How small changes to one eye's retinal image can transform the perceived shape of a very familiar object.

Vision can provide useful cues about the geometric properties of an object, like its size, distance, pose, and shape. But how the brain merges these properties into a complete sensory representation of a three-dimensional object is poorly understood. To address this gap, we investigated a visual illusion in which humans misperceive the shape of an object due to a small change in one eye's retinal image. We first show that this illusion affects percepts of a highly familiar object under completely natural viewing conditions. Specifically, people perceived their own rectangular mobile phone to have a trapezoidal shape. We then investigate the perceptual underpinnings of this illusion by asking people to report both the perceived shape and pose of controlled stimuli. Our results suggest that the shape illusion results from distorted cues to object pose. In addition to yielding insights into object perception, this work informs our understanding of how the brain combines information from multiple visual cues in natural settings. The shape illusion can occur when people wear everyday prescription spectacles; thus, these findings also provide insight into the cue combination challenges that some spectacle wearers experience on a regular basis.

Response to geometrical visual illusions in non-human animals: a meta-analysis.

Visual illusions have been studied in many non-human species, spanning a wide range of biological and methodological variables. While early reviews have proved useful in providing an overview of the field, they have not been accompanied by quantitative analysis to systematically evaluate the contribution of biological and methodological moderators on the proportion of illusory choice. In the current meta-analytical study, we confirm that geometrical visual illusion perception is a general phenomenon among non-human animals. Additionally, we found that studies testing birds report stronger illusion perception compared to other classes, as do those on animals with lateral-positioned eyes compared to animals with forward-facing eyes. In terms of methodological choices, we found a positive correlation between the number of trials during training or testing and the effect sizes, while studies with larger samples report smaller effect sizes. Despite studies that trained animals with artificial stimuli showing larger effect sizes compared with those using spontaneous testing with naturalistic stimuli, like food, we found more recent studies prefer spontaneous choice over training. We discuss the challenges and bottlenecks in this area of study, which, if addressed, could lead to more successful advances in the future.

Müller-Lyer Illusion susceptibility is conditionally predicted by autistic trait expression.

Müller-Lyer (ML) figures bias size estimation consistently, yet different methods can lead to different degrees of illusory bias. Autistic individuals may also be less likely to perceive illusory biases with varying levels of autistic trait expression proposed to modulate reported illusory biases. The Autism-Spectrum Quotient (AQ) and Systemizing Quotient (SQ) are self-report measures that quantify autistic trait expression and systemizing ability in neurotypical individuals. The current study sought to determine if perceptions of illusory size bias negatively correlate with autistic trait expression and the extent to which varying methods of illusion presentation change the magnitude of illusory bias. Thirty neurotypical adults completed both questionnaires as well as four size estimation tasks. Two tasks involved perceptual discrimination of ML figures by concurrent and successive presentation, where participants selected the longer figure by keypress. For Tasks 3 and 4, participants adjusted the size of a non-illusory line (Task 3) or complementary illusory figure (Task 4) to match the perceived length. Overall, task performance was not correlated with autistic trait expression. One exception was a negative correlation with AQ when adjusting a complementary illusory ML figure in Task 4. Illusory biases were also stronger when two illusory figures were presented concurrently. Given these results, illusion susceptibility to the ML is suggested to be reduced with increases in AQ, but only when the method of illusion measurement is adjustment of concurrent illusory figures. Taken together the results provide evidence that traits associated with autism in a neurotypical population may systematically modulate perception.

Exploring the Spectrum of Visual Illusions and Other Minor Hallucinations in Patients with Parkinson's Disease in Lithuania.

Background and Objectives: Parkinson's disease (PD) is associated with various non-motor symptoms, including minor hallucinations, comprising visual illusions and presence and passage hallucinations. Despite their occurrence, even in newly diagnosed PD patients, data regarding the prevalence and characteristics of minor hallucinations, visual illusions in particular, remain limited. The aim of this study was to address this knowledge gap by assessing the prevalence of minor hallucinations in PD patients, with a focus on visual illusions. Materials and Methods: In this prospective pilot study, we enrolled 35 PD patients without dementia and 35 age- and gender-matched PD-unaffected individuals. Cognitive function was assessed using the Montreal Cognitive Assessment, clinical data were collected, and all subjects were assessed via questionnaires regarding 20 types of visual illusions and other minor hallucinations. Results: The prevalence of minor hallucinations was significantly higher among PD patients compared to controls (45.7% vs. 11.4%, p = 0.003). PD patients reported visual illusions and presence hallucinations more frequently than the controls (37.1% vs. 8.6% and 22.9% vs. 2.9%, p = 0.009 and p = 0.028, respectively), with no significant difference in passage hallucinations (20% vs. 8.6%, p = 0.306). In the PD group, the most frequently observed visual illusions were complex visual illusions, kinetopsia, and pelopsia; the latter was also the most common visual illusion in the control group. PD patients experiencing visual illusions were more likely to report presence hallucinations compared to patients without visual illusions (53.8% vs. 4.5%, p = 0.002); no significant differences in other clinical characteristics were found. Conclusions: Minor hallucinations are a common phenomenon among PD patients without dementia, with a higher prevalence than among healthy controls. Visual illusions are the most prevalent type of minor hallucinations, affecting more than a third of PD patients, with complex visual illusions, kinetopsia, and pelopsia being the most frequently reported types.

People with high schizotypy experience more illusions in the Pattern Glare Test: Consistent with the hyperexcitability hypothesis.

Individuals diagnosed with schizophrenia spectrum disorders (SSD) exhibit a constellation of sensory and perceptual impairments, including hyporeactivity to external input. However, individuals with SSD also report subjective experiences of sensory flooding, suggesting sensory hyperexcitability. To identify the extent to which behavioural indices of hyperexcitability are related to non-psychotic symptoms of schizophrenia, we tested a non-clinical population measured for schizophrenia-like traits (schizotypy), and a behavioural measure of sensory hyperexcitability, specifically the number of illusions seen in the Pattern Glare Test. Two samples totaling 913 individuals completed an online version of the Schizotypal Personality Questionnaire - Brief Revised (SPQ-BR) and the Pattern Glare Test. Individuals with higher schizotypy traits reported more illusions in the Pattern Glare Test. Additionally, one of the three SPQ-BR factors, the disorganized factor, significantly predicted the number of illusions reported. These data illustrate the potential for research in non-clinical samples to inform clinically relevant research.

The influence of visual illusion perception on numerosity estimation could be evolutionarily conserved: exploring the numerical Delboeuf illusion in humans (Homo sapiens) and fish (Poecilia reticulata).

Discriminating between different quantities is an essential ability in daily life that has been demonstrated in a variety of non-human vertebrates. Nonetheless, what drives the estimation of numerosity is not fully understood, as numerosity intrinsically covaries with several other physical characteristics. There is wide debate as to whether the numerical and spatial abilities of vertebrates are processed by a single magnitude system or two different cognitive systems. Adopting a novel approach, we aimed to investigate this issue by assessing the interaction between area size and numerosity, which has never been conceptualized with consideration for subjective experience in non-human animals. We examined whether the same perceptual biases underlying one of the best-known size illusions, the Delboeuf illusion, can be also identified in numerical estimation tasks. We instructed or trained human participants and guppies, small teleost fish, to select a target numerosity (larger or smaller) of squares between two sets that actually differed in their numerosity. Subjects were also presented with illusory trials in which the same numerosity was presented in two different contexts, against a large and a small background, resembling the Delboeuf illusion. In these trials, both humans and fish demonstrated numerical biases in agreement with the perception of the classical version of the Delboeuf illusion, with the array perceived as larger appearing more numerous. Thus, our results support the hypothesis of a single magnitude system, as perceptual biases that influence spatial decisions seem to affect numerosity judgements in the same way.

Real-time wrinkle evaluation method using Visual Illusion-based image feature enhancement System.

BACKGROUND: Several advanced methods for evaluating wrinkles are currently available, however, with limitations in their application because wrinkle structures change in response to facial expressions and surrounding environments. A Visual Illusion-based image feature enhancement System (VIS) was used to develop a real-time evaluation method. OBJECTIVES: This study expands the VIS application into the wrinkle evaluation method by adjusting VIS to evaluate facial wrinkles, evaluating the age-dependent wrinkles, and validating it for real-time wrinkle evaluation. METHODS: Wrinkles in various Japanese men and women were evaluated using VIS and the current methods. Furthermore, the effectiveness of an eye cream containing niacinamide was evaluated before and after the 4-week treatment. RESULTS: VIS qualitatively detects even fine wrinkles and numerically records them without any special instrument. Moreover, VIS can be applied to moving images, revealing the effectiveness of the antiwrinkle formulation qualitatively and quantitatively even when the subjects are smiling. CONCLUSION: This paper presents an epoch-making wrinkle evaluation method that is qualitative and quantitative, with high sensitivity in real-time and relies solely on digital images without any difficulties. Therefore, these results imply that this method enables the wrinkle evaluation under real-life conditions.

The long and short of it? A novel geometric illusion.

Here we present what we believe to be a novel geometric illusion where identical lines are perceived as being of differing lengths. Participants were asked to report which of the two parallel rows of horizontal lines contained the longer individual lines (two lines on one row and 15 on the other). Using an adaptive staircase we adjusted the length of the lines on the row containing two to estimate the point of subjective equality (PSE). At the PSE, the two lines were consistently shorter than the row containing the fixed length of 15 lines demonstrating a disparity in perceived length such that lines of identical length are perceived as longer in a row of two than in a row of 15. The illusion magnitude was unaffected by which row was presented above the other. Additionally, the effect persisted when using one as opposed to two test lines, and when the line stimuli on both rows were presented with alternating luminance polarity the illusion magnitude decreased, but was not abolished. The data indicate a robust geometric illusion that may be modulated by perceptual grouping processes.

No evidence for a single oscillator underlying discrete visual percepts.

Theories of perception based on discrete sampling posit that visual consciousness is reconstructed based on snapshot-like perceptual moments, as opposed to being updated continuously. According to a model proposed by Schneider (2018), discrete sampling can explain both the flash-lag and the Fröhlich illusion, whereby a lag in the conscious updating of a moving stimulus alters its perceived spatial location in comparison to stationary stimulus. The alpha-band frequency, which is associated with phasic modulation of stimulus detection and the temporal resolution of perception, has been proposed to reflect the duration of perceptual moments. The goal of this study was to determine whether a single oscillator (e.g., alpha) is underlying the duration of perceptual moments, which would predict that the point of subjective equality (PSE) in the flash-lag and Fröhlich illusions are positively correlated across individuals. Although our displays induced robust flash-lag and Fröhlich effects, virtually zero correlation was seen between the PSE in the two illusions, indicating that the illusion magnitudes are unrelated across observers. These findings suggest that, if discrete sampling theory is true, these illusory percepts either rely on different oscillatory frequencies or not on oscillations at all. Alternatively, discrete sampling may not be the mechanism underlying these two motion illusions or our methods were ill-suited to test the theory.

Guppies (Poecilia reticulata) are deceived by visual illusions during obstacle negotiation.

Animals travelling in their natural environment repeatedly encounter obstacles that they can either detour or go through. Gap negotiation requires an accurate estimation of the opening's size to avoid getting stuck or being injured. Research on visual illusions has revealed that in some circumstances, transformation rules used to generate a three-dimensional representation from bidimensional retinal images fail, leading to systematic errors in perception. In Ebbinghaus and Delboeuf illusions, the presence of task-irrelevant elements causes us to misjudge an object's size. Susceptibility to these illusions was observed in other animals, although with large intraspecific differences. In this study, we investigated whether fish can accurately estimate gap size and whether during this process they may be deceived by illusory patterns. Guppies were extremely accurate in gap negotiation, discriminating holes with a 10% diameter difference. When presented with two identical holes surrounded by inducers to produce Ebbinghaus and Delboeuf patterns, guppies misperceived gap size in the predicted direction. So far, researchers have principally considered illusions as useful tools for exploring the cognitive processing underlying vision. Our findings highlight the possibility that they have important ecological implications, affecting the everyday interactions of an animal with its physical world besides its intra- and interspecific relationships.

When seeing is not believing: A mechanistic basis for predictive divergence.

Visual illusions provide a compelling case for the idea that perception and belief may remain incongruent. This can be explained by modular theories of mind, but it is not straightforwardly accommodated by the Predictive Processing framework, which takes perceptual and cognitive predictions to derive from the same underlying inferential hierarchy. Recent insights concerning the neural implementation of Predictive Processing may help elucidate this. Specifically, prior information is proposed to be approximated by mechanisms in both the top-down and bottom-up streams of information processing. While the former is context-dependent and flexible in updating, the latter is context-independent and difficult to revise. We propose that a stable divergence between perception and belief may emerge when flexible prior information at higher hierarchical levels contradicts inflexible prior information at lower ones. This allows Predictive Processing to account for conflicting percepts and beliefs while still maintaining a hierarchical and unitary conception of cognition.

The effect of font readability on the Moses illusion: A replication study.

This research is a replication study that sought to verify whether the readability of a font has an effect on the Moses illusion detection. It was designed to stimulate information retrieval from memory and confuse retrieval with a text's erroneous wording. Undergraduates aged 19-30 (N = 87, 80% women) were presented with two questions, one of which contained distorted information. We assumed that a difficult-to-read font would facilitate error detection, as it increases the focus of attention on the text. However, unlike the original study, we were unable to find support for this hypothesis, as font readability did not significantly affect error detection. In the difficult-to-read condition, 43% of participants reported an error, while, in the easy-to-read condition, errors were detected by 37% of the participants. Unlike the original study, our research results do not support the hypothesis that the visual presentation of a text affects the automatic retrieval of information from memory. This study clarifies the effect of text readability on error detection taking into consideration the role of long-term memory and visual perception.

The Analgesic Effects of Virtual Reality for People with Chronic Pain: A Scoping Review.

OBJECTIVE: Although virtual reality is shown to have short-term analgesic effects in acute pain settings, its long-term efficacy in chronic pain conditions has not been established. This scoping review aims to provide a summary of virtual reality approaches explored in chronic primary and secondary pain conditions as defined by the International Association for the Study of Pain. METHODS: A systematic literature search in Ovid PubMed and Ovid Embase was conducted between January 5 and January 10, 2021, with the use of the Arksey and O'Malley six-step scoping review criteria. Articles were searched via search terms and keywords relating to International Classification of Diseases-defined primary and secondary chronic pain conditions, virtual reality, virtual illusion, distraction, and effects on levels of pain. RESULTS: Of the 2,118 articles located, 44 were included, which covered a range of primary and secondary chronic pain conditions and used a variety of different computer screen and headset protocols, including gaming, mindfulness, exercise, relaxation, and proprioceptive skills. CONCLUSIONS: Studies show virtual reality to be an effective analgesic intervention for people with chronic pain. Given user satisfaction, a lack of side effects such as cybersickness, and relief of comorbid symptoms, virtual reality has potential as a worthwhile adjunct to chronic pain management programs, thus enabling patients to take control of their symptoms.

People Are Less Susceptible to Illusion When They Use Their Hands to Communicate Rather Than Estimate.

When we use our hands to estimate the length of a stick in the Müller-Lyer illusion, we are highly susceptible to the illusion. But when we prepare to act on sticks under the same conditions, we are significantly less susceptible. Here, we asked whether people are susceptible to illusion when they use their hands not to act on objects but to describe them in spontaneous co-speech gestures or conventional sign languages of the deaf. Thirty-two English speakers and 13 American Sign Language signers used their hands to act on, estimate the length of, and describe sticks eliciting the Müller-Lyer illusion. For both gesture and sign, the magnitude of illusion in the description task was smaller than the magnitude of illusion in the estimation task and not different from the magnitude of illusion in the action task. The mechanisms responsible for producing gesture in speech and sign thus appear to operate not on percepts involved in estimation but on percepts derived from the way we act on objects.

Why some size illusions affect grip aperture.

There is extensive literature debating whether perceived size is used to guide grasping. A possible reason for not using judged size is that using judged positions might lead to more precise movements. As this argument does not hold for small objects and all studies showing an effect of the Ebbinghaus illusion on grasping used small objects, we hypothesized that size information is used for small objects but not for large ones. Using a modified diagonal illusion, we obtained an effect of about 10% on perceptual judgements, without an effect on grasping, irrespective of object size. We therefore reject our precision hypothesis. We discuss the results in the framework of grasping as moving digits to positions on an object. We conclude that the reported disagreement on the effect of illusions is because the Ebbinghaus illusion not only affects size, but-unlike most size illusions-also affects perceived positions.

The influence of the Sander parallelogram illusion and early, middle and late vision on goal-directed reaching and grasping.

Vision is one of the most robust sensory inputs used for the execution of goal-directed actions. Despite a history of extensive visuomotor research, how individuals process visual context for the execution of movements continues to be debated. This experiment examines how early, middle and late visuomotor control is impacted by illusory characteristics in a reaching and grasping task. Participants either manually estimated or reached out and picked up a three-dimensional target bar resting on a two-dimensional picture of the Sander parallelogram illusion. Participants performed their grasps within a predefined time movement window based on their own average grasp time, allowing for the manipulation of visual feedback. On some trials, vision was only available before the response cue (an auditory tone), while on others vision was occluded until the response cue, becoming available for either the full, early, middle or late portions of the movement. While results showed that the effect of the illusion was stronger on manual estimations than on grasping, maximum grip apertures in the occluded vision and early vision grasping conditions were also consistent to a lesser extent with the illusion. The late vision condition showed longer movement time, wrist deceleration period, time to maximum grip aperture and lower maximum velocity. These findings indicate that visual context affects visuomotor control distinctly depending on when vision is available, and supports the notion that human vision is comprised of two functionally and anatomically distinct systems.

Guppies, Poecilia reticulata, perceive a reversed Delboeuf illusion.

Animals are often required to estimate object sizes during several fitness-related activities, such as choosing mates, foraging, and competing for resources. Some species are susceptible to size illusions, i.e. the misperception of the size of an object based on the surrounding context, but other species are not. This interspecific variation might be adaptive, reflecting species-specific selective pressures; according to this hypothesis, it is important to test species in which size discrimination has a notable ecological relevance. We tested susceptibility to a size illusion in the guppy, Poecilia reticulata, a fish species required to accurately estimate sizes during mate choice, foraging, and antipredator behaviours. We focussed on the Delboeuf illusion, in which an object is typically perceived to be larger when surrounded by a smaller object. In experiment 1, we trained guppies to select the larger of two circles to obtain a food reward and then tested them using stimuli arranged in a Delboeuf-like pattern. In experiment 2, we tested guppies in a spontaneous food choice task to determine whether the subjective size perception of food items is affected by the surrounding context. Jointly, our experiments indicated that guppies perceived the Delboeuf illusion, but in a reverse direction relative to humans: guppies estimated as larger the stimulus that human perceived as smaller. Our results indicated susceptibility to size illusions also in a species required to perform accurate size discrimination and support previous evidence of variability in illusion susceptibility across vertebrates.

Dynamic Network Communication in the Human Functional Connectome Predicts Perceptual Variability in Visual Illusion.

Ubiquitous variability between individuals in visual perception is difficult to standardize and has thus essentially been ignored. Here we construct a quantitative psychophysical measure of illusory rotary motion based on the Pinna-Brelstaff figure (PBF) in 73 healthy volunteers and investigate the neural circuit mechanisms underlying perceptual variation using functional magnetic resonance imaging (fMRI). We acquired fMRI data from a subset of 42 subjects during spontaneous and 3 stimulus conditions: expanding PBF, expanding modified-PBF (illusion-free) and expanding modified-PBF with physical rotation. Brain-wide graph analysis of stimulus-evoked functional connectivity patterns yielded a functionally segregated architecture containing 3 discrete hierarchical networks, commonly shared between rest and stimulation conditions. Strikingly, communication efficiency and strength between 2 networks predominantly located in visual areas robustly predicted individual perceptual differences solely in the illusory stimulus condition. These unprecedented findings demonstrate that stimulus-dependent, not spontaneous, dynamic functional integration between distributed brain networks contributes to perceptual variability in humans.

Human Occipital and Parietal GABA Selectively Influence Visual Perception of Orientation and Size.

GABA is the primary inhibitory neurotransmitter in human brain. The level of GABA varies substantially across individuals, and this variability is associated with interindividual differences in visual perception. However, it remains unclear whether the association between GABA level and visual perception reflects a general influence of visual inhibition or whether the GABA levels of different cortical regions selectively influence perception of different visual features. To address this, we studied how the GABA levels of parietal and occipital cortices related to interindividual differences in size, orientation, and brightness perception. We used visual contextual illusion as a perceptual assay since the illusion dissociates perceptual content from stimulus content and the magnitude of the illusion reflects the effect of visual inhibition. Across individuals, we observed selective correlations between the level of GABA and the magnitude of contextual illusion. Specifically, parietal GABA level correlated with size illusion magnitude but not with orientation or brightness illusion magnitude; in contrast, occipital GABA level correlated with orientation illusion magnitude but not with size or brightness illusion magnitude. Our findings reveal a region- and feature-dependent influence of GABA level on human visual perception. Parietal and occipital cortices contain, respectively, topographic maps of size and orientation preference in which neural responses to stimulus sizes and stimulus orientations are modulated by intraregional lateral connections. We propose that these lateral connections may underlie the selective influence of GABA on visual perception.SIGNIFICANCE STATEMENT GABA, the primary inhibitory neurotransmitter in human visual system, varies substantially across individuals. This interindividual variability in GABA level is linked to interindividual differences in many aspects of visual perception. However, the widespread influence of GABA raises the question of whether interindividual variability in GABA reflects an overall variability in visual inhibition and has a general influence on visual perception or whether the GABA levels of different cortical regions have selective influence on perception of different visual features. Here we report a region- and feature-dependent influence of GABA level on human visual perception. Our findings suggest that GABA level of a cortical region selectively influences perception of visual features that are topographically mapped in this region through intraregional lateral connections.

Truth is in the eye of the beholder: Perception of the Müller-Lyer illusion in dogs.

Visual illusions are objects that are made up of elements that are arranged in such a way as to result in erroneous perception of the objects' physical properties. Visual illusions are used to study visual perception in humans and nonhuman animals, since they provide insight into the psychological and cognitive processes underlying the perceptual system. In a set of three experiments, we examined whether dogs were able to learn a relational discrimination and to perceive the Müller-Lyer illusion. In Experiment 1, dogs were trained to discriminate line lengths using a two-alternative forced choice procedure on a touchscreen. Upon learning the discrimination, dogs' generalization to novel exemplars and the threshold of their abilities were tested. In the second experiment, dogs were presented with the Müller-Lyer illusion as test trials, alongside additional test trials that controlled for overall stimulus size. Dogs appeared to perceive the illusion; however, control trials revealed that they were using global size to solve the task. Experiment 3 presented modified stimuli that have been known to enhance perception of the illusion in other species. However, the dogs' performance remained the same. These findings reveal evidence of relational learning in dogs. However, their failure to perceive the illusion emphasizes the importance of using a full array of control trials when examining these paradigms, and it suggests that visual acuity may play a crucial role in this perceptual phenomenon.