When Your Eyes Tell Your Hands What to Think: You're Far
Less in Control of Your Brain Than You Think.
You've probably never given much thought to the fact that
picking up your cup of morning coffee presents your brain with a set of complex
decisions. You need to decide how to aim your hand, grasp the handle and raise
the cup to your mouth, all without spilling the contents on your lap.
A new Northwestern University study shows that, not only
does your brain handle such complex decisions for you, it also hides
information from you about how those decisions are made.
"Our study gives a salient example," said
Yangqing 'Lucie' Xu, lead author of the study and a doctoral candidate in
psychology at Northwestern. "When you pick up an object, your brain
automatically decides how to control your muscles based on what your eyes
provide about the object's shape. When you pick up a mug by the handle with
your right hand, you need to add a clockwise twist to your grip to compensate
for the extra weight that you see on the left side of the mug.
"We showed that the use of this visual information
is so powerful and automatic that we cannot turn it off. When people see an
object weighted in one direction, they actually can't help but 'feel' the
weight in that direction, even when they know that we're tricking them,"
Xu said.
The researchers conducted two experiments. In the first,
people were asked to grasp a vertical stick with a weight hanging from its left
or right side. People easily reported which side they felt the weight was on,
even when they had their eyes closed.
The researchers then used a set of mirrors to
occasionally flip the view of the object so that it looked like the weight was
on the left, when actually it was on the right. And although people were told
to report on which side they felt the weight (with their hands), the visual
image strongly influenced the direction that they felt the weight was coming
from, especially when the weights were lighter.
In the second experiment, the researchers tried harder to
convince people to ignore the visual information by carefully explaining the
nature of the "trick."
"People still could not ignore the visual
information," said Xu. "In fact, the effect even works on us, and we
designed the experiment!"
Steven Franconeri, co-author of the study and associate
professor of cognitive psychology at Northwestern, said the brain is constantly
making decisions for us that we don't know about or understand.
"These decisions are usually smart and based on vast
experience," he said. "In this study's example, your brain is
automatically using visual information to tell your hands what they are
feeling. We can show that these decisions are happening by manipulating the
information your brain receives -- we mirror-reverse the visual information and
your brain now tells your hands that they are feeling the reverse of what they
are actually feeling. This inference is mandatory -- you feel it even if you
know it's not true."
Franconeri said this is not a "bug" in the
brain's operation.
"In the vast majority of cases, you want to
'delegate' decisions like this to the unconscious parts of your brain, leaving
you free to focus on less straightforward problems, like following driving
directions or enjoying your cup of coffee."
Image Source: http://www.sxc.hu/photo/1287009
Image Source: http://www.sxc.hu/photo/1287009
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