Size-Weight Illusion

The “Size-Weight Illusion” is a perceptual phenomenon in which people perceive an object to be heavier when it is larger in size, even when the objects actually have the same weight.

This illusion occurs because our perceptions of size and weight are closely linked in our brain, and our expectations about the weight of an object are influenced by its size.

The Size-Weight Illusion, sometimes called the Charpentier illusion or the De Moor’s illusion, is thought to arise from the way our brain integrates sensory information from our hands, eyes, and other sources to form a coherent perception of the weight of an object. This information is then used to guide our actions and movements, such as lifting and carrying objects.

The “Size-Weight Illusion” has been extensively studied in the field of psychology and has been shown to be a robust phenomenon, occurring across a wide range of ages, cultures, and populations. It has practical implications in areas such as product design and ergonomics, where it is important to take into account the perception of size and weight when designing objects for human use.


Size Weight Illusion
Size-Weight Illusion


Table of Contents


How does the Size-Weight Illusion work?

The “Size-Weight Illusion” works by exploiting the close relationship between our perceptions of size and weight in the brain. The human brain integrates information from various sources, including touch and vision, to form a coherent perception of the weight of an object. When an object is larger in size, our brain unconsciously expects it to be heavier, and this expectation influences our perception of its weight.

The exact neural mechanisms underlying the “Size-Weight Illusion” are not completely understood, but some theories suggest that it may involve the activity of specialized brain regions that are responsible for processing information about object size, weight, and texture. These regions of the brain are thought to work together to generate a coherent perception of the weight of an object, and they may be influenced by factors such as past experience, expectations, and attention.

In summary, the “Size-Weight Illusion” works by exploiting the close relationship between our perceptions of size and weight in the brain, and by influencing our expectations about the weight of an object based on its size. This illusion demonstrates the complex and interrelated nature of our sensory experiences, and highlights the importance of the brain’s ability to integrate and process information from multiple sources to form a coherent perception of the world.


Versions of the Size-Weight Illusion

The following is an alternative Size-Weight Illusion example:



Size Weight Illusion



Illusions like the Size-Weight Illusion

The “Size-Weight Illusion” is a type of perceptual illusion. Perceptual illusions are instances in which our perceptions of the world around us are in conflict with the physical reality of the stimuli. In the case of the “Size-Weight Illusion,” our perception of the weight of an object is not in line with its actual weight, but is influenced by its size.

Perceptual illusions provide important insights into the workings of the human brain and how it processes sensory information to form our perceptions of the world. They demonstrate the complexity and interrelated nature of our sensory experiences and highlight the importance of the brain’s ability to integrate and process information from multiple sources to form a coherent perception of the world.

Overall, the “Size-Weight Illusion” is a type of perceptual illusion that demonstrates the close relationship between our perceptions of size and weight and highlights the importance of the brain’s ability to integrate and process information from multiple sources to form a coherent perception of the world.

Some related illusions include the following:

The missing square puzzle is a visual illusion that involves a square with a smaller square removed from one of its corners.

The puzzle is presented in such a way that the surrounding rectangles appear to be the same size, but when the lines of the squares are measured, it becomes clear that they are not.

The missing square puzzle is used to demonstrate the importance of context in visual perception and how our brain can be easily fooled into perceiving something that is not actually true.


Missing Square Puzzle
Missing Square Puzzle


Illusory contours are created by the brain’s interpretation of visual information, such as the arrangement and contrast of lines and shapes in the visual field.

Kanizsa Triangle Illusion
The Kanizsa Triangle

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.


müller-lyer illusion



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.


Poggendorff illusion transparent gray bar



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.

Cafe Wall Illusion



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.

Zöllner illusion

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.

Ebbinghaus Illusion


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.


T Illusion


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.


Moon Illusion



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

Ponzo Illusion


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 Size-Weight Illusion

The “Size-Weight Illusion” was first documented by a psychologist named Ernst Heinrich Weber in the late 18th century. Weber was one of the earliest researchers to systematically study the relationship between size, weight, and perceived weight, and his work laid the foundation for the modern field of psychophysics.

In his experiments, Weber asked participants to judge the weight of objects of different sizes and found that larger objects were consistently rated as being heavier than smaller objects of the same weight. This observation led him to conclude that there was a close relationship between size and perceived weight and that this relationship was influenced by expectations and previous experiences.

Since Weber’s original observations, the “Size-Weight Illusion” has been extensively studied and replicated by researchers in the fields of psychology and neuroscience. Today, it is considered a well-established phenomenon and is widely recognized as a classic example of a perceptual illusion.

The illusion is sometimes called the Charpentier illusion, after the French physician Augustin Charpentier because he was the first to demonstrate the illusion experimentally. It is also called De Moor’s illusion, after Belgian physician Jean Demoor.

References and Resources

Check out our complete list of illusions.

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