Difference between revisions of "Muller-Lyer illusion" - New World Encyclopedia

Revision as of 19:26, 17 October 2007

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.

Discovery

The Müller-Lyer illusion is named for Franz Carl Müller-Lyer, a German psychiatrist and sociologist. Müller-Lyer published fifteen versions of the illusion in an 1889 issue of the German journal Zeitschrift für Psychologie.^[1]

the Müller-Lyer optical illusion with arrows. Both set of arrows are exactly the same, the bottom one shows how the arrows are of the exact same length.

Description

The most well known version of the Müller-Lyer illusion consists of two parallel lines, one of which ends in inward pointing arrows, the other which ends with outward pointing arrows. When observing the two lines, the one with the inward pointing arrows appears to be significantly longer than the other. In other versions, one of each type of arrow is put at each end of a single line. The viewer attempts to identify the middle point of the line, only to find that he/she is consistently off to one side.

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.

In the three-dimensional world, we often use angles to judge depth and distance. Living in a "carpentered world", we have grown accustomed to seeing corners everywhere. The brain is used to viewing such angles and interpreting them as far and near corners, and also uses this information to make size judgments. When looking at the Müller-Lyer arrows, the brain interprets them as far and near corners, and overrides the retinal information that says both lines are the same length. This explanation is supported by studies comparing the response to the Müller-Lyer illusion by American children and both rural and urban Zambian children. American children were susceptible to the illusion, and the urban Zambian children were more susceptible than the rural Zambian children. Since the rural Zambian children were much less exposed to rectangular structures, this would seem to support the perspective (or "carpentered world") theory. Interestingly enough, the illusion also persists when the arrows are replaced by circles, which have nothing to do with perspective or corners, and would seem to negate the perspective theory.^[2]

Another popular theory has been the eye movement theory, which states that we perceive one line as longer because it takes more eye movements to view a line with inward pointing arrows than it does a line with outward pointing arrows. This explanation is largely dismissed, as the illusion persists even when there is no eye movement at all.

Also popular has been the assimilation theory, which states that we see one line as longer because the visual system is unable to separate the figure into parts. As a whole figure, the line with inward pointing arrows is indeed longer. This theory is also generally dismissed.^[3]

Applications

Like most visual and perceptual illusions, the Müller-Lyer illusion helps neuroscientists study the way the brain and visual system perceive and interpret images.

Notes

↑ "Müller-Lyer Illusion" 2001. Oxford University Press. Retrieved October 17, 2007.
↑ "Muller-Lyer Illusion" June 2002. Retrieved October 17, 2007.
↑ Howe, Catherine Q. and Dale Purves. "The Müller-Lyer illusion explained by the statistics of image–source relationships" December 2004. The Center for Cognitive Neuroscience at Duke University. Retrieved October 17, 2007.

References
ISBN links support NWE through referral fees

Godfrey-Smith, Peter. Theory and Reality: An Introduction to the Philosophy of Science August 2003. University of Chicago Press. ISBN 0226300633
Merleau-Ponty. Phenomenology of Perception May 2002. Routledge. ISBN 0415278414
Thomas, Ed. Gilovich. Heuristics and Biases: The Psychology of Intuitive Judgment 2002. Cambridge University Press. ISBN 0521796792

External links

Credits

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History of "Muller-Lyer illusion"

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[1] "Müller-Lyer Illusion" 2001. Oxford University Press. Retrieved October 17, 2007.

[2] "Muller-Lyer Illusion" June 2002. Retrieved October 17, 2007.

[3] Howe, Catherine Q. and Dale Purves. "The Müller-Lyer illusion explained by the statistics of image–source relationships" December 2004. The Center for Cognitive Neuroscience at Duke University. Retrieved October 17, 2007.

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[2]

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@@ Line 3: / Line 3: @@
 [[Category:Psychology]]
+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.
+==Discovery==
+The Müller-Lyer illusion is named for [[Franz Carl Müller-Lyer]], a German psychiatrist and sociologist. Müller-Lyer published fifteen versions of the illusion in an 1889 issue of the German journal ''Zeitschrift für Psychologie''.<ref>[http://www.encyclopedia.com/doc/1O87-MllerLyerillusion.html "Müller-Lyer Illusion"] 2001. Oxford University Press. Retrieved October 17, 2007.</ref>
 [[Image:Müller-Lyer illusion.svg|thumb|the Müller-Lyer optical illusion with arrows. Both set of arrows are exactly the same, the bottom one shows how the arrows are of the exact same length.|200px]]
+==Description==
+The most well known version of the Müller-Lyer illusion consists of two parallel lines, one of which ends in inward pointing arrows, the other which ends with outward pointing arrows. When observing the two lines, the one with the inward pointing arrows appears to be significantly longer than the other. In other versions, one of each type of arrow is put at each end of a single line. The viewer attempts to identify the middle point of the line, only to find that he/she is consistently off to one side.
+==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.
-The '''Müller-Lyer illusion''' is an [[optical illusion]] consisting of nothing more than an arrow. When viewers are asked to place a mark on the figure at the mid-point, they invariably place it more towards the "tail" end. Another variation consists of two arrow-like figures, one with both ends pointing in, and the other with both ends pointing out. When asked to judge the lengths of the two lines, which are equal, viewers will typically claim that the inward pointing pair is shorter. One possible explanation is that one sees the lines as three-dimensional, such as the outgoing and ingoing corners of a room. Another possible explanation is that the line with arrows pointing inwards may simply appear longer because the arrows themselves extend past the line.
+In the three-dimensional world, we often use angles to judge depth and distance. Living in a "carpentered world", we have grown accustomed to seeing corners everywhere. The brain is used to viewing such angles and interpreting them as far and near corners, and also uses this information to make size judgments. When looking at the Müller-Lyer arrows, the brain interprets them as far and near corners, and overrides the retinal information that says both lines are the same length. This explanation is supported by studies comparing the response to the Müller-Lyer illusion by American children and both rural and urban Zambian children. American children were susceptible to the illusion, and the urban Zambian children were more susceptible than the rural Zambian children. Since the rural Zambian children were much less exposed to rectangular structures, this would seem to support the perspective (or "carpentered world") theory. Interestingly enough, the illusion also persists when the arrows are replaced by circles, which have nothing to do with perspective or corners, and would seem to negate the perspective theory.<ref>[http://www.everything2.com/index.pl?node_id=773882 "Muller-Lyer Illusion"] June 2002. Retrieved October 17, 2007.</ref>
-The illusion is not cross-cultural. Non-[[Western world|Western]] subjects, and particularly subjects whose day-to-day surroundings are usually not rectangular (few buildings, doors, walls) are much less likely to be affected by it (Segall, et al., 1963).
+Another popular theory has been the ''eye movement theory'', which states that we perceive one line as longer because it takes more eye movements to view a line with inward pointing arrows than it does a line with outward pointing arrows. This explanation is largely dismissed, as the illusion persists even when there is no eye movement at all.
-==The perspective explanation==
+Also popular has been the ''assimilation theory'', which states that we see one line as longer because the visual system is unable to separate the figure into parts. As a whole figure, the line with inward pointing arrows is indeed longer. This theory is also generally dismissed.<ref>Howe, Catherine Q. and Dale Purves. [http://www.pnas.org/cgi/content/full/102/4/1234 "The Müller-Lyer illusion explained by the statistics of image–source relationships"] December 2004. The Center for Cognitive Neuroscience at Duke University. Retrieved October 17, 2007.</ref>
-One possible explanation states that the Müller-Lyer illusion occurs because the visual system processes that judge depth and distance assume in general that the “angles in” configuration corresponds to an object which is closer, and the “angles out” configuration corresponds to an object which is far away. Basically, there seems to be a simple heuristic that takes those configurations as 90º angles. This heuristic speeds up the interpretation process, but gives rise to many optical illusions in unusual scenes.
-Neural nets in the visual system of human beings learn how to make a very efficient interpretation of 3D scenes. That is why, when somebody goes away from us, we do not see him getting shorter. And when we stretch one arm and look at the two hands we do not see one hand smaller than the other. We should not forget that, as visual illusions show us quite clearly, what we see is an image created in our brain. Our brain projects the image of the smaller hand to its correct distance in our internal 3D model. This is what is called the size constancy mechanism.
+==Applications==
+Like most visual and perceptual illusions, the Müller-Lyer illusion helps neuroscientists study the way the brain and visual system perceive and interpret images.
-[[Image:Mueller_lyer.svg|thumb|left|160px|The Müller-Lyer effect in a non-illusion]]
+==Notes==
+<references/>
-In the Müller-Lyer illusion, the visual system detects the depth cues, which are usually associated with 3D scenes, and incorrectly decides it is a 3D drawing. Then the size constancy mechanism makes us see an erroneous length of the object which, for a true perspective drawing, would be more far away.
+==References==
+*Godfrey-Smith, Peter. ''Theory and Reality: An Introduction to the Philosophy of Science'' August 2003. University of Chicago Press. ISBN 0226300633
+*Merleau-Ponty. ''Phenomenology of Perception'' May 2002. Routledge. ISBN 0415278414
+*Thomas, Ed. Gilovich. ''Heuristics and Biases: The Psychology of Intuitive Judgment'' 2002. Cambridge University Press. ISBN 0521796792
-In the perspective drawing in the figure, we see that in usual scenes the heuristic works quite well. The length of the rug should obviously be considered shorter than the length of the wall in the back.
 ==External links==