Fig.6.16 Drawing used by Kennedy.

Although it would take us too far afield to engage in an analysis of the significance and psychological bases of these trompe l'œil works, I do want to point out the role of attention and expectation in creating the delusions to which these works can rise. John Kennedy has taken the first step toward elucidating the role of attention in tromp l'œil phenomena. He asked children to add a drawing of a figure in the midst of the children shown in Figure 6.16. When they concentrated on the central region of the picture, many of them absentmindedly tried to pick up the pencil. This observation suggests that although the standard claim about trompe l'œil - namely that it requires the representation of an object of shallow depth - is true enough, it fails to do justice to the psychological complexity of the phenomenon. It is perhaps correct as a statement of a necessary condition for the occurrence of the trompe l'œil effect, but it leaves the question of the effect's sufficient conditions unasked.⁹

What is it about the delusion of trompe l'œil that makes such works interesting? After all, there is nothing fascinating in a trompe l'œil painting until the delusion has been dispelled; and once it has been dispelled, the work is most often of no more than minor aesthetic interest. We enjoy examining an object endowed with the power to throw us into a delusory state of mind after it has divulged its secret to us; looking at it sends a shiver down our metaphysical spines much in the way we shiver when we think about an accident in which we were almost involved; we stare at it much as we might stare at the carcass of a wild animal that almost got the better of us. A trompe l'œil picture is an epistemological close call, a reminder that Descartes's evil being that continuously fills us with error may be disguised as a benevolent painter. The point I wish to make therefore is that what is interesting about a trompe l'œil painting arises in our minds after the painting has ceased to trompe our yeux; it is when we have ceased to be the unwitting targets of a practical joke, and we have decided to reflect upon the experience we have just gone through, that the painting acquires its meaning.

And then looking at a trompe l'œil painting after the delusion has been dispelled is fascinating because it shows us how utterly preposterous was Ruskin's famous idea of the "innocent eye." One tries in vain to be deluded again, but one can't; at best we are impressed by an illusion, which we obtain by actively cooperating with the artifices devised by the artist. But there is always a sense of innocence lost, a banishment from paradise, a fool's paradise to be sure, but paradise nevertheless.

I'm not totally convinced by this. I liked the previous para better, where we were alternating between the naive and knowledgable states. We may not be able to hold the naive state, but with a good trompe-l'oeuil you keep cycling through it to re-experience it.

All illusionistic art other than trompe l'œil relies for its effect on a collusion between the artist and the spectator. Consider illusionistic paintings of architecture for a moment. None of these paintings places the spectator at the center of projection at the moment the picture becomes visible. Is this true? I thought that the Peruzzi room was oriented to the entrance? And what about the Urbino Studiolo? For instance, Pozzo's imaginary architecture in the Church of Sant'Ignazio looks lopsided unless it is seen from the yellow marble disk in the center of the church's nave: Therefore, only a visitor who would have asked to be led blindfolded to the prescribed vantage point would see the painting correctly, as it were, at first sight; but to have prepared one's experience so carefully presupposes prior knowledge of the spectacle one was about to behold and enjoy. Most viewers deeply enjoy the experience despite having first seen it lopsided and distorted. These viewers are in mental collusion with the artist who designed and painted the illusionistic architecture because they know full well that they are experiencing an illusion when they view the ceiling from the center of projection.

This concept of mental collusion is similar to Coleridge's "willing suspension of disbelief for the moment, which constitutes poetic faith" (1907, Book II, Chapter 14, p. 6). The difference is one of degree: Willing suspension of disbelief refers to a cognitive operation, a voluntary adoption of a certain aesthetic attitude; by mental collusion with the artist, I mean an operation much closer to the roots of perception, more on the order of a suggestion than a frame of mind.

		Fig.6.17 The vase-face reversible figure.

The concept of mental collusion appears in non-aesthetic perceptual contexts as well. For instance, certain illusions do not occur spontaneously or involuntarily; they occur only after the viewer is informed what he or she is expected to see. But once that knowledge is imparted, there is little the viewer can do to escape its effect. As an example, consider the experiment in which Girgus, Rock, and Egatz (1977) measured the time it took observers to experience a figure-ground reversal in Rubin's (1915) vase-face figure (see Figure 6.17), which was thought to spontaneously reverse back and forth between the vase percept and the face percept. The observers were high-school students who had never seen the Rubin figure before. Every 5 seconds, the experimenter tapped a pencil to mark the moment at which the observer was to report what he or she was seeing in the figure. Every effort was made to communicate to the observers that certain figures could be described in more than one way, and that therefore their reports could differ from signal to signal, but they were not told that the Rubin figure was reversible and they were not told what the alternative descriptions could be. After having obtained the observers' reports, the experimenter interviewed them to ascertain whether unreported reversals had occurred at every tap. Even with this scoring procedure, which was most likely to overestimate the number of reversals seen spontaneously, only So ?5 percent of the observers saw the figure reverse within the first minute of viewing, a figure that went up to 6o percent within the first two minutes and to 65 percent within the first three minutes. During the interview, observers were taught to see both alternatives and to grasp the reversibility of the figure. Afterward, the observers were tested again and, as expected, all of them reported reversals.

		Fig.6.18 A Necker cube formed by phenomenal contours as a perceptual analog of willing suspension of disbelief.

To better clarify the notion of mental collusion, let us look at the wonderful illusion invented by Bradley, Dumais, and Petry (1976; see Figure 6.18). The initial impression one receives is of a white paper cutout of a Necker cube superimposed on a sheet of white paper on which eight black disks have been drawn in order to enable you to see the figure's critical features. Even though there are no lines joining the corners, you see them, an unconscious inference regarding the nature of the object that would create this sort of configuration. You are not free to see or not to see these phenomenal contours: even if you see the Necker cube as I described it, you always see the contours. When you do, you also can see the cutout as a representation of a three-dimensional object, and, because the representation is ambiguous, you can see it reverse, as does the Necker cube.

Now the interesting twist to this illusion comes when one's attention is drawn to another way of interpreting the eight spots. Imagine a sheet of paper with eight holes in it, and under it a sheet of black paper that can be seen through the holes. Now suppose we took the white paper cutout of the Necker cube and slipped it between these two sheets so that the critical features were visible through the eight portholes in the top white sheet of paper. When you interpret the figure in this fashion, you can still "see" the Necker cube, and you can still experience reversals of its orientation, but you do not see the phenomenal contours. The act of choosing to see the cutout of the cube behind a page with holes in it rather than in front of the page with spots on it is very much like a willing suspension of disbelief. But once one has made a commitment to that suspension of disbelief, the world we perceive is consistent with how we have chosen to perceive it. It is important to remember that we are not in a position to reinterpret every facet of our perceptual experience and to see how the implications of our choice propagate through the remainder of our experience. But there are certain aspects of experience that allow us to make such a choice, although, unfortunately, we do not understand what gives them this power.¹⁰

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⁹ See Liotard (1973, Chapter 1), cited in Gombrich (1969, p. 430). See also interesting discussions in Gombrich (1969, p. 430) and a major historical review in Mastai (1975), upon which the above discussion leans heavily. There are also briefer reviews in Dars (1979) and Leeman, Elfers, and Schuyt (1976).

¹⁰ It is interesting to think of the complexity of representation and to speculate on how many levels of representation can be embedded in each other. The simplest case I know is the drawing on a cereal box of a boy holding a cereal box, on which there is a drawing of a boy holding a cereal box, on which... This case is easy, because we need not keep track of which representation is represented by which. All we have to do is invoke a perceptual "etc. experience," well-described in Gombrich (1969, pp. 219-21). In language, the limit is memory: We are hard put to unravel the sentence, "The mouse that the cat that the fire burned ate." Any more deeply embedded phrases would render the sentence incomprehensible without resorting to syntactic analysis. In the case of Bradley, Dumais, and Perry's illusion, we have two levels: a drawing of a cutout and its background (one level of representation), and the cutout representing a cube (an embedded representation).