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Human language is influenced by sensory-motor experiences. Sensory experiences gathered in a spatiotemporal world are used as raw material to create more abstract concepts. In language, one way to encode spatial relationships is through spatial prepositions. Spatial prepositions that specify the proximity of objects in space, like far and near or their variants, are found in most languages. The mechanism for determining the proximity of another entity to itself is a useful evolutionary trait. From the taxic behavior in unicellular organisms like bacteria to the tropism in the plant kingdom, this behavior can be found in almost all organisms. In humans, vision plays a critical role in spatial localization and navigation. This computational study analyzes the relationship between vision and spatial prepositions using an artificial neural network. For this study, a synthetic image dataset was created, with each image featuring a 2D projection of an object placed in 3D space. The objects can be of various shapes, sizes, and colors. A convolutional neural network is trained to classify the object in the images as far or near based on a set threshold. The study mainly explores two visual scenarios: objects confined to a plane (grounded) and objects not confined to a plane (ungrounded), while also analyzing the influence of camera placement. The classification performance is high for the grounded case, demonstrating that the problem of far/near classification is well-defined for grounded objects, given that the camera is at a sufficient height. The network performance showed that depth can be determined in grounded cases only from monocular cues with high accuracy, given the camera is at an adequate height. The difference in the network's performance between grounded and ungrounded cases can be explained using the physical properties of the retinal imaging system. The task of determining the distance of an object from individual images in the dataset is challenging as they lack any background cues. Still, the network performance shows the influence of spatial constraints placed on the image generation process in determining depth. The results show that monocular cues significantly contribute to depth perception when all the objects are confined to a single plane. A set of sensory inputs (images) and a specific task (far/near classification) allowed us to obtain the aforementioned results. The visual task, along with reaching and motion, may enable humans to carve the space into various spatial prepositional categories like far and near. The network's performance and how it learns to classify between far and near provided insights into certain visual illusions that involve size constancy. [ABSTRACT FROM AUTHOR]

Abstract As the global population ages, understanding of the effect of aging on visual perception is of growing importance. This study investigates age-related changes in adulthood along size perception through the lens of three visual illusions: the Ponzo, Ebbinghaus, and Height-width illusions. Utilizing the Bayesian conceptualization of the aging brain, which posits increased reliance on prior knowledge with age, we explored potential differences in the susceptibility to visual illusions across different age groups in adults (ages 20–85 years). To this end, we used the BTPI (Ben-Gurion University Test for Perceptual Illusions), an online validated battery of visual illusions developed in our lab. The findings revealed distinct patterns of age-related changes for each of the illusions, challenging the idea of a generalized increase in reliance on prior knowledge with age. Specifically, we observed a systematic reduction in susceptibility to the Ebbinghaus illusion with age, while susceptibility to the Height-width illusion increased with age. As for the Ponzo illusion, there were no significant changes with age. These results underscore the complexity of age-related changes in visual perception and converge with previous findings to support the idea that different visual illusions of size are mediated by distinct perceptual mechanisms.

We describe a novel size illusion in which targets appear to either shrink or grow when enclosed within a narrow tube. The direction of size change is determined by the contrast step between display elements. We first noticed this effect in the context of the dynamic "rocking line" illusion (RLI), but it can also be easily seen in completely static displays. As with the RLI, the overall scale of the display seems to play an important role. We provide an online, interactive demo, enabling the reader to explore the relevant parameter space. [ABSTRACT FROM AUTHOR]

Parkinson’s disorder (PD) is a common neurodegenerative disorder affecting approximately 1–3% of the population aged 60 years and older. In addition to motor difficulties, PD is also marked by visual disturbances, including depth perception, abnormalities in basal ganglia functioning, and dopamine deficiency. Reduced ability to perceive depth has been linked to an increased risk of falling in this population. The purpose of this paper was to determine whether disturbances in PD patients’ visual processing manifest through atypical performance on visual illusion (VI) tasks. This insight will advance understanding of high-level perception in PD, as well as indicate the role of dopamine deficiency and basal ganglia pathophysiology in VIs susceptibility. Groups of 28 PD patients (Mage = 63.46, SD = 7.55) and 28 neurotypical controls (Mage = 63.18, SD = 9.39) matched on age, general cognitive abilities (memory, numeracy, attention, language), and mood responded to Ebbinghaus, Ponzo, and Müller-Lyer illusions in a computer-based task. Our results revealed no reliable differences in VI susceptibility between PD and neurotypical groups. In the early- to mid-stage of PD, abnormalities of the basal ganglia and dopamine deficiency are unlikely to be involved in top-down processing or depth perception, which are both thought to be related to VI susceptibility. Furthermore, depth-related issues experienced by PD patients (e.g., increased risk for falling) may not be subserved by the same cognitive mechanisms as VIs. Further research is needed to investigate if more explicit presentations of illusory depth are affected in PD, which might help to understand the depth processing deficits in PD. [ABSTRACT FROM AUTHOR]

Visual illusions provide a unique opportunity to understand cognitive and perceptual alterations in schizophrenia-spectrum conditions. Schizophrenia patients often exhibit increased susceptibility to the Müller-Lyer illusion. Here, we investigate susceptibility to the Müller-Lyer visual illusion in the general population with different levels of schizotypy. We assessed a population-based convenience sample (N = 263) on an online platform. In addition to basic demographics, participants completed the Müller-Lyer illusion, the Cardiff Anomalous Perceptions Scale (CAPS) to measure perceptual anomalies, and the Multidimensional Schizotypy Scale – Brief (MSS-B) for schizotypic traits. To evaluate what predicts susceptibility to the illusion, we fitted a large set of multilevel logistic regression models and performed model averaging over the coefficients. We found support for increased illusion susceptibility among individuals with high positive schizotypy. However, we did not find a comparable effect for anomalous perceptions alone, or for negative or disorganized schizotypy. The increased Müller-Lyer effect in positive schizotypy might be specific to delusion-like beliefs and magical ideation. Further research is needed to clarify how a hierarchical Bayesian formulation of brain function (e.g. imbalances between bottom-up perceptual processing and substantial reliance on prior expectations) can account for the Müller-Lyer effect in schizophrenia-spectrum conditions. [ABSTRACT FROM AUTHOR]

The Ponzo illusion is a famous optical illusion that is not well understood so far. Here we suggest that its origin is closely linked to distribution of spatial attention. In essence, it arises because the size of the attentional field varies between different parts of the stimulus layout, which comes with different spatial resolution and, as a consequence, different apparent sizes of the objects in the stimulus display. We report four experiments (conducted in 2022 and 2023), which support this approach. The illusion substantially decreases when the stimulus layout is modified so that the size of the supposed attentional field is equalized for the crucial parts (Experiment 1). Moreover, we induce a Ponzo-like illusion by means of attentional cues only (Experiment 2). The perceived spatial frequency differs for different parts of the stimulus layout consistent with predicted changes in spatial resolution (Experiment 3). Attentional cuing exerts an analogous influence on the apparent spatial frequency (Experiment 4). The presented approach provides a novel look at the origin of the Ponzo illusion and related phenomena. Public Significance Statement: In this study, we introduce and test a novel explanation of the Ponzo illusion. We propose that this optical illusion is a byproduct of different spatial resolutions for different parts of the stimulus layout resulting from different attentional distributions. Four experiments are reported which provide support for this approach. The presented idea provides a novel look at the origin of optical illusions. [ABSTRACT FROM AUTHOR]

Visuoperceptual dysfunction is common in Parkinson's disease (PD) and is also reported in its prodromal phase, isolated REM sleep behavior disorder (iRBD). We aimed to investigate color discrimination ability and complex visual illusions known as pareidolias in patients with iRBD and PD compared to healthy controls, and their associating clinical factors. 46 iRBD, 43 PD, and 64 healthy controls performed the Farnsworth–Munsell 100 hue test and noise pareidolia tests. Any relationship between those two visual functions and associations with prodromal motor and non-motor manifestations were evaluated, including MDS-UPDRS part I to III, Cross-Cultural Smell Identification Test, sleep questionnaires, and comprehensive neuropsychological assessment. iRBD and PD patients both performed worse on the Farnsworth–Munsell 100 hue test and had greater number of pareidolias compared to healthy controls. No correlations were found between the extent of impaired color discrimination and pareidolia scores in either group. In iRBD patients, pareidolias were associated with frontal executive dysfunction, while impaired color discrimination was associated with visuospatial dysfunction, hyposmia, and higher MDS-UPDRS-III scores. Pareidolias in PD patients correlated with worse global cognition, whereas color discrimination deficits were associated with frontal executive dysfunction. Color discrimination deficits and pareidolias are frequent but does not correlate with each other from prodromal to clinically established stage of PD. The different pattern of clinical associates with the two visual symptoms suggests that evaluation of both color and pareidolias may aid in revealing the course of neurodegeneration in iRBD and PD patients. [ABSTRACT FROM AUTHOR]

'Dazzle coloration' describes a wide variety of high-contrast patterns allegedly providing protection against attack during motion. Previous research falls into three broad groups. First, studies using humans demonstrate that certain surface patterns can cause significant misperceptions in controlled laboratory conditions, although the effects are inconsistent in both direction and magnitude. Second, experiments on target capture or tracking also show effects that are strongly dependent upon the test paradigm. It has not been established that these laboratory findings generalize to other species, or to the real world. Third, mainly comparative studies build a case for longitudinal striping being involved in escape strategies in some squamate reptiles. We suggest that: (1) the concept of dazzle conflates a description of appearance with presumed function; (2) some effects attributed to dazzle have not been distinguished clearly from other mechanisms of protective coloration; and (3) confusion persists over the evidence necessary to attribute a dazzle function to markings. We refine the definition of dazzle to exclude appearance: dazzle is coloration that interferes with target interception, as a result of misperception of its speed, trajectory and/or range. Our review clarifies discussion of dazzle, and sets out a coherent and practical framework for future research. [ABSTRACT FROM AUTHOR]

Pareidolia are perceptions of recognizable images or meaningful patterns where none exist. In recent years, this phenomenon has been increasingly studied in healthy subjects and patients with neurological or psychiatric diseases. The current study examined pareidolia production in a group of 53 stroke patients and 82 neurologically healthy controls who performed a natural images task. We found a significant reduction of absolute pareidolia production in left- and right-hemispheric stroke patients, with right-hemispheric patients producing overall fewest pareidolic output. Responses were categorized into 28 distinct categories, with ‘Animal’, ‘Human’, ‘Face’, and ‘Body parts' being the most common, accounting for 72% of all pareidolia. Regarding the percentages of the different categories of pareidolia, we found a significant reduction for the percentage of “Body parts” pareidolia in the left-hemispheric patient group as compared to the control group, while the percentage of this pareidolia type was not significantly reduced in right-hemispheric patients compared to healthy controls. These results support the hypothesis that pareidolia production may be influenced by local-global visual processing with the left hemisphere being involved in local and detailed analytical visual processing to a greater extent. As such, a lesion to the right hemisphere, that is believed to be critical for global visual processing, might explain the overall fewest pareidolic output produced by the right-hemispheric patients.

Parkinson’s disorder (PD) is a common neurodegenerative disorder affecting approximately 1–3% of the population aged 60 years and older. In addition to motor difficulties, PD is also marked by visual disturbances, including depth perception, abnormalities in basal ganglia functioning, and dopamine deficiency. Reduced ability to perceive depth has been linked to an increased risk of falling in this population. The purpose of this paper was to determine whether disturbances in PD patients’ visual processing manifest through atypical performance on visual illusion (VI) tasks. This insight will advance understanding of high-level perception in PD, as well as indicate the role of dopamine deficiency and basal ganglia pathophysiology in VIs susceptibility. Groups of 28 PD patients (Mage = 63.46, SD = 7.55) and 28 neurotypical controls (Mage = 63.18, SD = 9.39) matched on age, general cognitive abilities (memory, numeracy, attention, language), and mood responded to Ebbinghaus, Ponzo, and Müller-Lyer illusions in a computer-based task. Our results revealed no reliable differences in VI susceptibility between PD and neurotypical groups. In the early- to mid-stage of PD, abnormalities of the basal ganglia and dopamine deficiency are unlikely to be involved in top-down processing or depth perception, which are both thought to be related to VI susceptibility. Furthermore, depth-related issues experienced by PD patients (e.g., increased risk for falling) may not be subserved by the same cognitive mechanisms as VIs. Further research is needed to investigate if more explicit presentations of illusory depth are affected in PD, which might help to understand the depth processing deficits in PD.

Visual illusions have always fascinated people but they have often been confined to the field of entertainment. Although philosophers, psychologists and neuroscientists have used them to explore the bases of human perception and to teach about vision, these attractive tools have still remained largely underexploited. The goal of the present paper is to argue that visual illusions can also serve as a powerful medium to question our relation to the world and to others, as they demonstrate that we do not fully perceive reality and that each interpretation of the world may be equally sound. Further, specific 3D visual illusions, such as 3D ambiguous objects that give rise to two specific interpretations, enable the viewer to realize that their perception is tied to their viewing point, and that this may also apply to social cognition and interactions. Specifically, this low-level embodied experience should generalize to other levels and enhance the consideration of others' perspective independently of the type of representations. Therefore, the use of illusions in general, and 3D ambiguous objects in particular, constitutes an avenue for future interventions designed to increase our perspective-taking abilities and the pacification of social relations through mutual understanding, which is particularly relevant in the current era. • Illusions have an intrinsic positive affective value. • Illusions could enhance the consideration of others' perspective. • Illusions represent a powerful medium for bottom-up social cognitive interventions. [ABSTRACT FROM AUTHOR]

Visual illusions are popularly referred to as the phenomena where the eye sees something that is not there. The aim of this review is to show that illusions are not the occasional misinterpretations of the physical world. Illusions are critical to our understanding of perceptual processes. The cause of illusions can vary depending on the reflection or refraction of light, how the brain processes the information reaching the retina, or how the visual system works when perceiving depth. Illusions, which have inspired both artists and scientists, have been instrumental in our understanding of human perception and the functioning of the brain in general. At the beginning of this article, the classes that emerge from a scientific perspective will be defined in parallel with the hierarchical visual perception. Examples of illusions that inform us about the physiological (corresponding to the early stages of visual perception) processes and cognitive (corresponding to higher level stages of visual perception) strategies will be given, and the factors that may cause them will be examined. In the light of theoretical approaches and perceptual grouping concepts, I will discuss how these interpretations help us to understand the brain and human nature. Next, I will give examples of findings and applications in clinical populations to touch on the role of illusions in our understanding of visual perception in e.g. schizophrenia patients. [ABSTRACT FROM AUTHOR]

Visual illusions have long been used to study visual perception and contextual integration. Neuroimaging studies employ illusions to identify the brain regions involved in visual perception and how they interact. We conducted an Activation Likelihood Estimation (ALE) meta-analysis and meta-analytic connectivity modeling on fMRI studies using static and motion illusions to reveal the neural signatures of illusory processing and to investigate the degree to which different areas are commonly recruited in perceptual inference. The resulting networks encompass ventral and dorsal regions, including the inferior and middle occipital cortices bilaterally in both types of illusions. The static and motion illusion networks selectively included the right posterior parietal cortex and the ventral premotor cortex respectively. Overall, these results describe a network of areas crucially involved in perceptual inference relying on feed-back and feed-forward interactions between areas of the ventral and dorsal visual pathways. The same network is proposed to be involved in hallucinogenic symptoms characteristic of schizophrenia and other disorders, with crucial implications in the use of illusions as biomarkers.

Ponzo is a familiar name in psychology because of the illusion that takes his name. He had a long and productive career in Italy, and some of his work was translated for international journals already in his lifetime. However, few of these papers are available in English. We provide a commentary that considers how his name came to be associated with an illusion he did not discover. We explain the content of several papers, some of which are often cited in a wrong context in the literature (i.e., papers on touch mentioned in relation to the Ponzo illusion). More importantly, we discuss his contribution to the study of perceived numerosity, and provide a full translation of his important 1928 paper, including a redrawing of its 28 illustrations. [ABSTRACT FROM AUTHOR]

Partial replications of experiments reported by Cai et al. (Attention, Perception, & Psychophysics, 79(4), 1217–1226, 2017) on the so-called Horizontal-vertical illusion confirmed that dissecting L-figures into two separate lines yields greater overestimation of (near-)verticals than do intact Ls. However, contrary to Cai et al.'s findings, which had been obtained with a staircase procedure, with the method of constant stimuli, the amount of illusion was much smaller. This divergence is explained by the self-reinforcing nature of adjustment procedures. Another finding, already reported by Cormack and Cormack (Perception & Psychophysics, 16(2), 208–212, 1974), that obtuse angles between an L's lines yield greater bias than acute angles, was also replicated in one experiment but tended to be reversed in another. Mixing dissected, upright and top-down inverted Ls and laterally oriented Ts, both with tilted lines, within one experiment confirmed that the bias for Ts is opposite to the one for Ls: For Ts, the effect of (virtual) bisection dominates, yielding an overestimation of the length of the undivided line, whereas for Ls, the horizontal-vertical anisotropy dominates, yielding an overestimation of the length of the vertical line. The differential gap effects can possibly be explained by interactions within the neural substrate between orientation-sensitive and end-inhibited neurons, and the method effects by perceptual learning. [ABSTRACT FROM AUTHOR]

The findings on the association of schizotypal traits with the perception of visual illusions are scarce and inconsistent and have not taken into consideration potential effects of childhood traumatic experiences, a risk factor for schizophrenia‐spectrum conditions. Thus, the present study addressed the question of potential moderating effects of early traumatic experiences on the association between different aspects of schizotypal traits with the perception of the Müller‐Lyer and Navon's Hierarchical Letters (NHL) illusions. The study revealed that (a) increased suspiciousness was associated with increased liability to the Müller‐Lyer illusion, when the exposure to traumatic events was high, whereas the opposite pattern was true when the exposure to traumatic events was low; (b) negative schizotypy was associated with more accurate global perception, and high disorganized schizotypy was associated with superior accuracy when target letters were present during the NHL illusion, when early traumatic experiences were at lower levels; and (c) high negative, disorganized, and total schizotypy were associated with lower accuracy when target letters were present in the NHL paradigm, when early traumatic experiences were at higher levels. The findings of the study suggest that early traumatic events differentially moderate the relationship between various aspects of schizotypal traits and visual perceptual processing. [ABSTRACT FROM AUTHOR]

Visual illusions have long been used as tools to investigate sensory-perceptual deficits in schizophrenia. Recent conflicting accounts have called into question the assumption of abnormal illusion perception in patients and, therefore, the validity of this approach. Here, we present a systematic review of the current evidence regarding visual illusion perception abnormalities in patients with schizophrenia. Relevant publications were identified by a systematic search of PubMed, Literatura LILACS, PsycINFO, Embase, Scopus, Cochrane Central Register of Controlled Trials (CENTRAL), IBECS, BIOSIS, and Web of Science. Forty-five studies were selected which included illusions classified as 'Motion illusions', 'Geometric-optical illusions', 'Illusory contours', 'Depth inversion illusion', and 'Non-specific'. There is concordant evidence of abnormal processing of illusions in patients for most categories, especially in facial Depth Inversion and Müller-Lyer illusions. There were significant methodological disparities and shortcomings, but risk of bias was overall low for individual studies. The usefulness of visual illusions as tools in clinical settings as well as in basic research may be contingent on significant methodological refinements. [ABSTRACT FROM AUTHOR]

Perceiving and grasping an object present an animal with different sets of computational problems. The solution in primates entails the specialization of separate neural networks for visual processing with different object representations. This explains why the Ebbinghaus illusion minimally affects the grasping hand's in-flight aperture, which normally scales with target size, even though the size of the target disc remains misperceived. An attractive alternative account, however, posits that grasps are refractory to the illusion because participants fixate on the target and fail to attend to the surrounding context. To test this account, we tracked both limb and gaze while participants made forced-choice judgments of relative disc size in the Ebbinghaus illusion or did so in combination with grasping or manually estimating the size of one of the discs. We replicated the classic dissociation: grasp aperture was refractory to the measured illusory effect on perceived size, while judgments and manual estimates of disc size were not. Importantly, the number of display-wide saccades per second and the percentage of total fixation time or fixations directed at the selected disc failed to explain the dissociation. Our findings support the contention that object perception and goal-directed action rely on distinct visual representations. This article is part of a discussion meeting issue 'New approaches to 3D vision'. [ABSTRACT FROM AUTHOR]

We describe a new phenomenon-partial object doubling-in which the perceived contours of peripherally viewed moving targets become distorted and duplicated. The effect appears to arise due to interactions between physically drawn contours and the strong negative afterimages that are dynamically released during stable viewing of the displays. An online demo is provided where the effect can be experienced and relevant parameters manipulated., Competing Interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s) 2024.)

In order to investigate interrelations between the Oppel-Kundt- and the T-illusion, T-type figures, comprised of one dotted and one empty line (demarcated by its endpoints), separated by a gap of variable size, and rotated to oblique orientations, were judged with regard to the lengths of the two extents. The T-illusion (overestimation of the length of the undivided line) was greater for a T with a dotted undivided line and a small gap. When the divided line was dotted, the illusion vanished at a small gap and reversed at a larger one. Findings are interpreted to mirror activities of a neural T-schema as well as orientation- and density-sensitive neurons. [ABSTRACT FROM AUTHOR]

Visual illusions are phenomena in which the actual physical parameters of an object are out of alignment with visual perception, such as when an object that is not moving appears to move, or when the color, brightness, or size of an object appears to be different from its reality. It is also the perception of such discrepancies. Illusions have attracted many people for a long time because they are surprising to the viewer and have a strong entertainment value. Illusions are thought to express the characteristics of visual information processing in the eye and brain, and are an important tool in the study of vision, and the field of research has been developing remarkably. In recent years, research methods have actively incorporated not only psychophysical methods but also modern brain science methodologies such as fMRI, and more recently, research utilizing artificial intelligence has also progressed. This paper focuses on the study of visual illusions using deep neural networks (DNN) which is being conducted in the authors laboratory and is becoming popular worldwide. [ABSTRACT FROM AUTHOR]

Visual illusions represent an innovative method to investigate animal visual perception. One well known geometric illusion is the Ebbinghaus-Titchener illusion, which consists of two identically sized target circles with one surrounded by large inducer circles and the other surrounded by small inducer circles. Humans are susceptible to this illusion, underestimating the size of the target circle surrounded by larger inducers and overestimating the size of the target circle surrounded by smaller inducers. In the present study, we investigated whether pet dogs (Canis lupus familiaris) perceive the Ebbinghaus-Titchener illusion in a spontaneous choice task by adapting and replicating the methodology of Miletto Petrazzini et al. (2017). Twenty-five pet dogs were presented with two stimuli in which a food reward was embedded. Each subject participated in 18 total trials, 12 size discrimination control trials (where one food reward was larger than the other) and six illusion trials (where identically sized food rewards were presented). Dogs, as a group, failed to demonstrate a significant preference for the larger food reward in control trials, and demonstrated null susceptibility, performing at chance, in the illusion trials. The chance performance on controls prevents further interpretation regarding canine illusion susceptibility; however, it invokes a discussion regarding the methodological challenges associated with conducting spontaneous-choice tasks. In an attempt to provide guidance for future research, we provide a review of canine illusion susceptibility to the Ebbinghaus-Titchener illusion and detailed recommendations to help mitigate extraneous factors to help further research of animal illusion susceptibility.

The ability to complete partially missing contours is widespread across the animal kingdom, but whether this extends to dogs is still unknown. To address this gap in knowledge, we assessed dogs' susceptibility to one of the most common contour illusions, the Kanizsa's triangle. Six dogs were trained to discriminate a triangle from other geometrical figures using a two-alternative conditioned discrimination task. Once the learning criterion was reached, dogs were presented with the Kanizsa's triangle and a control stimulus, where inducers were rotated around their centre, so as to disrupt what would be perceived as a triangle by a human observer. As a group, dogs chose the illusory triangle significantly more often than control stimuli. At the individual level, susceptibility to the illusion was shown by five out of six dogs. This is the first study where dogs as a group show susceptibility to a visual illusion in the same manner as humans. Moreover, the analyses revealed a negative effect of age on susceptibility, an effect that was also found in humans. Altogether, this suggests that the underling perceptual mechanisms are similar between dogs and humans, and in sharp contrast with other categories of visual illusions to which the susceptibility of dogs has been previously assessed. [ABSTRACT FROM AUTHOR]

The visual mechanisms underlying approximate numerical representation are still intensely debated because numerosity information is often confounded with continuous sensory cues (e.g., texture density, area, convex hull). However, numerosity is underestimated when a few items are connected by illusory contours (ICs) lines without changing other physical cues, suggesting in turn that numerosity processing may rely on discrete visual input. Yet, in these previous works, ICs were generated by black-on-gray inducers producing an illusory brightness enhancement, which could represent a further continuous sensory confound. To rule out this possibility, we tested participants in a numerical discrimination task in which we manipulated the alignment of 0, 2, or 4 pairs of open/closed inducers and their contrast polarity. In Experiment 1, aligned open inducers had only one polarity (all black or all white) generating ICs lines brighter or darker than the gray background. In Experiment 2, open inducers had always opposite contrast polarity (one black and one white inducer) generating ICs without strong brightness enhancement. In Experiment 3, reverse-contrast inducers were aligned but closed with a line preventing ICs completion. Results showed that underestimation triggered by ICs lines was independent of inducer contrast polarity in both Experiment 1 and Experiment 2, whereas no underestimation was found in Experiment 3. Taken together, these results suggest that mere brightness enhancement is not the primary cause of the numerosity underestimation induced by ICs lines. Rather, a boundary formation mechanism insensitive to contrast polarity may drive the effect, providing further support to the idea that numerosity processing exploits discrete inputs. [ABSTRACT FROM AUTHOR]

Two experiments tested a prediction derived from the recent finding that the Oppel-Kundt illusion – the overestimation of a filled extent relative to an empty one – was much attenuated when the empty part of a bipartite row of dots was vertical and the filled part horizontal, suggesting that the Horizontal-vertical illusion – the overestimation of vertical extents relative to horizontal ones – only acted on the empty part of an Oppel-Kundt figure. Observers had to bimanually indicate the sizes of the two parts of an Oppel-Kundt figure, which were arranged one above the other with one part vertical and the other part tilted -45°, 0°, or 45°. Results conformed to the prediction but response bias was greater when observers had been instructed to point to the extents' endpoints than when instructed to estimate the extents' lengths, suggesting that different concepts and motor programs had been activated. [ABSTRACT FROM AUTHOR]

Visual illusions are fascinating phenomena that have been used and studied by artists and scientists for centuries, leading to important discoveries about the neurocognitive underpinnings of perception, consciousness, and neuropsychiatric disorders such as schizophrenia or autism. Surprisingly, despite their historical and theoretical importance as psychological stimuli, there is no dedicated software, nor consistent approach, to generate illusions in a systematic fashion. Instead, scientists have to craft them by hand in an idiosyncratic fashion, or use pre-made images not tailored for the specific needs of their studies. This, in turn, hinders the reproducibility of illusion-based research, narrowing possibilities for scientific breakthroughs and their applications. With the aim of addressing this gap, Pyllusion is a Python-based open-source software (freely available at https://github.com/RealityBending/Pyllusion), that offers a framework to manipulate and generate illusions in a systematic way, compatible with different output formats such as image files (.png,.jpg,.tiff, etc.) or experimental software (such as PsychoPy). [ABSTRACT FROM AUTHOR]

Research on how children with neurodevelopmental disorders perceive, process, and interpret visual illusions (VIs) has been extensively focused on children with autism spectrum disorder providing controversial findings. In this study, we investigated the patterns of vulnerability to a wide set of VIs comprising 23 standard text book VIs and their variations in a clinical sample of children with neurodevelopmental disorders compared to typically developing children (TD). A total of 176 children, aged between 4.6 and 13.8 years old, were distributed into four groups: high-functioning autism (HFA; N = 23), attention-deficit/hyperactivity disorder (ADHD; N = 42), specific learning disorder (SLD; N = 70), and TD (N = 41). Regression models, adjusted for sex, age, and non-verbal IQ, showed that HFA was associated with greater responses accuracy than TD children to the full battery of VIs, to the cognitive illusions, to the distortions, and to both geometrical illusions of size/shape (cognitive distortions) and lightness contrast effects (physical distortions). The susceptibility of ADHD children was found attenuated for illusory contours and greater for paradoxical illusions in comparison with TD children. No significant differences were shown between the SLD group and the TD children. Our findings, which were adjusted for the same duration of visual working memory across groups, showed that there is a potential specific tendency of HFA children to failure of processing visual information in context. Contrarily, children with ADHD showed in general normal global processing such as children diagnosed with SLD. [ABSTRACT FROM AUTHOR]

Data from three functional magnetic resonance imaging (fMRI) studies that involved in total about 100 participants and showed that the strength of several visual illusions such as the Ebbinghaus, Ponzo, and Muller-Lyer illusions depends on neuroanatomical subject measures such as visual cortex surface area and parahippocampal cortex gray matter volume were evaluated using a dynamical systems perspective to determine brain bifurcation parameters. Bifurcation parameters that involved power laws and captured relational dependencies were fitted separately to the three fMRI studies. The bifurcation parameter hypothesis that states that such parameters show unique quantities and are no longer correlated to structural systems properties was tested. The power law exponents and mean bifurcation parameter values were determined. For all three studies and three illusion types, the bifurcation parameter hypothesis was supported. Accordingly, the constructed parameters characterized the reactions of the participants under the Ebbinghaus, Ponzo, and Muller-Lyer illusions in terms of unique threshold values that no longer depended on neuroanatomical subject measures. Power law exponents in the range from 1 to 7 were found. The fMRI data describing gray matter volume of certain active regions in the parahippocampal cortex showed some interesting relationship between the mean bifurcation parameter values. [ABSTRACT FROM AUTHOR]

We introduce a novel class of visual illusion -- motionpareidolia -- in which sequential presentations of randomtextures can trigger percepts of coherent apparent motion. Intwo experiments we presented observers with sequences ofrandom 140x140 pixel arrays refreshing at 2.5Hz. InExperiment 1, observers were primed with a coherent motionpattern, such as fixed texture shifting up-and-down acrossframes. After 8 priming frames, the textures becamecompletely random from frame to frame. Participants wereinstructed to indicate when they could no longer perceive theprimed motion pattern. Participants' responses were delayedby an average of 6 frames (or 2.4 seconds). In Experiment 2,observers detected motion patterns in 6-frame sequencesunder different noise levels and falsely identified coherentmotion in 39% of the purely random sequences. To accountfor this phenomenon, we propose a selective visual attentionprocess that is biased to detect expected motion.

While the cognitive predictors of visual illusions have been widely researched, thus far, the temperamental ones have not been studied. The dataset provides data on cognitive and temperamental determinants of the Müller-Lyer illusion recorded in a group of 170 participants aged 20–33. The cognitive predictors included: the field dependent-independent cognitive style and the efficacy of attention networks: alerting, orienting, and executive control. The dataset is related to the research findings in the paper ‘Cognitive and temperamental determinants of susceptibility to the Müller-Lyer illusion’ published in Personality and Individual Differences.

How we perceive our bodies is fundamental to our self‐consciousness and our experience in the world. There are two types of interrelated internal body representations—a subjective experience of the position of a limb in space (body schema) and the subjective experience of the shape and size of the limb (body image). Body schema has been extensively studied, but there is no evidence of the brain structure and network dynamics underpinning body image. Here, we provide the first evidence for the extrastriate body area (EBA), a multisensory brain area, as the structural and functional neural substrate for body shape and size. We performed a multisensory finger‐stretch illusion that elongated the index finger. EBA volume and functional connectivity to the posterior parietal cortex are both related to the participants' susceptibility to the illusion. Taken together, these data suggest that EBA structure and connectivity encode body representation and body perception disturbances. [ABSTRACT FROM AUTHOR]

Visual illusions have provided compelling evidence for a dissociation between perception and action. For example, when two different-sized objects are placed on opposite ends of the Ponzo illusion, people erroneously perceive the physically smaller object to be bigger than the physically larger one, but when they pick up the objects, their grip aperture reflects the real difference in size between the objects. This and similar findings have been demonstrated almost entirely for the right hand in right handers. The scarce research that has examined right and left-handed subjects in this context, has typically used only small samples. Here, we extended this research with a larger sample size (more than 50 in each group) in a version of the Ponzo illusion that allowed us to disentangle the effects of real and illusory size on action and perception in much more powerful way. We also collected a wide range of kinematic measures to assess possible differences in visuomotor control in left and right handers. The results showed that the dissociation between perception and action persisted for both hands in right handers, but only for the right hand in left handers. The left hand of left handers was sensitive to the illusion. Left handers also showed more variable and slower movements, as well as larger safety margins in both hands. These findings suggest that grasping in left handers may require more cognitive supervision, which could lead to greater sensitivity to visual context , particularly with their dominant left hand. • In right handers, visual illusions affect perceptual judgements of size but not grasping. • We tested this dissociation in left handers. • Surprisingly, the left but not the right hand of left handers was affected by the illusion. • Left handers showed more variable grasping and were more cautious in later stages of the movement. • The relations between action and perception are modulated by handedness. [ABSTRACT FROM AUTHOR]

Aposematic signal variation is a paradox: predators are better at learning and retaining the association between conspicuousness and unprofitability when signal variation is low. Movement patterns and variable colour patterns are linked in non-aposematic species: striped patterns generate illusions of altered speed and direction when moving linearly, affecting predators' tracking ability; blotched patterns benefit instead from unpredictable pauses and random movement. We tested whether the extensive colour-pattern variation in an aposematic frog is linked to movement, and found that individuals moving directionally and faster have more elongated patterns than individuals moving randomly and slowly. This may help explain the paradox of polymorphic aposematism: variable warning signals may reduce protection, but predator defence might still be effective if specific behaviours are tuned to specific signals. The interacting effects of behavioural and morphological traits may be a key to the evolution of warning signals.

The Oppel–Kundt illusion consists in the overestimation of the length of filled versus empty extents. Two experiments explored its relation to the horizontal-vertical illusion, which consists in the overestimation of the length of vertical versus horizontal extents, and to the oblique effect, which consists in poorer discriminative sensitivity for obliquely as opposed to horizontally or vertically oriented stimuli. For Experiment 1, Kundt's (1863) original stimulus was rotated in steps of 45° full circle around 360°. For Experiment 2, one part of the stimulus remained at a horizontal or vertical orientation, whereas the other part was tilted 45° or 90°. The Oppel–Kundt illusion was at its maximum at a horizontal orientation of the stimulus. The illusion was strongly attenuated with L-type figures when the vertical part was empty, but not enhanced when this part was filled, suggesting that the horizontal-vertical illusion only acts on nontextured extents. There was no oblique effect. [ABSTRACT FROM AUTHOR]

The past few years have witnessed a fervent theoretical debate about the exact visual mechanisms supporting nonsymbolic number processing. The idea that quantity information is extracted through a primitive visual segmentation algorithm has been challenged by recent models, which rather tap on low-level features confounded with numerosity (i.e., density, convex hull, or total area). Here we used an original manipulation based on visual illusions to disentangle whether visual numerosity processing operates over discrete units or rather over continuous variables. In particular, we generated a set of stimuli composed by open inducers (e.g., like a pac-man shape) that simulate physical connections with Kanizsa-like illusory contours (ICs). Test sets contained pairs of collinear open inducers items that prompted 0 IC, 2 IC, or 4 IC lines connecting 2 objects. Critically, low-level visual features were fully controlled across connectedness levels. We found a systematic underestimation as we increased the IC connections when participants had to select the larger between 2 sets of objects (Experiment 1) but not in the case of aligned closed inducers preventing illusory lines (Experiments 2A and 2B). We also found a systematic numerosity underestimation when both IC connections and continuous features (e.g., convex hull) were independently manipulated in test stimuli (Experiment 3). Finally, these results were shown to be task independent because the same effects of IC connections were replicated in an estimation task (Experiment 4). Taken together, our findings indicate that numerosity perception relies on basic visual-segmentation mechanisms, pointing out the need of new theoretical frameworks integrating both continuous and discrete perceptual number signals. Public Significance Statement: This study indicates that our brain is endowed with the ability to rapidly extract approximate information about the number of discrete items in a visual collection. In contrast with previous proposals, however, we show that this visual ability is not merely driven by continuous physical information (e.g., density, item size, convex hull, etc.) that may be correlated or confounded with numerosity itself. Rather, our study demonstrates a crucial role of perceptual organization and visual segmentation in number processing. [ABSTRACT FROM AUTHOR]

We describe a transparency illusion that can be observed with an ordinary metal knife and fork. Placed in the correct configuration relative to the fork, the metal knife appears transparent, with some observers experiencing a bistable percept in which transparency alternates with reflective appearance. The effect is related to other illusory percepts that follow from careful placement of mirrored surfaces, but to our knowledge, it is unique in that the key feature of the illusion is how the mirrored surface (in this case, the knife) is perceived rather than how a mirror induces altered perception of other objects and surfaces. We describe conditions that do and do not affect the strength of the illusion and point out its connections to previously reported phenomena. [ABSTRACT FROM AUTHOR]

We considerWilson-Cowan-type models for the mathematical description of orientationdependent Poggendorff-like illusions. Our modelling improves two previously proposed corticalinspired approaches, embedding the sub-Riemannian heat kernel into the neuronal interaction term, in agreement with the intrinsically anisotropic functional architecture of V1 based on both local and lateral connections. For the numerical realisation of both models, we consider standard gradient descent algorithms combined with Fourier-based approaches for the efficient computation of the sub-Laplacian evolution. Our numerical results show that the use of the sub-Riemannian kernel allows us to reproduce numerically visual misperceptions and inpainting-type biases in a stronger way in comparison with the previous approaches. [ABSTRACT FROM AUTHOR]