Argument
Müller-Lyer illusion
Overview
The Müller-Lyer illusion is an optical illusion consisting of three stylized arrows. When viewers are asked to place a mark on the figure at the midpoint, they tend to place it more towards the "tail" end. The illusion was devised by Franz Carl Müller-Lyer (1857–1916), a German sociologist, in 1889.
Research suggests all humans are susceptible to the illusion across cultures.
A variation of the same effect (and the most common form in which it is seen today) consists of a set of arrow-like figures. Straight line segments of equal length comprise the "shafts" of the arrows, while shorter line segments (called the fins) protrude from the ends of the shaft. The fins can point inwards to form an arrow "head" or outwards to form an arrow "tail". The line segment forming the shaft of the arrow with two tails is perceived to be longer than that forming the shaft of the arrow with two heads.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
Possible passages
Found by search and not yet checked by a person; they may only mention the idea in passing.
The picture is called _The Prisoner’s Dream_, and the subject of the dream must undoubtedly be his escape. It is a happy thought that the prisoner is to escape by the window, for it is through the window that the ray of light has entered and roused him from sleep.
Sigmund Freud, Introductory lectures on psycho-analysis
States what Müller-Lyer illusion is.
Let the sun shine diagonally into an empty cubical vessel, so that the opposite side be illumined, but not the bottom: let water be then poured into this vessel, and the direction of the light will be immediately altered; for a part of the bottom is shone upon. At the point where the light enters the thicker medium it deviates from its rectilinear direction, and appears broken: hence the phenomenon is called the…
Johann Wolfgang von Goethe, Goethe's Theory of Colours
States what Müller-Lyer illusion is.
This complementary association is met with in a striking manner, when a real assimilation is hindered by the associated elements belonging to different senses. In this case the difference in sense-quality erects, as it were, a partition-wall, which prevents the unobservable union of the elements. But at the same time even then close combinations can be formed, which at the operation of a sense-impression immediately…
Wilhelm Max Wundt, An Introduction to Psychology Translated from the Second German Edition
States what Müller-Lyer illusion is.
Philosophers who discussed Müller-Lyer illusion
Related ideas
Place in the tradition
Part of Direct and indirect realism.