The influence of physical illumination on lightness perception in simultaneous contrast displays

Three experiments investigated the role of physical illumination on lightness perception in simultaneous lightness contrast (SLC). Four configurations were employed: the classic textbook version of the illusion and three configurations that produced either enhanced or reduced SLC. Experiment 1 tested the effect of ambient illumination on lightness perception. It simulated very dark environmental conditions that nevertheless still allowed perception of different shades of gray. Experiment 2 tested the effect of the intensity of Gelb lighting on lightness perception. Experiment 3 presented two conditions that integrated illumination conditions from Experiments 1 and 2. Our results demonstrated an illumination effect on both lightness matching and perceived SLC contrast: As the intensity of illumination increased, the target on the black background appeared lighter, while the target on the white background was little affected. We hypothesize the existence of two illumination ranges that affect lightness perception differently: low and normal. In the low range, the SLC contrast was reduced and targets appeared darker. In the normal range, the SLC contrast and lightness matchings for each background were little changed across illumination intensities

Et Facta Est Lux: Experiencing Luminosity in Art and in the Real World

The experience of light determined some of the most intriguing cultural universals, yet it is an underrepresented problem in vision sciences. In their attempt to represent cultural universals, artists adopted empirical solutions to the representation of light sources. We believe that such graphic solutions are showcases of visual indexes related to the phenomenology of light, and therefore they already constitute a level of explanation for luminosity perception. This claim is supported by psychophysical experiments on the ‘glare effect’, an illusion that generates a vivid impression of self-luminosity only by means of quasi-linear luminance ramps. Recent studies show that a similar illusion can be obtained in absence of physically continuous luminance ramps. Results from several experiments suggest that: 1) the key features for luminosity perception lie within the photo-geometric structure of the proximal stimulus; 2) the processes involved in luminosity perception are intrinsically different from those involved in surface color perception

San Lorenzo and the Poggendorff illusion in Ravenna

In the Mausoleum of Galla Placidia (Ravenna, Italy), the San Lorenzo lunette shows two peculiar visual effects: a transparency effect of gold seen through gold and perceptual collinearity between two parts of a cross which are physically misaligned. Both effects are found within the area of the halo surrounding the saint’s head. In this work we addressed the problem posed by the physical misalignment of the cross. Our hypothesis is that the physical misalignment went unnoticed throughout history because the artist produced a perceptual alignment to correct for the Poggendorff illusion. Hence, we asked observers to align two ends of a cross in a reproduction showing the silhouette of San Lorenzo’s torso holding the cross. Results support our hypothesis: both direction and magnitude of adjustments comply with the alignment in the original mosaic

Mishaps, errors, and cognitive experiences: on the conceptualization of perceptual illusions

Although a visual illusion is often viewed as an amusing trick, for the vision scientist it is a question that demands an answer, which leads to even more questioning. All researchers hold their own chain of questions, the links of which depend on the very theory they adhere to. Perceptual theories are devoted to answering questions concerning sensation and perception, but in doing so they shape concepts such as reality and representation, which necessarily affect the concept of illusion. Here we consider the macroscopic aspects of such concepts in vision sciences from three classic viewpoints—Ecological, Cognitive, Gestalt approaches—as we see this a starting point to understand in which terms illusions can become a tool in the hand of the neuroscientist. In fact, illusions can be effective tools in studying the brain in reference to perception and also to cognition in a much broader sense. A theoretical debate is, however, mandatory, in particular with regards to concepts such as veridicality and representation. Whether a perceptual outcome is considered as veridical or illusory (and, consequently, whether a class of phenomena should be classified as perceptual illusions or not) depends on the meaning of such concepts

Mona Lisa's smiles in Leonardo's drawings

‘Mona Lisa’ (1503-05) is the most-visited, written about and parodied work of ‎art in the world. However, the ambiguous allure it features is not unique. Soranzo & Newberry (‎‎2015) found a similar display of ambiguity in the lesser-known painting ‘La Bella Principessa’. They suggested that most of the ambiguity of both portraits can be explained in terms of a spatial frequency contingent illusion concerning the direction of the mouth. When viewed closely, the slant of the ‎mouth appears to turn downwards, but when viewed from afar, or when the image is blurred, the edges ‎of the mouth appear to take an upward turn. This apparent modification in mouth slant results in a change of facial expression. The ambiguity may therefore be explained by the perceptual instability of the mouth slant. We have now extended this line of research and discovered that a similar illusion of direction is also present in two Leonardo's drawings: La Scapigliata (1508) and another Female Head (1470-76). This discovery supports the suggestive hypothesis that Leonardo studied the generation of ambiguity in the expression of portrayed subjects as matter to ‘moti mentali’, i.e. what we may now identify as micro expressions

Mona Lisa’s smiles in Leonardo’s drawings

The Mona Lisa is the most-visited, most written about and most parodied work of ‎art in the world. However, the ‘uncatchable smile’ that makes Leonardo da Vinci’s ‎Mona Lisa so special is not unique. In previous research, Soranzo & Newberry (‎‎2015, VR) found that the technique which would later give his most famous subject ‎her mysterious allure was first executed in the lesser-known painting, La Bella Principessa, recently claimed to be a "Leonardo" (Kemp & Cotte,2010). ‎Soranzo & Newberry suggested that most of the "mysterious allure" of both Mona Lisa and La Bella Principssa can be explained by an illusion of direction of the mouth of the portrayed subjects which is spatial frequency dependend: When viewed directly the slant of the ‎mouth of the subjects appears to turn downwards, but when viewed from far away the edges ‎of the mouth appear to take an upward turn. At its turn, this perceived change in the mouth slant, generate a perceived change in the facial expression. We have now extended this line of research and discovered that a similar illusion is present in different Leonardo's paintings. By asking participants to judge how much a figure painted by Leonardo is smiling, we found that the ratings depend on the spatial frequency: when judged from far away or in blurring conditions, the figures are smiling more. This illusion is present in some of the women, angels and babies painted by the Master but we couldn't find it in any of the males. This discovery support to the hypothesis that Leonardo worked on "ambiguity" in the expression of the portrayed subjects over the years before producing it in the most famous masterpiece, Mona Lisa and leaves the open question of why he did not want to portray this illusion on male figures

The Glare Effect Test and the Impact of Age on Luminosity Thresholds

The glare effect (GE) is an illusion in which a white region appears self-luminous when surrounded by linearly decreasing luminance ramps. It has been shown that the magnitude of the luminosity effect can be modulated by manipulating the luminance range of the gradients. In the present study we tested the thresholds for the GE on two groups of adults: young (20–30 years old) and elderly (60–75 years old). Purpose of our perspective study was to test the possibility of transforming the GE into a test that could easily measure thresholds for luminosity and discomfort glare. The Glare Effect Test (GET) consisted in 101 printed cards that differed from each other for the range of luminance ramps. Participants were assessed with GET and a battery of visual tests: visual acuity, contrast sensitivity, illusion of length perception, and Ishihara test. Specifically in the GET, participants were required to classify cards on the basis of two reference cards (solid black-no gradient; full range black to white gradient). PSEs of the GE show no correlation with the other visual tests, revealing a divergent validity. A significant difference between young and elderly was found: contrary to our original expectations, luminosity thresholds of GE for elderly were higher than those for young, suggesting a non-direct relationship between luminosity perception and discomfort glare

The Poggendorff illusion in Ruben's Descent from the Cross in Antwerp: Does the illusion even matter?

Two experiments are described, the purpose of which was to investigate the presence of a misalignment illusion caused by Poggendorff-like conditions in two paintings by Peter Paul Rubens, both depicting the Descent from the Cross, one located in Antwerp (Belgium), the other in Lille (France). The first shows a geometrical misalignment made by Rubens in a minor detail, which is considered proof that the artist observed the Poggendorff illusion. The second painting, instead, shows a perfect geometrical alignment in a similar detail. In experiment 1, participants were asked to align a top segment to a lower one in two types of stimuli: a full-size digitally manipulated reproduction of the painting and a Poggendorff-like configuration that recalled the painting's lines displacement and tilt. Adjustments were performed from two distances, one up close (painting distance) and one from below and far (observation distance). Results confirmed the presence of the Poggendorff illusion, but mean adjustments significantly differed from the misalignment perpetrated by Rubens. Experiment 2 was set up in a similar fashion with the Lille painting. Results confirmed the presence of the Poggendorff illusion also in this painting; however, the alignment by Rubens coincides with the geometrical one. Results from both experiments do not support the claim that Rubens observed the Poggendorff illusion and therefore corrected for it in the Antwerp painting. An alternative account is discussed, which relates to the structural layout of the painting