﻿ Perspective Illusion)

# Perspective illusion

All these illusions demonstrate how lines can seem to be distorted by their background. There are many variants, including Ponzo Illusion, Jastrow illusion, Muller-Lyer illusion, Zollner illusion, Poggendorff illusion, Hering illusion, Wundt illusion, Orbison illusion, Ehrenstein Illusion and Ames Room illusion.

## Introduction: Visual Perspective

Perspective, in the context of vision and visual perception, is the way in which objects appear to the eye based on their spatial attributes; or their dimensions and the position of the eye relative to the objects.

According to the book Practice of Looking: An Introduction to Visual Culture, Lisa Cartwright and Marita Sturken state, "Perspective refers to a set of systems or mechanisms used to produce representations of objects in space as if seen by an observer through a window or frame. In perspective, the size and detail of objects depicted corresponds to their relative distance from the imagined position of the observer" (page 151).

As objects become more distant they appear smaller because their visual angle decreases. The visual angle of an object is the angle subtended at the eye by a triangle with the object at its base. The greater the distance of the object from the eye, the greater is the height of this triangle, and the less the visual angle. This follows simply from Euclidean geometry.(Wikipedia)

# Ponzo Illusion

The Ponzo illusion is a geometrical-optical illusion that was first demonstrated by the Italian psychologist Mario Ponzo (1882–1960) in 1911. He suggested that the human mind judges an object's size based on its background. He showed this by drawing two identical lines across a pair of converging lines, similar to railway tracks. The upper line looks longer because we interpret the converging sides according to linear perspective 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 – a farther object would have to be longer than a nearer one for both to produce retinal images of the same size.

The Moon illusion is an example of the Ponzo illusion, with objects appearing "far away" (because they are "on" the horizon) appearing bigger than objects "overhead".
(Wikipedia)

## Ponzo Illusion (Railway Lines Illusion)

The upper line looks longer but actually two horizontal lines are the exact same length.

Explanation:
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. (New World Encyclopedia)

Additional images can be seen at: www.moillusions.com

## Ponzo Illusion (Three soldiers)

Three soldiers are actually the exact same size.

## Ponzo Illusion (Three rectangles)

Three rectangles are actually the exact same size.

## Ponzo Illusion (Three cars - SUV Illusion)

Three cars are actually the exact same size.

Three soldiers and three cars are actually the exact same size as shown by moving the soldier, the rectangle, and the car cover on the left to the right.

# Jastrow illusion

The Jastrow illusion is an optical illusion discovered by the American psychologist Joseph Jastrow in 1889. In this illustration, the two figures are identical, although the lower one appears to be larger. The short edge of the upper figure is compared to the long side of the lower one. (Wikipedia)

Two identical curved figures are placed with one on top of the other.
Although they are both exactly the same size, one appears to be larger.

## Jastrow illusion - Explanation

The fact that the shorter side of one figure is next to the longer side of the other somehow tricks the brain into perceiving one shape as longer and the other as shorter.

Additional images can be seen at: library.thinkquest.org   www.moillusions.com   faculty.washington.edu

# Muller-Lyer illusion

The Müller-Lyer illusion is an optical illusion consisting of a set of lines that end in arrowheads. The orientation of the arrowheads affects one's ability to accurately perceive the length of the lines. (New World Encyclopedia)

Explanation:
It is unclear exactly what causes the Müller-Lyer illusion to take place, but there are a number of theories. One of the most popular is the perspective explanation. (New World Encyclopedia)
Explanation at faculty.washington.edu Click Enter and then select Müller-Lyer Illusion illusion.

Additional image can be seen at: www.michaelbach.de

### The Science of Müller-Lyer illusion.

References:The Müller-Lyer illusion explained by the statistics of image–source relationships
Abstract : The Müller-Lyer effect, the apparent difference in the length of a line as the result of its adornment with arrowheads or arrow tails, is the best known and most controversial of the classical geometrical illusions. By sampling a range-image database of natural scenes, we show that the perceptual effects elicited by the Müller- Lyer stimulus and its major variants are correctly predicted by the probability distributions of the possible physical sources underlying the relevant retinal images. These results support the conclusion that the Müller-Lyer illusion is a manifestation of the probabilistic strategy of visual processing that has evolved.

## Dynamic Müller-Lyer Illusion

Best Illusion of The Year Contest 2017, Third prize
Gianni A. Sarcone: “Dynamic Müller-Lyer Illusion”. Archimedes Laboratory Project. Italy

Author description: Müller-Lyer’s illusion proves that a segment can visually appear longer or shorter depending on the sense of the arrow heads at its ends. As shown in the animation, the red dot in the middle of the line is equidistant from the other two red dots, although the ends of the line visually appear to alternately stretch and shrink like a rubber band! The radial version of the illusion is even more impressive: http://goo.gl/sas92D   Copy. The perceptual increasing and decreasing of the segments occurs in a very short time. Thus, I suppose it is more a physiological phenomenon, rather than a psychological bias. Our attention seems to be attracted by the receptive field WITHIN the V-shaped arrow heads, causing an illusory inward or outward shift of the ends of the line.

# Zollner illusion

The Zöllner illusion is a classic optical illusion named after its discoverer, German astrophysicist Johann Karl Friedrich Zöllner (1860).
In this figure the black lines seem to be unparallel, but in reality they are parallel. The shorter lines are on an angle to the longer lines. This angle helps to create the impression that one end of the longer lines is nearer to the viewer than the other end. This is very similar to the way the Wundt illusion appears. It may be that the Zöllner illusion is caused by this impression of depth.
If the illusion is printed in green on a red background and the red and green are equally bright, the illusion disappears.
This illusion is similar to the Hering illusion, the Poggendorff illusion and the Müller-Lyer illusion. All these illusions demonstrate how lines can seem to be distorted by their background. (Wikipedia)

The black lines seem to be unparallel, but in reality they are parallel.

Explanation:
The shorter lines are on an angle to the longer lines.This angle helps to create the impression that one end of the longer lines is nearer to us than the other end.
Additional evidence can be seen at:
www.questacon.edu.au Click the button or move the short lines around.

Additional images can be seen at: www.visualillusion.net   www.alma.edu

# Poggendorff illusion

The Poggendorff illusion is a geometrical-optical illusion that involves the misperception of the position of one segment of a transverse line that has been interrupted by the contour of an intervening structure (here a rectangle). It is named after Poggendorff, the editor of the journal, who discovered it in the figures Johann Karl Friedrich Zöllner submitted when first reporting on what is now known as the Zöllner illusion, in 1860.(Wikipedia)

In the picture above, a straight black and red line is obscured by a grey rectangle. The blue line, rather than the red line, appears to be a continuation of the black one, which is clearly shown not to be the case on the second picture. Instead there is an apparent position shift of the lower portion of the line. The magnitude of the illusion depends on the properties of the obscuring pattern and the nature of its borders. (Wikipedia)

Explanation:
Many detailed studies of the illusion, including "amputating" various components point to its principal cause: acute angles in the figure are seen by viewers as expanded though the illusion diminishes or disappears when the transverse line is horizontal or vertical. Other factors are involved.(Wikipedia)
Explanation at www.enane.de Explanation.

Additional images can be seen at: www.cut-the-knot.org   Circular Poggendorff illusion.

# Hering illusion

The Hering illusion is a one of the geometrical-optical illusions and was discovered by the German physiologist Ewald Hering in 1861. When two straight and parallel lines are presented in front of radial background (like the spokes of a bicycle), the lines appear as if they were bowed outwards. (Wikipedia)

The two vertical lines are both straight, but they look as if they were bowing outwards. The distortion is produced by the lined pattern on the background, that simulates a perspective design, and creates a false impression of depth.

Explanation:
The effect of the Hering illusion is often attributed to "angular displacement," where the perception of the straight parallel lines is skewed because of the effect of the angular lines surrounding them. The distortion may also be produced by the lined pattern on the background, which simulates a perspective design and creates a false impression of depth. (New World Encyclopedia)

# Wundt illusion

The Wundt illusion is an optical illusion that was first described by the German psychologist Wilhelm Wundt in the 19th century. The two red vertical lines are both straight, but they may look as if they are bowed inwards to some observers. The distortion is induced by the crooked lines on the background, as in the Orbison illusion. The Hering illusion produces a similar, but inverted effect.(Wikipedia)

The two red vertical lines are both straight, but they may look as if they are bowed inwards to some observers. The distortion is induced by the crooked lines on the background.

# Orbison illusion

The Orbison illusion is an optical illusion that was first described by the psychologist William Orbison (1909 – 1981) in 1939. It consists of a figure placed over a background of concentric circles or radial lines. The bounding rectangle and inner square both appear distorted in the presence of the circles or radiating lines. The background gives us the impression there is some sort of perspective. As a result, a distorted shape is seen. This is a variant of the Hering and Wundt illusions. (Wikipedia)

The bounding rectangle and inner square both appear distorted in the presence of the radiating lines.

# Ehrenstein illusion

The Ehrenstein illusion is an optical illusion studied by the German psychologist Walter Ehrenstein (1899 – 1961) in which the sides of a square placed inside a pattern of concentric circles take an apparent curved shape.

The sides of a square placed inside a pattern of concentric circles take an apparent curved shape.

Note: The name "Ehrenstein illusion" is also associated with a type of the illusory contour.

# Optical Illusion Ames Room

An Ames room is a distorted room that is used to create an optical illusion. Likely influenced by the writings of Hermann Helmholtz, it was invented by American ophthalmologist Adelbert Ames, Jr. in 1934, and constructed in the following year.
An Ames room is viewed with one eye through a pinhole such as to avoid any clues from stereopsis, and it is constructed so that from the front it appears to be an ordinary cubic-shaped room, with a back wall and two side walls parallel to each other and perpendicular to the horizontally level floor and ceiling. However, this is a trick of perspective and the true shape of the room is trapezoidal: the walls are slanted and the ceiling and floor are at an incline, and the right corner is much closer to the front-positioned observer than the left corner (or vice versa). (See overhead view diagram to the right)
As a result of the optical illusion, a person standing in one corner appears to the observer to be a giant, while a person standing in the other corner appears to be a dwarf. The illusion is so convincing that a person walking back and forth from the left corner to the right corner appears to grow or shrink.
Studies have shown that the illusion can be created without using walls and a ceiling; it is sufficient to create an apparent horizon (which in reality will not be horizontal) against an appropriate background, and the eye relies on the apparent relative height of an object above that horizon.
(Wikipedia)

## House of Mystery at the Oregon Vortex

This twisted old rebuilt assay house is called the House of Mystery at the ridiculous Oregon Vortex,
a pseudoscience tourist trap that uses optical illusions to entertain travellers.