Ponzo optical illusion. Explanation. Pictures and descriptions illusions

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Ponzo optical illusion
The Ponzo illusion is an optical illusion where a pair of converging lines distorts the perception of two identically sized lines. Like most visual and perceptual illusions, the Ponzo illusion helps neuroscientists study the way the brain and visual system perceive and interpret images. Artists have also utilized the illusion to great effect in their works.
The Ponzo illusion is often illustrated with two converging lines that mimic railroad tracks disappearing into the distance. Two horizontal lines or bars are placed across these "tracks," one higher than the other. When looking at the image, viewers routinely see the upper bar (where the converging lines are closer) as larger than the lower bar. In reality, the two bars are of identical size.

Ponzo optical illusion

Mario Ponzo (Milano, 23 June 1882 – Torino, 9 January 1960), Italian psychologist
Mario Ponzo was an Italian academic psychologist. He was born in Rome and studied under Federico Kiesow at Turin where, in 1911, he published an article in the journal Archives Italiennes de Biologie which presented the well-known optical illusion known as the Ponzo illusion. In the same year he wrote for the Atti della Regia Accademia delle Scienze di Torino what has been described as the first article in Italian on psychology and the cinema. In 1931 he succeeded Sante De Sanctis to the chair in psychology at the Universita degli studi di Roma "La Sapienza".

Explanation of the Ponzo illusion
The effect of the Ponzo illusion is often attributed to linear perspective. The upper line looks longer because we interpret the converging sides as parallel lines receding into the distance. In this context, we interpret the upper line as though it were farther away, so we see it as longer. In the three dimensional world, an object located farther away would have to be larger than a nearby object for both to produce retinal images of the same size. This explanation is often referred to as the perspective hypothesis.
The more visual cues present surrounding the two horizontal lines, the more powerful the illusion. The framing effect, where objects that appear to fill an enclosing border appear larger than the same object surrounded by a larger frame, also contributes to the illusion. The difference in the separation or gap of the horizontal lines from the framing converging lines helps to create the sense that the upper bar, which is closer to the bordering lines, is larger than the lower one. Interestingly enough, the Ponzo illusion also appears to be present in other species. Studies have show that pigeons, rhesus monkeys, and chimpanzees all perceive the Ponzo illusion, although the relative strength of various contributing factors like figure orientation was different among each species.

REFERENCES Visual Phenomena & Optical Illusions:
• Brislin, R. W. (1974). The Ponzo illusion: Additional cues, age orientation and culture. Journal of Cross-Cultural Psychology, 5, 139-161.
• Diaz, L. F., & Delay, E. R. (1992). Response confidence and the Ponzo illusion. Perceptual and Motor Skills, 74, 265-266.
• Renier L, C. Laloyaux, O. Collignon, D. Tranduy, A. Vanlierde, R. Bruyer, and De Volder A.G. 2005. "The Ponzo illusion using auditory substitution of vision in sighted and early blind subjects" Perception, 34:857–867.
• Robinson, J. O. The Psychology of Visual Illusion. Dover Publications, 1998.
• Fineman, Mark. The Nature of Visual Illusion. Dover Publications, 1996.
• Renier L, De Volder A.G. 2005. "Cognitive and brain mechanisms in sensory substitution of vision: a contribution to the study of human perception" Journal of Integrative Neuroscience, Special Edition in Honor of Paul Bach-y-Rita, 4:489-503.

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