William Ittelson—Visual Perception of Markings

WIlLIAM H. ITTELSON
"Visual perception of markings"
Psychonomic Bulletin & Review
1996.3(2),171-187

[178] Every photograph or precisely rendered perspective painting has a single optically correct viewpoint. However, we rarely look at pictures with our eye at precisely that point, as Leonardo suggested we should. What are the perceptual consequences of such incorrect viewpoints? Leonardo was definite: "It is impossible that your perspective should not look wrong, with every false relation and disagreement of proportion that can be imagined." Leonardo based this conclusion on what has come to be called variously the problem of inverse optics, of inverse perspective, or of inverse projection (Epstein, 1995). A word of definition: Given a real-world scene and a viewpoint, linear perspective asks, what is the proper perspective rendition on a given picture surface? This is a problem in geometry; it has been worked out in detail and provides a unique solution. Any change of the viewpoint entails a corresponding change in the perspective. The problem of inverse optics asks the opposite question: Given a viewpoint and a perspective rendition on a picture surface, what real-world scene is represented? As a problem in geometry this does not have a unique solution. An unlimited number of external configurations can give rise to the same perspective rendition. A unique geometric solution requires some additional constraining assumptions (e.g., rectangularity). However, granted the appropriate assumptions, a unique geometric solution can be reached, and that solution is sensitive to any changes in the perspective rendition due to changing viewpoints.

Perception of the real world seems to follow this pattern; it is immensely sensitive to changes in the perspective view. As we move about the world, our visual system receives constantly changing views that are woven together into the perception of a continuous and stable world. If changes in the perspective views are not consistent with a stable world, the world will appear to move and distort, as illustrated by Pozzo's ceiling and as shown, for example, in some ofthe "Ames demonstrations" (Ittelson, 1952) and the phenomenon of "illusory concomitant motion" (Peterson, 1986). If we look at pictures from any point except the optically correct viewpoint, the pictorial assumption coupled with inverse optics predicts the same effects. Leonardo's prediction should come to pass, but we all know that doesn't happen. We walk through museums and thumb through our photograph albums; everything looks fine

[179]

even though our eyes are rarely, if ever, at the optically correct viewpoint. This apparent refusal of picture perception to follow the rules of inverse optics (Pirenne, 1970; Polanyi, 1970) has been labeled the robustness of perspective (Kubovy, 1986; Nicholls & Kennedy, 1993). This phenomenon poses a critical problem for the understanding of picture perception. Perceiving the real world is sensitive to small changes in perspective; perceiving pictures is seemingly indifferent to large changes.

My note says:
“Robustness of perspective” — a very useful term...and quite an elusive quality in musical presentation, what with performers having virtually no say in acoustics, technologists having equally little say in the devices listeners use to listen to recordings, etc. Vision being dominant, perhaps it is also more robust. At the same time, clearly visual artists also struggle with the environments in which their work is necessarily presented.

...

[184] At least three levels of intent underlie the creation of any marking: the immediate content, the medium used to express that content, and the general principle intended to be conveyed. While this is true of all markings, it is most easily demonstrated in art. The immediate content of, for example, Picasso's "Les Demoiselles d' Avignon" is 5 women. There is no doubt that Picasso intended to paint 5 women, and to perceive this painting as a picture of 5 women is certainly correct. But it is equally obvious that Picasso intended to do more than paint another picture of 5 women. He chose a particular medium, a constellation of design, form, color, paint, scale, and so forth, because he intended to evoke a particular affectance, a particular cognitive, affective, and imaginal state in the viewer. In all markings, the medium is, and always has been, at least part of the message. But underlying the choice of both content and medium is the intention to convey a general principle-in Picasso's case, a new way of looking at art and at human existence. This complex interweaving of levels of intent, so clearly illustrated in art, is characteristic of all markings although frequently hidden under a patina of accepted customs and usage. Even a graph in a scientific article is not immune. The immediate intent is to present a set of data, but the choice of how those data are presented-the medium used-is heavily dependent on what aspects of the data are intended to be emphasized, and that in tum grows out of what general principles and conclusions are intended to be drawn. The intent underlying any marking is a difficult and elusive quarry.

The creation and the subsequent perception of a marking involve a definite sequence of events: the creator of the marking starts with a set of intentions and produces a marking; the perceiver starts with the marking and tries to reconstruct the intentions. We need to examine this path in more detail. If there were a clear causal sequence, with intentions fully determining the marking and then being uniquely derivable from the marking, correct perception, in terms of recovering the original intent, would present no problem. There would always be, at least in principle, a correct solution. But that turns out not to be the case. Far from being a recognizable causal chain, the route from intention to marking and from marking back to intention is strewn with multiple choices and complex contingencies. This is also true of the creation and design of artifacts in general (Petroski, 1993), of which markings are a special case.

Markings, like all artifacts, start with an intention or purpose and end with a physical structure or form. If the process is successful, the form actualizes the intention so perfectly that it seems inevitable. Nevertheless, it is the product of a continuous series of choices based on social practices, individual experiences, and aesthetic judgments (Willats, 1990). The considerations impinging on and constraining future choices are contingent on earlier choices in a process that is as idiosyncratic and unique as the individuals involved. Many of the decisions along the way are "rational." They are in principle "computable" on the basis of some hypothetical algorithm. But some, perhaps most, are not. They are based on a feeling on the part of the creator of the marking that, of all possible paths, this one is the "right" way to go. This is most obvious in the case of the creative artist, but it is equally true for the creators of all types of markings. The number of potentially acceptable designs seems to be as countless as the number of possible sentences. Presenting quantitative information by diagrams offers an equally endless array of possibilities. "To envision information ... is to work at the intersection of image, word, number, art. ... And the standards of quality are those derived from visual principles that tell us how to put the right mark in the right place" (Tufte, 1990, p. 9). These decisions are properly termed aesthetic. "When is it finished?" is perhaps the most interesting decision of all and represents the final creative aesthetic judgment. No marking can be created without a continuing exercise of aesthetic judgments, although they may on occasion be so hidden in established practice as to be unrecognizable. And the thought, feeling, or image the marking is intended to communicate or express cannot be separated from the aesthetics of the marking.

Now another individual is faced with the marking. What is it? The most obvious solution is to derive from the physical form the original intent of the maker. The wonder of art is that it "evokes a corresponding resonance in the mind of the maker and the recipient" (Arnheim, 1993, p. 197). But this is rarely achieved. Between the original intent and the final markings are many possible "alternative histories," only one of which was followed and cannot in principle be retrieved from the marking alone. We can, of course, ask the creator of the marking, if available, what the marking is intended to mean. This may work in a few simple cases, but, in the general case, it runs into a curious paradox. This seemingly innocuous question asks the originator of the marking to produce a second marking that will elucidate the first. Will this marking be more easily understood than the original? Presumably not, or it would have been created in the first place. So we enter an endless regress. In most cases, perhaps fortunately, the originator is not accessible; in others, the original intent may be considered irrelevant, as with "found" art or religious icons used as decorative pieces. We can, as an alternative approach, ignore the original intent and assess the marking entirely within the nexus of contemporary social structure and practice. But this produces multiple answers, no one of which can be demonstrated to be uniquely correct. In actually dealing with markings, we inevitably combine both approaches. There is, in principle, no way of determining a single, stable answer to the correct perception of a marking.

Nevertheless, in dealing with markings, we do not experience anarchy; instead, we typically perceive a definite meaning that we are confident is correct. We can do this because the form or structure of the marking does provide powerful constraints on the meaning. These are

[185]

the same constraints that guide the hand of the maker of the marking, and they have been listed earlier: (1) the inherent constraints on what makes a design decorative or aesthetically satisfactory, (2) the socially agreed upon meanings and usages surrounding writing, (3) the conventions regarding the construction of diagrams that are further constrained by the nonvisual data, and (4) the need for depictions of all kinds to have some formal relationship between the visual information provided by the world and that provided by the depiction. These constraints rarely lead us astray. Markings that have the form of a random array of lines rarely are intended to be designs. Markings that have the form Have gone to the store are rarely intended to mean Am in the kitchen cooking dinner. Markings that have the form of a street map are rarely intended to be abstract portraits or graphs of data. Markings that have the form of a cat are rarely intended to represent dogs. When we couple these constraints with equally powerful constraints imposed by current social usage, very little room may be left for multiple interpretations.

This process works; we generally deal successfully with the vast numbers of markings we daily encounter. But this is a pragmatic, not principled, solution to the problem of the correctness of the perception of markings, and it can be wrong. Suppose, for example, that someone puts a complex arrangement of lines and colors on a canvas and declares, "That is a nude descending a staircase." You and I and all our friends look at it and declare, strongly and unanimously, that, whatever else it may be, it most certainly is not a nude descending a staircase. But it turns out that we are wrong. Similarly, Have gone to the store may be intended to be read as I am angry with you and don't want to be home when you arrive. The perception of markings is a pragmatic affair enmeshed in a complex of individual, social, and cultural processes applied to the interpretation of forms that always underdetermine meanings.

Individual, social, and cultural meanings are in constant flux. So also are the perceptions of markings: witness the "Nude Descending a Staircase." The perception of markings is subject to both long-term and sudden, "catastrophic," changes. The perception of markings-or more generally, the perception of affectances-is divergent and open-ended. This is the dilemma, the challenge, and the opportunity facing us every time we create a marking. We construct a form, but we can never fully determine how that form will be perceived. Each perceiver can, and indeed must, perceive it idiosyncratically to a greater or lesser extent.

My note says:
“a pragmatic, not principled, solution” !!

[emailed to self, 18 May 2020]