Ambiguous Illusions

The Kanizsa triangle is a visual illusion that was first described by the Italian psychologist Gaetano Kanizsa in 1955. The illusion consists of a white equilateral triangle that appears to be surrounded by three Pac-Man-like shapes, which are black and have white crescents facing inwards.

The three Pac-Man-like shapes are actually made up of three partially-overlapping circles with white edges that create the illusion of a triangle.

The Kanizsa triangle is an example of an “amodal completion” illusion, in which the brain fills in missing information to complete an object or shape. In this case, the brain completes the triangle by connecting the three white crescents of the circles together. The illusion is thought to occur because the brain is wired to perceive objects as whole and complete, even when they are not fully present in the visual field.

Table of Contents

• How does the Kanizsa Triangle work?
• Versions of the Kanizsa Triangle Illusion
• Illusions like the Kanizsa Triangle
• Discovery of the Kanizsa Triangle
• References and Resources

How does the Kanizsa Triangle work?

The Kanizsa triangle illusion works by exploiting the way our brain processes visual information. The brain tends to group together similar elements in an image to form a coherent whole, a process called “Gestalt grouping” . In the case of the Kanizsa triangle, the brain groups the three partially-overlapping circles with white edges together and interprets them as the edges of a triangle, even though the triangle is not physically present.

Another aspect that is thought to contribute to the illusion is the way the brain uses “Amodal completion” to perceive objects. Amodal completion refers to the brain’s ability to fill in missing information to complete an object or shape. In this case, the brain fills in the missing parts of the triangle by connecting the three white crescents of the circles together, creating the illusion of a complete white equilateral triangle.

Additionally, the visual cues of the overlapping circles and the angles of the white crescents contribute to the perception of the triangle as well, making it look as if the triangle is emerging from behind the circles, even though it is not physically present.

Overall, the Kanizsa triangle works by exploiting the brain’s ability to group together similar elements and fill in missing information to create the illusion of a complete, non-existent triangle.

Versions of the Kanizsa Triangle

The following are some alternate versions of the Kanizsa Triangle:

Illusions like the Kanizsa Triangle

Illusory contour illusions are a type of visual illusion in which the brain perceives contours or edges that are not physically present in an image.

These illusions can be created by using a variety of visual cues, such as shading, texture, or the arrangement of simple shapes, to create the illusion of a more complex shape. Some examples of illusory contour illusions include:

The Muller-Lyer illusion: an illusion in which two lines of the same length appear to be of different lengths due to the presence of arrowheads at the ends of the lines.

The Poggendorff illusion: an illusion in which two lines that are parallel in reality appear to be skewed or converging due to the presence of a third shape in the foreground.

The Café Wall illusion: an illusion in which the lines that form a tiled wall appear to be skewed or distorted due to the presence of contrasting colored tiles.

The Zöllner illusion: an illusion in which parallel lines appear to be skewed or converging due to the presence of intersecting lines at an angle.

All these illusions work by exploiting the way the brain processes visual information and the way it interprets the relationship between different elements in an image. Illusory contours are thought to be created by the activity of neurons that respond selectively to edges and contours in the visual field, which can be influenced by different visual cues.

Discovery of the Kanizsa Triangle

The Kanizsa triangle is a visual illusion that was first described by the Italian psychologist Gaetano Kanizsa in 1955.

Gaetano Kanizsa (1913-1993) was an Italian psychologist and neuropsychologist, known for his research in the field of visual perception and his contributions to the understanding of visual illusions. He is most famous for his work on amodal completion, which refers to the brain’s ability to fill in missing information to complete an object or shape, and for his description of the Kanizsa triangle, one of the most famous and studied amodal completion illusion.

He was a professor of Psychology at the University of Trieste in Italy, and his research focused on the relationship between perception and reality. He also developed the concept of “subjective contours” which refers to the ability of the brain to perceive contours that are not physically present in an image, and was a pioneer in the field of neuropsychology. His work has had a significant impact on the field of cognitive psychology and has influenced the work of many researchers in the field of visual perception.

References and Resources

Check out our complete list of illusions.

The Müller-Lyer illusion is a visual perception illusion that consists of two lines of equal length, with arrows at each end pointing either inward or outward. The line with the inward-pointing arrows appears shorter than the line with the outward-pointing arrows, even though they are actually the same length. This illusion is often used in research on visual perception and the neural basis of perception.

Table of Contents

• How does the Müller-Lyer Illusion work?
• Versions of the Müller-Lyer Illusion
• Illusions like the Müller-Lyer Illusion
• Discovery of the Müller-Lyer Illusion
• References and Resources
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How does the Müller-Lyer Illusion work?

The Müller-Lyer illusion works by exploiting the brain’s tendency to interpret the visual information it receives in the context of other visual information. In the case of the Müller-Lyer illusion, the brain interprets the lines with inward-pointing arrows as being part of a concave shape, and the lines with outward-pointing arrows as being part of a convex shape. This interpretation leads the brain to perceive the lines with inward-pointing arrows as being shorter than they actually are, and the lines with outward-pointing arrows as being longer than they actually are.

This illusion is thought to be caused by the visual system’s use of depth cues, such as the size and angle of the arrowheads, to infer the three-dimensional structure of the lines. The visual system uses these cues to perceive the lines as being part of a 3D figure and not just a 2D representation. The perception of depth and distance are affected by the context of the arrowheads, which fool the visual system into perceiving the lines as if they were in different distances and therefore different sizes.

Another explanation of the illusion is based on the concept of “Gestalt grouping” where the brain organizes different elements in a scene into groups based on certain rules such as proximity, similarity, and continuity. The arrowheads in the Müller-Lyer illusion creates a sense of continuation and proximity between the lines and the arrowheads which leads to the perception of the lines as being different in length.

Versions of the Müller-Lyer Illusion

The following are some alternate versions of the Müller-Lyer Illusion:

Illusions like the Müller-Lyer Illusion

There are many other visual perception illusions that work in similar ways to the Müller-Lyer illusion. Some examples include:

The Poggendorff illusion: This illusion is similar to the Müller-Lyer illusion, but instead of arrowheads, it uses a diagonal line that intersects two parallel lines. The brain perceives the diagonal line as being tilted, causing the parallel lines to appear as if they are not parallel.

The Ebbinghaus illusion: This illusion involves circles of different sizes, but with the same-sized circles placed close to each other. The brain perceives the smaller circles as being larger when they are placed next to larger circles.

The T illusion: This illusion involves a T-shaped figure with a horizontal bar and a vertical bar. The brain perceives the vertical bar as being longer than the horizontal bar, even though they are the same length.

The Kanizsa triangle: This illusion is created by placing Pac-Man-like shapes around an invisible triangle. The brain perceives the triangle as if it were a real, visible triangle.

The Zöllner illusion: This illusion involves parallel lines with diagonal lines intersecting them. The brain perceives the lines as if they were not parallel and that the diagonal lines are converging.

Moon illusion: This illusion involves the perception of the Moon appearing larger when it is near the horizon compared to when it is high in the sky.

Ponzo illusion: This illusion involves the perception of an object appearing larger or smaller depending on the size of the surrounding context.

The Café Wall Illusion is a visual illusion that is created by a grid of alternating light and dark horizontal and vertical lines. The lines appear to be bent or tilted, even though they are actually straight.

All these illusions are based on the brain’s perception of visual context, depth cues, and grouping rules. These illusions help to understand how the brain interprets visual information and how it can be deceived.

Discovery of the Müller-Lyer Illusion

The Müller-Lyer illusion is a visual perception illusion that was first described by Franz Carl Müller-Lyer in 1889.

Franz Carl Müller-Lyer (1857-1916) was a German sociologist, psychologist, and philosopher. He is best known for his work on visual perception and the Müller-Lyer illusion, which is named after him. He studied at the University of Heidelberg and later at the University of Leipzig, where he received his Ph.D. in 1879.

In 1882, he published a book “Visual illusions: their causes, characteristics, and applications,” in which he described and illustrated the Müller-Lyer illusion, which is considered one of the most famous illusions in the field of psychology. He also wrote several books on the topic of social psychology, including “The People of Primitive Societies” and “The Social Order.”

Müller-Lyer was also a social reformer and advocated for better housing and living conditions for the working class. He was also interested in the relationship between society and the individual and his work aimed to bridge the gap between the social sciences, such as sociology and psychology.

Müller-Lyer died in 1916 in Munich, Germany. His work on the Müller-Lyer illusion and his contributions to the field of social psychology are still widely studied today.

References and Resources

Check out our complete list of illusions.

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