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This article comes from the official account of Wechat: back to Park (ID:fanpu2019), author: Xu Zilong (Southeast University)

We have to study not only human delusions but also animals.

A long time ago, there was a saying that miscarriage of justice is part of football, or part of its charm. Later, of course, this claim was self-defeating, and the FIFA FIFA could not withstand the pressure from all sides to launch reforms, introducing goal-line technology for the first time at the 2014 World Cup in Brazil, with high-tech "eagle eyes" assisting referees.

Why are referees sometimes unreliable? Not to mention the angle problem, the attention problem does not see clearly, even if the ball passes by in front of our eyes, there are also misjudgments. Take a look at the following picture:

Figure 1. Flash lag effect | Source: Wikipedia when the red square moves to the center of the image, the green square flashes at the same time, but we feel that the red square has already flashed by when the green square flashes. This illusion is called the "flash lag effect" (Flash lag effect). To put it uncommonly, the flash lag effect is that when a visual stimulus moves along a continuous track, relative to the unexpected events (such as flashes) that may occur on that track, the moving stimulus is sensed earlier than the actual position (figure 1) [1].

In a football match, the assistant referee may make a misjudgment due to the flash lag effect when judging whether the attacking player is offside [2] (figure 2). In the offside judgment scene, the receiver of the attacking side is equivalent to the red square of continuous movement, while the passing action of the passer is equivalent to an emergency (green flash), and the moment of passing is the time sign for the assistant referee to decide offside. Due to the flash lag effect, the assistant referee will think that the passing event lags behind, and the running catcher is perceived to be closer to the goal than the actual position, resulting in flag-raising errors (Flag error,FE).

Figure 2. The map of the misjudgment of the assistant referee. ▲ attacking team member; △ assistant referee perceived offensive player position; ● defensive side's position of the penultimate player; ■ assistant referee. (the picture is modified from the reference [2], click to see the larger picture) (A) geometric diagrams of in-place position and offside position. The moment the offensive player passes the ball, the relative position between the receiver and the penultimate defender is the criterion for determining whether the ball is offside or not. (B) schematic diagram of the influence of flash lag effect on offside judgment. When the attacking catcher in the shaded area of the picture is running towards the opponent's goal, the moment the passing teammate touches the ball, the position perceived by the assistant referee (white hollow triangle) is likely to be closer to the goal than its actual position (black solid triangle), resulting in miscalculation. Obviously, understanding the optical illusion can let us know that in some cases the referee is innocent _ (3) ∠) _ in addition to the illusion that people can avoid the flash lag effect, there are also some "good" illusions that can be used to make mistakes.

For example, from the perspective of visual scientists, the famous psychological projection test, the Rorschach inkblot test (Rorschach test), can be said to be based on visual illusion. More precisely, our brains are always looking for known patterns in random structures with low information, a psychological phenomenon known as "pareidolia" [3].

Figure 3. Example of Rorschach ink projection test | Source: Wikipedia of course, all faces on Mars, rabbits on the moon, demons / gods in tornadoes, Buddha statues in the sea of clouds are all the work of utopian misconception.

From the above two examples, we can know that vision is not just a "feeling" in the "five senses" (audio-visual smell touch), but a "perception" that requires the brain to participate in interpretation. When there is a deviation in interpretation, there is an illusion.

Visual illusion is the best adaptation of our visual system to the visual scene. These adaptations are "solidified" in our brains and can lead to inappropriate interpretation of visual scenes. Just as medicine studies the human body from patients, psychology and neuroscience can also use visual "errors" to expose the structure and function of the visual system and understand the mechanism of vision.

There are a large number of visual illusions, most of which have not been effectively explained. We already know that brightness and contrast, motion, geometry or angle, three-dimensional interpretation (size constancy and impossible pictures), cognitive / gestalt effect and so on can cause visual illusion. From the perspective of generation mechanism, visual illusion can be divided into three kinds: geometric illusion caused by the structure of the image itself, physiological illusion caused by sensory organs, and cognitive illusion caused by psychological reasons.

01. Visual illusion caused by brightness and contrast the classic "Hermann grid" was discovered by the German physiologist Ludimar Hermann (1838-1914) in the 1870s. Scan the white grid in the image below and notice that there are dim gray patches at the intersection of the white lines, but if you stare directly at the intersection of the white lines, the gray patches fade or disappear.

Figure 4. Source: another common illusion in Wikipedia is the "flicker grid illusion" (scintillating grid illusion) discovered in 1994. It is often regarded as a variant of Hermann's illusion.

Figure 5. Scintillation grid? source: Wikipedia these two illusions are very similar. They both involve the same processing of the visual nervous system: lateral inhibition.

The human eye is like a sophisticated camera, and the retina at the bottom of the eye is like a piece of photographic film, made up of a large number of optic nerve cells (see figure 6).

Figure 6. Anatomical structure of retina [4]

Figure 7. Retinal layered structure [4] when light enters the retina, the retina converts light signals into nerve impulses, which are transmitted from the pathway of photoreceptor cells (photoreceptor), → bipolar cells (bipoloar cell) and → ganglion cells (ganglion cell) to the visual center of the cerebral cortex. The area where visual nerve cells respond to light stimuli is called the "receptive field" [4].

The receptive field of most visual nerve cells is divided into the central part and the surrounding part (figure 7), which is called "central-peripheral receptive field" (center-surround receptive field). One of its important characteristics is that the responses of the central and surrounding parts to light are antagonistic to each other. For example, in figure 8, light on the periphery of the receptive field (red) inhibits the response of the central part of the receptive field (blue) to light.

Figure 8. Central-peripheral receptive field intention [4] for half a century, the classical theory of "lateral inhibition" has been used to explain the Hermann illusion. The so-called lateral inhibition, also known as lateral inhibition, means that excited neurons excited by stimulation will inhibit the activity of adjacent neurons. Let's take a look at exactly what happened in the Hermann illusion.

Figure 9 explanation of Hermang's lateral inhibition | Source: michaelbach.de in figure 9, we assume that the red disk represents the receptive field of an optic ganglion cell. When the receptive field accidentally falls at the intersection of the grid (the center of the upper-left disc), there are four bright inhibitory blocks around it, making the middle look dim (gray); when ganglion cells look at the street, there are only two inhibitory blocks around (the center of the lower left disc), so it gets a higher amount of stimulation than the neurons at the cross, that is, it looks white.

However, when we look directly at the cross, the receptive field is very small (the small red disk on the right). Such small receptive fields, whether or not they are located at the cross, will not be affected.

However, the latest research shows that the above classical explanation may be problematic. If you twist the grid lines slightly, the illusion will disappear (on the right side of the image below). This shows that the visual cortex processes information with directional selectivity, also known as the directional selectivity of neurons [5].

Figure 10. Disappearance of Hermann illusion | Source: Bach, M. Optical illusions, 200602, Motion Illusion

Figure 11. Motion illusion, Source: Bach, M. Optical illusions, 2006 sometimes, the still image looks like it is moving slowly, and the disk in the picture above seems to be spinning slowly. At present, we have not fully understood the neural mechanism of motion illusion, we can only say that the prerequisite for this illusion is the asymmetric luminance level [6].

It is obvious that each large circle in figure 11 is made up of many radial fans (which are very narrow). Each fan contains a series of color sequences, the repeating unit of which is "bright white-bright yellow-dark black-dark blue-bright white".

Figure 12. The key to the illusion of the color sequence contained in figure 11 is that the position of the color or luminance sequence in the adjacent radiant sector is misaligned and offset [3]. When such an image suddenly appears in front of you, the asymmetric brightness level triggers the motion detector of the visual system, making it feel as if the image is spinning. Grouping can enhance the effect of illusion, but color is not necessary.

03. Geometry and angle illusion

Figure 13. Z ö llner illusion | Source: Bach, M. Optical illusions, 2006 Zorna illusion (Z ö llner illusion) is another common visual illusion. In 1860, Johann Karl Friedrich Z ö llner, a German astrophysicist, discovered that parallel lines that intersect a short line at an acute angle appear to diverge. In figure 13, there is a series of oblique lines that overlap the short line. it looks like these lines are scattered and will soon intersect-but in fact these nine "inclined lines" are all parallel.

Similar delusions are the Poggendorff illusion, the Hering illusion, and the combination of Herring and Zorna illusions (figure 14).

Figure 14. Several common geometric and angular illusions: (a) Pogendorf illusion; (b) Herring illusion; (c) the combination of Herring illusion and Zorna illusion [6] the researchers believe that the Zorna illusion is caused by the depth perception caused by the angle between the short line and the long line. Based on the perspective principle, the direction of the intersection of long and short lines will feel like the "depth" of the paper, while the opening of the angle will feel that it points to the "shallower" place. At this point, our visual system automatically adjusts again-"pull closer" the two flat lines adjacent to the "deep" part, and "push away" the parallel oblique long lines at the "shallower" part-to ensure the correct perception of the size of the near and the far. But in fact, the lines are all drawn on a two-dimensional plane of paper, without any depth, so it looks like the long line is not parallel.

04. The mechanism of constancy is the inherent mechanism of human brain cognition. The farther away an object is from us, the smaller the image is on the retina, but we don't think it becomes smaller just because we are farther away from it. This is the constant size mechanism at work.

When the distance of the object is halved, the size of the object image is doubled. The visual system multiplies the size of the projection on the retina by the assumed distance, allowing us to estimate the size of the object without being affected by geometric perspective. When the distance information is invalid, our visual system will reset the "default setting", which makes it impossible to estimate the size of the object correctly. For example, photographers often use the "moon illusion": the moon appears larger when it is close to the ground plane than when it is high in the sky, because the moon is too far away from us to estimate.

Figure 15. Muller-Lyer illusion | Source: the Miller-Lyle illusion discovered by The Scientist German sociologist Franz Carl M ü ller-Lyer in 1889 can be explained by visual constancy. In this illusion, the visual system detects a depth clue-the direction of the arrows at both ends of the segment. "convex corner" means a closer distance, such as the protruding corner of the room, and "concave corner" means a longer distance, such as the concave corner of the room. According to the visual system, the inward arrow (concave angle) indicates that the line segment is far away from us; the outward arrow (convex angle) indicates that the line segment is closer to us. Next, the size constant mechanism corrects the image we observe by increasing the length of segments that are "farther" (with inward arrows at both ends) and reducing the length of segments with "nearer" (arrows at both ends pointing outward). As a result, we think that the length of the upper ("far") segment is longer than the lower ("closer") segment.

05. Gestalt effect

Figure 16. Caniza square [5] Caniza square was first described by Italian psychologist Gaetano Caniza (1955). Although everyone can perceive the square in the picture, its outline is the main outline automatically generated by the viewer.

Gestalt psychologists use the law of closure, one of the rules of Gestalt perceptual organization, to explain this illusion. According to this law, objects grouped together tend to be regarded as part of the whole. We tend to ignore the gaps and perceive the contours so that the pictures are combined as a whole.

Gestalt holds that people tend to perceive an object as a whole, rather than just paying attention to the gaps that may be contained in the object. When a part of a picture is missing, our perception automatically fills in the missing part. Studies have shown that the reason why the perceptual system is like this is to increase the integrity of surrounding stimuli.

Figure 17. The impossible Trident, also known as the "devil's fork" [1] in figure 17, the upper part of the picture on the left looks like three towers. At the bottom is a curved U-shaped rod. If you connect the lines as shown on the right, the "impossible object" appears. Line extensions are inappropriate because they transform the empty background between the towers into a U-shaped bottom surface. This gives observers an incredible feeling that art and science are connected here: Mauritius-Escher painted the famous "rise and fall" just two years after Penrose released his "stairs of the impossible".

Do dogs have delusions? Enlightened scientists have done some interesting experiments.

Sarah Byosiere of La Trobe University University in Australia showed dogs the Ebinghaus-Ebbinghaus-Titchener illusion. It is an illusion of relative size, named after German psychologist Hermann Ebbinghaus and British psychologist Edward B. Titchener.

Figure 18. Ebinghaus-Ebbinghaus-Titchener illusion [7] in the most classic version, two circles of the same size are close to each other, but one is surrounded by a larger circle and the other is surrounded by a smaller circle. When the two groups are placed side by side, what we perceive is that the central circle surrounded by a large circle appears smaller than the circle surrounded by a small circle. One of the main reasons for this illusion is the size contrast effect between the central target circle and the surrounding induced circle.

So, does the Ebbinghaus-Tecchina illusion have any impact on dogs?

Byosiere's team designed a device that allows dogs to express what they feel: a small test room, a small test room that displays touch screens with different visual illusions, and dogs can interact with the screen with their noses. Each dog has been trained to touch the screen with his nose to select the picture in which the middle circle appears larger.

Figure 19. Test the response of dogs to the Ebbinghaus-Tecchina illusion [8] the results show that dogs also have the Ebbinghouse-Tecchina illusion. But! But dogs are different from humans, who feel that the solid circles around smaller rings look larger, while dogs choose the opposite.

Figure 20. Delboeuf illusion | Source: The Scientist psychophysicist Joseph Delbov established the Delboeuf illusion in 1865 (figure 20). Two black circles of the same actual size are surrounded by rings of different sizes. Usually, to people's vision, the black circle on the left looks slightly smaller than the one on the right.

Distance effect is an important factor in Delbov illusion. When the outer induction ring is close to the central target circle, the central target circle appears larger; when far away, the central target circle appears smaller. As a result, we exaggerate the size of the center circle on the right because it is almost the same size as the outer circle, and underestimate the size of the center circle on the left because it is much smaller than the outer circle.

What is the delusion of Delbov in the eyes of dogs?

Christian Agrillo of the University of Padua (University of Padua) in Italy and his colleagues tried to use dog food tied in circles to test how different breeds of dogs were affected by Delbov illusion (figure 21).

Figure 21. Test the dog's response to the Delboeuf illusion [8] the Agrillo group gave each dog two plates of food, one meter apart. In the control group, dogs were asked to choose between two plates of the same size and different sizes, while in the test group, dogs were asked to choose between two plates of the same size and different sizes. Agrillo assumes that no matter what the situation is, dogs will choose the part where they feel bigger. So, if dogs also have the Delbov illusion, they should choose smaller plates in the test group, and the pile of dog food in the small plates seems to be larger.

However, they did not! In the control experiment, the dog did walk to the larger portion; in the test experiment, when it was asked to choose between the same amount of dog food on plates of different sizes, "their performance was basically random." However, the researchers say the results are not enough to figure out whether it means that the dog is not vulnerable to these visual illusions, or that the test conditions are simply not suitable for testing him. It may also be because the dogs in the experiment were rewarded with food no matter which one they chose, so they had little incentive to choose the one that looked slightly larger.

However, dogs and humans seem to have similar responses to some types of visual illusions, such as the previously mentioned Muller-Lyer illusion (figure 15).

A few years ago, researchers at the University of Lincoln (University of Lincoln) conducted an experiment in which dogs interacted with a touchscreen that displayed the Miller-Lyle illusion. The team found that dogs trained to choose longer segments often chose arrows pointing inward, just as humans tend to choose when doing the same task-providing the possible conclusion that dogs and humans have the same perception of this particular illusion.

But additional controlled experiments and detailed analysis of the data by the researchers in the study suggest another explanation for the findings: dogs will not choose inward arrows based on perceived segment lengths. They will choose the largest stimulus overall.

Interestingly, people have also studied the visual illusion of fish, such as the response of fish to Delboff illusion. Fish delusions about this should depend on the species of fish. A study shows that the response of damselfish to Delbov illusion is similar to that of humans and dolphins, while that of peacock fish (guppy) is the opposite. Bamboo sharks (bamboo shark) usually do not make choices that are significantly higher than chance [9].

So, back to the ultimate question, why do human beings care not only about their own delusions, but also about other animals? The essence remains the same, and in the end, we have to answer questions about the human brain.

In cases where dogs and humans show different responses, dogs choose the opposite stimulus or show no sensitivity at all, which may be that the dog's visual system responds differently to different kinds of visual stimuli. Humans are particularly good at perceiving global patterns in images made up of small elements. In contrast, dogs may be more likely to perceive local stimuli in those images. This may explain why dogs react differently to Ebinghaus-Tecchina illusion and Del Bove illusion-both of which require perception on a global scale to have the desired effect.

This cross-species distinction may reflect different evolutionary pressures between dogs and humans. In order to adapt to the specific environment, different species have evolved different physiological characteristics and functions. When the same information enters the visual system, different species may make different processing and interpretation [10]. At present, there is some evidence in the scientific literature that dogs do not have the same strong preference for global stimuli as humans, but there is only a small amount of research on this subject [11].

Chouinard points out another way to understand the differences in perception between dogs and humans: the extent to which an animal treats similar stimuli as identical to each other, rather than paying attention to subtle differences between them. The study found that dogs are less likely than humans to perceive differences between similar stimuli.

Many delusions in the future are still not fully understood, but they provide rich resources for later experimenters and technological development. There are already some cutting-edge technologies that use more elaborate techniques to measure the human brain and explore the internal mechanism of illusion from the perspective of cognitive neuroscience.

Plato has told us the difference between perception and reality in his Cave Fable. It is very likely that we will never be able to turn around and see the real reality, but we can try our best to understand it. Fortunately, we can not only understand the mysteries of vision through illusions, but also appreciate and enjoy the artistic beauty they bring to us.

reference

[1] Bach, M. Optical illusions, 2006

[2] M. V. C. Baldo, R. D. Ranvaud, and E. Morya, "Flag errors in soccer games: the flash-lag effect brought to real life," Perception, vol. 31, no. 10, Art. No. 10, 2002.

[3] https://en.wikipedia.org/wiki/Pareidolia

[4] Mark F. Bea, Barry W. Connors, Michael A. Paradiso, translated by Wang Jianjun. Neuroscience explores the brain. Higher education outbound club. 2004

[5] D. M. Eagleman, "Visual illusions and neurobiology," Nature Reviews Neuroscience, vol. 2, no. 12, Art. No. 12, 2001.

[6] https://michaelbach.de/ot/

[7] B. Roberts, M. G. Harris, and T. A. Yates, "The roles of inducer size and distance in the Ebbinghaus illusion (Titchener circles)," Perception, vol. 34, no. 7, Art. No. 7, 2005.

[8] https://www.the-scientist.com/infographics/infographic-what-do-dogs-perceive-68288

[9] https://www.verywellmind.com/optical-illusions-4020333

[10] S.Mure E. Byosiere, P. A. Chouinard, T. J. Howell, and P. C. Bennett, "What do dogs (Canis familiaris) see? A review of vision in dogs and implications for cognition research," Psychonomic bulletin & review, vol. 25, no. 5, Art. No. 5, 2018.

[11] E. Pitteri, P. Mongillo, P. Carnier, and L. Marinelli, "Hierarchical stimulus processing by dogs (Canis familiaris)," Animal Cognition, vol. 17, no. 4, Art. No. 4, 2014.

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