25/09/2022
WHEN I WAS TEN YEARS OLD, the most magical object in my house was a book on optical
illusions. Its pages introduced me to the Müller-Lyer lines whose arrow-tipped ends made them
appear as though they were different lengths even though a ruler showed them to be identical, the
Necker cube that appeared to have an open side one moment and then an open top the next, the
drawing of a chalice that suddenly became a pair of silhouetted faces before flickering back into a
chalice ag*in (see figure 1). I would sit on the floor in my father’s study and stare at that book for
hours, mesmerized by the fact that these simple drawings could force my brain to believe things that
it knew with utter certainty to be wrong. This is when I learned that mistakes are interesting and
began planning a life that contained several of them. But an optical illusion is not interesting simply
because it causes everyone to make a mistake; rather, it is interesting because it causes everyone to
make the same mistake. If I saw a chalice, you saw Elvis and a friend of ours saw a paper carton of
moo goo g*i pan, then the object we were looking at would be a very fine inkblot but a lousy optical
illusion. What is so compelling about optical illusions is that everyone sees the chalice first, the faces
next, and then–flicker flicker–there’s that chalice ag*in. The errors that optical illusions induce in
our perceptions are lawful, regular and systematic. They are not dumb mistakes but smart mistakes–
mistakes that allow those who understand them to glimpse the elegant design and inner workings of
the visual system.
