Hermann Grid Research Articles

A geometric calibration method for thermal cameras using a ChArUco board

Accurate and efficient geometric calibration is important to precisely acquire geometric information in thermal cameras. Typically, the calibration procedure involves obtaining defined control points from the images of a calibration target and utilizing them to estimate the geometric calibration parameters based on a camera model. Calibration targets include checkerboards, circle grids, Hermann grids, and specially designed patterns. Thermal cameras typically have lower resolution than visible cameras and the control points are localized by creating contrast through heating. These differences make the calibration process of thermal cameras more complex. Conventional thermal camera calibration methods require that the entire calibration target is captured and that all the control points from each image are identified. Due to these limitations, geometric calibration of a thermal camera traditionally requires advanced image processing or substantial manual intervention.This work presents a calibration method using a ChArUco board as the calibration target. The proposed method allows the calibration to be performed with partial-view images and does not require that all the control points from each image are extracted, thereby allowing the calibration to be performed without requiring complex image processing. The proposed calibration method was successfully implemented to estimate the calibration parameters of two different thermal cameras; in both cases achieving an overall mean reprojection error below 0.4 pixels. The effectiveness of the approach was further demonstrated by performing the calibration with a lower mean reprojection error than the MATLAB camera calibrator app. Furthermore, the effectiveness of using different heat sources to create contrast was evaluated.

Investigation of the Scintillating Grid Illusion in Patients with Amblyopia

Investigation of the Scintillating Grid Illusion in Patients with Amblyopia

Investigation of the Scintillating Grid Illusion in Patients with Amblyopia

The work is devoted to the study of the manifestations of the scintillating grid illusion in patients with amblyopia. 133 schoolchildren with bilateral refractive amblyopia and 146 control group schoolchildren without ophthalmopathology were observed. In the work, we used our own test images developed on the basis of classical images that cause of the scintillating grid illusion. It is shown that the phenomenon of the illusory disappearance is more pronounced, and the strength of the scintillating grid illusion is significantly lower in children with amblyopia compared with children without ophthalmopathology. When the test images are rotated by 45°, an increase in the phenomenon of the illusory disappearance of disappearance is observed both in children with amblyopia and in children of the control group. The severity of the scintillating grid illusion in children with amblyopia is significantly lower than in children without ophthalmopathology.

Spatial Properties of Scintillating Grid Illusion by Visual Experiment and Numerical Simulation

Spatial Properties of Scintillating Grid Illusion by Visual Experiment and Numerical Simulation

The Hermann grid illusion fails to fool patients with schizophrenia: Experimental support for a reduced lateral inhibition hypothesis

A large body of evidence indicated that patients with schizophrenia spectrum disorders show deficit in perceptual and visual processing, but little is known about the origin of this defect. One of the strategies used to reveal the origin of such defects is to use tests that have a strong neuropsychological basis in normal individuals. In this study, we used the Hermann grid task to reveal the source of visual deficit in patients with schizophrenia. Several findings have shown that the Hermann grid illusion results from lateral inhibition of neuro-visual pathway cells. We compared 26 patients with schizophrenia to 26 participants with high schizotypy traits and 26 normal controls in a computer test we designed for the Hermann grid illusion. Chi-square analysis revealed that the patients with schizophrenia and the participants with high schizotypy traits reported significantly less the Hermann grid illusion than healthy controls. Therefore, the results support the hypothesis of a defect in lateral inhibition of patients with schizophrenia. This might suggest that the visual pathway cells in schizophrenic patients failed to properly combine the data from the visual receptors as they do in healthy people. • The Hermann grid illusion has wealthy neuropsychological background. • Visual perception difficulties in schizophrenia have been always reported. • Patients with schizophrenia do not report the Hermann grid illusion. • Evidence show that lateral inhibition contributes in the Hermann grid illusion. • Lack of Hermann grid illusion support a lateral inhibition defect in schizophrenia.

The Mechanisms of the Visual System Behind Visual Illusions: From Eye to Brain

Visual illusion is a psychological phenomenon characterized by perception that appears to differ from physical reality. Illusory perception persists even though the sufferers are aware of the physical properties of what they are observing. Thus, studying visual illusions has led to an improved understanding of the neural mechanism underlying visual information processing. Visual illusions are important tools in neuroscience. Some brightness illusions, such as the Hermann grid illusion or Chevreul illusion, can be explained by the function of the center-surround antagonistic receptive field of retinal ganglion cells. Additionally, color aftereffects were found to be produced in the retina. In addition, neurons in the primary visual cortex are responsible for the orientation-contingent color aftereffect, known as the McCollough effect. ISI reversal, a visual motion illusion, is known to be caused by a biphasic temporal mechanism located in the retinal or lower visual areas. Higher visual areas are responsible for the production of visual illusions such as the Ponzo illusion, size constancy illusion, or tabletop illusion. These illusions are perceived through the process of achieving size constancy from a two-dimensional retinal image. Thus, both low-level and high-level vision are involved in the perception of visual illusions.

Scintillating Starbursts: Concentric Star Polygons Induce Illusory Ray Patterns.

Here, we introduce and explore Scintillating Starbursts, a stimulus type made up of concentric star polygons that induce illusory scintillating rays or beams. We test experimentally which factors, such as contrast and number of vertices, modulate how observers experience this stimulus class. We explain how the illusion arises from the interplay of known visual processes, specifically central versus peripheral vision, and interpret the phenomenology evoked by these patterns. We discuss how Starbursts differ from similar and related visual illusions such as illusory contours, grid illusions such as the pincushion grid illusion as well as moiré patterns.

Hermann Grid Optical Illusion and The Rebelling Dots of Reality

Hermann Grid Optical Illusion and The Rebelling Dots of Reality

Scintillating Grid Illusion Without the Grid.

The scintillating grid illusion is a phenomenon where illusory black spots are perceived on white patches located at the intersections of a grid pattern. In this study, I report that the illusory spots as observed in the illusion are perceived with a stimulus pattern without grid bars. In two experiments, I investigated the perceptual properties of the scintillating illusion without grid bars. I found that the strength of the illusion depends on the contour shape of the patch components as in the scintillating grid illusion, while neither the density nor spatial alignment largely affect the illusory percepts. These findings undermine the previous theories on the mechanism of the scintillating grid illusion, as it was assumed that the grid bars are the essential component to induce the illusion. The results suggest that the illusory spots of the scintillating grid illusion could be induced by the limited processing of the patch stimuli in the peripheral vision and that the grid could play a supplementary role by enhancing the effect by further interfering with the processing.

Tiny Squares at the Hermann Grid Corners Can Completely Remove the Illusion.

A novel modification of the Hermann grid stimulus is demonstrated. It is shown that introduction of extremely tiny squares at the corners of the grid squares in the classical stimulus, keeping the position and orientation of the grid squares fixed, can reduce the strength and even completely wipe out the illusory dark spots. The novel perturbing stimulus was investigated further and a gray-level intensity threshold was measured for the tiny corner squares beyond which the illusory blobs disappear completely. It was also found that this threshold remains practically unchanged over a wide range of grid square size for an observer.

Dissociation of perceived size and perceived strength in the scintillating grid illusion

The scintillating grid illusion is a geometric visual illusion where illusory dark spots are perceived on white circular patches that are located at the intersections of a grid pattern. Previous studies have measured the perceived strength of the illusory spots by varying stimulus and viewing conditions, to elucidate the mechanisms underlying the illusion; however, findings remain inconclusive. In the present study, we measured the perceived size of the illusory spots, in addition to their perceived strength, by varying the size of the geometric components and the orientation of the stimulus, to further investigate the mechanism behind this illusion. We found that the dependency of perceived spot size on the change of the stimulus parameters is dissociated from that of the perceived spot strength. The perceived size of the illusory spots linearly correlated with the size of the white patches and was less dependent on the width of the grid bars and the orientation of the stimulus, while the perceived strength was characterized by a quadratic relationship with patch size and bar width and was monotonically modulated depending on the orientation of the stimuli. These results suggest that different factors separately constrain size and strength within the processes that elicit the illusory spots. We propose that the mechanism underlying the scintillating grid illusion is based on the interruption of the surface formation process of white patches by the interference of the orientation signals of gray bars.

The Sequin Illusion.

The Sequin Illusion can be seen when shapes are drawn in dotted lines, against a background of different brightness. This can be done either with bright dots over a dark background or with dark dots over a bright background, though the latter usually works better. The illusion appears as a wave of dark (or bright) spots inside the dotted shapes (like sequins!) in peripheral vision. Although similar in appearance with the Hermann Grid, the Sequin Illusion occurs inside the shapes; persists despite slanted, disrupted, or nonrectangular edges; and is only eliminated when the dotted contour is formed by colors of similar brightness. Therefore, this illusion is driven by brightness (not color) contrasts in contours, which possibly points to the magnocellular channel in lateral geniculate nucleus.

How comparatively widespread are visual illusions?

Researchers and artists have long been interested in visual illusions because they illustrate the interesting, complicated, and constrained ways in which we perceive the world. Although we may not be familiar with the names of the many different visual illusions that exist (e.g., the Necker cube, the Müller-Lyer illusion, and the Hermann grid illusion, to name a few), people with typically functioning will certainly have seen many of these. We have known for centuries that humans perceive these illusions. We have known for the past few decades that nonhuman mammals can perceive these illusions, and very recent work has revealed that birds and fish perceive some of these illusions, though sometimes in a way opposite to how our own species does. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Fission line illusion: A report of a variant of grid illusion and a study on its perceptual properties

Fission line illusion: A report of a variant of grid illusion and a study on its perceptual properties

Experimental Observations of the Visibility Threshold of Illusory effects in Hermann Grid, Sinusoidal and Square Gratings and their Possible Implications

Experimental Observations of the Visibility Threshold of Illusory effects in Hermann Grid, Sinusoidal and Square Gratings and their Possible Implications

Contrast Sensitivity and Lateral Inhibition Are Enhanced With Macular Carotenoid Supplementation.

Once deposited in the retina, the so-called macular carotenoids lutein (L), zeaxanthin (Z), and mesozeaxanthin (MZ) have been shown to enhance visual performance. The purpose of our study was to investigate whether increasing macular pigment optical density (MPOD) could enhance lateral inhibitory processes, and thereby improve contrast sensitivity (CS). A total of 59 young (18-25 years), healthy individuals participated in this 1-year, double-masked, placebo-controlled study. MPOD was assessed via heterochromatic flicker photometry. Lateral inhibition sensitivity (LIS) was determined with a computer-based, user-adjustable Hermann grid. CS (at 8 cycles/degree) was determined with a two-alternative, forced-choice procedure. Subjects received either the placebo (n = 10), 12 mg total macular carotenoids (n = 24), or 24 mg total macular carotenoids (n = 25). MPOD, LIS, and CS increased significantly in treatment groups between baseline and 6 months, and between 6 and 12 months (P < 0.05 for all) versus placebo. The relationships between changes in MPOD and both LIS and CS were significant at 6 and 12 months (P < 0.05 for both). Changes in CS and LIS over the 12-month study period were found to be significantly related (r = 0.41; P = 0.0014). Increases in MPOD led to enhanced lateral inhibitory processes, which correspond to improved CS. Because optical filtering has the same net effect on dark versus light bars, it cannot explain these improvements. Improvement in CS with increases in MPOD therefore appears to involve enhancement of the fundamental physiological systems that give rise to edge detection.

Eggs illusion: Local shape deformation generated by a grid pattern.

In this study, we report a new visual shape illusion, the eggs illusion, in which circular disks located at the midpoints between adjacent grid intersections are perceived as being deformed to ellipses. In Experiment 1, we examined the eggs illusion by using a matching method and found that grid luminance and patch size play a critical role in producing the illusory deformation. In Experiment 2, we employed several types of elliptic or circular patches to examine the conditions in which the illusory deformation was cancelled or weakened. We observed that the illusory deformation was dependent on local grid orientation. Based on these results, we found several common features between the eggs illusion and the scintillating grid illusion. This resemblance suggests a possibility that similar mechanisms underlie the two phenomena. In addition to the scintillating grid illusion, we also considered several known perceptual phenomena that might be related to the eggs illusion, i.e., the apparent size illusion, the shape-contrast effect, and the Orbison illusion. Finally, we discuss the role of orientation processing in generating the eggs illusion.

Illusory Streaks from Corners and Their Perceptual Integration.

Perceptual grouping appears both as organized forms of real figural units and as illusory or “phantom” figures. The phenomenon is visible in the Hermann grid and in configurations which generate color spreading, e.g., “neon effects.” These configurations, generally regular repetitive patterns, appear to be crossed by illusory bands filled with a brighter shade or a colored tinge connecting the various loci of illusory effects. In this work, we explore a particular new illusion showing a grouping effect. It manifests as illusory streaks irradiating from the vertexes of angular contours and connecting pairs of figures nearby. It is only clearly visible when more than one figure is shown, and takes the shape of a net crossing their corners. Although the grouping effect is vivid, the local source of the illusion is completely hidden. Theories explaining this effect as due to the irradiation of illusory streaks (mainly that of Grossberg and Mingolla, 1985a,b) do not fully explain the figural patterns presented here. Illusory effects have already been documented at the angles of various figures, causing them to alter in amplitude and brightness; however, the figure illustrated here appears to have different features and location. Phenomenological observations and an experiment were conducted to assess the role played by geometric and photometric parameters in this illusion. Results showed that sharp angles, in low contrast with the surround, are the main source of the illusion which, however, only becomes visible when at least two figures are close together. These findings are discussed with respect to theories of contour processing and perceptual grouping, and in relation to other illusions.

Puzzle task ERP response: time-frequency and source localization analysis.

Perceptual decision making depends on the choices available for the presented task. Most event-related potential (ERP) experiments are designed with two options, such as YES or NO. In some cases, however, subjects may become confused about the presented task in such a way that they cannot provide a behavioral response. This study aims to put subjects into such a puzzled state in order to address the following questions: How does the brain respond during puzzling moments? And what is the brain’s response to a non-answerable task? To address these questions, ERP were acquired from the brain during a scintillation grid illusion task. The subjects were required to count the number of illusory dots, a task that was impossible to perform. The results showed the presence of N130 over the parietal area during the puzzling task. Coherency among the brain hemispheres was enhanced with the complexity of the task. The neural generators’ source localizations were projected to a multimodal complex covering the left postcentral gyrus, supramarginal gyrus, and angular gyrus. This study concludes that the brain component N130 is strongly related to perception in a puzzling task network but not the visual processing network.

The colour conditions by which streaming is perceived in the horizontal and vertical bars in the chromatic Hermann grid

The colour conditions by which streaming is perceived in the horizontal and vertical bars in the chromatic Hermann grid