Why We Can't Tickle Ourselves
The
difficulty of effectively tickling yourself says more about your brain than
your sense of humor.
But George Van Doorn, a psychologist at
Federation University in Australia, wanted to find out if the brain’s
predictive power really explains why we can’t tickle ourselves. It’s a serious
question, since tickling gives us a clue as to how the brain processes
sensations, and can even teach us a bit about mental illness. (People with
schizophrenia, for instance, actually can tickle themselves, for unknown
reasons.)
“The dominant theory also suggests that in
highly surprising situations, a person will be able to tickle themselves,” Van
Doorn says. The brain’s predictive abilities become too poor. To simulate this
in the lab, Van Doorn and colleagues set up an experiment where the participant
and experimenter would sit on either side of a rod with foam at both ends.
Either person could move the rod, causing the foam to make light contact with
both people’s left palms. The study’s participants would then don goggles
connected to a camera on a helmet. When the experimenter wore the helmet, the
participant saw from the experimenter’s perspective. This created what researchers
call a body-swap illusion in the participant: “Their hand felt as though it was
the experimenter’s,” Van Doorn explains, allowing the participant to surprise
himself. “You’re tickling yourself, but feel another person is doing it.”
“According to the current thinking,
people in this situation should be able to feel the tickle, but we found they
couldn’t,” Van Doorn says. The self-tickling lost out every time, even when
including visual delays to make sure the brain wasn’t just adapting to the illusion.
“Our results challenge this widely
accepted theory about how our brains work,” he says. They also provide the
first evidence supporting an alternative theory of tickling called active
inference, which suggests that the brain simply dampens all sensory input
during any movement, including tickling, to better react to new sensations.
Further tests are necessary to determine exactly which theory gets the last
laugh.
[This article originally appeared in
print as "Tickle Yourself, Elmo."]
The entire online article,
including images, can be found at: http://discovermagazine.com/2014/sept/2-tickle-yourself-elmo
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