Müller-Lyer Illusion
Don’t press the button “Ruler” yet! Rather:
Grab the central arrow with your mouse and drag its tip to the centre
between the outer arrowheads.
Now you may press “Show Ruler” and learn how you fared…
I hope you have enjoyed the “Müller-Lyer Illusion” (1889). When
one bisects the horizontal line it is quite normal that large errors are made, so
don’t be annoyed or disappointed (I err by at least 1 cm).
This phenomenon is placed in the category “size constancy” because I
find the perspective explanation (see bottom) very convincing. Müller-Lyer's original
figure showed two double-ended arrows, here I used the Brentano variant.
The German satirical magazine ‘Pardon’ published in ≈1970 an article
on this illusion. It was accompanied by the two pictures on the below, demonstrating
a Müller-Lyer effect on enclosed objects ;-). [The right elephant not only
looks larger, but also happier…]
The picture on the below (from
Amazingart) demonstrates the perspective explanation (Gregory 1968): When
you place the mouse pointer over the picture, the blue lines indicate that the two
red arrows are of equal length. The arrow configuration “angles in” (near the ticket
counter) is always the front side of an object, the “angles out” configuration occurs
at the far end of a room, for instance (here next to the door). So, given no further
information (as in the Müller-Lyer arrangement at top), the brain assumes the “angles
in” configuration to be closer, computes size constancy on it, and –given identical
retinal size of the two angle arrangements– concludes that the “angle in”-line is
shorter.
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Some sources
Müller-Lyer FC (1889) Optische Urteilstäuschungen. Archiv für Physiologie Suppl.
263–270
Brentano F (1892) Über ein optisches Paradoxen. Zeitschrift für Psychologie 3:349–358
Müller-Lyer FC (1894) Über Kontrast und Konfluxion. Zeitschrift für Psychologie
IX p 1 / X p 421
Lewis EO (1909) Confluxion and contrast effects in the Mueller-Lyer illusion. Brit
J Psychol 3:21–41
Rudel R & Teuber HL (1963) Decrement of visual and haptic Müller-Lyer illusion
on repeated trials: A study of cross-modal transfer. Quarterly Journal of Experimental
Psychology 15:125–131
Segall HH, Campbell DT, Herskovits MJ (1966) The Influence of Culture on Visual
Perception. Bobbs-Merrill, Indianapolis
Dewar RE (1967) Stimulus determinants of the magnitude of the Mueller-Lyer illusion.
Perceptual and Motor Skills, 24 , 708–710
Gregory RL (1968) Perceptual illusions and brain models. Proc R Soc Lond B Biol
Sci 171:24279–296Christie PS (1975) Asymmetry in the Mueller-Lyer illusion: Artifact
or genuine effect? Perception 4:453–457
Restle F & Decker J (1977) Size of the Mueller-Lyer illusion as a function of
its dimensions: Theory and data. Perception & Psychophysics 21:489–503
Adam J & Bateman L (1983) A correlational analysis of symmetry between the arrowhead
and featherhead Mueller-Lyer illusions. Perception 12:119–129
Pressey AW & Martin NS (1990) The effects of varying fins in Mueller-Lyer and
Holding illusions. Psychol Res 52:46–53
Created: 2002-08-16
Last update: 2013-10-04