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The Ames room illusion is one of the best-known geometrical illusions but its geometrical properties are often misunderstood. This study discusses the differences in the geometrical properties between the original Ames room and what have been often referred to as "Ames rooms" in recent studies.

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We introduce a new illusory color phenomenon. The illusion is evoked by two alternating displays comprising various colored disks. Although the colors in the alternating displays are the same, the color appearance of the two displays are quite different. We suggest that apparent motion of the disks modulates the color percepts.

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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.

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Two dots shown in quick succession at one point and a third at a distance on the same linear path creates an illusion of intervening flashes on a visual field, a phenomenon known as the reduced visual rabbit illusion or visual saltation illusion. This study presents this illusion in a novel way by altering the position of the second flash, which has been typically presented only in the same position as the first flash. A series of experiments were conducted to observe whether saltation would occur if the second flash was presented in the same position as the third flash, out of sequential order relative to the first and last flash, or out of linear alignment at the midpoint between the first and the last flash. When all three flashes were presented in quick succession, participants misperceived the second flash to occur close to the midpoint between the first and last flash. Saltation was achieved in all three novel conditions, hinting a particular neurological process may be responsible for shared outcomes.

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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.

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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.

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Humans are typically inept at evaluating their abilities and predispositions. People dismiss such a lack of metacognitive insight into their capacities while even enhancing (albeit illusorily) self-evaluation such that they should have more desirable traits than an average peer. This superiority illusion helps maintain a healthy mental state. However, the scope and range of its influence on broader human behavior, especially perceptual tasks, remain elusive. As belief shapes the way people perceive and recognize, the illusory self-superiority belief potentially regulates our perceptual and metacognitive performance. In this study, we used hierarchical Bayesian estimation and machine learning of signal detection theoretic measures to understand how the superiority illusion influences visual perception and metacognition for the Ponzo illusion. Our results demonstrated that the superiority illusion correlated with the Ponzo illusion magnitude and metacognitive performance. Next, we combined principal component analysis and cross-validated regularized regression (relaxed elastic net) to identify which superiority components contributed to the correlations. We revealed that the "extraversion" superiority dimension tapped into the Ponzo illusion magnitude and metacognitive ability. In contrast, the "honesty-humility" and "neuroticism" dimensions only predicted Ponzo illusion magnitude and metacognitive ability, respectively. These results suggest common and distinct influences of superiority features on perceptual sensitivity and metacognition. Our findings contribute to the accumulating body of evidence indicating that the leverage of superiority illusion is far-reaching, even to visual perception.

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Visual motion signals can produce self-motion perception known as vection in observers. Vection can be generated by illusory motions in the form of global expantion in still images as well as by visual motion signals. The perception of vection can be enhanced by flickering images at a rate of 5 Hz. This study examined the illusory motion and vection induced by a printed static image under flickering ambient light at rates up to 100 Hz. The perception of illusory motion and vection were enhanced by flickering ambient lights at 50, 75, and 100 Hz. The enhancement effect was higher for the flicker rates expected to be detectable by humans. The findings of this study suggest that alternating bright and dark signals to the cone receptors and primary visual cortex trigger perceptions of illusory motions.

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An adequate foot clearance height while stepping over an obstacle is important for safety in daily life. In the present study, we examined whether visual illusions affect foot clearance during a stepping-over action, and whether this is further influenced by gaze behavior. Twelve participants stepped over an obstacle placed four meters away under conditions of three different obstacle characteristics: white, horizontal, or vertical lines. We measured the participants' foot clearances during the step-over action and their gaze behavior during the approaching phase. Participants stepped significantly higher over the obstacles in the vertical lines (illusion) condition. The duration of gaze fixation on the obstacle positively correlated with increased foot clearance in the vertical condition, suggesting that the effect of the visual illusion on foot clearance was enhanced by prolonged gaze fixation. Conversely, prolonged fixation negatively correlated with foot clearance in the white (control) condition, implying that a cautious perception of an obstacle may contribute to efficient stepping-over action.

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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.

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An object appears to move at higher speed than another equally fast object when brief nonspatial tones coincide with its changes in motion direction. We refer to this phenomenon as the beep-speed illusion (Meyerhoff et al., 2022, Cognition, 219, 104978). The origin of this illusion is unclear; however, attentional explanations and potential biases in the response behavior appear to be plausible candidates. In this report, we test a simple bias explanation that emerges from the way the dependent variable is assessed. As the participants have to indicate the faster of the two objects, participants possibly always indicate the audio-visually synchronized object in situations of perceptual uncertainty. Such a response behavior potentially could explain the observed shift in perceived speed. We therefore probed the magnitude of the beep-speed illusion when the participants indicated either the object that appeared to move faster or the object that appeared to move slower. If a simple selection bias would explain the beep-speed illusion, the response pattern should be inverted with the instruction to indicate the slower object. However, contrary to this bias hypothesis, illusion emerged indistinguishably under both instructions. Therefore, simple selection biases cannot explain the beep-speed illusion.

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Fish of any variety are nowadays being kept captive for several purposes, from recreational to alimentary to research. It is possible that we humans often underestimate or misunderstand the basic, natural needs of the species we use for our purposes. Sociality is likely to play an extensive and fundamental role in the quality of life of animals such as zebrafish. This study aimed to develop a dummy conspecific that included depth and motion illusions in order to assess whether these stimuli could represent a valid alternative to a conspecific in triggering shoaling behaviour in a well-known model in genetics and neuroscience, the zebrafish (Dario rerio). We thus replaced the natural livery of a zebrafish shape with three visual illusions: the Ouchi-Spillmann illusion, which generates an effect of local tilting motion; and another two which should create pictorial cues of tridimensionality. Via a binary shoal choice test, we assessed the time spent close to each of the three artificial dummies compared to neutral control stimuli such as grey ellipses. We found no preference for the illusory patterns, suggesting that the illusion was not perceived or, alternatively, that the perception of the illusion was not enough to elicit recognition of the dummy as conspecific and subsequent social behaviours.

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In the "classic" vanishing ball illusion (VBI), a magician pretends to throw a ball and the audience sees it go up and then disappear. To gain a better understanding of the mechanisms involved, we conducted two experiments to analyze the permeability of this type of illusion to auditory information. A modified version of the VBI (i.e., the Vanishing Coin Illusion [VCI]), was presented, and this was either accompanied by a sound or was not. The results show that the presence of a sound adds to the success of the illusion (Experiment 1), especially when this sound is congruent with the illusion (Experiment 2). Based on these results, we discuss the mechanisms at work in this illusion.

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Background: Minor hallucinations (MHs) are the most common psychiatric symptom associated with Parkinson's disease (PDPsy), but little is known about their characteristics in different motor phenotypes, especially postural instability gait difficulty (PIGD). The aim of this study was to explore the clinical features of MHs in different subtypes of PD. Methods: In this cross-sectional study, 213 patients with Parkinson's disease (PD) were recruited, and the data obtained included comprehensive demographics, motor subtypes, clinical scale scores, and MH contents. Motor subtypes were classified as tremor-dominant (TD), PIGD or indeterminate according to Stebbins' method. Results: A total of 213 PD patients were included: 90 (42.3%) TD patients, 98 (46.0%) PIGD patients and 25 (11.7%) indeterminate. In total, 70 (32.9%) patients experienced MHs. Compared to patients with the TD phenotype, we found that patients with the PIGD phenotype had more severe motor and nonmotor symptoms. They also had a higher incidence of visual illusions (VIs) and a shorter MH latency. Conclusion: Our study demonstrated that compared to patients with the TD phenotype, patients with the PIGD phenotype had a higher incidence of MHs, especially VIs, which may lead to a higher incidence of visual hallucinations (VHs). They also had a shorter latency of MHs than patients with the TD phenotype, suggesting an earlier onset of MHs and a worse prognosis.

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Humans perceive 3D shapes even from 2D images. A slant can be perceived from images of slanted rectangular objects, which include texture gradients and linear perspective contours. How does the visual system integrate and utilize these pictorial depth cues? A new visual illusion that provides some insights into this issue was examined. A box-like object with disk figures drawn on its upper surface was rendered in a linear perspective image. The length of the object's upper surface side line was overestimated, probably due to the foreshortened disks serving as slant cues. This illusory effect occurred even when observers estimated the line length on the image plane, suggesting that the slant perception from the disks was mandatory. Five experiments revealed that multiple depth cues were utilized for the slant perception; the aspect ratio of the disks, texture gradients, trapezium/parallelogram contours, and the side surfaces of the box-like object. However, foreshortened disks outside the object were not utilized as depth cues. These results suggested that various depth cues belonging to the target object are integrated for the slant perception.

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Physical objects behave following the principle of solidity: One solid object cannot pass through another. To what extent does the visual system integrate this physical regularity as a prior constraint? A new variant of the Pulfrich effect demonstrates a surprising degree of tolerance for violations of solidity when pitted against motion and depth cues. When adult participants view a pendulum swinging in the fronto-parallel plane with both eyes (one of which was covered by a light-attenuating filter), they falsely perceive the pendulum as swinging in an elliptical path (known as the "Pulfrich effect"). Here, we show that even when the pendulum's motion takes place entirely behind a solid horizontal bar, observers nevertheless see the pendulum pass through the bar while moving in an ellipse. This illusion suggests that the Pulfrich effect and the underlying stereoscopic depth cues can be robust to object solidity.

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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.

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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.

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Predicting information is considered to be an efficient strategy to minimise processing costs by exploiting regularities in the environment, and to allow for adaptation in case of irregularities, i.e. prediction errors. How such errors impact conscious perception is unclear, especially when predictions concern elementary visual features. Here we present results from a novel experimental approach allowing us to investigate the perceptual consequences of violated low-level predictions about moving objects. Observers were presented with two squares moving towards each other with a constant speed, and reported whether they were in contact or not before they disappeared. A compelling illusion of a gap between the squares occurred when the leading edges of those squares contacted briefly. The apparent gap was larger than a physical and stable separation of 2.6 min of arc between the squares. The illusion disappeared only when the contact did not violate extrapolations of the contrast edge between the moving object and the background. The pattern of results is consistent with an early locus of the effect and cannot be explained by decisional biases, guesses, top-down, attentional or masking effects. We suggest that violations of the contrast edge extrapolation in the direction of motion have strong perceptual consequences.

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