Ponzoillusie

Ponzoillusie is a perceptual illusion in which observers misjudge the size of two identical objects when they are presented within a setting of linear perspective. In classic demonstrations, two bars of equal length are placed between two converging lines that resemble railway tracks receding into the distance; the upper bar typically appears longer than the lower.

The phenomenon is named after the Italian psychologist Mario Ponzo, who described it in 1911. The illusion arises from depth cues and the brain's use of size–distance relationships: the converging lines provide a cue that indicates increased distance for the upper element, leading the observer to interpret it as larger to maintain consistent angular size.

Research has shown the Ponzo illusion is robust across variations in line spacing, color, and enclosure, and can be modulated by attention and context. It is discussed in studies of top-down versus bottom-up processing, depth perception, and size constancy. The illusion has implications for art, design, and visual displays, where perspective cues can influence perceived scale.

Related topics include the Ponzo illusion and other depth-related visual illusions.

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