Baingio Pinna

Surface color from boundaries : a new 'watercolor' illusion

A colored line flanking a darker border will appear to assimilate its color onto the enclosed white area over distances of up to 45 deg (the Watercolor Effect). This coloration is uniform and complete within 100 ms. We found that thin (6 arcmin), winding inducing lines with different contrasts to the ground are generally more effective than thick, straight, and equiluminant lines. Blue and red lines induce the strongest effects, but watercolor spreading may also be seen with green and yellow. On a white background, color spreading is stronger than on chromatic, gray or black backgrounds. Little or no color is perceived when a narrow white zone (gap) is inserted in between the two inducing lines. However, chains of colored dots instead of continuous lines suffice to produce spreading. Edge-induced color is also observed when the two colored lines are presented dichoptically, suggesting a cortical origin. The Watercolor Effect described here may serve to enhance figure-ground segregation by imparting surface color onto the enclosed area, and to promote grouping between distant stimulus elements. As a grouping factor, watercolor coloration wins over proximity. Assimilative color spreading may arise in two steps: First, weakening of the contour by lateral inhibition between differentially activated edge cells (local diffusion); and second, unbarriered flow of color onto the enclosed area (global diffusion).

A new visual illusion of relative motion

We present a remarkably simple illusion that manifests whenever a certain class of flat static patterns are moved across our peripheral visual field. A relative motion is perceived in a direction perpendicular to the true motion. Translatory, looming, and rotational movements of the head or the pattern can all elicit it. Each pattern is constructed of simple elements that define, through luminance, an orientation polarity. This polarity could be encoded by spatiotemporally tuned, orientation sensitive units in area V1. We offer an explanation for the illusion based on how such units from V1 may be combined to feed the processes that subsequently interpret motion.

The watercolor illusion and neon color spreading: a unified analysis of new cases and neural mechanisms

Coloration and figural properties of neon color spreading and the watercolor illusion are studied using phenomenal and psychophysical observations. Coloration properties of both effects can be reduced to a common limiting condition, a nearby color transition called the two-dot limiting case, which clarifies their perceptual similarities and dissimilarities. The results are explained by the FACADE neural model of biological vision. The model proposes how local properties of color transitions activate spatial competition among nearby perceptual boundaries, with boundaries of lower-contrast edges weakened by competition more than boundaries of higher-contrast edges. This asymmetry induces spreading of more color across these boundaries than conversely. The model also predicts how depth and figure-ground effects are generated in these illusions.

The watercolor effect: a new principle of grouping and figure–ground organization

The watercolor effect is perceived when a dark (e.g., purple) contour is flanked by a lighter chromatic contour (e.g., orange). Under these conditions, the lighter color will assimilate over the entire enclosed area. This filling-in determines figure-ground organization when it is pitted against the classical Gestalt factors of proximity, good continuation, closure, symmetry, convexity, as well as amodal completion, and past experience. When it is combined with a given Gestalt factor, the resulting effect on figure-ground organization is stronger than for each factor alone. When the watercolor effect is induced by a dark red edge instead of an orange edge, its figural strength is reduced, but still stronger than without it. Finally, when a uniform surface is filled physically using the color of the orange fringe, figure-ground organization is not different from that for the purple contour only. These findings show that the watercolor effect induced by the edge could be an independent factor, different from the classical Gestalt factors of figure-ground organization.

Contrast Polarities Determine the Direction of Café Wall Tilts

We propose an explanatory approach to Café Wall type illusions that is simple yet fairly comprehensive. These illusions are constructed out of basic elementary units in a jigsaw-like manner. Each unit, in general, contains both a solid body and a thin tail: the contrast polarity between the two determines the direction of the contributory illusory tilt produced by that element—according to a heuristic rule illustrated in figure 1. Ensembles of these elements exhibit illusory tilts only when the tails of the elements align along a common line in an additive manner. When elements of opposing polarity alternate, the illusion is cancelled. This approach extends and supersedes those presented in Pinnas illusion of angularity and Kitaokas ‘acute’ corner effect. Furthermore, it appears to be, in part, compatible with existing mechanisms proposed to account for the emergence of local tilt cues, and it suggests several novel variations on the Café Wall theme.

The role of the Gestalt principle of similarity in the watercolor illusion.

The watercolor illusion presents two main effects: a long-range assimilative color spreading (coloration effect), and properties imparting a strong figure status (figural effect) to a region delimited by a dark (e.g. purple) contour flanked by a lighter chromatic contour (e.g. orange). In four experiments, the strength of the watercolor illusion to determine figure-ground organization is directly compared (combined or pitted against) with the Gestalt principle of similarity both of color and line width. The results demonstrated that (i) the watercolor illusion and, particularly, its figural effect won over the classical Gestalt factors of similarity; (ii) the watercolor illusion cannot be due to the coloration effect as suggested by the similarity principle; (iii) coloration and figural effects may be independent in the watercolor illusion, and (iv) the watercolor illusion can be considered as a principle of figure-ground segregation on its own. Two parallel and independent processes as proposed within the FACADE model (Grossberg, 1994, 1997) are suggested to account for the two effects of coloration and figural enhancement in the watercolor illusion.

What Comes Before Psychophysics? The Problem of 'What We Perceive' and the Phenomenological Exploration of New Effects

The psychophysical methods were developed by Fechner to find out the perceptual threshold of a stimulus, that is, the weakest stimulus that could be perceived. In spite of the strong efficiency in measuring thresholds, psychophysics does not help to define the multiplicity and complexity of possible percepts emerging from the same stimulus conditions, and accordingly, of what we perceive. In order to define what we perceive it is also necessary to define what we can perceive within the multiplicity of possible visual outcomes and how they are reciprocally organized. Usually the main experimental task is aimed at focusing on the specific attribute to be measured: what comes before psychophysics, i.e., the phenomenological exploration, is typically not fully investigated either epistemologically or phenomenally, even if it assumes a basic role in the process of scientific discovery. In this work, the importance of the traditional approach is not denied. Our main purpose is to place the two approaches side by side so that they complement each other: the phenomenological exploration complements the quantitative psychophysical measurement of the qualities that emerge through the preliminary exploration. To demonstrate the basic role played by the phenomenological exploration in complementing the psychophysical investigation we introduce three critical visual conditions, called visual gradient of perceptibility, perceptible invisibility and visual levels of perceptibility. Through these conditions several new illusions are studied and some phenomenological rules are suggested.

Perceptual organization of shape, color, shade, and lighting in visual and pictorial objects

The main questions we asked in this work are the following: Where are representations of shape, color, depth, and lighting mostly located? Does their formation take time to develop? How do they contribute to determining and defining a visual object, and how do they differ? How do visual artists use them to create objects and scenes? Is the way artists use them related to the way we perceive them? To answer these questions, we studied the microgenetic development of the object perception and formation. Our hypothesis is that the main object properties are extracted in sequential order and in the same order that these roles are also used by artists and children of different age to paint objects. The results supported the microgenesis of object formation according to the following sequence: contours, color, shading, and lighting.

The Organization of Shape and Color in Vision and Art

The aim of this work is to study the phenomenal organization of shape and color in vision and art in terms of microgenesis of the object perception and creation. The idea of “microgenesis” is that the object perception and creation takes time to develop. Our hypothesis is that the roles of shape and color are extracted in sequential order and in the same order these roles are also used by artists to paint objects. Boundary contours are coded before color contours. The microgenesis of the object formation was demonstrated (i) by introducing new conditions derived from the watercolor illusion, where the juxtaposed contours are displaced horizontally or vertically, and based on variations of Matisse’s Woman, (ii) by studying descriptions and replications of visual objects in adults and children of different ages, and (iii) by analyzing the linguistic sequence and organization in a free naming task of the attributes related to shape and color. The results supported the idea of the microgenesis of the object perception, namely the temporal order in the formation of the roles of the object properties (shape before color). Some general principles were extracted from the experimental results. They can be a starting point to explore a new domain focused on the microgenesis of shape and color within the more general problem of object organization, where integrated and multidisciplinary studies based on art and vision science can be very useful.

New illusions of sliding motion in depth.

Apparent sliding motion in the so-called Ouchi illusion has been attributed to the global integration of local motion vectors arising from the aperture effect (Fermüller et al, 2000 Vision Research 40 77–96; Mather, 2000 Perception 29 721–727). In a number of variants of the Ouchi illusion, we here demonstrate that sliding motion will also arise without a directional motion bias from local elements. Specifically, we show that in a disk-annulus pattern made from wiggly lines, sliding motion occurs although the local orientations within the disk and annulus are the same. We then argue that in an array of square-shaped checks, sliding motion originates from the interaction between the explicit orientation of the checks and the implicit orientation of the invisible diagonals. Finally, we demonstrate that a central array of filled black circles surrounded by a grey edge appears to slide relative to a surround of empty circles. We tentatively account for sliding motion in this figure by differences in speed signals, figure-ground segregation and apparent depth due to contrast polarity, edge blur, demarcation by a frame, and difference in shape.