the Old

6.7 This very early artist intuitively created the illusion of motion and depth in the so-called Chinese horse, which measures about 1.4 meters long. Note that the horse's left legs are not attached to its body but instead float, giving depth. The effectiveness of this sophisticated technique depends on the mind's eye to complete the visual illusion. This technique did not reappear in the history of art for thousands of years and gives unusual grace and charm to this painting.

Kingdom, and woe to the artist who depicted people—especially members of the Pharaonic family and deities—outside the rigid formula. Nevertheless, some very interesting illusionary effects may be found in tomb paintings, especially in tombs of lesser officials, and in the depiction of slaves. Greater artistic license was granted in some of these paintings than in the way the powers—earthly or heavenly—were shown.

Figure 6.8 depicts a reflecting pond with objects being shown from a psychological rather than an actual view. The artist has shown trees that surround a pond as they might appear on a horizon. The top trees stand upright, those to the side emanate from the left side of the pond, while those on the bottom maintain a

6.8 A pond in the garden of Nebamun in Thebes, 18th Dynasty (about 1400 B.C.). British Museum, London. Note the position of the trees, fish, fowl, and lotus.

veridical view of trees on the horizon. The fish, fowl, and lotuses in the pond are neither beneath, on top of, nor in the water, as they would appear naturally, but are all placed on the water in an impossible orientation. However, and this is an important point in understanding the psychology of Egyptian art, the objects in this picture are shown without distortion so that they might be reproduced in the af-terworld. The intention of tomb art was not to be seen on a bright Sunday afternoon in Paris by idle tourists, but to carry an image of important items into the hereafter so that when the lucky stiff got there he could enjoy earth in heaven.

An ingenious visual illusion of musicians—a class of people not as carefully protected by the technical canons as were nobles and deities—is shown in figure 6.9. Considerable artistic license was applied to these musicians and dancers. The young female dancers on the right are represented by fluid lines that suggest move-

6.9 An Egyptian visual illusion showing music. Thebes, 18th Dynasty. British Museum, London.

ment and grace. One of the musicians keeps the rhythm with cymbals (or hand clapping) and the other, presumably, plays a melody on what must have been a very tricky double flute. Consider how the artist showed music. Certainly, the rhythmic flow of the dancers' lithe bodies produce a visual illusion of musical sounds. Notice also the musicians' ringlets dancing in agitated tempo to the beat of the tune— a technique that made it to the funny pages during the twentieth century.

Illusions in Rome and Beyond

No other edifice from antiquity creates as sensational an illusion as does the Pantheon in Rome. The building fused Roman engineering and beauty in a temple for all gods. It is also huge and remained the largest domed building in the world for centuries. Its enormous size is a tribute to inventive engineering techniques, but its psychological impact is caused by a compelling visual illusion that makes the interior appear even more grandiose. The cella of the Pantheon is fashioned after a giant sphere (as shown in figure 6.10), and what could be a more fitting shape to

honor all the gods? From the outside the building appears to be a large, somewhat stubby-looking cylinder, but on entering one sees a strikingly different effect. The interior vault is not perceived as a hemisphere but soars skyward in the shape of a celestial spheroid, capped with an open oculus. A magnificent rendition of the interior and the visual illusion created is shown in Panini's Interior of the Pantheon shown in figure 6.11.

As shown, the dome appears to be spheroidal, almost like half of a football in shape. Thus, the ceiling seems much higher as people strain their necks to gaze at it and at the open eye in the center. The oculus is entirely exposed to the elements and, as shown in the painting, lets in views of the sky, stars, moon, and sunshine (notice the circle of light on the wall), as well as rain and occasionally snow. As impressive as the visual illusion is in Panini's painting, the sensation is even more astonishing when one sees it in person. It is difficult to imagine that the dome is actually a hemisphere, not ellipsoidal.

The illusion of greater height is achieved by placing niches to the gods around the circumference (Raphael is buried in one of them), accentuated with huge columns in between. Thus, the walls contain a strong vertical orientation. But it is the coffering in the dome that most significantly contributes to the feeling of height. The visual effect is achieved by using the principles of perception illustrated earlier in the Ponzo illusion (see figure 6.2) and Shepard's monsters (see figure 6.6). Please take a moment to review these figures and then look at figure 6.11. Notice that the panels at the lower part of the dome are large and become progressively smaller as they reach the oculus at the apex. Since the large ones at the bottom are close and since we assume that distant objects are smaller, the upper part of the dome, where

6.11 Giovanni Paolo Panini, Interior of the Pantheon (1740). National Gallery of Art, Washington, DC. When viewed from inside, the dome appears to be spheroidal and much more grandiose than one might expect from the outside.

the small coffers are (reasons the brain), must be very far away. The same effect is shown in the Ponzo illusion and even more clearly in Shepard's monsters, where the blocks in the tunnel are very similar to the ceiling design in the Pantheon. The effect is fUrther enhanced by making each panel a visual illusion unto itself with a series of nested rectangles.

"Mr. Poggendorff, Meet Mr. Rubens"4

For centuries, artists and architects showed people visual illusions of a fantastic world. Renaissance painters were particularly adept at creating three-dimensional impressions from a two-dimensional canvas, wall, or ceiling—a topic to be discussed in the next chapter. Baroque painters, who initially crafted their art in Rome, exhibited unusual skill in communicating pathos in their paintings. In the original meaning, baroque referred to irregular, contorted, and even grotesque interpretations of art. It certainly is "busy" art. The Flemish painter Peter Paul Rubens developed a personal style that even today carries his name. The Poggendorffillusion (figure 6.3) was discovered in I860,5 but 250 years earlier Mr. Rubens encountered a Poggendorff problem in his monumental work The Descent from the Cross, which is the central piece in the triptych located in the Antwerp Cathedral. (See figure 6.12 and plate 21.)

In the dramatic moment shown, Christ is being tenderly lowered from the cross. Our attention is directed to Jesus who, in typical baroque manner, is brightly contrasted from the dark background. Rubens has also shown nine faces expressing different emotions, each contributing to the complexity of the work.

The artist did run into a knotty problem. With the mid part of the parallel lines of the ladder occluded by a man (which was central to the overall composition of the piece), the right strut in the lower part of the ladder would seem not to align with the upper part shown above the man's head. The Poggendorff illusion would be created. The solution to the problem: shift the upper part to disambiguate the illusionary effect caused by this illusion. Did Rubens understand that the lines in his finished product did not match? X-ray photography of an earlier sketch (in the Courtauld Institute in London) shows that the lines had once been physically aligned but later were changed. It is likely that Rubens knew what he was doing and decided to make the painting psychologically correct rather than geometrically correct. He was, after all, a member of the school of art that contorted reality, but here the contortion was psychologically congruent and graphically incongruent.

6.12 Peter Paul Rubens, The Descent from the Cross (1612—1614). This is the central figure in a triptych located in Antwerp Cathedral in Belgium. Note that the lower part of the ladder (bottom right) does not physically line up with the upper part. Yet the psychological effect is not discordant. The illusion of visual congruity is maintained because Rubens made the ladder visually correct rather than graphically correct.

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