Meanings and qualities are fundamental attributes of visual awareness. We propose "eidolons" as a tool for establishing equivalence classes of appearance along meaningful dimensions. The "eidolon factory" is an algorithm that generates stimuli in such a meaningful and transparent way. The algorithm allows us to focus on location, scale, and size of perceptually salient structures, proto-objects, and perhaps even semantics rather than global overall parameters, such as contrast and spatial frequency. The eidolon factory is based on models of the psychogenesis of visual awareness. It affects the image in terms of the disruption of image structure across space and spatial scales. This is a very general method with many potential applications. We illustrate a few instances. We present results for the example of tarachopic amblyopia, showing that scrambled vision is indeed an apt interpretation.

Classical theories of space perception posit continuous distortions of subjective space. These stand in contrast to the quantitatively and qualitatively different distortions experienced in space that is represented pictorially. Wechallenge several aspects of these theories. Comparing real-world objects with depictions of the same objects, we investigated to what extent distortions are introduced by the photographic medium. Comers of irregularly shaped buildings had to be judged in terms of the vertical dihedral angles subtended by two adjacent walls. Across all conditions, a robust effect of viewing distance was found: Buildingcomers appear to flatten out with distance. Moreover,depictions of comers produce remarkably similar results and should not receive a different theoretical treatment than do real-world scenes. The flattening of vertical angles cannot be explained by a linear distortion of the entire visual space. We suggest that, for natural scenes, compression of space is local and dependent on contextual information. Visually perceived depth in spatial arrangements has been studied within the context of two rather distinct frameworks. First, many theories of subjective space are based on the notion that perceived space is distorted in a uniform fashion and that a specific transformation can be found that describes the mapping relations between the Euclidean space of the world and our subjective space. Second, theories of spatial representation are concerned with distortions that arise in the process of representing space-mainly, the effects caused by pictorial rendition, such as projective distortions or the apparent flattening of the scene. In this study, we attempt to establish a relationship between the two frameworks by comparing judgments made in real scenes with judgments based on photographic renditions ofthe same scenes. Surprisingly, we found distortions to be very similar. We had observers judge the dihedral angles of building comers from a va-H

Summary Prägnanz was suggested by Max Wertheimer in the 1920s as subsuming all “Laws of Gestalt” as they apply to visual awareness. Thus, it assumes a prominent position in any account of Gestalt phenomena. From a phenomenological perspective, some visual stimuli evidently “have more Prägnanz” than others, so Prägnanz seems to be an intensive quality. Here, we investigate the intricacies that need to be faced on the way to a definition of formal scales. Such measures naturally depend both upon the stimulus and upon the observer. Structural complexity bottlenecks of visual systems play a role, as well as the relevance to biological fitness, that is the affinity to the optical user interface. This positions the notion of Prägnanz squarely within the realm of biology. Indeed, the familiar “releasers” of ethology are singular cases of extremely high Prägnanz.

Introduction Throughout the history of Western art one encounters frequent systematic deviations from true linear perspective. It is debated whether these are due to unfamiliarity (before the`invention' of linear perspective in the early Renaissance, Alberti 1435^1436/1970) or are intentional digressions (as in modern art). In this paper we show that many of such deviations reflect a hitherto hardly undocumented trait of human vision (Kepler

Phenomenal transparency is commonly studied by using a stimulus configuration introduced by Metelli: a bipartite patch, divided into equal left and right halves is overlaid with a smaller, concentric bipartite patch, divided along the same line. Observers are instructed to report either a transparent patch over an opaque bipartite field or a mosaic of four opaque patches. We show theoretically and empirically that these are only two of five generic perceptual categories, namely, transparent patch, transparent annulus (hole), mosaic, partial transparency, and multiple transparency (ambiguous) cases. Thus Gestalt factors complicate the interpretation "phenomenal transparency." We propose a framework that avoids this complication. There is excellent agreement between predictions and results.

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The “zograscope” is a “visual aid” (commonly known as “optical machine” in the 18th century) invented in the mid-18th century, and in general use until the early 20th century. It was intended to view single pictures (thus not stereographic pairs) with both eyes. The optics approximately eliminates the physiological cues (binocular disparity, vergence, accommodation, movement parallax, and image blur) that might indicate the flatness of the picture surface. The spatial structure of pictorial space is due to the remaining pictorial cues. As a consequence, many (or perhaps most) observers are aware of a heightened “plasticity” of the pictorial content for zograscopic as compared with natural viewing. We discuss the optics of the zograscope in some detail. Such an analysis is not available in the literature, whereas common “explanations” of the apparatus are evidently nonsensical. We constructed a zograscope, using modern parts, and present psychophysical data on its performance.

RGB–display space, that is, the ‘RGB–cube’, was sampled at 3,000 locations, uniformly and randomly distributed. Fifty observers contributed 60 samples each. At each location, participants synthesised a copy of the target, using a generic colour picker. The statistical distributions of errors as a function of location are used to define an overall measure of graininess. A smooth field of interpolated three-dimensional covariance ellipsoids represents an explicit, empirical Riemannian metric. The unit step size is about 20 times larger than the size of the classical MacAdam ellipses. We speculate that this metric might be found useful in various settings involving applications, because it reflects typical fuzziness encountered in generic tasks involving colour patterns such as images. Some of the more obvious applications are discussed.