the original
illusions
BYJESS ROMEO
ILLUSTRATION BYLENA VARGASILLUSIONS HAVE FASCINATED HUMANS FOR
centuries. Before we fully understood the science of sensation and
perception, philosophers like Aristotle simply observed the world—
and picked up on some weird stuff. According to Vincent Hayward,
who studies such phenomena at the Institute for Intelligent Sys-
tems and Robotics in Paris, these tricks occur when experience
and context make you expect one feeling but perceive another due
to abnormal circumstances. Here are three of Aristotle’s earliest
observed illusions, explained by modern science.3 /Aristotle’s illusion
Close your eyes and hold any
rounded object like your nose or
a pen (Aristotle may have used a
pea) between two crossed fingers.
The resulting sensation feels like
two separate objects. Your nog-
gin isn’t used to the opposite sides
of your fingers touching the same
thing. Without your sight to set
you straight, the brain assumes it’s
touching two different items.2 /Afterimages
After staring directly at the sun
(not recommended), Aristotle saw
a glowing disc shaped like our
local star in his vision for a few
lingering moments. When you fix-
ate on something, color receptors
in your eyes become overstimu-
lated. Upon looking away, those
receptors keep firing and create
an imprint, or afterimage, of that
object everywhere you look.1 /Waterfall illusion
While watching a moving river,
Aristotle noticed that when he
shifted his attention to stationary
rocks, they wiggled upstream.
Neurons that process motion tire
after focusing on the same activ-
ity. When struck with a still object,
cells that track movement in the
opposite direction have a stron-
ger impact in comparison, and
send it swimming away.114 SPRING 2020 / POPSCI.COM
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