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 Pinna's illusion of angularity and Kitaoka's ‘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.

We report some novel 'lighting' and 'backlighting' effects in plane figures similar to those which induce the 'watercolor illusion', that is, figures made with outlines composed of juxtaposed parallel lines varying in brightness and chromatic color. These new effects show 'illumination' as an emergent percept, and show how arrangements of 'dark and light' along the boundaries of various plane figures model the volume and strengthen the illusion of depth. To account for these various effects we propose several phenomenological 'laws of figurality' to add to the Gestalt laws of organization and figure-ground segregation. We offer a set of meta-laws which are speculative but which serve to integrate and organize the phenomenological laws. These laws indicate how luminance gradient profiles across boundary contours define both the 3D appearance of figures and the properties of the light reflected from their volumetric shapes.

We investigated the effect of chromatic variations on the reading process with normal and dyslexic readers. We demonstrate that color can induce wholeness, parts-whole organization and phenomenal fragmentation during reading and comprehension tasks within written texts made up of words and non-words in the following conditions: monochromatic (the whole text colored with only one color), word (each word colored in different color), half word (half word colored with a color different from the one of the second half), syllable (every syllable colored with a different color) and letter (each letter with a different color). The dependent variables considered were reading time, reading errors and incorrect answers to a comprehension test. The main results demonstrated that these parameters of reading performance are all influenced by the five aforementioned chromatic conditions. These outcomes manifest similar trends in four groups of readers: children and adults combined with normal or dyslexic readers. Possible applied research and clinical applications are discussed together with some basic questions related to color vision suggesting that the main purposes of color for living beings is to generate wholeness, parts-whole organization and perceptual segmentation.

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.