taking
something from the other side. This approach works because it draws the victim’s attention to the
wrong side of his body, which distracts his brain from events on the side where the important action
is.
Expectations do not only influence our responses; they actually influence what we feel. Your
perception of the body’s sensations comes from the interaction of two processes: signals coming from
receptors in your body, and activity in brain pathways that control your response to these signals—
including, in some cases, whether they get passed along to the brain at all. This interaction is apparent
not only in pickpocketing, but also in phenomena as diverse as pain and ticklishness.
Of course, the physical stimuli on your body also affect what you feel. Your skin contains a
multitude of different receptors—specialized nerve endings that sense things like touch, vibration,
pressure, skin tension, pain, and temperature. The brain knows which kind of sensor is activated, and
where it is on the body, because each sensor has a “private line” that uses spikes to carry only one
kind of information to the brain. Some parts of your body are more sensitive than others. The highest
density of touch receptors is found on the fingertips, with the face a close second. Your fingers
contain many more receptors than your elbows, which is why you don’t explore an object with your
elbow when you’re trying to figure out what it is.
Another set of receptors in your muscles and joints gives you information about the positioning of
your body and the tension in your muscles. This system is what allows you to be aware of the position
of your arm when your eyes are shut. When these sensors are damaged, people find all kinds of
movement to be very difficult, and they have to watch themselves as they move to avoid making
mistakes.
Did you know? Why can’t you tickle yourself?
When doctors examine a ticklish patient, they place the patient’s hand over theirs during
the exam to prevent the tickling sensation. Why does this work? Because no matter how
ticklish you may be, you can’t tickle yourself. Go ahead. Try it. The reason is that with
every move you make, part of your brain is busy predicting the sensory consequences of
that movement. This system keeps your senses focused on what’s happening in the world so
important signals aren’t drowned out in the endless buzz of sensations caused by your own
actions.
For instance, as we write, we are unaware of the feel of the chair and the texture of our
socks. Yet we’d immediately notice a tap on the shoulder. If the only information your brain
received was pure touch sensation, you wouldn’t be able to tell whether someone was
punching your shoulder or whether you’d just bumped into a wall. Since you’d want to
react very differently to those two situations, it’s important for your brain to be able to tell
them apart effortlessly.
How does your brain accomplish this goal? To study this, scientists in London
developed, of all things, a tickling machine. When a person presses a button, a robot arm
brushes a piece of foam across the person’s own hand. If the robot arm brushes the hand as
soon as she presses the button to activate it, the person feels the sensation but it doesn’t
tickle. However, the effect can be enhanced by introducing a delay between the button press
and the touch. A delay of one-fifth of a second is enough to fool the brain into thinking the
robot’s touch has been delivered by someone else—and then it tickles.
Even better, if the robot’s touch is delivered in a different direction than the one in
which the person pulls the lever, then a delay as short as one-tenth of a second is enough to
generate a tickling sensation. This experiment shows that, at least for tickling, your brain is
best at predicting the sensory outcome of a movement on the time scale of a fraction of a
second.
So what happens in the
something from the other side. This approach works because it draws the victim’s attention to the
wrong side of his body, which distracts his brain from events on the side where the important action
is.
Expectations do not only influence our responses; they actually influence what we feel. Your
perception of the body’s sensations comes from the interaction of two processes: signals coming from
receptors in your body, and activity in brain pathways that control your response to these signals—
including, in some cases, whether they get passed along to the brain at all. This interaction is apparent
not only in pickpocketing, but also in phenomena as diverse as pain and ticklishness.
Of course, the physical stimuli on your body also affect what you feel. Your skin contains a
multitude of different receptors—specialized nerve endings that sense things like touch, vibration,
pressure, skin tension, pain, and temperature. The brain knows which kind of sensor is activated, and
where it is on the body, because each sensor has a “private line” that uses spikes to carry only one
kind of information to the brain. Some parts of your body are more sensitive than others. The highest
density of touch receptors is found on the fingertips, with the face a close second. Your fingers
contain many more receptors than your elbows, which is why you don’t explore an object with your
elbow when you’re trying to figure out what it is.
Another set of receptors in your muscles and joints gives you information about the positioning of
your body and the tension in your muscles. This system is what allows you to be aware of the position
of your arm when your eyes are shut. When these sensors are damaged, people find all kinds of
movement to be very difficult, and they have to watch themselves as they move to avoid making
mistakes.
Did you know? Why can’t you tickle yourself?
When doctors examine a ticklish patient, they place the patient’s hand over theirs during
the exam to prevent the tickling sensation. Why does this work? Because no matter how
ticklish you may be, you can’t tickle yourself. Go ahead. Try it. The reason is that with
every move you make, part of your brain is busy predicting the sensory consequences of
that movement. This system keeps your senses focused on what’s happening in the world so
important signals aren’t drowned out in the endless buzz of sensations caused by your own
actions.
For instance, as we write, we are unaware of the feel of the chair and the texture of our
socks. Yet we’d immediately notice a tap on the shoulder. If the only information your brain
received was pure touch sensation, you wouldn’t be able to tell whether someone was
punching your shoulder or whether you’d just bumped into a wall. Since you’d want to
react very differently to those two situations, it’s important for your brain to be able to tell
them apart effortlessly.
How does your brain accomplish this goal? To study this, scientists in London
developed, of all things, a tickling machine. When a person presses a button, a robot arm
brushes a piece of foam across the person’s own hand. If the robot arm brushes the hand as
soon as she presses the button to activate it, the person feels the sensation but it doesn’t
tickle. However, the effect can be enhanced by introducing a delay between the button press
and the touch. A delay of one-fifth of a second is enough to fool the brain into thinking the
robot’s touch has been delivered by someone else—and then it tickles.
Even better, if the robot’s touch is delivered in a different direction than the one in
which the person pulls the lever, then a delay as short as one-tenth of a second is enough to
generate a tickling sensation. This experiment shows that, at least for tickling, your brain is
best at predicting the sensory outcome of a movement on the time scale of a fraction of a
second.
So what happens in the
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