Illusion as a Cognitive Clash Rooted in Perception.

Illusions are important 'tools' in the study of perceptual processes. Their conception is typically linked to the notion of veridicality in a dual-world framework, in which we either see the macro physical world as it is (ecological approaches) or we derive a faithful representation (cognitive approaches) of it. Within such theoretical views, illusions are errors caused by inadequate sensory information (because of poor quality, insufficient quantity, contradictory, etc.

The influence of arm posture on the Uznadze haptic aftereffect.

The role of arm posture in the Uznadze haptic aftereffect is investigated: two identical test stimuli (i.e., spheres, TS) clenched simultaneously appear haptically different in size after hands have been adapted to two spheres (adapting stimuli, AS) differing in size: the hand adapted to a small AS feels TS bigger than the hand adapted to a big AS.

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 , 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.

Looking Into Mona Lisa's Smiling Eyes: Allusion to an Illusion.

We present results from two experiments aimed at studying the direction of 's gaze and its affective expression. In experiment 1 we studied the effect of retinal image size on the perception of her gaze by manipulating observation distances of a high-quality print of the painting. Participants ( = 30) were asked to answer a simple question (is the person portrayed looking at you?) from six different distances ranging from 55 to 755 cm.

Distinct processes of lighting priors for lightness and 3-D shape perception.

The visual system often relies on prior assumptions when interpreting ambiguous visual inputs. A well-known example is the light-from-above prior, which aids the judgment of an object's three-dimensional (3-D) shape (i.e.

The Interpretation of E-Motions in Faces and Bodies Derived from Static Artworks by Individuals with High Functioning Autistic Spectrum.

E-motions are defined as those affective states the expressions of which-conveyed either by static faces or body posture-embody a dynamic component and, consequently, convey a higher sense of dynamicity than other emotional expressions. An experiment is presented, aimed at testing whether e-motions are perceived as such also by individuals with autism spectrum disorders (ASDs), which have been associated with impairments in emotion recognition and in motion perception. To this aim we replicate with ASD individuals a study, originally conducted with typically developed individuals (TDs), in which we showed to both ASD and TD participants 14 bodiless heads and 14 headless bodies taken from eleven static artworks and four drawings.

Asymmetric Brightness Effects With Dark Versus Light Glare-Like Stimuli.

The glare effect is a brightness illusion that has captured the attention of the vision community since its discovery. However, its photometrical reversal, which we refer to here as photometrical reversed glare (PRG) stimuli, remained relatively unexplored. We presented three experiments that sought to examine the perceived brightness of a target area surrounded by luminance gradients in PRG stimuli and compare them with conventional glare effect configurations.

Brightness perception changes related to pupil size.

Dilating the pupils allow more quanta of light to impact the retina. Consequently, if one pupil is dilated with a pharmacological agent (Tropicamide), the brightness of a surface under observation should increase proportionally to the pupil dilation. Little is known about causal effects of changes in pupil size on perception of an object's brightness.

See What You Feel: A Crossmodal Tool for Measuring Haptic Size Illusions.

The purpose of this research is to present the employment of a simple-to-use crossmodal method for measuring haptic size illusions. The method, that we call , was tested by employing Uznadze's classic haptic aftereffect in which two spheres physically identical (test spheres) appear different in size after that the hands holding them underwent an adaptation session with other two spheres (adapting spheres), one bigger and the other smaller than the two test spheres. To measure the entity of the illusion, a three-dimensional visual scale was created and participants were asked to find on it the spheres that corresponded in size to the spheres they were holding in their hands out of sight.

Evidence of top-down modulation of the Brentano illusion but not of the glare effect by transcranial direct current stimulation.

Transcranial direct current stimulation (tDCS) has been widely used for modulating sensory, motor and cognitive functions, but there are only few attempts to induce and change illusory perception. Visual illusions have been the most traditional and effective way to investigate visual processing through the comparison between physical reality and subjective reports. Here we used tDCS to modulate two different visual illusions, namely the Brentano illusion and the glare effect, with the aim of uncovering the influence of top-down mechanisms on bottom-up visual perception in two experiments.

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.

Sensual Light? Subjective Dimensions of Ambient Illumination.

This work concerns the subjective impression of perceived illumination. The purpose of the study is to test attributes expressing qualitative experiences referring to ambient lighting that can be applied as descriptors. Seventy participants viewed an actual model room, with the fourth wall removed (viewing booth).

The Eye Pupil's Response to Static and Dynamic Illusions of Luminosity and Darkness.

Pupil diameters were recorded with an eye-tracker while participants observed cruciform patterns of gray-scale gradients that evoked illusions of enhanced brightness () or of enhanced darkness. The illusions were either presented as images or as animations which initially appeared as a pattern of filled squares that-in a few seconds-gradually changed into gradients until the patterns were identical to the ones. Gradients could either converge toward the center, resulting in a central region of enhanced, illusory, brightness or darkness, or oriented toward each side of the screen, resulting in the perception of a peripheral ring of illusory brightness or darkness.

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).

The Poggendorff illusion before Poggendorff.

This paper is about the Poggendorff illusion in pictorial artworks. In particular, it deals with the role played by the Poggendorff illusion in the making of the geometrical misalignments in the mosaic known as Lunetta di San Lorenzo in Ravenna (Italy) and in Rubens's oil on panel Descent from the Cross in Antwerp (Belgium). Three experiments are presented.

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.

The size illusion and lightness contrast effect in Delboeuf-like displays: possible evidence of percept-percept coupling.

We conducted two experiments to test the relationship between Delboeuf's size-contrast illusion and a concomitant lightness contrast effect that can be observed when achromatic disks are employed as targets. In experiment 1 participants were asked to adjust the diameter of a target (D1) surrounded by a small circular size-inducer (C1) to match in size a comparison target (D2) surrounded by a circular size-inducer (C2) either equal or greater in diameter than C1. Experiment 2 was similar to experiment 1, except that D1 and D2 were physically equal in size, and participants were asked to adjust the luminance of D1 to match D2 in lightness.

Seeing further than your nose.

Among monocular depth cues, ocular parallax (first described formally by Brewster in 1844) remains mostly unknown, its role in perception still not investigated scientifically. Given that every single eye movement induces ocular parallax, it is a potentially useful depth cue. This paper is an attempt to revive interest in the topic.

Lightness effects in Delboeuf and Ebbinghaus size-contrast illusions.

We examined lightness effects observed in Delboeuf and Ebbinghaus size-contrast illusions. Results of four experiments are reported. Experiment 1 was conducted with Delboeuf-like stimuli and shows that the disk that appears bigger appears either lighter or darker than the disk that appears smaller, depending on the contrast polarity between disks and background.

Measuring the meter: on the constancy of lightness scales seen against different backgrounds.

The constancy of a 16-step achromatic Munsell scale was tested with regards to background variations in two experiments. In experiment 1 three groups of observers were asked to find lightness matches for targets in simultaneous lightness displays by using a 16-step achromatic Munsell scale placed on a white, black, or white-black checkered background. In experiment 2, a yellow-blue checkered background and a green-red checkered background replaced Munsell scales on the black and on the white backgrounds.

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.

On the portability of computer-generated presentations: the effect of text-background color combinations on text legibility.

Objective: The aim of our study was to investigate which text-background (TB) color combinations improve legibility and pleasantness of texts either presented on a computer screen or projected on a wider surface.

Background: Our work stems from the observation that multimedia presentations, even those by professionals in visual disciplines, are often spoiled by illegibility, which affects readability and the pleasantness of attending to such presentations.

Methods: We investigated this problem through three experiments.

When figure-ground segmentation modulates brightness: the case of phantom illumination.

In the phantom illumination illusion, luminance ramps ranging from black to white induce a brightness enhancement on an otherwise homogeneous dark background. The strength of the illusion was tested with regard to the extension of the brightness inducing perimeter, surrounding the target area by manipulating the number of inducers (exp. 1) and the size of the inducers (exp.

The representation of time course events in visual arts and the development of the concept of time in children: a preliminary study.

By means of a careful search we found several representations of dynamic contents of events that show how the depiction of the passage of time in the visual arts has evolved gradually through a series of modifications and adaptations. The general hypothesis we started to investigate is that the evolution of the representation of the time course in visual arts is mirrored in the evolution of the concept of time in children, who, according to Piaget (1946), undergo three stages in their ability to conceptualize time. Crucial for our hypothesis is Stage II, in which children become progressively able to link the different phases of an event, but vacillate between what Piaget termed 'intuitive regulations', not being able to understand all the different aspects of a given situation.

The glare effect does not give rise to a longer-lasting afterimage.

The glare effect is an illusion in which a region appears self-luminous when flanked by gradients that decrease in luminance with distance from the region (Zavagno, 1999 Perception 28 835-838). This region also appears brighter than a surface of the same luminance. We investigated, using the paradigm of afterimages, whether a low-level mechanism at the level of the retina or LGN could account for this apparent brighter sensation.