The "Double Ring Illusion": The physical constraint of solidity shapes visual processing

Who does not like visual illusions? Not only do they offer a wondrous experience to viewers, but they also compellingly reveal the inner workings of our visual system. Out of the myriad of existing illusions, however, rarely are they produced thanks to priors about the physics of our world. Here, we present a novel illusion of this kind-the Double Ring Illusion-which demonstrates that a representation of the physical constraint of solidity (i.e., objects cannot pass through one another) shapes perception. Thus, when viewing ambiguously rotating rings that are compatible with multiple interpretations, the percept is strongly altered by the solidity constraint: Observers predominantly perceive the interpretation respecting solidity rather than the alternative interpretation where solidity is violated. A series of experiments first confirmed that observers reliably experienced this illusion. We then demonstrated that the effects of the illusion influence orthogonal perceptual judgments of object width, thus ruling out decision-level processes as a driver of these effects. Furthermore, we showed that the solidity constraint shapes visual processing even when the stimuli are unambiguous thanks to additional motion and depth information. And finally, we found that the visual system predictably makes use of solidity even in contexts other than the Double Ring Illusion. Together, these results demonstrate the existence of a robust prior for solidity in visual processing, guiding the computations of object motion and interaction. (PsycInfo Database Record (c) 2025 APA, all rights reserved).

Visual illusions occur around us all the time, which present in nature and appear when you least expect it. It is well known that visual illusions can have a dramatic effect upon our visual perception of an object 's size and position. However, whether visual illusions have a similar influence on visual guided action or not, it remains the subject of much debate. The purpose of this study is to explore whether the visual information used to identify and categorize an object would be similar to the visual information used to plan and control visually guided movements directed toward that object. The outcome of this study will be helpful for designers to understand our visual information system and apply that knowledge to the design practice. In order to achieve the purpose of this study mentioned above, three visual illusions as the experiment's apparatus are applied to examine the relative effect of visual illusions on both the visual perceived center of an object and the position of a grasp on that object when a balanced lift is required. The results of the experiment show that (1) Illusions influence both the perceived and the grasped estimates of the center position, but the grasp center is more veridical; (2) Judd-illusion, one of the three visual illusions, has a bigger degree of effect than two other illusions on both the perceived and the grasped estimates of the center position; (3) By providing the participants with a mean to guide their visual perception of these illusions, the errors from the estimation of the center position can be significantly reduced.

The science and technology of image transmission and display has evolved primarily from the diciplines of computer science, electrical engineering and physics. Thus, it is only natural that techniques and attitudes which have developed are characterized by the style in which people in these areas approach the subject of images and their transmission, display, and processing. For example, one finds many important differences between the methods of television and those of photography. Moreover, an even greater contrast is found when comparing the methods of electrical engineering, physics, television and photography with those now understood to be employed by the human eye and the human visual system. Specifically, let us contrast the method by which television, photography and the human visual system, represent image information. In television (particularly digital imaging), image values are represented by signals analogous to quantities of light. They are called intensities. In photography, on the other hand, the representing quantities are concentrations of silver or dyes. Consequently, due to the natural exponentiating laws governing the interaction of light with these media, they are analogous to the logarithm of quantities of light. They are called densities. The human visual system, on the other hand, (while being generally logarithmically sensitive) moves a large step further away from representation by physical quantities of light and produces at very early stages in its processing highly modified versions of the patterns of light or their logarithms. The natural question then arrises, why should the human visual system try to do this; and since it does, what consequences are implied in terms of the television and photographic presentations normally employed?

Unimpaired performance during cognitive and visual manipulations in persons with anterior cruciate ligament reconstruction compared to healthy adults

Links between global and local shape perception, coloured backgrounds, colour discrimination, and non-verbal IQ

Transcranial direct current stimulation (tDCS) has been widely used for modulating sensory, motor and cognitive functions, but there are only few attempts to induce and change illusory perception. Visual illusions have been the most traditional and effective way to investigate visual processing through the comparison between physical reality and subjective reports. Here we used tDCS to modulate two different visual illusions, namely the Brentano illusion and the glare effect, with the aim of uncovering the influence of top-down mechanisms on bottom-up visual perception in two experiments. In Experiment 1, to a first group of subjects, real and sham cathodal tDCS (2mA, 10min) were applied over the left and right posterior parietal cortices (PPC). In Experiment 2, real and sham cathodal tDCS were applied to the left and right occipital cortices (OC) to a second group of participants. Results showed that tDCS was effective in modulating only the Brentano illusion, but not the glare effect. tDCS increased the Brentano illusion but specifically for the stimulated cortical area (right PPC), illusion direction (leftward), visual hemispace (left), and illusion length (160mm). These findings suggest the existence of an inhibitory modulation of top-down mechanisms on bottom-up visual processing specifically for the Brentano illusion, but not for the glare effect. The lack of effect of occipital tDCS should consider the possible role of ocular compensation or of the unstimulated hemisphere, which deserves further investigations.

Defining visual illusions in Parkinson's disease: Kinetopsia and object misidentification illusions

This paper presents a new frame-rate up conversion method for video plus depth representation. The proposed method improves the quality of video using additional depth information. The depth information is utilized in three ways to improve the accuracy of motion estimation. One usage is that depth frame is added in block matching criterion to estimate initial motion. Another usage is to detect object boundary region combining depth value variation and local depth distribution adjustment technique. Finally, motion vector field is refined adaptively by segmenting macroblocks into object regions. Any existing block-based motion-compensated frame interpolation methods may utilize our method to refine motion vector field by using depth frames. Experimental results verify that the proposed method outperforms the conventional motion-compensated frame interpolation algorithms, while preserving object structure.

Reliable and real-time crowd counting is one of the most important tasks in intelligent visual surveillance systems. Most previous works only count passing people based on color information. Owing to the restrictions of color information influences themselves for multimedia processing, they will be affected inevitably by the unpredictable complex environments (e.g. illumination, occlusion, and shadow). To overcome this bottleneck, we propose a new algorithm by multimodal joint information processing for crowd counting. In our method, we use color and depth information together with a ordinary depth camera (e.g. Microsoft Kinect). Specifically, we first detect each head of the passing or still person in the surveillance region with adaptive modulation ability to varying scenes on depth information. Then, we track and count each detected head on color information. The characteristic advantage of our algorithm is that it is scene adaptive, which means the algorithm can be applied into all kinds of different scenes directly without additional conditions. Based on the proposed approach, we have built a practical system for robust and fast crowd counting facing complicated scenes. Extensive experimental results show the effectiveness of our proposed method.

Contours projected from geodesic boundaries of developable surfaces (as are formed by folding and twisting flat surfaces) are particularly salient cues to 3-D surface shape. Textures which are strongly anisotropic (highly oriented) provide a similar source of information. The natural definition of homogeneity for such textures leads to the constraint that the oriented ‘flow’ of texture on a surface follows geodesics of the surface (on average). In the current work, it is shown that the shapes of contours projected from geodesics of developable surfaces, and analogously of oriented texture flow, reliably determine the shapes of the surfaces. On the basis of this analysis, it is suggested that human perception of surface shape from texture has two modes of operation: an isotropic mode, in which the visual system infers surface shape from local texture compression information, and a texture flow mode, in which the curvature of local texture flow determines local surface curvature, based on a geodesic constraint. In order to test the theory, planar texture patterns have been isometrically mapped with varying degrees of global orientation (ranging from isotropic to purely oriented) onto developable surfaces. The theory predicts that subjects' ability to make judgements about surface shape will be good for the isotropic textures and for highly oriented textures, but not for anisotropic textures that are only weakly oriented. As predicted, images of the surfaces with isotropic texture patterns induce strong percepts of shape, as do those of highly oriented textures. Images of anisotropic, weakly oriented patterns, however, elicit only weak percepts of shape.

2 - The human visual system described through visual illusions

Compare with traditional 2D video, 3D video can provide viewers with more realistic stereo experiences because of the depth information. In the paper, a new objective quality assessment algorithm for 3D videos is proposed. And experiments show that it is more accurate than peak signal-to-noise (PSNR) and structural similarity index measurement (SSIM). According to human visual system (HVS), we abstract contrast information, edge information, motion information and depth information from the test 3D video sequences and then build salient maps. The objective quality is calculated on the basis of SSIM/PSNR and salient maps. In order to test the accuracy of the algorithm, a subjective assessment experiment is designed according to related standards. Results have shown that the performance of proposed algorithm is better than original PSNR and SSIM measurements.

No-reference light field image quality assessment based on depth, structural and angular information

Visual illusions affect both movement planning and on-line control: A multiple cue position on bias and goal-directed action

With the growing interest of integrating robotics into everyday life and industry, the requirements towards the quality and quantity of applications grows equally hard. This trend is profoundly recognized in applications involving visual perception. Whereas visual sensing in home environments tend to be mainly used for recognition and localization, safety becomes the driving factor for developing intelligent visual control algorithms. More specifically, a robot operating in a human environment should not collide with obstacles and executed motion should be as smooth as possible. Furthermore, as the environment is not known on beforehand, a high demand on the robustness of visual processing is a necessity. On the other hand, in an industrial setting, the environment is known on beforehand and safety is mainly guaranteed by excluding a human operator. Despite these reasons, and the fact that visual servoing has gained much attention from industry to become a standard solution for robotic automation tasks, applications are highly simplified. For example, methods such as visual fault detection are already a mature technique in industrial manufacturing, where a fixed camera observes a product (e.g., on a conveyor belt) and checks whether it meets certain requirements. These operations can be executed at a fairly high rate due to the simplicity of the system (e.g., static camera) and the simplification of the processing task (e.g., binary images). For both areas the identified difficulties are similar. Foremost, this is the slow nature of (robust) visual processing, in respect to the ever growing demand of increasing speed and reducing delay. These two application areas with analogous limitations motivate the design of more direct approaches of vision in visual control systems. Therefore, in order to meet the requirements for next generation visual control systems, this thesis presents approaches which employ visual measurements as a direct feedback to design constrained motion. First, for industrial robotics, in order to obtain the required positioning accuracy, the measurement and fixation system have to be highly rigid and welldesigned, implying high cost and long design time. By measuring the position of objects directly with a camera, instead of indirectly by motor encoders, the requirements of the measurement and fixation system are less demanding. Moreover, this motivates the miniaturization of the complete control system. The approach is validated in experiments on a simplified 2D planar stage (i.e., considerable friction, poor fixation), which attains similar performance compared to encoder-based positioning systems. Secondly, in a human-centred environment, this direct sensing can improve traditional visual control systems, when subject to certain disturbances. More specifically, a method is proposed that uses an image-based feedforward controller on top of traditional position-based visual servo control to overcome disturbances such as friction or poorly designed local motor controllers. This visual feedforward control action is only active when an image-based error is present and vanishes when that error goes to zero. The method is validated on an anthropomorphic robotic manipulator with 7 degrees of freedom, intended for operation in the human care environment. Third, sensing the product directly gives rise to designing motion directly. Whereas in traditional approaches the motion trajectory is designed offline and can not be changed at runtime, direct trajectory generation computes the motion of the next step based on current state and events. This means that at any instance in time, the trajectory of a motion system can be altered with respect to certain desired kinematic or dynamic constraints. For industrial applications this makes manufacturing on near-repetitive or non-rigid structures (e.g. flexible displays) possible. When applied to a robotic manipulator, this enables obstacle avoidance to no longer be on path planning level, but on trajectory planning level, where kinematic or dynamic constraints can be taken into account. This results in a motion that is smoother than when obstacle avoidance with path planning is employed. For both application areas this direct trajectory generation method is implemented and shows high flexibility in constrained motion trajectory design.