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The Café Wall illusion (seen on the tiles of a local café) is a Münsterberg chequerboard figure, but with horizontal parallel lines which may have any luminance separating the rows of displaced squares. These (the 'mortar' lines) display marked wedge distortion which is especially affected by: contrast of the squares ('tiles'); width of the 'mortar...
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... can also explain why there is any distortion in the limiting case of the Münsterberg illusion where the mortar line is lost, as it is isoluminant with the black tiles. Here the different widths of the black regions bordering the white tiles-the thin black lines and the much wider black tiles-serve to give this illusion: as they must do because they are the only asymmetry in the figure (see the caption to figure 12). ...
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... figure 11. There is repeated small-scale asymmetry (as in the Café Wall though with non-isoluminant mortar lines), for the white rectangles (analogous to the light tiles of the Café Wall figure) are bounded for half their length by narrow black lines, and for the other half by wide black lines-the black rectangles. ...
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... have suggested that border locking gives a functional modus operandi for these border shifts: but a complete explanation requires details of the physiological mechanisms and their functional range which may not be optimal. Figure 11. Explanation of the Münsterberg illusion. ...
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... tiles should all have wedge distortions in the same direction for each row, and the direction of the wedge convergences should reverse for each alternate row. This should be clear from figure 1 2. Under some conditions, especially when the display is blurred, each tile is seen as a separate wedge, rather than as sections of row-long wedges. It was supposed by Fraser (1908) that such large-scale asymmetries are produced by spatial integration of each small- scale distortion (or, for the Fraser figures, misleading line elements), but it is also possible that constancy scaling is set inappropriately by the tile-sized wedges. ...
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... To design an effective attack against these MDE methods, we shall identify the most vulnerable visual cues for MDE. Taking human visual perception as an analogy, it is reasonable to hypothesize that perspective cues (i.e., the spatial attributes of geometry and texture that indicate the relative locations among the objects in the scene) are essential for MDE and subject to manipulation, as there are various notable optical illusions that deceive human visual perception [23,39]. These illusions involve parallel lines that seem to differ in length, orientation, or slope depending on the surrounding patterns, all of which distort the perspective cues. ...
Monocular depth estimation (MDE) plays a crucial role in modern autonomous driving (AD) by facilitating 3-D scene understanding and interaction. While vulnerabilities in deep neural networks (e.g., adversarial perturbations) have been exploited to compromise MDE, existing attacks face challenges in target accessibility and stealthiness. To address these limitations , we introduce π-Jack, a novel physical-world attack on MDE via perspective hijacking. It is based on an observation that MDE relies heavily on perspective cues to infer depth, yet these cues can be manipulated by strategically placing common 3-D objects in AD scenes. With an optimization-based approach, π-Jack "hijacks" the perspective information and alters the target pixels' depths perceived by the MDE model in a black-box manner. We also show via experiments that π-Jack is effective across various MDE models and scenarios, confirming generalizability of perspective hijacking. Our extensive evaluations demonstrate that π-Jack is effective across different target and attack vectors, and increases the mean depth error by over 14 meters. Moreover, in our end-to-end AD simulation, π-Jack results in compromised lane change, sudden braking, and life-threatening collisions.
... The complexity and diversity of visual illusions, along with the complexity of their underlying mechanisms, necessitate the investigation of multiple visual illusions in DNNs to determine the presence of any similarities or patterns in their responses. While the phenomenon of visual illusions has been extensively studied in psychophysics [13][14][15][16], recent work has begun to investigate how these illusions manifest in deep neural networks (DNNs). These studies in psychophysics have laid the foundation for understanding the mechanisms of visual illusions, such as the role of neural inhibitory responses and the ventral visual pathway. ...
The analogy between the brain and deep neural networks (DNNs) has sparked interest in neuroscience. Although DNNs have limitations, they remain valuable for modeling specific brain characteristics. This study used Skye’s Oblique Grating illusion to assess DNNs’ relevance to brain neural networks. We collected data on human perceptual responses to a series of visual illusions. This data was then used to assess how DNN responses to these illusions paralleled or differed from human behavior. We performed two analyses:(1) We trained DNNs to perform horizontal vs. non-horizontal classification on images with bars tilted different degrees (non-illusory images) and tested them on images with horizontal bars with different illusory strengths measured by human behavior (illusory images), finding that DNNs showed human-like illusions; (2) We performed representational similarity analysis to assess whether illusory representation existed in different layers within DNNs, finding that DNNs showed illusion-like responses to illusory images. The representational similarity between real tilted images and illusory images was calculated, which showed the highest values in the early layers and decreased layer-by-layer. Our findings suggest that DNNs could serve as potential models for explaining the mechanism of visual illusions in human brain, particularly those that may originate in early visual areas like the primary visual cortex (V1). While promising, further research is necessary to understand the nuanced differences between DNNs and human visual pathways.
... apparent changes in line orientation and contour shape) are triggered by the difference in luminance between the figure and its background. Classically, the café wall illusion (Fraser, 1908;Gregory & Heard, 1979) may be the best-known example of this type of phenomenon, and new discoveries have been continued over the past ten years or so. For example, the jaggy diamond illusion (Kawabe et al., 2010) is a phenomenon in which diamonds placed at the intersections of grids appear to have jaggy illusory 'thorns'; the eggs illusion (Qian & Mitsudo, 2016, 2019, 2020) is a phenomenon in which white circles located at the midpoint of the intersection of grids on a black background appears to be deformed into ellipses; the curvature blindness illusion (Takahashi, 2017) is a phenomenon in which smooth sinusoidal curves, which have abrupt luminance change at the peak of the curve, appear to be triangular corrugated zig-zag lines; Kite mesh illusion is an illusion in which the edges of kite-like rhombus appears to bend inward depending on the luminance of the figure outlines and their background (Bertamini & Kitaoka, 2018;Oppel, 1855). ...
... In terms of the luminance difference between adjacent regions determining the direction of the perceived distortion, BCI is similar to the Café Wall illusion (Gregory & Heard, 1979). In addition, the 'checkered illusion', which was derived from a deliberation of the mechanism of Café Wall illusion (Kitaoka, 1998;Wade, 1982), seems to be closely related to BCI, because in this illusion, the luminance of small squares adjacent to relatively larger squares distorts the shape of the larger squares. ...
... Most existing explanations of the Café Wall illusion, such as the border-locking theory (Gregory & Heard, 1979), the luminance induction theory (McCourt, 1982), and the Fraser illusion reduction theory (Morgan & Moulden, 1986), pre-request the existence of straight lines flanked by rectangles, and thus cannot be directly applied to the explanation of BCI, which does not have straight lines. It has also been pointed out that these theories have limitations in explaining the Café Wall illusion (Kitaoka, 1998). ...
A new visual illusion in which circles placed on the checkered-pattern background appear to be polygons is reported. In this article, we first demonstrated that the apparent distortion of circles in this ‘bumpy circle illusion (BCI)’ depends on the luminance difference between the circles and the components of the background. Then, with the aim of clarifying the mechanism that causes this phenomenon, the ‘low-pass filtering theory’ the ‘segmentation theory’, the ‘corner effect theory’, and the ‘completion theory’ were investigated. As a result, the low-pass filtering theory and the completion theory were rejected because they predicted the occurrence of the illusion in some modulated BCI figures that produced no illusion. The ‘segmentation theory’, which postulated that the same mechanism as in the curvature blindness illusion produces BCI, was also rejected because the same luminance assignment as for BCI image components does not produce the curvature blindness illusion. In addition, the curvature of lines appears to deform in the curvature blindness illusion, whereas the BCI does not produce an illusion of line circles, which also shows the difference between the two phenomena. The ‘corner effect theory’ is the most promising because it correctly predicts (1) how the apparent distortion of the circles appears and (2) the presence/absence of illusion with the outline circles depending on the checkerboard luminance alteration cycles inside and outside of the circles. However, the corner effect theory can only be justified if it is assumed that the strength of the effect is different depending on whether the checkered pattern is applied to the inside or outside of the circles. Whether such asymmetry does exist and the reason why the asymmetry occurs needs further investigation.
... It is worth mentioning that, sensation information is not always consistent with our perception and this bias is caused by many different factors (Raghubir & Krishna, 1996). One of the most famous examples is Café wall illusion (Gregory & Heard, 1979), in which the lines with alternating dark and light bricks appear to be sloped, not parallel as they really are. Similarly, this bias between stimuli and perception can also be caused by the cross-modal interaction and then even affect people's behavior. ...
Video tipping takes a remarkable share in the income of online streaming platforms such as Bilibili. There are some specific mappings between the audio and visual signals that viewers can sense (e.g., congruency of pitch and size), which is generally called visual-audio correspondence (VAC). And it is believed to influence viewer satisfaction with video clips. The way to automatically measure VAC, however, still remains missing and its possible effect on video tipping is rarely examined in previous efforts. In this study, a deep neural network with two sub-networks, namely VAC-Net, is established to map both visual and audio stimuli into a shared embedding space. And the Euclidean distance between visual and audio representations in this space is accordingly presented to be the indicator of VAC. Pre-trained models of both modalities and the triplet loss are further leveraged to train the VAC-Net and it competently evaluates VAC of video clips with a test accuracy of 68.37% by outperforming alternative baselines and even exceeding humans on the similar task. Lab-experiments further show that the VAC measurement of VAC-Net conforms to human cognition. Second, considering that viewers' tipping behavior (TIP) on videos is consistent with the pricing strategy Pay What You Want (PWYW), it is hypothesized that VAC would indirectly influence TIP by reshaping viewer satisfaction (VS). Regression models are thus built to test the hypotheses and it is found that VAC can promote TIP by enhancing VS significantly. Additional tests also demonstrate the robustness of this mechanism by considering various controls and measurement errors. Our results supplement PWYW in streaming videos with a new motive of VAC for viewer tipping and provide streaming practitioners with an automatic tool to estimate the tips videos will receive.
... Prototype cases of such illusions, sampled from older and more recent reviews, are shown in Figure 1 [1][2][3][4][5]; see [6][7][8][9] for related illusions that may occur outdoors or under other "real-life" conditions. An example of a visual illusion that is not purely geometrical is the "Shifted checkerboard figure" ("Verschobene Schachbrettfigur" [10]) or "Kindergarten pattern" [11], later rediscovered as the "Café wall illusion" by Gregory and Heard [12]parallel rows of equal-sized rectangles, alternately colored black and white, and the rows offset against one another by half a unit-because such a design involves areas filled with color. In fact, the illusion-the apparent nonparallelism of the rows-is attenuated after the introduction of grey "mortar lines" (ibid.), and disappears completely with isoluminant colors [13], testifying to effects of lightness; see [14] for additional optical and physiological variables. ...
For nine popular geometrical visual-illusion figures, a mathematical analysis is provided along with a characterization of the figures’ psychological effectiveness. Supported by graphical illustrations, for the L and the T, it is shown how mathematical singularities of these figures can be isolated, and the illusions annihilated. For the Poggendorff, the Hering, and the Zöllner figures, building on observations from Kennedy and Portal (1990), sighting the figures from specific vantage points at a shallow angle is proposed as a means to overcome these illusions. For the T, the Oppel–Kundt, the Müller–Lyer, and the Ebbinghaus figures, a new experiment demonstrated that observers were able to find a slant of the stimuli at which the illusory impressions vanished. Task demands on part of the beholders comprise discrimination and identification. The observed independence of response bias and sensitivity in psychometric functions can possibly be explained by the intrusion of identifying responses into discrimination tasks.
... One cannot first use the existing illusory percept as justification for developing a model of the aberrant processing, then declare the FIGURE 1 | (A) Poggendorf illusion with a ruler as the test figure (from Blakemore, 1973). (B) Café Wall illusion (Gregory and Heard, 1979) with a ruler overlaid on one of the apparently slanted lines, verifying its physical straightness. (C) Hering curved line illusion with the same ruler as its test figure. ...
This overview discusses the nature of perceptual illusions with particular reference to the theory that illusions represent the operation of a sensory code for which there is no meaningful ground truth against which the illusory percepts can be compared, and therefore there are no illusions as such. This view corresponds to the Bayesian theory that “illusions” reflect unusual aspects of the core strategies of adapting to the natural world, again implying that illusions are simply an information processing characteristic. Instead, it is argued that a more meaningful approach to the field that we call illusions is the Ebbinghaus approach of comparing the illusory percept with a ground truth that is directly verifiable as aberrant by the observer in the domain of the illusory phenomenology (as opposed to relying on the authority of other experts). This concept of direct verifiability not only provides an operational definition of “illusion”; it also makes their interactive observation more effective and informative as to the perceptual processes underlying the illusory appearance. An expanded version of Gregory’s categorization of types of illusion is developed, and a range of classic and more recent illusions that illustrate the differences between these philosophical viewpoints is considered in detail. Such cases make it clear that the discrepancies from the measurable image structure cannot be simply regarded as idiosyncrasies of sensory coding, but are categorical exemplars of perceptual illusions. The widespread existence of such illusory percepts is indicative of the evolutionary limits of adaptive sensory coding.
... With both eyes open, this example also illustrates chromostereopsis. 6, Try to see the horizontal lines here (Gregory & Heard 1979). 7, This is a variation on the Hermann grid, with the addition of yellow dots. ...
... This activity was run in the context of Public Engagement events within a Bristol (UK) community (n ¼ 49) and alongside two scientific conferences (6th Visual Science of Arts Conference, and 41st European Conference on Visual Perception) in 2018 (n ¼ 97) at events open to the general public. Illusions included two black and white patterns perceived as "wavy," with alternating 3D "furrows and ridges" (named Lisbon Straight and Lisbon Angled after the tiling patterns in Rossio Square in Lisbon, Portugal; Figure 1C); the coloured Primrose Field illusion (Kitaoka, 2005, p. 22); and a kindergarten pattern first described by (Pierce, 1898) as a variant of the Cafe Wall illusion (Gregory & Heard, 1979). Note that this latter illusion was intended to serve as a kind of high-luminance contrast, high spatial frequency control pattern without 3D effect. ...
... Similarly, the highest walking discomfort was reported for the Lisbon Straight pattern, followed by the Lisbon Angled pattern, whilst both the Primrose and the Caf e Wall patterns (Kitaoka, 2005, p. 22), LS and LA mimicking the pattern in Rossio Square on a smaller scale (i.e., higher spatial frequency); and the kindergarten pattern (Pierce, 1898) as a variant of the CW illusion (Gregory & Heard, 1979). Each floor consisted of the same vinyl material and was 6 m long and 1.50 m wide. ...
In nature, sensory and physical characteristics of the environment tend to match; for example, a surface that looks bumpy is bumpy. In human-built environments, they often don’t. Here, we report observations from people exploring if mismatch between visual and physical characteristics affected their perceived walking experience. Participants walked across four flat floors, each comprising of a visual illusion: two patterns perceived as alternating 3D “furrows and ridges,” the Primrose Field illusion, and a variant of the Cafe Wall illusion as a control pattern without perceived 3D effects. Participants found all patterns intriguing to look at; some describing them as “playful” or “gentle.” More than half found some of the patterns uncomfortable to walk on, aversive, affecting walking stability, and occasionally even evoking fear of falling. These experiences raise crucial research questions for the vision sciences into the impact of architectural design on well-being and walkability.
... This effect with the appearance of tilted line segments in the edge map has an effect on the appearance of square tiles which look similar to trapezoids, inducing convergent and divergent mortar lines. The trapezoid shape has been referred to as wedges in some previous studies on the Café Wall pattern and declared to be the explanation for the tilt effect in the Café Wall illusion [60]. On the other hand, the output of lower scale DoG filters preserves the outline and shape of the tiles and the connectivity of them by the mortar line. ...
Over the last decade, a variety of new neurophysiological experiments have deepened our understanding about retinal cells functionality, leading to new insights as to how, when and where retinal processing takes place, and the nature of the retinal representation and encoding sent to the cortex for further processing. Based on these neurobiological discoveries, we provide computer simulation evidence to suggest that Geometrical illusions are explained in part, by the interaction of multiscale visual processing performed in the retina supporting previous studies [1, 2]. The output of our retinal stage model, named Vis-CRF which is a filtering vision model is presented here for a sample of Café Wall pattern and for an illusory pattern, in which the final percept arises from multiple scale processing of Difference of Gaussians (DoG) and the perceptual interaction of foreground and background elements.
... This effect with the appearance of tilted line segments in the edge map has an effect on the appearance of square tiles which look similar to trapezoids, inducing convergent and divergent mortar lines. The trapezoid shape has been referred to as wedges in some previous studies on the Café Wall pattern and declared to be the explanation for the tilt effect in the Café Wall illusion(Gregory and Heard, 1979). On the other hand, the output of lower scale DoG filters preserves the outline and shape of the tiles and the connectivity of them by the mortar line. ...
Over the last decade, a variety of new neurophysiological experiments have led to new insights as to how, when and where retinal processing takes place, and the nature of the retinal representation encoding sent to the cortex for further processing. Based on these neurobiological discoveries, in our previous work, we provided computer simulation evidence to suggest that Geometrical illusions are explained in part, by the interaction of multiscale visual processing performed in the retina. The output of our retinal stage model, named Vis-CRF, is presented here for a sample of natural image and for several types of Tilt Illusion, in which the final tilt percept arises from multiple scale processing of Difference of Gaussians (DoG) and the perceptual interaction of foreground and background elements (Nematzadeh and Powers, 2019; Nematzadeh, 2018; Nematzadeh, Powers and Lewis, 2017; Nematzadeh, Lewis and Powers, 2015).
