Here are two
vertical lines of identical length. One has reversed arrowheads ('fins') while the other's look
normal. One of the lines looks longer!
Something about the arrowheads distorts
our perception. It may be our "built-in" sense of perspective.
vertical line on the left by pulling the top, or bottom end.
When both lines appear to be the
Press reset to do another measure (starting with a
randomly selected line length).
Illusion by Franz Müller-Lyer, 1889.
Java Applet: ©1997 Tony Azevedo
modified for instuctional usage (changing variables and quantitative measurements),
Eugene Switkes, CfAO/COSMOS Program 2001